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Global mean sea level has been rising at a rate of 3.25 ± 0.4 mm yr−1 over 1993–2018. Yet several regions are increasing at a much faster rate, such as the Beaufort Gyre in the Arctic Ocean at a rate of 9.3 ± 7.0 mm yr−1 over 2003–2014. At interannual to decadal time scales, the Beaufort Gyre sea level is controlled by salinity changes due to sea ice melt and wind‐driven lateral Ekman convergence–divergence of freshwater. This study uses recent Greenland discharge and river runoff estimates to isolate and quantify the sea level response to freshwater fluxes variability over the period 1980–2018. It relies on sensitivity experiments based on a global ocean model including sea‐ice and icebergs. These sensitivity experiments only differ by the freshwater fluxes temporal variability of Greenland and global rivers which are either seasonal climatologies or fully time varying, revealing the individual and combined impact of these freshwater sources fluctuations. Fully varying Greenland discharge and river runoff produce an opposite impact on sea level trends over 2005–2018 in the Beaufort Gyre region, the former driving an increase, while the latter, a decrease. Their combined impact leads to a fairly weak sea level trend. The sea level response is primarily driven by salinity variations in the upper 300 m, which are mainly caused by salinity advection involving complex compensations between passive, active, and nonlinear advection. This study shows that including the temporal variability of freshwater fluxes in forced global ocean models results in a better representation of regional sea level change. Plain Language Summary: Sea level is rising globally but not at the same rate everywhere. In the Arctic Ocean, the Beaufort Gyre sea level has been increasing at a fast rate of 9.3 ± 7.0 mm yr−1 over 2003–2014. At long time scales, the Beaufort Gyre sea level change is controlled by salinity, which depends mainly on continental freshwater runoff—particularly high in this region—and sea ice melt. This study uses recent estimates of Greenland discharge and river runoff in a global ocean model. The aim is to isolate and quantify the sea level response of the Beaufort Gyre to freshwater fluxes variability. We compare numerical simulations where Greenland discharge and river runoff are fully varying or set to a repeated seasonal cycle to reveal the individual and combined impacts of the variability of these freshwater sources on regional sea level. Both Greenland discharge and global river runoff impact remotely the Beaufort Gyre sea level. They induce salinity variations in the upper 300 m of the gyre through salinity advection. This study highlights the importance of the variability of continental freshwater fluxes in models in order to better represent regional sea level variability. Key Points: Greenland discharge and river runoff variability contribute to sea level rise and fall in the Beaufort GyreThe positive impact of Greenland is greater than the negative impact of rivers in the 0–78‐m range, and vice versa in the 78–300‐m rangeSea level change in the sensitivity experiments is mostly halosteric with salinity changes mainly controlled by advection [ABSTRACT FROM AUTHOR]

Marine sequences on Wollaston Forland, North‐East Greenland have provided rich belemnite assemblages of Barremian (Early Cretaceous) age. Most common are belemnites of Boreal affinities, closely related to northwest European faunas. Remarkable are the findings of 47 rostra of Duvalia, a genus of Tethyan origin. In addition to Duvalia grasiana, Duvalia arctica sp. nov., Duvalia aff. silesiaca and Duvalia sp. have been recognized. Duvalia grasiana is well known from the Barremian–Aptian of the western Tethys. The other three taxa differ, however, morphologically from contemporaneous Duvalia species common in the Barremian of the Tethys. Our findings suggest a migration of D. grasiana to North‐East Greenland in the early Barremian and a subsequent in situ evolution of D. arctica in the Greenland Norwegian Seaway. Duvalia aff. silesiaca, second in abundance, most probably also evolved from a Tethyan precursor species (Duvalia silesiaca). The taxonomic affinities of Duvalia sp. remain unclear. Duvalia arctica, D. aff. silesiaca and Duvalia sp. are all characterized by small size, indicating an endemic evolution and adaptation to a well‐confined position in the food chain. The niche occupied by these small‐sized Duvalia species must have differed substantially to that occupied by co‐occurring Boreal belemnites, which have robust, stout rostra. The findings make North‐East Greenland part of a migration route from the Tethys via the north Atlantic to the high Boreal. The Duvalia Event corresponds stratigraphically to the middle Barremian warming. [ABSTRACT FROM AUTHOR]

This study investigates the biogeochemical drivers of aragonite saturation state (ΩAr) in Baffin Bay, with a focus on the relatively undersampled west Greenland shelf. Our findings reveal two main depth‐dependant processes controlling the spatial distribution of ΩAr in Baffin Bay; within the upper 200 m, lower ΩAr coincides with increasing fractions of Arctic‐outflow waters, while below 200 m organic matter respiration decreases ΩAr. A temporal analysis comparing historical measurements from 1997 and 2004 with our 2019 data set reveals a significant decrease in the ΩAr of Arctic‐outflow waters, coinciding with reduced total alkalinity (TA). However, no discernible anthropogenic ocean acidification signal is identified. Significant Arctic water fractions (20%–40%) are found to be present on the west Greenland shelf, associated with reduced TA and ΩAr. A numerical modeling simulation incorporating a passive tracer demonstrates that periodic changes in wind direction lead to a switch from onshore to offshore Ekman transport along the Baffin Island current, transporting Arctic waters toward the west Greenland shelf. This challenges the conventional understanding of Baffin Bay's circulation and underscores the need for further research on the region's physical oceanography. Based on salinity‐TA relationships, surface waters on the west Greenland shelf have a significantly lower meteoric TA end‐member compared to waters of the Baffin Island Current in western Baffin Bay. The low eastern TA freshwater end‐member agrees well with recent glacial meltwater TA measurements, suggesting that glacial meltwater is the main freshwater source to surface waters on the west Greenland shelf. Plain Language Summary: Baffin Bay, with its complex interplay of Atlantic and Arctic water masses, is particularly susceptible to ongoing ocean acidification, mainly due to the presence of relatively fresh and low‐alkalinity Arctic waters. To date measurements of the inorganic carbon system in Baffin Bay have primarily been captured at key entrance and exit gateways, and on the Canadian side of the bay, leaving the west Greenland shelf relatively undersampled. This study provides a bay‐wide perspective of the main factors influencing aragonite saturation state (ΩAr; an indicator of ocean acidification impacts on marine calcifying organisms) across Baffin Bay, including the west Greenland shelf. We found that within the upper 200 m, low ΩAr coincides with increased presence of Arctic waters, while below 200 m the breakdown of organic matter decreases ΩAr. Historical data from 1997 and 2004 compared to our 2019 measurements show a significant drop in ΩAr of Arctic waters, but no clear signal of anthropogenic ocean acidification was observed. Surprisingly, the west Greenland shelf has significant fractions (20%–40%) of Arctic water. A numerical modeling simulation suggests that periodic changes in wind direction can transport Arctic waters from across Baffin Bay, challenging our traditional understanding of the bay's circulation. Key Points: Increased fractions of Arctic waters decrease aragonite saturation state (ΩAr) in the upper 200 m, while respiration does so below 200 mDecreased ΩAr of Arctic waters over the last two decades is associated with decreased alkalinity, not additional CO2Significant fractions of Arctic‐outflow waters on the west Greenland shelf challenges current knowledge of circulation in Baffin Bay [ABSTRACT FROM AUTHOR]

The beginning, peak and end of the eclipse are marked as in Figure 4. gl Surface air temperature averaged from 254 MMS sites shows a marked reduction in the rate of increase of temperature around the time of peak eclipse (Figure 6a). In addition, the maximum and minimum temperatures recorded every 10min were also available for many of these sites, so we were alternatively able to quantify the temperature decrease based on the highest temperature between 0830 and 0930 utc (near the start of the eclipse) and the lowest temperature between 1000 and 1100 utc (around the eclipse peak). Iceland Conditions here too were generally cloudy during the eclipse (Table S3), but the eclipse magnitude was much larger than over the British Isles, being typically ~70% magnitude or ~60% coverage of the solar disk at peak eclipse (Figure 1). Also, all of the nine sites with relatively less cloud cover had significant changes in cloud cover during the eclipse, so were not a suitable subset to use for studying the eclipse influence on surface air temperature. [Extracted from the article]

Perennial water storage in firn aquifers has been observed within the lower percolation zone of the southeast Greenland ice sheet. Spatially distributed seismic and radar observations, made ~50 km upstream of the Helheim Glacier terminus, reveal spatial variations of seismic velocity within a firn aquifer. From 1.65 to 1.8 km elevation, shear‐wave velocity (Vs) is 1,290 ± 180 m/s in the unsaturated firn, decreasing below the water table (~15 m depth) to 1,130 ± 250 m/s. Below 1.65 km elevation, Vs in the saturated firn is 1,270 ± 220 m/s. The compressional‐to‐shear velocity ratio decreases in the downstream saturated zone, from 2.30 ± 0.54 to 2.01 ± 0.46, closer to its value for pure ice (2.00). Consistent with colocated firn cores, these results imply an increasing concentration of ice in the downstream sites, reducing the porosity and storage potential of the firn likely caused by episodic melt and freeze during the evolution of the aquifer. Plain Language Summary: An integrated geophysical analysis of seismic, radar, and borehole measurements has been completed over a firn aquifer in southeast Greenland. We show the stiffness of the aquifer increases at lower elevations, closer to sea level, which leads to a decrease in pore space for the meltwater to be stored. This corresponds to an increase in ice content within the firn at lower elevations, as observed in borehole measurements, and likely caused by the meltwater refreezing within and below the aquifer. Key Points: Characterizing the storage potential of firn aquifers is important for predicting water budgets in a warming worldMultiple geophysical methods are combined to evaluate the elastic properties and porosity of the firn aquiferSeismic velocities detect an increase in ice content in the aquifer downslope, reducing the porosity and storage potential of the firn [ABSTRACT FROM AUTHOR]

Greenland ice sheet melt is a large contributor to rising global sea level and melt is dependent on surface air temperature. Arctic temperatures are strongly coupled to clouds but spatial connections between clouds and temperature have yet to be established across Greenland. By mapping spaceborne lidar measurements and surface observations, it is shown that radiatively opaque clouds generally coincide with anomalously warm near‐surface temperatures at Greenland sites. These results indicate that both temperatures over 0 °C as well as positive daily temperature anomalies relate to spatially extensive opaque cloud cover. While prior studies indicate that clouds enhance extreme melt events, this research shows that opaque cloud cover and surface warming are closely related across the Greenland ice sheet, particularly in the ablation region. These findings establish broadly the spatial relationships between opaque clouds and temperatures and demonstrate the importance of direct observations across Greenland. Plain Language Summary: Greenland ice sheet melt linked to temperatures is a large contributor to rising global sea level. Arctic temperatures are related to cloud cover but spatial changes in clouds and temperature for Greenland have yet to be quantified. Here we show that a specific type of clouds, determined by a measurement signature, coincide with warm temperatures at the Greenland surface. These results indicate that unusual occurrences of temperatures above 0 °C relate closely to cloud cover. While prior work has shown that clouds enhance extreme melt events, this research shows that cloud cover and surface warming are closely tied across the Greenland ice sheet, particularly in the regions of high mass loss. These findings establish the variability in clouds and demonstrate the importance of direct observations across Greenland. Key Points: Daily variability of opaque cloud cover and temperatures are closely linkedAnomalies in opaque clouds and temperatures are tied to circulation regimeThe largest positive anomalies in both opaque clouds and temperatures relate to days with southerly transport [ABSTRACT FROM AUTHOR]

