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The accessibility and simplicity of monitoring instruments and processing methods are crucial for environmental monitoring worldwide. There is growing evidence that proglacial discharge may be observed by listening to the glacier terminus using sophisticated tools, such as the micro‐barometer arrays that are used for nuclear‐test monitoring and the fiber‐optic technologies that are becoming increasingly used in geophysics. However, the prohibitive cost, instrumental complexity, overwhelming data volumes, and computational demands of these approaches mean that only the wealthiest countries can afford such technologies. We employ an intentionally inexpensive approach to monitor proglacial discharge by recording the audible sound that is generated near the glacier terminus, and we show that a simple microphone can tell us how much water is discharged by a glacier. This study demonstrates that sound can provide essential information on runoff and therefore contribute to environmental assessments of glaciers and disaster risk reduction of glacial flood events. Plain Language Summary: Glacier monitoring is essential for sea‐level‐rise forecasting, water management, and providing an early warning of potential glacial flooding; however, the necessary monitoring data are currently scarce and often difficult to collect. Recent studies on turbulent streams and melting glaciers have suggested that the acoustic signals that are generated from these systems can serve as a proxy for high‐resolution discharge monitoring. We collected acoustic and runoff records from the terminus of Qaanaaq Glacier, Greenland, to examine this sound–glacier discharge relationship. We demonstrate that the proglacial discharge can be estimated from the audible sound that is generated near the terminus, without the need for expensive monitoring equipment and sophisticated machine‐learning analysis. We identify that the 50–375 Hz frequency band may serve as the most efficient proxy and associate the recorded sound (and previously reported persistent infrasound) with the turbulent proglacial stream. Our non‐invasive approach is ∼100 times cheaper than current fiber‐optic technology, can easily be deployed at any safe location near the terminus, and requires only basic processing of the recorded signal, thereby making it a safe, affordable, and effective approach to monitoring discharge. It may also be a viable tool for long‐term glacier monitoring, particularly where glacial flooding events pose a risk. Key Points: Sound propagating in the atmosphere can be used to estimate proglacial dischargeAudible frequencies between 50 and 375 Hz are most informative at a short rangeA simple microphone is a promising and economical tool for glacial hydrology [ABSTRACT FROM AUTHOR]

An increasing body of work has shown the potential impacts of subglacial discharge from marine‐terminating glaciers on the marine environment around Greenland. Upwelling of nutrients associated with rising buoyant plumes near the front of marine‐terminating glaciers plays a key role in maintaining the high productivity of connected fjords. The response of protist communities to subglacial discharges into fjords nevertheless remains poorly understood. Here we show data of water properties, nutrients, and protist communities during two summers in 2018 and 2019 in a Greenlandic fjord system fed by marine‐terminating glaciers. This study included the period of intense summer melting of the Greenland Ice Sheet in 2019. The data revealed high nutrient concentrations in 2019 that were attributed to intensified upwelling of nutrients and dissolved iron into the subsurface layer. The source of the iron and the nutrients was subglacial discharge and deep fjord water, respectively. Intense glacial discharges in 2019 mitigated nitrate and phosphate limitations of phytoplankton in the fjord and resulted in an increase of chlorophyll a in the subsurface layer and growth of large diatoms. Heterotrophic protists such as dinoflagellates, tintinnids, and nanoflagellates were more abundant in the summer of 2019. We concluded that nutrient upwelling by subglacial discharges was the major driver of the structure of lower trophic levels in fjord ecosystems. We hypothesize that the more intense melting of glaciers and related increase in subglacial discharge will enhance nutrient upwelling, and increased summer productivity in fjords until the glaciers retreat and terminate on land. Key Points: Higher nutrient concentrations in a Greenlandic fjord with marine‐terminating glaciers were found in 2019 compared to 2018Intense summer melting during 2019 led to higher subglacial discharge and enhanced nutrient upwellingIntensified upwelling of nutrients into the euphotic zone increased productivity of large diatoms [ABSTRACT FROM AUTHOR]