Increased oceanic heat transport plays a key role in the accelerated mass loss of Greenland's marine‐terminating glaciers. The melt rate of major glaciers in Northeast Greenland (NEG) is controlled by ocean variability, in particular warm Atlantic Intermediate Water (AIW), on the continental shelf. A high‐resolution configuration of the ocean sea‐ice model FESOM2.1 is assessed at local and regional scales, and used to investigate the drivers of AIW temperature variability on the NEG continental shelf. The seasonal to decadal variability of AIW is characterized, featuring both pronounced interannual fluctuations and a long‐term warming trend. A major source of AIW is Atlantic Water (AW) originating from the West Spitsbergen Current that recirculates in Fram Strait. AW anomalies are advected westwards and partly control the AIW temperatures on the continental shelf. Increased AIW temperatures are also connected to pronounced northern and central branches of recirculating AW in Fram Strait, and enhanced AW temperatures more regionally. The strengthening of the pathways brings more warmer AIW onto the northern part of the NEG continental shelf. There, it circulates anti‐cyclonically and results in shelf‐wide warming. Regional atmospheric forcing is connected to the changes in the AW circulation. The strengthening of the northern AW branches is likely caused by anticyclonic wind anomalies over the Barents Sea that drive an enhanced northward AW transport in Fram Strait. Thus, controlled by a combination of both upstream and regionally forced circulation conditions, the changes in local AIW temperatures may also affect the oceanic heat transport reaching the Central Arctic Ocean. Plain Language Summary: The Greenland Ice Sheet has been melting at faster rates in the last two decades, likely due to rising ocean temperatures. Warm water found below the glaciers in Northeast Greenland controls the submarine melting. Changes in the temperature of the water are connected to ocean currents on the continental shelf of Northeast Greenland and in Fram Strait. The warm water found under the glaciers originates from the West Spitsbergen Current (WSC), over several hundred kilometers away, which carries warm water northwards within the Arctic Ocean. Part of the current turns westwards and transports the warm water toward Greenland. The changes in the strength of the westward flow are connected with particular wind patterns in the Barents Sea, as the wind forcing impacts the northward transport of the warm water in the WSC. This means that more warm water flows across the continental shelf edge at higher latitudes so there is more warm water circulating on the continental shelf itself. The circulation guides this warm water through a deep channel toward the glaciers. Therefore, the variability of the water temperature below the glaciers in Northeast Greenland is controlled by both regional winds and changes in the upstream ocean currents. Key Points: Warm temperature anomalies in the West Spitsbergen Current partly control Atlantic Water temperatures on the Northeast Greenland continental shelfPronounced northern recirculation branches transport more Atlantic Water across Fram Strait to the northern shelf where it circulatesAnomalous anticyclonic winds over the Barents Sea drive the enhanced recirculation of more northern Atlantic Water pathways [ABSTRACT FROM AUTHOR]

Higher than expected concentrations of dissolved lead (dPb) have been consistently observed along glaciated coastlines and it is widely hypothesized that there is a net release of dPb from glacier‐derived sediments. Here we further corroborate that dPb concentrations in diverse locations around west Greenland (3.2–252 pM) and the Western Antarctic Peninsula (7.7–107 pM) appear to be generally higher than can be explained by addition of dPb from glacier‐derived freshwater. The distribution of dPb across the salinity gradient is unlike any other commonly studied trace element (e.g., Fe, Co, Ni, Cu, Mn, and Al) implying a dynamic, reversible exchange between dissolved and labile particulate Pb. Incubating a selection of glacier‐derived particles from SW Greenland (Ameralik and Nuup Kangerlua) and Svalbard (Kongsfjorden), with a range of labile particulate Pb (LpPb) content (11–113 nmol g−1), the equivalent of 2–46% LpPb was released as dPb within 24 hr of addition to Atlantic seawater. Over longer time periods, the majority of this dPb was typically readsorbed. Sediment loading was the dominant factor influencing the net release of dPb into seawater, with a pronounced decline in net dPb release efficiency when sediment load increased from 20 to 500 mg L−1. Yet temperature also had some effect with 68 ± 22% higher dPb release at 11°C compared to 4°C. Future regional changes in dPb dynamics may therefore be more sensitive to short‐term suspended sediment dynamics, and potentially temperature changes, than to changing interannual runoff volume. Plain Language Summary: Glacier runoff is a minor source of the element lead (Pb) into the ocean. Lead that was deposited on ice surfaces from atmospheric deposition is ultimately released in runoff and drains into the ocean. Changes in the concentration of Pb in fresh and marine waters are of concern because Pb is a toxic element with the potential to have detrimental effects on ecosystems and public health. Across most of the Atlantic and Arctic, Pb concentrations have been strongly affected by the historical use of Pb as a fuel additive. This led to elevated atmospheric deposition of Pb until the 1990s when these additives were extensively phased out. Around glaciated coastlines however, evidence is emerging worldwide of a natural Pb source too large to be explained by atmospheric deposition. This source is thought to be related to the release of Pb from glacier erosion. Here we corroborate these observations in southwestern Greenland and the Western Antarctic Peninsula showing that a dynamic release and readsorption of Pb from glacier‐derived particles explains the observed distribution of dissolved Pb in seawater. Key Points: Glacier‐derived particles release 2–46% of labile particulate lead (Pb) upon mixing with seawaterPb dynamics in glacier fjords are characterized by a rapid release of dissolved Pb followed by readsorption on a timescale of hours‐to‐daysDissolved Pb release from the Greenland Ice Sheet is likely within the range 0.2–1 Mmol yr−1 [ABSTRACT FROM AUTHOR]

Radio Echo Sounding (RES) surveys conducted in May 2010 and April 2011 revealed a 2 km2 flat area with increased bed reflectivity at the base of Isunnguata Sermia at the western margin of the Greenland Ice Sheet. This flat reflector was located within a localized subglacial hydraulic potential (hydropotential) minimum, as part of a complex and elongated trough system. By analogy with comparable features in Antarctica, the initial interpretation of such a feature was a potential subglacial lake. In September 2013 a co‐located seismic survey revealed a 1,750 m by 540 and 37 m thick stratified lens‐shaped bedform at the base of a subglacial trough system. Amplitude Versus Angle (AVA) analysis yields a derived reflection coefficient R = 0.09 ± 0.14 indicative of consolidated sediments possibly overlain by dilatant till. The bed and flank on the northern side of the trough consist of unconsolidated, possibly water‐bearing sediments with R = −0.10 ± 0.08, whereas on the southern side it consists of more consolidated material. We interpret the trough as a key component of the wider subglacial drainage network, for which the sediments on its northern side act as a localized water‐storage reservoir. Given the observation of seasonally forming and rapidly draining supraglacial meltwater lakes in this area, we interpret the lens‐shaped bedform as deposited by episodically ponding meltwater within the subglacial trough system. Our results highlight the importance of transient subglacial hydrological and sedimentological processes such as drainage events for the interaction of ice sheets and their substrates, to understand ice dynamics in a warming climate. Plain Language Summary: A ground based radar survey in West Greenland showed an unusually flat, highly reflective zone in an otherwise rough bed suggesting a possible subglacial lake beneath the ice. The highly reflective zone was part of a drainage system transporting meltwater under the ice sheet. We performed a detailed seismic survey across the area which, unlike radar signals, has the advantage of penetrating through the overlying ice into any rock, sediments and water below it. Analysis of our reflection data reveal that the flat area was in fact an elongated lens‐shaped bedform consisting of layered (stratified) sediments. However at a larger angle of incidence, analysis showed the bedform is possibly overlain by a thin layer of water‐bearing sediments likely saturated by ponding water. Our interpretation is that episodically draining meltwater from upstream is locally accumulating beneath the ice sheet at this locality, thereby depositing the lens‐shaped bedform over many melt seasons. Key Points: Seismic data show that a subglacial lake implied by high reflectivity in radar data is in fact a lens‐shaped sediment bedformSeismic reflectivity analysis suggests the lens‐shaped bedform is possibly overlain by a thin layer of water‐bearing sedimentsThe subglacial bedform is stratified and likely deposited through episodically ponding of upstream derived meltwater [ABSTRACT FROM AUTHOR]

The warming climate is rapidly changing the circumpolar region, presenting new opportunities and challenges for agricultural production in South Greenland. The warming climate is projected to increase the frequency of drought periods, but little is known about the soil–water retention (SWR) and the plant available water (PAW) of the agricultural soils in the region. This study aimed to measure the SWR and PAW of Greenlandic agricultural soils and evaluate the effect of organic carbon (OC) and clay (CL) content using pedotransfer functions based on OC and CL. The study included 464 South Greenlandic agricultural soil samples from 20 fields with a wide distribution in clay (0.016–0.184 kg kg−1) and OC contents (0.006–0.254 kg kg−1). Pedotransfer functions were successfully developed for estimating the gravimetric water content (w) at five soil–water potentials (−1500, −100, −30, −10, and −5 kPa) and PAW. The OC content was the primary variable governing the gravimetric water content at each soil–water potential, evidenced by R2 values consistently above 0.80. The effect of OC on the gravimetric water content at −1500 kPa was close to the range reported in the literature, but OC effects were markedly higher between −100 and −5 kPa. Overall, this study highlights a substantial effect of OC on the PAW as a 1% increase in OC increased PAW by more than 4%, which is almost twice the value of a recent meta‐study. Our study highlights the potentially dominating effects of organic matter on soil–water balance and availability in high‐latitude agriculture. Core Ideas: This is the first comprehensive study measuring the soil–water retention (SWR) of Greenlandic agricultural soils.The SWR and plant available water (PAW) were determined for 464 soils originating from 20 agricultural fields.Pedotransfer functions were developed to evaluate the effect of organic carbon (OC) and clay content.OC was the primary variable governing the SWR of these subarctic soils, especially at matric potentials ≥−100 kPa.The impact of OC content on the SWR and PAW was high compared to the literature. [ABSTRACT FROM AUTHOR]

Evergreen dwarf shrubs respond swiftly to warming in the cool and dry High Arctic, but their response in the warmer Low Arctic, where they are expected to be outcompeted by taller species under future warming, remains to be clarified. Here, 12,528 annual growth increments, covering 122 years (1893–2014), were measured of 764 branches from 25 individuals of the evergreen dwarf shrub Cassiope tetragona from a Low‐Arctic erect dwarf‐shrub tundra site in western Greenland. In addition, branch initiation and mortality frequency time series were developed. The influence of seasonal climate and correspondence with fluctuations in regional normalized difference vegetation index (NDVI), a satellite‐proxy for vegetation productivity, were studied. Summer temperatures were the main driver of growth, while winter temperatures were the main non‐summer‐climate driver. During past and recent warm episodes, shrub growth diverged from summer temperatures. In recent decades, early summer precipitation has become the main growth‐limiting factor for some individuals, likely through micro‐topography‐determined soil moisture availability, and more than half of the shrubs studied became irresponsive to summer temperatures. There was correspondence between climatic drivers, C. tetragona growth and branch initiation frequency, and satellite‐observed vegetation productivity, suggesting the area's shrub‐dominated tundra vegetation is limited by similar climatic factors. Winter warming events were likely the predominant cause of branch mortality, while branching increased after years with poor growth and cooler‐than‐average summers. These findings show that the erect dwarf‐shrub tundra in the Low Arctic has already and will likely become decreasingly temperature‐ and increasingly moisture‐limited and that winter warming supports shrub growth, but increased extreme winter warming event frequency may increase branch mortality and vegetation damage. Such counter‐acting mechanisms could offer an explanation for the vegetation stability observed over large parts of the Arctic. [ABSTRACT FROM AUTHOR]