A period of 18 years of infrasonic recordings was analyzed from a microbarometer array (I18DK) in northwestern Greenland, near Qaanaaq. A huge number of infrasonic detections, over 700,000, have been made in I18DKs soundscape during the Arctic summers. Simultaneously identified were both calving events from marine‐terminating glaciers and discharge related acoustics from a land‐terminating glacier. This infrasonic activity is correlated to sea‐surface and atmospheric temperature, respectively. Inter‐yearly to daily variations were retrieved showing a strong variability in infrasonic detection rates and hence glacier activity. The highest number of infrasonic detections were found in recent years from the land‐terminating glacier. The latter is supported by actual discharge measurements and partly by a discharge model. It is concluded that monitoring infrasound from glaciers can complement other techniques to remotely and passively get insights into glacier dynamics with high temporal and spatial resolution. Plain Language Summary: Infrasound is inaudible sound and created when large volumes of air are displaced in the atmosphere. Such infrasound is continuously measured in northwestern Greenland, near the village of Qaanaaq. Recordings over 18 years have been analyzed. Both land and marine‐terminating glaciers were identified, being active at the same time. Variations in activity of the glaciers were found between different years and also on a daily basis. The activity is related to calving of pieces of ice from the glacier and material running off the glacier. In recent years, the highest activity in discharge was observed. The latter is support by modeling and measurements of discharge which have been taken locally over 3 years. It is concluded, that infrasound measurements can help in gaining more insights into glacier dynamics, with high temporal and spatial resolution. As such, the detection and identification of inaudible sound complements other (remote) monitoring techniques. Key Points: Infrasound monitoring of multiple glaciers simultaneously revealed details on glacier dynamics with a high temporal and spatial scaleInter‐yearly to daily variations for marine (calving) and land‐terminating glaciers (melt water run‐off) were observedover 18 yearsInfrasound activity related to glacier discharge was highest in recent years, supported by both modeling and actual discharge measurements [ABSTRACT FROM AUTHOR]

Outlet glaciers in Greenland exhibited rapid frontal retreat, thinning, and flow acceleration in the 21st century. In contrast to a number of studies in the last two decades, long-term glacier changes are not well known, hence limiting the understanding of ongoing glacier retreat. In this study, we present surface elevation changes of 16 glaciers along the coast of Prudhoe Land, northwestern Greenland, using digital elevation models between 1985 and 2018. All the glaciers experienced surface lowering at a mean rate of -0.55 ± 0.24 m a-1 over the period of study. Surface elevation change has shown a clear shift from 0.14 ± 0.17 m a-1 in 1985-2001 to -1.31 ± 0.20 m a-1 in 2001-2018. Thinning after 2001 was more significant at the glaciers terminating in Inglefield Bredning, represented by the most rapid thinning of Tracy and Farquhar Glaciers at -3.91 ± 0.13 and -2.91 ± 0.18 m a-1, respectively. Glaciers terminating in shallower fjords directly connected to Baffin Bay showed a thinning rate 40% slower than those in the Inglefield Bredning region. Warming trends in atmospheric and ocean temperature since the late 1990s are most likely triggers of the glacier regime shift around 2001. The heterogeneity in the glacier change is attributed to the glacier geometry and fjord bathymetry of each individual glacier, since glaciers terminating in deep fjords are subjected to greater acceleration and are more affected by deep ocean warming. [ABSTRACT FROM AUTHOR]