Increased Greenland ice sheet melting has an impact on global mean and regional sea level rise and the ocean circulation. In this study, we explore whether Greenland melting signatures found in ocean model simulations are visible in observations from radar altimetry, satellite gravimetry and Argo floats. We have included Greenland freshwater flux (GF) in the global Finite‐Element‐Sea ice‐Ocean Model (FESOM) for the years 1993–2016. The reference run is computed by excluding Greenland freshwater input. These experiments are performed on a low resolution (ca. 24 km) and a high resolution (ca. 6 km) eddy‐permitting mesh. For comparison with the model experiments, we use different observational data, such as Argo floats, satellite observations, and reanalyses. We find that surface GF maps into signatures in temperature and salinity down to about 100 m in the surroundings of Greenland. The simulated melting signatures are particularly visible in steric heights in Baffin Bay and Davis Strait. Here, we find an improvement of the mean square error of up to 30% when including GF. For the Nordic part of the Nordic Seas, however, we find no improvement when including GF. We compare steric heights with reanalysis data and a new setup of the inversion method from gravimetric and altimetric satellite data. We cannot confirm that the GF signatures on variables such as temperature and salinity are visible in the observations on the time scales considered. However, we find that increased model resolution often causes larger improvements than occur due to including the simulated melting effect. Plain Language Summary: In recent years, Greenland's freshwater contribution to the ocean has increased due to the accelerated melting of its ice sheet and glaciers. In this study, we investigate the importance of this melting in reproducing the observed characteristics of the northern part of the North Atlantic Ocean in a numerical ocean model. To do that, we compare the results of two model simulations, one with and one without Greenland melt, with in situ observations or data from satellites. The inclusion of Greenland melt results in a better model representation of the ocean in terms of salinity, temperature, and sea level anomalies, especially in Baffin Bay on the west side of Greenland. We also discuss the role of a higher model resolution on the simulations in reproducing observations. Our study shows that progress in modeling how Greenland melt affects the nearby ocean is best achieved by improving model resolution so that small‐scale processes can be well represented. Key Points: Greenland freshwater flow yields distinct signatures in temperature and salinity within the upper 100 mSteric heights and sea level anomalies are sensitive to the Greenland freshwater intrusion especially in Baffin BayIncreasing the spatial model resolution improves the agreement with observations more than if only Greenland meltwater is included [ABSTRACT FROM AUTHOR]

Greenland's outlet glaciers have been a leading source of mass loss and accompanying sea‐level rise from the Greenland Ice Sheet (GrIS) over the last 25 years. The dynamic component of outlet glacier mass loss depends on both the ice flux through the terminus and the inland extent of glacier thinning, initiated at the ice‐ocean interface. Here, we find limits to the inland spread of thinning that initiates at glacier termini for 141 ocean‐terminating outlet glaciers around the GrIS. Inland diffusion of thinning is limited by steep reaches of bed topography that we call "knickpoints." We show that knickpoints exist beneath the majority of outlet glaciers but they are less steep in regions of gentle bed topography, giving glaciers in gentle bed topography the potential to contribute to ongoing and future mass loss from the GrIS by allowing the diffusion of thinning far into the ice sheet interior. Plain Language Summary: Fast‐flowing outlet glaciers around the edge of the Greenland Ice Sheet transport ice from the ice sheet interior to the ocean. In response to a warming climate, many of these glaciers have retreated, causing thinning at the edge of the ice sheet that spreads into the interior. Depending on the shape of each outlet glacier, thinning can either spread far into the interior or stall where the glacier flows over particularly steep bedrock beneath the glacier. By investigating the shapes of 141 outlet glaciers around Greenland, we find that steep bedrock features, which we call "knickpoints," can effectively stall the inland spread of thinning in regions where the bedrock beneath the ice sheet is mountainous. On the other hand, in regions of more gentle topography, these knickpoints are either not present or are less steep and cannot stall thinning from spreading far into the ice sheet interior. This means that numerous small glaciers flowing over the gentle topography of Northwest Greenland may allow thinning to spread to the center of the ice sheet. Because of this, these smaller glaciers may play as big of a role in future sea‐level rise as the more well‐known and well‐studied larger glaciers. Key Points: Greenland glaciers with high potential to contribute to mass loss identified using novel metricThe majority of thinning limits are set by a knickpoint, a steep drop in bed topographyGlaciers that transmit thinning far inland are preferentially in regions with gentle bed topography [ABSTRACT FROM AUTHOR]

A daily, gridded 1‐km rainfall climatology (1958–2020) for Greenland is presented, including the Greenland ice sheet (GrIS), the peripheral glaciers and ice caps (GIC), and ice‐free tundra. It is obtained by statistically downscaling the 5.5 km output of the regional atmospheric climate model version 2 to a resolution of 1 km, using the elevation dependence of snowfall fraction. Based on this new product, the average total annual rainfall in Greenland during 1958–2020 is estimated to be 111.4 ± 11.2 Gt/year, of which 28.6 ± 6.1 Gt/year falls on the GrIS, 11.4 ± 1.4 Gt/year on the GIC, and 71.4 ± 9.0 Gt/year on the tundra. The downscaled 1 km product better resolves especially the relatively small GIC, more than doubling (+124%) their rainfall compared to the 5.5 km product. The relatively warm southern regions of Greenland have the highest rainfall amounts, with annual values locally exceeding 1,000 mm. We confirm a significant positive trend in Greenland rainfall (>40 mm/decade), notably in the northwest and mainly due to an increase in rainfall fraction (>3.5%/decade) during July and August. For the whole of Greenland, during 1991–2020 the seasonal rainfall peak has shifted from July to August, with significant increases in September, which receives more rain than June. An analysis of rainfall fraction and near‐surface temperature shows that local warming rates are a good predictor of recent rainfall changes. Key Points: The downscaled daily, gridded 1 km RACMO2.3p2 rainfall product better resolves especially the relatively small peripheral glaciers and ice caps, more than doubling their rainfall compared to the native 5.5 km productA significant positive trend is found in northwest Greenland rainfall, mainly attributable to an increase in rainfall fraction during July and AugustHigh correlations between rainfall fraction and near‐surface temperature shows that local warming rates are a good predictor of recent Greenland rainfall changes [ABSTRACT FROM AUTHOR]

Soil nutrient pools in the dry low Arctic are likely to be released under climatic change and this bioavailability has the potential to increase both terrestrial and aquatic productions. As well as the direct effect of warming, external disturbances such as nutrient deposition and grazing can also drive ecosystem change. This study in the low Arctic Kangerlussuaq area of southwest Greenland compared soil nutrient pools in terms of both topographic position on a catena and by soil depth in two small catchments with contrasting muskox abundance. We tested the hypotheses that there were differences between soil carbon (C), nitrogen (N) and phosphorus (P) across a soil catena (ridge ‐ slope ‐ valley) and by soil depth (litter ‐ 0–5 cm ‐ 25–30 cm) for the two sites (SS17b, muskox present, versus ‐ SS85, no muskox). Total C and N concentrations of soils were on average lower at SS17b compared to SS85. Moreover, the soil N concentration increased downslope in the catena with higher amounts in the valleys compared to the slopes and ridges. Soil P concentration (0.70 g P kg−1) was similar between catchments; however, litter P content was substantially different. The difference in soil nutrients between the two catchments was most likely due to the presence of muskox at SS17b, and hence grazing associated processes (defecation, altered microbiology and nutrient cycling). This study emphasises the heterogeneity of arctic landscapes and need for ecosystem specific research. Highlights: Soil nutrient pools in two low‐arctic catchments in Greenland were compared.Grazing and dung inputs by muskox affect soil nutrient pools in Greenland.Soil P stores in Kangerlussuaq are similar to intensively managed farmland in Europe.The heterogeneity of arctic landscapes and need for ecosystem‐specific research are emphasised. [ABSTRACT FROM AUTHOR]

Knowledge about the deglaciation history of the Greenland Ice Sheet (GrIS) is important to put the recent observations of ice loss into a longer‐term perspective. In southern Greenland, the deglaciation history is generally well constrained. In this study, we use 43 new 10Be surface exposure ages combined with existing minimum‐limiting 14C ages to constrain the deglaciation history of eastern North Greenland, including the three major fjord systems – Independence Fjord, Hagen Fjord and Danmark Fjord. The 10Be ages are generally scattered and many of the samples are significantly older than expected, with pre‐LGM ages being a result of inheritance from previous exposures. By using a Bayesian statistical approach to combine the new 10Be ages and existing 14C ages, we are able to constrain the deglaciation history. We find that the outer coast and deep fjords were rapidly deglaciated between ̃11 and 10 ka. Subsequently, the deglaciation progressed far inland up the fjords, probably as a result of increased summer surface temperatures and subsurface ocean temperatures during the Holocene Thermal Maximum. The rapid retreat of the Middle Holocene slowed when the ice sheet became land‐based in the central and southern part of the study area where the ice margin first reached its present extent by ̃6.7 ka. As the onset of Neoglacial ice advance had already commenced at ̃5 ka this limits the period when the ice margin could retreat farther inland and it probably remained within max. 30–40 km of its present extent. The contrasting behaviour between the fjords and inter‐fjord areas shows a clear topographic effect on the stability of the GrIS. These results inform how the GrIS may respond to a warmer climate in various topographic settings and may provide useful constraints for future ice‐sheet models. [ABSTRACT FROM AUTHOR]

Greenland Ice Sheet surface melting has increased since the 1990s, affecting the rheology and scattering properties of the near‐surface firn. We combine firn cores and modeled firn densities with 7 years of CryoVEx airborne Ku‐band (13.5 GHz) radar profiles to quantify the impact of melting on microwave radar penetration in West Central Greenland. Although annual layers are present in the Ku‐band radar profiles to depths up to 15 m below the ice sheet surface, fluctuations in summer melting strongly affect the degree of radar penetration. The extreme melting in 2012, for example, caused an abrupt 6.2 ± 2.4 m decrease in Ku‐band radar penetration. Nevertheless, retracking the radar echoes mitigates this effect, producing surface heights that agree to within 13.9 cm of coincident airborne laser measurements. We also examine 2 years of Ka‐band (34.5 GHz) airborne radar data and show that the degree of penetration is half that of coincident Ku‐band. Plain Language Summary: Radar waves emitted by satellites can be used to measure changes in surface elevation of the Greenland Ice Sheet. However, they do not reflect off the ice sheet surface itself but penetrate into the snow to a depth of about 15 m for radar wavelengths of 2.3 cm. When the snow melts, meltwater can percolate into the snow or refreeze at the surface. Layers of refrozen ice sharply reduce the degree of radar penetration and may be mistaken for an elevation increase in radar measurements. Here, we combine firn cores and modeled firn densities with 7 years of airborne radar data collected during field campaigns in West Central Greenland to quantify this effect. We identify internal layers corresponding to annual stratigraphy within the snowpack, and we show that more melt means less radar penetration into the firn. The unprecedented surface melting which occurred across Greenland in 2012 caused a sharp reduction in the degree of radar penetration, from 11.5 to 5.3 m. However, if the effects of penetration are corrected for, radar altimeters can accurately measure the surface elevation of the ice sheet. Key Points: We use airborne radar, firn cores, and firn models to confirm that summer melting is the principal source of radar penetration fluctuationsThe largest fluctuations are recorded after the extreme melt event of 2012, which caused a 6.2 ± 2.4 m reduction in radar penetrationEcho retracking compensates for radar penetration fluctuations, leading to surface heights that agree with laser data to within 13.9 cm [ABSTRACT FROM AUTHOR]

The mineralogical and geochemical compositions of three sediment cores from the northwestern Greenland continental margin (AMD14‐204 and AMD14‐210) and Kane Basin (AMD14‐Kane2B) were investigated using quantitative X‐ray diffraction and energy‐dispersive X‐ray fluorescence in order to document the impact of ice‐ocean interactions on the sediment provenance and transport pathways during the Holocene. Unmixing of the sediment composition and ratios such as quartz/clays and K/Fe indicate that detrital sediments in cores from the northwest Greenland margin are derived mainly from Prøven granite and reworked Archean gneiss, whereas sediments from Kane Basin are derived mainly from detrital carbonate (Ellesmere Island) and Proterozoic gneiss (Humboldt Glacier). Mineralogical and geochemical signatures also reveal that changes in detrital sediment provenance and transport in the region are strongly interconnected to regional ice stream dynamics, especially during the early Holocene with strong meltwater discharge from the Greenland Ice Sheet associated with the end of deglaciation. With the establishment of milder conditions during the mid‐Holocene and reduced glacial activity once ice sheets retreated inland, sediment inputs via ocean currents became more effective. Thus, detrital proxies in core AMD14‐204, located in the Upernavik cross‐shelf trough, support the hypothesis of an intensification of the West Greenland Current influence after 7.7 cal ka BP, which eventually affected the regional sediment dynamic by a greater contribution from basalt to the sediment supply. Finally, our results suggest that the interactions between climate, glacial dynamics, and surface ocean circulation controlled the paleoenvironmental changes observed in the three cores. Key Points: Sediment provenance is used as indicator of palaeoceanographic changes in northeast Baffin BayDetrital proxies reveal a stronger influence of the West Greenland Current after ~7.7 cal ka BPVariations in sediment provenance on the northwestern margin are interconnected to regional ice streams activity [ABSTRACT FROM AUTHOR]

Heat transport via ocean currents can affect the melting of marine‐terminating glaciers in Greenland. Studying past changes of marine‐terminating glaciers allows assessing the regional sensitivity of the Greenland Ice Sheet to ocean temperature changes in the context of a warming ocean. Here, we present a high‐resolution multiproxy marine sediment core study from Skjoldungen Fjord, close to the marine‐terminating Thrym Glacier. Grain‐size data are obtained to reconstruct the calving activity of Thrym Glacier; sortable silt is used as a proxy for fjord water circulation, and sea surface temperatures (SSTs) are reconstructed from alkenone paleothermometry (Uk'37). Measurements of 210Pb, 137Cs, and 14C indicate that the core covers the past 220 years (1796–2013 CE). Comparisons with modeled SST data (Hadley Centre Sea Ice and SST) and instrumental temperatures (International Council for the Exploration of the Sea) suggest that the SST proxy record reflects temperature variability of the surface waters over the shelf and that alkenones are advected into the fjord. Additionally, average temperatures and the amplitude of fluctuations are influenced by alkenones advected from upstream the Irminger Current. We find that the SST record compares well with other alkenone‐based reconstructions from SE‐Greenland and thus features regional shelf water variability. The calving activity as well as the terminus position of Thrym Glacier did not seem to respond to the SST variability. Limited ice‐ocean interactions owing to the specific setting of the glacier would explain this. Instead, the fjord circulation may have been influenced by enhanced meltwater production as well as to larger scale changes in the Atlantic Meridional Overturning Circulation. Key Points: Alkenone‐based sea surface temperature reconstructions reveal common SE‐Greenland shelf variability during the 20th centuryIncreasing ocean temperature did not result in a retreat of Thrym GlacierSortable silt parameters indicate that fjord water column flow is influenced by increased meltwater release and/or shelf water circulation [ABSTRACT FROM AUTHOR]

The article in the Journal of Medical Virology reports the first confirmed case of Jamestown Canyon virus (JCV) in Greenland, a region not typically associated with vector-borne diseases. Mosquitoes collected in Greenland tested positive for JCV RNA, specifically in the Aedes impiger species. The study suggests that Aedes impiger may be a potential regional vector for JCV and highlights the need for increased vector surveillance in the Arctic due to changing climates and landscapes. [Extracted from the article]

Greenland's glacial fjords modulate the exchange between the ice sheet and ocean. Subglacial‐discharge‐driven plumes adjacent to glaciers may exert an important influence on fjord water properties, submarine glacier melting and the export of glacially‐modified waters to the shelf. Here we use a numerical plume model in conjunction with observations from proximal to 14 glaciers in northwest Greenland to assess the impact of these plumes on near‐glacier water properties. We find that in late summer, waters emanating from glacial plumes often make up >50% of the fjord water composition at intermediate depths. These plume waters are comprised largely of upwelled Atlantic Water, warming the near‐glacier water profile and likely increasing submarine melting. Our findings demonstrate the key role played by plumes in driving water modification in Greenland's fjords, and the potential for simple models to capture these impacts across a range of settings. Plain Language Summary: Fjords form an important point of contact between the Greenland Ice Sheet and surrounding ocean. Warm ocean waters in these fjords melt the submerged sections of marine‐terminating glaciers, whilst freshwater draining from the ice sheet modifies coastal water properties, impacting ocean circulation. In this study, we use observations of fjord temperature and salinity in combination with numerical modeling to evaluate the mechanisms through which glaciers modify fjord circulation and water properties. Across 14 glaciers in northwest Greenland, we find that the input of glacial meltwater drives the upwelling of warm, deep Atlantic‐origin waters, which mix with the cooler Arctic‐origin waters typically found above ∼250 m depth. These glacially modified waters thus cause a substantial warming of fjord waters relative to those off the coast, a feedback that will amplify the oceanic melting of these glaciers. Key Points: We assess the impact of subglacial‐discharge plumes on water properties proximal to 14 tidewater glaciers in northwest GreenlandIn late summer, waters emanating from glacial plumes often make up >50% of the fjord water composition at intermediate depthsThese plume waters are comprised largely of upwelled Atlantic Water, warming the near‐glacier water profile and likely increasing submarine melting [ABSTRACT FROM AUTHOR]

The Last Glacial Maximum extent of the North American Ice Sheets is well constrained empirically but has proven to be challenging to simulate with coupled Climate‐Ice Sheet models. Coupled Climate‐Ice Sheet models are often too computationally expensive to sufficiently explore uncertainty in input parameters, and it is unlikely that values calibrated to reproduce modern ice sheets will reproduce the known extent of the ice at the Last Glacial Maximum. To address this, we run an ensemble with a coupled Climate‐Ice Sheet model (FAMOUS‐ice), simulating the final stages of growth of the last North American Ice Sheets' maximum extent. Using this large ensemble approach, we explore the influence of numerous uncertain ice sheet albedo, ice sheet dynamics, atmospheric, and oceanic parameters on the ice sheet extent. We find that ice sheet albedo parameters determine the majority of uncertainty when simulating the Last Glacial Maximum North American Ice Sheets. Importantly, different albedo parameters are needed to produce a good match to the Last Glacial Maximum North American Ice Sheets than have previously been used to model the contemporary Greenland Ice Sheet due to differences in cloud cover over ablation zones. Thus, calibrating coupled climate‐ice sheet models on one ice sheet may produce strong biases when the model is applied to a new domain. Plain Language Summary: At the peak of the last ice age, an ice sheet covered much of North America. The extent of this ice sheet is well‐understood after decades of intensive data collection, but producing a computer simulation of the ice sheet which matches our observations has been a challenge. This is partly because of uncertainty about the "correct" model set‐up to create the best simulation, and partly because the computer models used in the simulations require large computing resources. In this paper, we present a series of simulations of the North American Ice Sheet at the peak of the last ice age using a fast‐running computer model in which the atmosphere and ice sheets interact. We run hundreds of simulations to tackle the uncertainty about the optimum values for unknown input parameters. We find that the model's representation of how reflective the ice sheet surface is has the most impact on the size and shape of the simulated ice sheet. Importantly, the parameter values that produce the best simulations of modern‐day Greenland produce poor simulations of the North American Ice Sheets during the last ice age, calling into question whether the parameters chosen for modern Greenland are appropriate from simulating ice sheets under different conditions. Key Points: Simulating the Last Glacial Maximum North American Ice Sheets successfully requires de‐tuning the coupled Climate‐Ice Sheet model FAMOUS‐iceAfter running a large ensemble, we identify multiple acceptable simulations of the LGM North American Ice SheetThe LGM North American cloud cover revealed overtuned albedo parameters to compensate for modern Greenland cloud biases [ABSTRACT FROM AUTHOR]

Changes in ice‐sheet size impact atmospheric circulation, a phenomenon documented by models but constrained by few paleoclimate records. We present sub‐centennial‐scale records of summer temperature and summer precipitation hydrogen isotope ratios (δ2H) spanning 12–7 ka from a lake on Baffin Island. In a transient model simulation, winds in this region were controlled by the relative strength of the high‐pressure systems and associated anticyclonic circulation over the retreating Greenland and Laurentide ice sheets. The correlation between summer temperature and precipitation δ2H proxy records changed from negative to positive at 9.8 ka. This correlation structure indicates a shift from alternating local and remote moisture, governed by the two ice‐sheet high‐pressure systems, to only remote moisture after 9.8 ka, governed by the strong Greenland high‐pressure system after the Laurentide Ice Sheet retreated. Such rapid atmospheric circulation changes may also occur in response to future, gradual ice‐sheet retreat. Plain Language Summary: Continental ice sheets alter atmospheric circulation, influencing global heat and moisture distribution. Records of atmospheric circulation during previous periods of ice‐sheet retreat can provide insights into the changes that are possible in the future. This study examines summer atmospheric circulation in Baffin Bay from 12,000 to 7,000 years ago, a period of dramatic ice‐sheet retreat. Precipitation isotopes reflect moisture source, which responds to changes in air temperature and atmospheric circulation. This study uses records of temperature and precipitation isotopes from the same sediment archive to tease apart the influence of temperature from that of atmospheric circulation. The precipitation isotopes in this record distinct changes in moisture sources, which a climate model simulation suggests was caused by retreating ice sheets. Before about 10 ka, when the Laurentide Ice Sheet (LIS) covered eastern Canada, summer winds in Baffin Bay shifted regularly between south and north, carrying air with unique temperature and precipitation isotope signatures. As the LIS retreated, the Greenland Ice Sheet (GIS) remained relatively large and dominated atmospheric circulation, causing a rapid shift to southeasterly winds. As the GIS retreats in the future, atmospheric circulation may undergo similar rapid changes. Key Points: Summer precipitation isotopes in the Arctic reflect temperature and moisture transport historyPaired records of summer temperature and precipitation isotopes isolate the influence of temperature from that of transportMoisture delivery to the eastern Canadian Arctic changed dramatically due to Early Holocene Laurentide Ice Sheet retreat [ABSTRACT FROM AUTHOR]

Greenland glaciers have three primary seasonal ice flow patterns, or "types": terminus‐driven, runoff‐driven, and runoff‐adapting. To date, glacier types have been identified by analyzing flow at a single location near the terminus; information at all other locations is discarded. Here, we use principal component (PC)/empirical orthogonal function (EOF) analysis to decompose multi‐year time series of glacier speed, combined from three satellite‐derived products at four glaciers feeding Sermilik Fjord, Greenland. This improves on single‐point methods by yielding spatial patterns (EOFs), which ensure the result reflects data at all locations on the glacier, and associated temporal patterns (PCs), which allow identification of glacier type. We find that the leading EOF is uniformly signed over the entire glacier domain, that this mode explains the majority of the variance in speed, and therefore that glacier type can be inferred from the leading PC. We find that Helheim Glacier was terminus‐driven, Fenris Glacier and Midgard Glacier were runoff‐adapting, and Pourquoi Pas Glacier was runoff‐driven over 2016–2021. Our classification agrees with previous work for Helheim and Midgard Glaciers, but differs at the other two. At all but Fenris Glacier, the leading PC correlates significantly with the speed pattern observed at the single point used in previous analyses. Thus, Fenris Glacier has more complex flow patterns than single‐point analysis can capture, and wider spatial analysis techniques such as EOF/PC are required. We suggest that, due to its low computational cost and inclusion in standard analysis packages, EOF/PC analysis should be used for assessing glacier type. Plain Language Summary: Glaciers change their flow speed throughout the year. Most glaciers move slowest in winter and more quickly during summer, but subtle differences in the timing give us clues as to what controls the speed of the glacier. Some glaciers respond to ocean conditions ("terminus‐driven"), others respond to ice melting at the top surface of the glacier ("runoff‐driven"), and still others adjust their water systems as the ice melts, responding to the same melt in a different way ("runoff‐adapting"). We do not know the types of all glaciers, nor what causes a glacier to be a certain type. Previous work identified the types of a few dozen glaciers around Greenland by manually examining ice flow at a single point on each glacier. Here, we take a wider approach by mathematically extracting patterns in ice flow across the entire glacier, not just a single point. We analyze four glaciers that flow into the same fjord in East Greenland. Our results broadly agree with the previous simpler analyses, but differ at two glaciers and identify possible "multi‐type" glaciers. Thus, our method holds promise in the quest to discover what controls the seasonal flow patterns of Greenland glaciers. Key Points: Glacier type varies across Sermilik Fjord: Helheim is terminus‐driven, Fenris and Midgard are runoff‐adapting, and Pourquoi Pas is runoff‐drivenDecomposition by empirical orthogonal functions and principal components reveals glacier type using data at all points in the glacier domainInferred glacier types differ slightly from previous work because we weight all locations equally and isolate the seasonal component [ABSTRACT FROM AUTHOR]