As a result of climate warming, glacial meltwater discharge has been increasing in Greenland. During the summers of 2015 and 2016, there were rapid increases in discharge from Qaanaaq Glacier in northwestern Greenland. These discharges resulted in floods that destroyed the road linking the settlement of Qaanaaq to Qaanaaq Airport. Field measurements were performed and a numerical model of glacier runoff was developed to quantify these discharges. The high discharge associated with the 2015 flood, estimated at 9.1 m3 s−1 (hourly mean), resulted from intensive glacier melting due to warm air temperature and strong winds, while the high discharge associated with the 2016 flood resulted from heavy rainfall (90 mm d−1) that led to a peak discharge estimated at 19.9 m3 s−1. The developed model, when used to investigate future glacier runoff under warming conditions, revealed a nonlinear increase in glacial melt with increasing temperature. Additionally, the model forecasted a threefold increase in total summer discharge, owing to a 4 °C rise in temperature. Thus, this study quantified the impact of a changing climate on glacier runoff, which gives insight into future risks of flood hazards along the coast of Greenland. [ABSTRACT FROM AUTHOR]

Supraglacial lakes form on the Greenland ice sheet during the melting season as meltwater accumulates in topographic depressions on the surface. They have the potential to increase ablation by reducing albedo and enhance ice flow when water drains to the bed. Despite recent progress in understanding the surface hydrology of the Greenland ice sheet, the seasonal and year-to-year variations of supraglacial lakes remain poorly understood. Here, we employed a machine learning method trained with random forest classifiers on Landsat 8 and Sentinel-2 imagery within Google Earth Engine for detecting supraglacial lakes. We applied this method to two large marine-terminating glaciers (Heilprin Glacier and Tracy Glacier) in northwestern Greenland to investigate the distribution, inter-annual and seasonal evolutions of supraglacial lakes between 2014 and 2021. Over the eight study years, cumulated maximum lake extent on Heilprin Glacier (22.84 km2) was approximately three times larger than that of Tracy Glacier (7.60 km2) despite the similarity in the glacier areas (654 km2 and 540 km2). The lake extent exhibited significant interannual variability controlled by summer PDD (sum of positive degree days), and the upper limit of lake formation coincided approximately with ELA (equilibrium line altitude). Greater lake areas were observed in 2016 and 2019, but obviously below-average areas in 2017–2018. The variabilities were pronounced in the region above 800 m a.s.l., particularly at Tracy Glacier. On the seasonal scale, lakes begin forming in early- to mid-June and disappear toward the end of August. The lake formation was triggered by the initiation of runoff in the regions below 800 m a.s.l., while it coincided with the onset of surface melt at the higher elevations due to the presence of ice/snow-buried lakes. Cascading rapid lake drainage events were observed in the mid-elevation areas (400–800 m a.s.l.) of Heilprin Glacier, which induced an abrupt decrease in the lake area at the beginning of July in the years of 2019 and 2020. Our study demonstrates the potential of the machine learning method to analyze supraglacial lakes in dense satellite images. The results imply inland expansion of supraglacial lakes under warming climate in Greenland and a possible interaction between draining lake water and glacier dynamics. • Machine learning method performs well in the classification of supraglacial lakes. • Interannual variability of lake extent is controlled by summer PDD. • The upper limit of lake formation coincided approximately with ELA. • The seasonal variability of lake evolution differs at various elevations. [ABSTRACT FROM AUTHOR]

Ice mass loss from the Greenland ice sheet is the largest single contributor to sea level rise in the 21st century. The mass loss rate has accelerated in recent decades mainly due to thinning and retreat of its outlet glaciers. The diverse calving mechanisms responsible for tidewater glacier retreat are not fully understood yet. Since a tidewater glacier's sensitivity to external forcings depends on its calving style, detailed insight into calving processes is necessary to improve projections of ice sheet mass loss by calving. As tidewater glaciers are mostly thinning, their calving styles are expected to change. Here, we study calving behaviour changes under a thinning regime at Bowdoin Glacier, north-western Greenland, by combining field and remote-sensing data from 2015 to 2019. Previous studies showed that major calving events in 2015 and 2017 were driven by hydro-fracturing and melt-undercutting. New observations from uncrewed aerial vehicle (UAV) imagery and a GPS network installed at the calving front in 2019 suggest ungrounding and buoyant calving have recently occurred as they show (1) increasing tidal modulation of vertical motion compared to previous years, (2) absence of a surface crevasse prior to calving, and (3) uplift and horizontal surface compression prior to calving. Furthermore, an inventory of calving events from 2015 to 2019 based on satellite imagery provides additional support for a change towards buoyant calving since it shows an increasing occurrence of calving events outside of the melt season. The observed change in calving style could lead to a possible retreat of the terminus, which has been stable since 2013. We therefore highlight the need for high-resolution monitoring to detect changing calving styles and numerical models that cover the full spectrum of calving mechanisms to improve projections of ice sheet mass loss by calving. [ABSTRACT FROM AUTHOR]