The abrupt deceleration of accelerated Greenland Ice Sheet (GrIS) melting since 2013, after a period of acceleration previously noted, is studied here. It is shown that the deceleration of GrIS melting since 2013 is due to the reduction in short‐wave solar radiation in the presence of increasing total cloud cover, which is driven by a more persistent positive summer North Atlantic Oscillation on the decadal time scale. By presenting the coherence with the temperature variability at the weather stations in Greenland, which have century‐long records, we deduce that the acceleration of GrIS melting during the early 2000s and the subsequent deceleration since 2013 will reoccur frequently on decadal time scales, with the amplitude nearly half of the multidecadal warming trend of the GrIS melt. It can reduce the mass loss from the GrIS on short to medium time scales but is unlikely to halt mass loss related to climate change in the future. This finding highlights the importance of internal climate variability on the mass budget of the GrIS and therefore on predictions of future global sea level change and may help to assist planning for associated social and economic consequences. Plain Language Summary: The Greenland Ice Sheet (GrIS) mass change and its contribution to the global sea level variability is a topic that naturally piques our curiosity. Since the satellite first captured the Greenland‐wide ice sheet mass variability in 2002, the GrIS experienced accelerated melting, leading to global sea level acceleration. The long‐term GrIS melting depends on climate change such as greenhouse warming. However, recently, this acceleration is slowed down due to the summer North Atlantic Oscillation phase changing to positive. We use century‐long surface temperature records as index to estimate the contribution of this slowdown phenomenon and find that the amplitude of this internal variability is nearly half of the multidecadal warming trend of the GrIS; therefore, this cycle can slow down but cannot stop the loss of the Greenland Ice Sheet mass at present and in the near future. This finding highlights the role of the internal variability of the GrIS on predictions of future global sea level change and the associated social and economic consequences. Key Points: Greenland Ice Sheet exhibits decelerated melt since 2013The deceleration is due to increased cloud during positive summer NAOThe accelerated and decelerated GrIS melt will reoccur on decadal time scale [ABSTRACT FROM AUTHOR]

Zeolites are a diverse group of calcium and sodium aluminosilicate minerals. They are tectosilicates (3‐D arrays of SiO4 tetrahedra), but vary in chemistry and crystal symmetry. Some readily exchange sodium for calcium and are used as water softeners. They also find applications as molecular sieves in petroleum refining, although the bulk of zeolites used industrially today are synthetic. These minerals form at low temperatures under well‐defined conditions and can be used as indicators of palaeotemperatures. In the same environment, but at higher temperatures, other minerals form including quartz, calcite, prehnite and even native copper. The Inuit of East Greenland, a Stone Age people, may have utilized native copper from this environment as did the Copper Inuit of the central Canadian Arctic. [ABSTRACT FROM AUTHOR]

Perchlorate in the environment originates from both natural and anthropogenic sources. A previous study of a 300‐year Greenland ice core perchlorate record found that anthropogenic impact on environmental perchlorate became significant starting around 1980, while natural formation is the only significant source of environmental perchlorate prior to that. The study also found increased perchlorate deposition in the Arctic following certain volcanic eruptions and suggested that at least some volcanic eruptions could enhance natural perchlorate production. Here we compare the perchlorate record with the volcanic record from sulfate in the same Greenland ice core and find that only stratospheric eruptions—large eruptions injecting volcanic substances directly into the stratosphere—enhance perchlorate production. No contribution to naturally formed perchlorate is detected from non‐stratospheric eruptions. The high‐resolution ice core perchlorate data are used to quantify contributions from volcanic eruptions, non‐volcanic natural processes, as well as from human activities during different periods. For the location in the Arctic in the perchlorate Pre‐Anthropogenic Era (1701–1979), the magnitude (0.26 μg m−2 yr−1 on average) of perchlorate produced during sporadic stratospheric eruptions is comparable to that (0.23 μg m−2 yr−1) produced by non‐volcanic natural processes. In the Anthropogenic Era (1980–2006), the magnitude of both the volcanic and non‐volcanic natural perchlorate production is similar to the enhancement (0.29 μg m−2 yr−1) by human activities. Plain Language Summary: Perchlorate is widespread in the environment. In remote regions such as the Arctic, environmental perchlorate primarily comes from natural formation in the atmosphere from common‐place chemicals containing chlorine. Previously, we studied a 300‐year chronological perchlorate record from a Greenland ice core and found that, prior to 1980, perchlorate production was not affected by human activities. We also found that certain volcanic eruptions may increase the amount of perchlorate produced in the atmosphere and deposited in Greenland snow. In this study, we use the ice‐core perchlorate and sulfate data to determine that only very large eruptions can cause additional perchlorate to be formed in the atmosphere. On average, large volcanic eruptions contribute about 50% of perchlorate from all natural sources at this location in the Arctic. Since 1980, human activities have contributed approximately the same amount of perchlorate to the environment as that from all natural sources. Key Points: Atmospheric perchlorate formation is enhanced by only stratospheric volcanic eruptions, not by non‐stratospheric eruptionsVolcanic perchlorate in the Arctic is on average approximately 50% of all naturally produced perchlorate prior to 1980Contribution from anthropogenic activities since 1980 is approximately equal to that from natural perchlorate sources [ABSTRACT FROM AUTHOR]

Mass loss of the Greenland Ice Sheet (GrIS) plays a major role in the global sea level rise. The west coast of the GrIS has contributed 1,000 Gt of the 4,488 Gt GrIS mass loss between 2002 and 2021, making it a hotspot for GrIS mass loss. Surface melting is driven by changes in the radiative budget at the surface, which are modulated by clouds. Previous works have shown the impact of North Atlantic transport for influencing cloudiness over the GrIS. Here we used space‐based lidar cloud profile observations to show that a polar low circulation promotes the presence of low clouds over the GrIS west coast that warm radiatively the GrIS surface during the melt season. Polar low circulation transports moisture and low clouds from the sea to the west of Greenland up over the GrIS west coast through the melt season. The concomitance of the increasing presence of low cloud in fall over the Baffin Sea due to seasonal sea‐ice retreat and a maximum occurrence of Polar low circulation in September results in a maximum of low cloud fraction (∼14% at 2.5 km above sea level) over the GrIS west coast in September. These low clouds warm radiatively the GrIS west coast surface up to 80 W/m2 locally. This warming contributes to an average increase of 10 W/m2 of cloud surface warming in September compared to July on the GrIS west coast. Overall, this study suggests that regional atmospheric processes independent from North Atlantic transport may also influence the GrIS melt. Plain Language Summary: The melting of Greenland plays a major role in the global sea level rise. The west coast of Greenland has contributed to 22% of Greenland mass loss between 2002 and 2021, making it a hotspot for Greenland mass loss. Clouds modulate the energy that reaches the surface of Greenland and, therefore, might accelerate or decelerate surface melt. To explain what leads to cloud presence over Greenland, previous studies focused on the connection between the mid‐latitudes and the Greenland cloud cover. Using a combination of satellite cloud observation and models, we highlight that a low‐pressure system over the Arctic brings moisture and low clouds from the sea west of Greenland to the Greenland west coast. Then, we assess the strong surface warming effect of these low clouds. Overall, our study demonstrates that local Arctic processes lead to formation of low clouds where Greenland melts. Key Points: The Greenland Ice Sheet (GrIS) west coast by itself represents 22% of the GrIS mass loss over the last two decadesA polar low promotes the presence of low clouds over the GrIS west coast during the melt seasonThe cloud surface radiative warming on the Greenland west coast is +10 W/m2 larger in September than July due to these low clouds [ABSTRACT FROM AUTHOR]

Glacial fjord circulation determines the import of oceanic heat to the Greenland Ice Sheet and the export of ice sheet meltwater to the ocean. However, limited observations and the presence of both glacial and coastal forcing—such as coastal‐trapped waves—make uncovering the physical mechanisms controlling fjord‐shelf exchange difficult. Here we use multi‐year, high‐resolution, realistically forced numerical simulations of Sermilik Fjord in southeast Greenland to evaluate the exchange flow. We compare models, with and without a plume, to differentiate between the exchange flow driven by shelf variability and that driven by subglacial discharge. We use the Total Exchange Flow framework to quantify the exchange volume transports. We find that a decline in offshore wind stress from January through July drives a seasonal reversal in the exchange flow increasing the presence of warm Atlantic Water at depth. We also find that including glacial plumes doubles the exchange flow in the summer. Our results show that the plume‐driven circulation is more effective at renewal with a flushing time 1/3 that of the shelf‐driven circulation near the fjord head. Plain Language Summary: Glacial fjords are narrow coastal inlets with a glacier at the landward edge. The flow of water within fjords plays a crucial role in exchanging heat and freshwater between the glacial ice and ocean. The circulation of water is driven, in part, by melting at the ice surface which falls through cracks in the ice and enters the fjord near the sea bed. The meltwater is less dense than ocean water causing it to rise as a plume before leaving the fjord close to the surface. However, fjord circulation is also impacted by storms close to the coast and offshore wind. We used a model of a fjord in Greenland to isolate and study the effects of coastal winds and meltwater on fjord circulation. Our model experiments reveal that weaker than average winds can lead to warmer water within the fjord. Also, we find that the circulation speed doubles with the addition of meltwater and a plume. These results increase our understanding of fjord circulation. Key Points: We present a set of realistically forced, multi‐year numerical simulations of Sermilik Fjord in GreenlandThe shelf‐driven circulation is tied to along‐shelf wind stress and drives a reversal in the exchange flow as winds intensify in SeptemberThe plume‐driven circulation is more effective at renewal with a flushing time 1/3 that of the shelf‐driven circulation near the fjord head [ABSTRACT FROM AUTHOR]

The Northeast Water Polynya is a significant annually recurring summertime Arctic polynya, located off the coast of Northeast Greenland. It is important for marine wildlife and affects local atmospheric and oceanic processes. In this study, over 40 years of observational and reanalysis products (ERA5 and ORAS5) are analyzed to characterize the polynya's climatology and ascertain forcing mechanisms. The Northeast Water Polynya has high spatiotemporal variability; its location, size and structure vary interannually, and the period for which it is open is changing. We show this variability is largely driven by atmospheric forcing. The polynya extent is determined by the direction of the near‐surface flow regime, and the relative locations of high and low sea‐level pressure centers over the region. The surface conditions also impact the oceanic water column, which has a strong seasonal cycle in potential temperature and salinity, the amplitude of which decreases with depth. The ocean reanalyses also show a significant warming trend at all depths and a freshening near the surface consistent with greater ice melt, but salinification at lower depths (∼200 m). As the Arctic region changes due to anthropogenic forcing, the sea‐ice edge is migrating northwards and the Northeast Water Polynya is generally opening earlier and closing later in the year. This could have significant implications for both the atmosphere and ocean in this complex and rapidly changing environment. Plain Language Summary: Polynya's are areas of open water surrounded by sea ice. These features are important for marine wildlife and can impact how the atmosphere and ocean interact. The Northeast Water Polynya is one example from the Arctic. Each summer, it appears off the coast of Northeast Greenland. In this research we use data from the last 40 years to study this polynya. We find that its location, size and structure varies from year to year. The period for which it is open each year also changes. We conclude that these differences are due to changes in the wind direction near the surface. Winds that flow from south to north over the region are linked to a larger polynya. Winds that flow from north to south are linked to a smaller polynya. With climate change, the Northeast Water Polynya is opening earlier and closing later in the year. In the future, this polynya may no longer form as it does now, which will impact the local environment and wildlife. Key Points: A climatological study of the Northeast Water Polynya reveals spatial, interannual and decadal variabilityThe summertime polynya extent closely correlates to near‐surface winds, largely dictated by the orientation of the pressure gradient across Fram StraitBetween 1980 and 2022, the duration of the Northeast Water Polynya, and associated oceanic warming, increased [ABSTRACT FROM AUTHOR]

Supraglacial lakes have been observed to drain within hours of each other, leading to the hypothesis that stress transmission following one drainage may be sufficient to induce hydro‐fracture‐driven drainages of other nearby lakes. However, available observations characterizing drainage‐induced stress perturbations have been insufficient to evaluate this hypothesis. Here, we use ice‐sheet surface‐displacement observations from a dense global positioning system array deployed in the Greenland Ice Sheet ablation zone to investigate elastic stress transmission between three neighboring supraglacial lake basins. We find that drainage of a central lake can place neighboring basins in either tensional or compressional stress relative to their hydro‐fracture scarp orientations, either promoting or inhibiting hydro‐fracture initiation beneath those lakes. For two lakes located within our array that drain close in time, we identify tensional surface stresses caused by ice‐sheet uplift due to basal‐cavity opening as the physical explanation for these lakes' temporally clustered hydro‐fracture‐driven drainages and frequent triggering behavior. However, lake‐drainage‐induced stresses in the up‐flowline direction remain low beyond the margins of the drained lakes. This short stress‐coupling length scale is consistent with idealized lake‐drainage scenarios for a range of lake volumes and ice‐sheet thicknesses. Thus, on elastic timescales, our observations and idealized‐model results support a stress‐transmission hypothesis for inducing hydro‐fracture‐driven drainage of lakes located within the region of basal cavity opening produced by the initial drainage, but refute this hypothesis for distal lakes. Plain Language Summary: Mass loss from the Greenland Ice Sheet is accelerating, partly due to increasing rates of ice flow to the ocean. Ongoing increases in ice‐sheet surface melting play a complex role in this process: meltwater flows down through conduits and fractures to the ice‐sheet bed, lubricates the ice‐bed interface, and modulates ice‐flow speeds on hourly to decadal timescales. Drainage of supraglacial lakes via hydro‐fracture—water‐driven fracture propagation—produces the highest rates of meltwater flux to the ice‐sheet bed. The geographical range of lakes on the ice sheet has expanded in recent decades, but not all supraglacial lakes drain by hydro‐fracture: whether a hydro‐fracture‐driven drainage occurs in any particular lake basin is controlled by the ice‐sheet stress state. Here, we investigate whether one lake drainage can generate stress changes in neighboring lake basins that trigger hydro‐fracture initiation. We find that the drainage of one lake does lead to tensional stresses that promote hydro‐fracture initiation in a neighboring lake basin, but also that this initial lake drainage leads to a more compressive stress state that inhibits hydro‐fracture initiation in a different neighboring lake basin. Key Points: Drainage of one lake can place neighboring basins in tensional or compressional stress, promoting or inhibiting hydro‐fracture initiationTensional surface stresses are predominantly caused by basal cavity opening, with smaller contributions from basal slipThe first‐order control on elastic stress‐coupling length scales is the region of the bed over which basal cavity opening occurs [ABSTRACT FROM AUTHOR]

The Northeast Greenland shelf is a broad Arctic shelf located between Greenland and Fram Strait. It is the principal gateway for sea ice export and sea ice‐associated freshwater from the Arctic Ocean. Sea ice thickness has decreased by 15% per decade since the early 1990s and meteoric freshwater discharge has increased. The consequence of changing sea‐ice and freshwater conditions in the region on ocean dynamics and the biological system remains unknown. Determining the source(s) of freshwater is important to be able to understand how the area will react to future upstream change. Here we present a synoptic survey of the Northeast Greenland shelf and slope with observations of hydrography, the nutrients nitrate, phosphate and silicate, and conservative tracers δ18O, δ2H, and total alkalinity during late summer 2017. We compare these to previously published values, including those which identify Pacific and Atlantic water, the Siberian shelf seas, and the six largest Arctic rivers. We show that a major source of freshwater on the Northeast Greenland shelf during late summer 2017 is the Laptev Sea and find no conclusive evidence of Pacific Water. Our observations indicate a direct link between Northeast Greenland hydrology and processes occurring on Eurasian shelves. Plain Language Summary: The Northeast Greenland shelf is a shallow marine environment between Greenland and the adjacent Fram Strait, where a large fraction of the Arctic Ocean freshwater is exported into the North Atlantic. To predict the regional response to climate change, it is important to determine what the remote sources of freshwater on the shelf are and how these influence mixing. We compare the chemistry of the water found at different locations on the shelf with those found in other areas of the Arctic Ocean to determine where it comes from and conclude that most of the water on the Northeast Greenland shelf in late summer of 2017 is from the Laptev Sea, while surface waters have subsequently been modified by sea ice melt. Key Points: Northeast Greenland Winter Water is fresher than in the 1990sThe cold halocline layer is a brine‐enhanced mixture of river discharge and Atlantic WaterThe river discharge is primarily sourced from the Laptev Sea [ABSTRACT FROM AUTHOR]

Aim: Previous studies have found high rates of stunted linear growth in Greenlandic children. We measured growth patterns in Greenland and compared them with international growth charts., Methods: The study cohort comprised 279 healthy children aged 6-10 years in 2012. They participated in two pregnancy and birth cohorts in Greenland and longitudinal growth data as birth was extracted from their medical records. Growth reference ranges were estimated with the lambda-mu-sigma (LMS) method and compared with growth charts from Denmark and the World Health Organization (WHO)., Results: The children's mean length, weight and head circumference were significantly larger than the WHO growth charts (p < 0.001). We found that 21-28% of the children aged zero to one years exceeded the WHO growth chart for length by more than two standard deviations. For weight and head circumference, 9-16% of the children aged 0-10 years and 9-11% of the children from zero to two years exceeded the WHO charts by more than two standard deviations. The Danish references were exceeded to a lesser degree., Conclusion: This study showed that the growth of Greenlandic children up to 10 years was no longer stunted. Major determining factors suggested are genetic admixture, maternal overweight, changes in nutrition and improved health., (©2018 The Authors. Acta Paediatrica published by John Wiley & Sons Ltd on behalf of Foundation Acta Paediatrica.)

Arctic‐origin and Greenland meltwaters circulate cyclonically in the boundary current system encircling the Labrador Sea. The ability of this freshwater to penetrate the interior basin has important consequences for dense water formation and the lower limb of the Atlantic Meridional Overturning Circulation. However, the precise mechanisms by which the freshwater is transported offshore, and the magnitude of this flux, remain uncertain. Here, we investigate wind‐driven upwelling northwest of Cape Farewell using 4 years of high‐resolution data from the Overturning in the Subpolar North Atlantic Program west Greenland mooring array, deployed from September 2014–2018, along with Argo, shipboard, and atmospheric reanalysis data. A total of 49 upwelling events were identified corresponding to enhanced northwesterly winds, followed by reduced along‐stream flow of the boundary current and anomalously dense water present on the outer shelf. The events occur during the development stage of forward Greenland tip jets. During the storms, a cross‐stream Ekman cell develops that transports freshwater offshore in the surface layer and warm, saline, Atlantic‐origin waters onshore at depth. The net fluxes of heat and freshwater for a representative storm are computed. Using a one‐dimensional mixing model, it is shown that the freshwater input resulting from the locus of winter storms could significantly limit the wintertime development of the mixed layer and hence the production of Labrador Sea Water in the southeastern part of the basin. Plain Language Summary: The western Labrador Sea is one of the few locations in the world ocean where open‐ocean convection forms intermediate waters. This happens when strong winds and large air‐sea heat fluxes densify surface waters and mix them to depth. The presence of surface freshwater can inhibit this process, and, curiously, the deepest convection occurs in the western Labrador Sea even though the wintertime air‐sea fluxes are comparable in the eastern Labrador Sea. In this study, we use 4 years of temperature, salinity, and velocity mooring data and atmospheric reanalysis data from the west Greenland shelf and slope to demonstrate that freshwater is transported from the shelf to the interior eastern Labrador Sea due to short, intense storms known as forward Greenland tip jets. The strong winds set up a temporary cross‐stream circulation called an Ekman cell that transports freshwater offshore in the surface layer and heat onshore at depth. Over the 4 years, 49 such events were observed, which we describe and characterize. Importantly, we show that during the winter season, these storms flux enough freshwater offshore to inhibit the densification of surface waters in the eastern Labrador Sea, thus explaining why deep convection is only observed in the west. Key Points: Forward Greenland tip jets trigger oceanic upwelling along the southwest coast of GreenlandThe wind‐induced upwelling fluxes freshwater offshore at the surface and heat onshore at depth via the cross‐stream Ekman circulationThe freshwater flux could inhibit wintertime convection in the eastern basin, thus explaining why Labrador Sea Water is not formed there [ABSTRACT FROM AUTHOR]

This role for alternatives (or similar) in non-decision HT ht -values is not new: after first discussing some exceptions Cox ([2], section 2.7) acknowledges how alternatives generally drive choice of divergence measures. Finally, I very much doubt this process will be compatible with the strong likelihood principle - but if so, that would be a problem for the strong likelihood principle, and not divergence HT ht -values. Decision P$$ P $$-values: A Distinction Worth Making in Theory and Keeping in Practice - or, How Divergence P$$ P $$-values Measure Evidence Even When Decision P$$ P $$-values Do Not" by Sander Greenland. [Extracted from the article]

Accelerated mass loss from the Greenland ice sheet leads to glacier retreat and an increasing input of glacial meltwater to the fjords and coastal waters around Greenland. These high latitude ecosystems are highly productive and sustain important fisheries, yet it remains uncertain how they will respond to future changes in the Arctic cryosphere. Here we show that marine-terminating glaciers play a crucial role in sustaining high productivity of the fjord ecosystems. Hydrographic and biogeochemical data from two fjord systems adjacent to the Greenland ice sheet, suggest that marine ecosystem productivity is very differently regulated in fjords influenced by either land-terminating or marine-terminating glaciers. Rising subsurface meltwater plumes originating from marine-terminating glaciers entrain large volumes of ambient deep water to the surface. The resulting upwelling of nutrient-rich deep water sustains a high phytoplankton productivity throughout summer in the fjord with marine-terminating glaciers. In contrast, the fjord with only land-terminating glaciers lack this upwelling mechanism, and is characterized by lower productivity. Data on commercial halibut landings support that coastal regions influenced by large marine-terminating glaciers have substantially higher marine productivity. These results suggest that a switch from marine-terminating to land-terminating glaciers can substantially alter the productivity in the coastal zone around Greenland with potentially large ecological and socio-economic implications. [ABSTRACT FROM AUTHOR]

Observed and model‐projected sea ice loss enhances warming in the Arctic. We investigate to what extent warming on Greenland can be attributed to changes in the sea ice cover in different parts of the Arctic. Using Climate Model Intercomparison Project phase 5 model projections of the future, we perform multilinear regressions to separate the simulated warming on Greenland in two parts; one following global warming and one following regional sea ice changes. This reveals the magnitude and spatial pattern of warming on Greenland, which can be attributed to sea ice loss in different Arctic regions. The results indicate that the impact of sea ice loss is largely confined to the coastal parts of Greenland. We find the strongest links to sea ice loss in adjacent regions; remote regions only have a limited impact. Overall, warming attributable to sea ice variability is a minor contribution but can be a dominant signal locally in coastal regions. Plain Language Summary: The observed decline of the Arctic sea ice cover is projected to continue with continued global warming. Sea ice loss contributes to amplified warming in the Arctic region, which could increase melting on the Greenland Ice Sheet and thereby contribute to global sea level rise. Here, we study the long‐term warming impact from sea ice loss using data from 10 climate models covering the period 1850–2300. Our aim is to isolate the warming contribution from sea ice loss and study how it varies across Greenland for sea ice loss in different parts of the Arctic. The results indicate that sea ice loss occurring near Greenland has a warming impact along the adjacent coasts but only a limited impact on the central, more elevated ice sheet. Sea ice loss occurring in more remote parts of the Arctic has no substantial impact on Greenland. Finally, our analysis suggests that sea ice loss provides a minor contribution to Greenland warming overall, but it can be a dominant effect locally in coastal areas. Key Points: Warming in coastal parts of Greenland can in part be attributed to nearby sea ice lossOnly a limited part of the warming on central Greenland can be attributed to sea ice lossSea ice loss in more remote regions has a minor impact on Greenland warming [ABSTRACT FROM AUTHOR]

Sediment cores from 13 lakes in a 1500 km transect along the eastern North American Arctic contain up to four superposed stratified interglacial units. All 13 lakes contain one unit with sediment similar in character and mass to Holocene gyttja, with 14C ages >40 ka, luminescence ages 90 to 120 ka, and pollen assemblages that require nearly complete Laurentide deglaciation, supporting a Last Interglacial (LIG; MIS 5e) age. Two lakes preserve an older interglacial, with luminescence ages suggesting an MIS 7 age. Four adjacent lakes record a thin, stratified organic unit between the LIG and Holocene units with 14C ages >50 ka, that is probably from late in MIS 5. Temperature estimates from biotic proxies suggest LIG summer temperatures 4–6°C above mid‐20th century values; pollen, chironomids and DNA document a poleward expansion of woody plants and invertebrate species during the LIG, supporting arguments that positive feedbacks native to the Arctic amplified insolation‐driven summer temperature increases. The stratigraphic succession implies the Laurentide Ice Sheet remained intact with sea level below ‐40 m from ~115 ka to ~11 ka, and places new constraints on the interpretation of cosmogenic radionuclide inventories in erratic boulders older than the Holocene throughout this region. [ABSTRACT FROM AUTHOR]

Abstract: The surface mass balance of the Greenland ice sheet critically depends on the intensity of ice melt/snowmelt in its ablation zone, but in situ data have been too limited to quantify the error of regional climate models. Here we use 23 years of NASA satellite and airborne laser altimetry from the Airborne Topographic Mapper; Land, Vegetation, and Ice Sensor; and Ice, Cloud, and land Elevation Satellite to generate time series of elevation change to compare with surface mass balance products from the Regional Atmospheric Climate Model and from the Modèle Atmosphérique Régional. For 1994–2016, the results agree at the 15–26% level, with the largest discrepancy in North Greenland. During the cold summer of 2015, the root‐mean‐square discrepancy is 40% in the north, 30% in the southwest, and 18–25% at low elevation. The difference drops to 23% in the southwest and 14% at low elevation during the 2016 warm summer. [ABSTRACT FROM AUTHOR]

Surface crevasses on the Greenland Ice Sheet (GrIS) capture nearly half of the seasonal runoff, yet their role in transferring meltwater to the bed has received little attention relative to that of supraglacial lakes and moulins. Here, we present observations of crevasse ponding and investigate controls on their hydrological behavior at a fast‐moving, marine‐terminating sector of the GrIS. We map surface meltwater, crevasses, and surface‐parallel stress across a ∼2,700 km2 region using satellite data and contemporaneous uncrewed aerial vehicle (UAV) surveys. From 2017 to 2019 an average of 26% of the crevassed area exhibited ponding at locations that remained persistent between years despite rapid advection. We find that the spatial distribution of ponded crevasses does not relate to previously proposed controls on the distribution of supraglacial lakes (elevation and topography) or crevasses (von Mises stress thresholds), suggesting the operation of some other physical control(s). Ponded crevasse fields were preferentially located in regions of compressive surface‐parallel mean stress, which we interpret to result from the hydraulic isolation of these systems. This contrasts with unponded crevasse fields, which we suggest are readily able to transport meltwater into the wider supraglacial and englacial network. UAV observations show that ponded crevasses can drain episodically and rapidly, likely through hydrofracture. We therefore propose that the surface stress regime influences a spatially heterogeneous transfer of meltwater through crevasses to the bed of ice sheets, with consequences for processes, such as subglacial drainage and the heating of ice via latent heat release by refreezing meltwater. Plain Language Summary: Surface crevasses on the Greenland Ice Sheet (GrIS) transfer nearly half of all the ice sheet's meltwater to the bed, yet when, where, and how this occurs is poorly understood. We use large‐scale satellite analysis and uncrewed aerial vehicle (UAV) surveys to assess the spatial variability of meltwater ponding in crevasses across a fast‐flowing sector of the western GrIS. Between 2017 and 2019 an average of a quarter of crevasse fields ponded, in roughly the same area every year. However, the locations of such ponding cannot be explained in the same way as supraglacial lakes, which collect in surface basins. Instead, we find that ponded crevasses exist in regions of compressive surface stress. We suggest that this is because compressive regimes close pathways that elsewhere allow crevasses to drain into the wider surface hydrological system. Using UAV surveys, we show that these ponded crevasses instead drain rapidly to the bed by hydrofracture. Differing drainage processes in regions of compressive and extensional regimes may have distinct consequences for subglacial drainage and the heating of the ice sheet due to energy release during meltwater refreezing. Key Points: At a marine‐terminating sector of the Greenland Ice Sheet, 26% of all crevasses ponded between 2017 and 2019; the rest remained unfilledPonded crevasse locations persist between years but, unlike supraglacial lakes, this distribution is not topographically controlledCrevasses pond in compressive stress regimes, likely due to hydraulic isolation by creep closure, and drain predominantly via hydrofracture [ABSTRACT FROM AUTHOR]

The observed crustal uplift rates in Greenland are caused by the combined response of the solid Earth to both ongoing and past surface mass changes. Existing elastic Earth models and Maxwell linear viscoelastic GIA (glacial isostatic adjustment) models together underpredict the observed uplift rates. These models do not capture the ongoing mantle deformation induced by significant ice melting since the Little Ice Age. Using a simple Earth model within a Bayesian framework, we show that this recent mass loss can explain the data‐model misfits but only when a reduced mantle strength is considered. The inferred viscosity for sub‐centennial timescale mantle deformation is roughly one order of magnitude smaller than the upper mantle viscosity inferred from GIA analysis of geological data. Reconciliation of geological sea‐level and modern crustal motion data may require that the model effective viscosity be treated with greater sophistication than in the simple Maxwell rheological paradigm. Plain Language Summary: There are 57 permanent Global Navigation Satellite System (GNSS) stations on bedrock in Greenland. These stations provide point‐measurements of three‐dimensional crustal motion. We can model a large portion of the observed crustal uplift rates as elastic Earth response to ongoing rates of ice‐mass loss. We model the remaining part of the uplift rates as the ongoing viscous response of the solid Earth to past ice‐ocean mass exchange—a process termed glacial isostatic adjustment (GIA). Earth structure and deglaciation history in GIA models are usually constrained by geological data that record paleo sea level and past ice margins. To fully explain the GNSS‐measured uplift rates, we propose that these geologically constrained GIA models should additionally resolve: (a) ice‐mass changes during and after the Little Ice Age; and (b) broadband mantle relaxation processes. While such features are challenging to implement, they offer a more granular model paradigm appropriate to the improved temporal sampling that the collective geological and geodetic data sets now provide. Key Points: GIA models constrained by geological data underpredict the modern crustal uplift rates corrected for the elastic loading effectsMass loss since the Little Ice Age explains the residual uplift rates provided a reduced mantle viscosity on sub‐centennial timescalesReconciling geological and modern geodetic data requires a more sophisticated mantle rheology model than generally used in loading studies [ABSTRACT FROM AUTHOR]

Aggregated clusters of acritarchs are relatively common among assemblages of organic‐walled microfossils, yet such associations have received relatively little attention. Here we report a new diversity of acritarch clusters from the early Cambrian Buen Formation of North Greenland. The aggregation patterns of four genera (Skiagia, Comasphaeridium, Asteridium and Synsphaeridium) are described together with their background population characteristics (presence of openings, inner bodies and overall disparity) in order to better understand the palaeobiology of these acritarchs. The majority of Skiagia clusters were found to be monospecific despite significant intraspecific variability, a pattern that is suggestive of a strong environmental influence on Skiagia morphologies and aggregation habits. Abundant small (<20 μm) Comasphaeridium vesicles were recovered in a broad range of chiefly monospecific clusters that are likely to have been formed under bloom conditions. A colonial habit is tentatively inferred from the tightly packed appearance of monogeneric Asteridium aggregates, and clearly evidenced by the highly conserved cellular structure of recovered Synsphaeridium clusters. A lack of excystment structures in Comasphaeridium and Asteridium vesicles suggest these taxa represent actively growing cells rather than resting cysts. Altogether, these findings shed new light on the diversity of cellular structures and lifestyles represented among Cambrian acritarchs, and illustrate a range of reproduction and defence strategies adopted by plankton in the face of novel environmental pressures. [ABSTRACT FROM AUTHOR]

The Arctic has warmed almost four times faster than the rest of the globe during the past four decades. This has led to multiple impacts in the Arctic such as the melting of glaciers and the Greenland ice sheet, sea ice retreat, permafrost thaw, altered species distribution and abundance, changes in hydrology and snow conditions, and altered wildfire regimes. These documented and projected impacts in the region can also propagate across borders, creating risks and opportunities requiring adaptation responses well beyond the Arctic. By undertaking a systematic literature review that uses a conceptual framework for cross‐border climate change impacts, we demonstrate how local impacts of the type described above, which are often analyzed separately in the literature, may initiate knock‐on effects that can be transmitted and transformed across borders. We illustrate examples of six categories of cross‐border risks resulting from this impact transmission and potentially requiring adaptation. These concern biophysical impacts, trade, infrastructure, finance, geopolitical relationships and human security and social justice. We examine potential adaptation options for responding to such cross‐border risks that are of relevance for Europe. The systemic approach taken in this paper promotes improved understanding of trade‐offs between potential benefits and risks, assists priority‐setting for targeting adaptation interventions, and can account for the important role of non‐climatic drivers in amplifying or dampening the cross‐border risks of climate change impacts in the Arctic. This article is categorized under:Trans‐Disciplinary Perspectives > Regional ReviewsAssessing Impacts of Climate Change > Observed Impacts of Climate ChangeAssessing Impacts of Climate Change > Evaluating Future Impacts of Climate ChangeVulnerability and Adaptation to Climate Change > Learning from Cases and Analogies [ABSTRACT FROM AUTHOR]

We investigated highly mature sedimentary rocks exposed along both sides of the Fram Strait in the northern North Atlantic using apatite fission track and (U‐Th)/He thermochronology to obtain information on the thermal imprint of rifting and continental breakup processes along a sheared margin. Our data showed that the conjugate margins experienced several heating episodes, which we explain as resulting from heat transfer along segments of the De Geer Fracture Zone, a large continental transform system which connected magmatic centers north and south of the Fram Strait. Heating occurred prior to and during the Eurekan intraplate orogeny, which occupied the position of the present‐day Fram Strait during the Eocene. Heat transfer may have caused or contributed to lithospheric weak zones, which focussed deformation during intraplate orogeny. Movements along the transform fault system continued during the Oligocene, after the end of the Eurekan Orogeny, causing further structural weakening of pre‐existing fault zones. These were exploited during the final continental breakup leading to the opening of the Fram Strait. No unambiguous thermal signature associated with this latest stage of breakup was detected. Our data underline recent studies on the importance of structural inheritance and continental transform faults for the prolonged and complex processes of continental rifting and breakup. Key Points: Thermal anomalies along the Fram Strait are related to tectonic processes from Late Cretaceous rifting to Miocene continental breakupThe De Geer Fracture Zone influenced the thermal evolution and structural weakening of the crust, which contributed to the Eurekan orogenyStructural inheritance and transform faults influence continental rifting and the development of continental margins [ABSTRACT FROM AUTHOR]

Outcrops of coarse‐grained, high‐angle clinoform sets are mainly thought to represent Gilbert‐type deltas. Superficially similar clinoform sets may, however, form in marine, sub‐wave base settings. They are interpreted to have formed as a result of storms where downwelling, seaward‐directed currents transported sand from the coastal area and shoreface across the shelf in suspension or as bedload to be deposited as clinothems. An additional transport of sand took place by strong coast‐parallel currents. The clinoform sets appear to be associated with rift events, the creation of accommodation space and an increasing supply of coarse‐grained sediment. A major protracted rift phase was initiated in East Greenland in Middle Jurassic times and intensified through the Late Jurassic to reach a climax close to the Jurassic–Cretaceous boundary. Rifting caused uplift of borderlands, creation of accommodation space and development of shallow marine shelves passing offshore into submarine slopes and deeper basinal areas. Each rift event was accompanied by the formation of clinoform sets prograding seawards towards the east and southeast away from the cratonic coastline in water depths below the wave base. The clinoform sets are interpreted as typical motifs for rift events in the relatively shallow epeiric Jurassic seaway between East Greenland and Norway. Outcrops of such sets represent a little‐known, commonly misinterpreted sedimentary system and may serve as motifs for rifting in shallow marine areas elsewhere in the geological record. Similar sets have been recorded in outcrop from the Mediterranean, and elsewhere and are probably more common than hitherto realized. [ABSTRACT FROM AUTHOR]

Rainfall high on the Greenland Ice Sheet is an emerging phenomenon with consequences for the thermal and structural makeup of the surface layer. We document changes to Greenland's firn column due to a 4‐day cold‐season warm/rain event. Heavy precipitation occurred with a sudden 30°C increase in air temperature, reaching 0°C at 2,000 m elevation. Thermistor strings within the firn layer across a 35 km transect show rapid warming of 6°–23°C reaching depths of 2–10 m. Antecedent conditions governed the magnitude, duration, and depth‐distribution of sensible and latent heat added to the firn column. Heat fluxes from the firn layer required up to 8 weeks to recover to baseline, a significant fraction of the winter period. The amount of liquid water refrozen in the firn column was ∼20%–100% of the prior summer demonstrating the impact of extreme weather events on the ice sheet's evolution and runoff characteristics. Plain Language Summary: Based on measurements from a network of sensors installed on the Greenland Ice Sheet, we document changes in the firn layer (snow in transition to ice) due to a late Autumn extraordinary warm/rain event. After an extended period of cold‐season cooling of the firn, the event caused the firn layer to warm by 6°–23°C, mainly in one day, as rainwater and surface melt penetrated up to 6 m depth and refroze. The water added to the firn layer during this extreme weather event was ∼25%–100% of what was added during the entire previous summer melt season. The unusual timing of water input during the cold‐season likely altered the firn differently than summer input from melt or rain. Our results demonstrate that only a minor increase in the frequency and magnitude of similar rain events has potential for outsized impact on the thermal and density transformation of Greenland's firn layer which has implications for future runoff processes. Key Points: A cold‐season rainstorm on the Greenland Ice Sheet demonstrates outsized impact of extreme weather events on evolution of the firn layerFirn layer temperature quickly increased by up to 23°C, altering heat fluxes and requiring up to 2 months to thermally recoverThe liquid water refrozen within the firn layer was ∼20%–100% of the amount of water refrozen during the previous summer [ABSTRACT FROM AUTHOR]

We study the 3‐D P wave velocity (Vp) structure of the whole mantle beneath Greenland and surrounding regions using the latest P wave arrival time data. We use a new method of global seismic tomography by setting 3‐D grid nodes densely in the study volume to enhance the resolution. We invert ~5.6 million arrival times of P, pP, and PP waves from 16,257 earthquakes extracted from the ISC‐EHB catalog, which were recorded at 12,549 seismic stations in the world. Our results reveal a hot plume rising from the core‐mantle boundary beneath central Greenland, which is called the Greenland plume. This plume has the main conduit and two branches in the lower mantle, and the main conduit rises to the mantle transition zone (MTZ) beneath eastern Greenland, so it is distinguishable from the Iceland plume that appears to rise from a midmantle depth (~1,500 km) beneath Iceland. The Iceland plume itself is a powerful plume, but it may also be fed by hot mantle materials from three joints with other plumes: a branch of the Greenland plume at ~1,500 km depth, a plume beneath Western Europe at ~1,000 km depth, and the main conduit of the Greenland plume at the MTZ, leading to many active volcanoes in Iceland. We deem that the main conduit of the Greenland plume mixes with the Iceland plume incompletely and splits mainly into the Jan Mayen and Svalbard plumes in the upper mantle, which supply magma to the Jan Mayen hotspot and a geothermal area in western Svalbard, respectively. Plain Language Summary: Greenland and its surrounding regions have many clues for understanding global‐scale tectonics of the Earth. Seismic tomography is a well‐established method for obtaining 3‐D images of the underground structure by inverting a large number of seismic wave arrival times. We obtain detailed tomographic images of the whole mantle beneath Greenland and adjacent regions using the latest dataset. Our high‐resolution results show that the so‐called Iceland plume could be composed of two plumes. One is located directly beneath Iceland but rising from ~1,500 km depth, which we call the Iceland plume. The other is rising from the core‐mantle boundary beneath central Greenland, which we call the Greenland plume. The Greenland plume has the main conduit and two branches in the lower mantle, and the main conduit rises to the mantle transition zone beneath eastern Greenland. Although the Iceland plume itself is a powerful plume, it may also have three joints with other plumes: the main conduit and a branch of the Greenland plume, and a plume beneath Western Europe, resulting in many active volcanoes in Iceland. The main conduit of the Greenland plume may also supply magmas to the Jan Mayen hotspot and a geothermal area in western Svalbard. Key Points: Three‐dimensional P wave velocity structure of the whole mantle beneath Greenland and surrounding regions is investigatedA hot plume (Greenland plume) rising from the core‐mantle boundary beneath central Greenland is discoveredThe Iceland and Greenland plumes are connected and supplying magmas to Iceland, Jan Mayen, and Svalbard hotspots [ABSTRACT FROM AUTHOR]

Greenland Ice Sheet surface elevation is changing as mass loss accelerates. In understanding elevation change, the magnitudes of physical processes involved are important for interpretation of altimetry and assessing changes in these processes. The four key processes are surface mass balance (SMB), firn densification, ice dynamics, and isostatic adjustment. We quantified these processes at Summit, Greenland, where monthly Global Navigation Satellite System (GNSS) snowmobile traverses measured elevation change from 2008 to 2018. We find an elevation increase of 0.019 m a−1. The sum of the effects of the four processes reproduces the measured elevation time series, in linear trend and in intra‐annual variability. The short‐term variability in elevation is primarily explained by the variability in SMB. Since SMB has not changed significantly over the last century, and the other processes change over longer time scales, the elevation change likely has been ongoing for at least the last 100 years. Key Points: Measurements of ice sheet elevation, flow divergence, firn densification, and accumulation are self‐consistent at Summit, GreenlandThe ice sheet surface at Summit, Greenland, is rising at 1.9 cm/year over the last decade, a trend likely unchanged in the last centuryShort‐term ice sheet elevation changes are dominated by surface mass balance changes [ABSTRACT FROM AUTHOR]

Blocked atmospheric flows over Greenland and the North Atlantic Arctic (NAA) can be defined by the appearance of an anomalous ridge, many times off the western margin of continents, that deflects traveling cyclones from their usual storm tracks. Atmospheric blocking often produces a strong equatorward deflection of polar air on the eastern flank of the anticyclone, including severe cold episodes in winter, and severe droughts and heat waves in summer. Recent changes in low‐frequency atmospheric circulation in the NAA have increased sensible heat and moisture advection from the mid‐latitudes into this region. In this study, we explore the frequency and seasonality of extreme Greenland blocking, and we explore the relationship between extreme blocking and moisture transport into and over the region. We quantify atmospheric flow blocking over Greenland using the Greenland Blocking Index, and extreme blocking is defined from 1980 to 2019 at the 90th, 95th, 97th, and 99th percentiles for both summer (June to August) and winter (December to February) seasons. Moisture transport over Greenland was defined by calculating daily integrated vapor transport from the ERA‐Interim reanalysis over the region from 15° to 85°W and 55° to 80°N. The frequency of extreme blocking over Greenland was found to have increased in the most recent two decades (2000–2019) compared to the period 1980–1999. In addition, the probability of above‐average moisture transport occurring on a day with extreme blocking is high in both summer and winter, with the highest probability of high moisture transport during an extreme Greenland Blocking Index day in winter. These findings are unique to this work and suggest future work on the role of moisture transport in developing or sustaining blocks over Greenland. [ABSTRACT FROM AUTHOR]

During the past four decades significant decrease in Arctic sea ice and a dramatic ice mass loss of the Greenland Ice Sheet (GIS) has been coincident with global warming and an increase in atmospheric CO2. In Northeast Greenland significant mass loss from the outlet glaciers Nioghalvfjerdsbræ (79NG) and Zachariæ Isstrøm (ZI) and intensive seasonal breakup of the local Norske Øer Ice Barrier (NØIB) have also been observed since 2000. In order to better understand the processes driving these modern changes, studies of paleoclimate records are important and of major societal relevance. A multiproxy study including organic‐biogeochemical and micropaleontological proxies was carried out on a marine sediment core recovered directly in front of 79NG. Data from Core PS100/270 evidenced a strong inflow of warm recirculating Atlantic Water across the Northeast Greenland shelf from the early Holocene between ~10 and 7.5 ka. An overall high in phytoplankton productivity occurred within a stable sea ice margin regime, accompanied by 79NG retreat most probably triggered by peak solar insolation and changes in the local ocean circulation. Enhanced basal melt of the underside of 79NG at ~7.5 ka then led to the total disintegration of the ice shelf. The released freshwater would have driven water column stratification and promoted the formation of the local landfast ice barrier, which is shown by lowered biomarker values and foraminifera abundances toward the end of the early Holocene. Near perennial sea ice conditions with short summers and 79NG retreat to the inner fjord then prevailed from ~7.5 to ~0.8 ka. Key Points: Multiproxy record allowed reconstruction of NEG ice sheet retreat and sea ice history from the last deglaciation to the late HoloceneIncreased inflow of warm recirculating Atlantic Water linked to retreat and disintegration of the 79NG between 10 and 7.5 kaExtended to even perennial sea ice conditions were predominant on the inner NE Greenland shelf since 7.5 ka [ABSTRACT FROM AUTHOR]