Glacial fjords in Greenland show high productivity owing to the runoff of meltwater from the glaciers. Macronutrient dynamics (of nitrate, phosphate, and silicate) associated with subglacial discharge plumes in front of marine‐terminating glaciers are widely cited as important drivers of summer phytoplankton blooms in the fjords. However, the dynamics of iron (Fe), an essential micronutrient for primary production, remain largely unstudied in glacial fjords. To investigate the role of subglacial discharge plumes in Fe supply processes in glacial fjords, a comprehensive survey of Bowdoin Fjord, adjacent to the marine‐terminating Bowdoin Glacier in northwestern Greenland, was conducted. The subglacial discharge of Fe‐rich meltwater induces a buoyancy‐driven upwelling plume in front of the glacier that entrains nutrient‐rich Arctic‐ and Atlantic‐origin waters. The plume water potentially carried 4.5–8.7 × 107 g day−1 of total dissolvable Fe out of Bowdoin Fjord in summer. The concentration of dissolved Fe (dFe) in the plume water (~15.6 nmol kg−1) was 4 times higher than that in the water in the outer part of the fjord (~3.8 nmol kg−1). The dFe:nitrate + nitrite ratio (mmol mol−1) in the plume water varied between 0.58 and 3.2, several orders of magnitude higher than the phytoplankton cellular Fe:nitrate ratio estimated using the hypothetical Fe:C ratio and observed particulate organic carbon:nitrate ratio of the fjord. Hence, the plume water is replete with Fe with respect to phytoplankton demands. Subglacial discharge drives the upwelling of Fe and macronutrients toward the euphotic zone, which is vital for the generation of summer phytoplankton growth in glacial fjords. Key Points: Iron transport by a subglacial discharge plume was quantified in GreenlandAn upwelling plume distributes iron‐ and nutrient‐rich water into a fjordPlume water is replete with iron to meet phytoplankton demands [ABSTRACT FROM AUTHOR]

Greenland runoff, from ice mass loss and increasing rainfall, is increasing. That runoff, as discharge, impacts the physical, chemical, and biological properties of the adjacent fjords. However, where and when the discharge occurs is not readily available in an open database. Here we provide data sets of high-resolution Greenland hydrologic outlets, basins, and streams, as well as a daily 1958 through 2019 time series of Greenland liquid water discharge for each outlet. The data include 24 507 ice marginal outlets and upstream basins and 29 635 land coast outlets and upstream basins, derived from the 100 m ArcticDEM and 150 m BedMachine. At each outlet there are daily discharge data for 22 645 d – ice sheet runoff routed subglacially to ice margin outlets and land runoff routed to coast outlets – from two regional climate models (RCMs; MAR and RACMO). Our sensitivity study of how outlet location changes for every inland cell based on subglacial routing assumptions shows that most inland cells where runoff occurs are not highly sensitive to those routing assumptions, and outflow location does not move far. We compare RCM results with 10 gauges from streams with discharge rates spanning 4 orders of magnitude. Results show that for daily discharge at the individual basin scale the 5 % to 95 % prediction interval between modeled discharge and observations generally falls within plus or minus a factor of 5 (half an order of magnitude, or +500 % /-80 %). Results from this study are available at 10.22008/promice/freshwater and code is available at http://github.com/mankoff/freshwater (last access: 6 November 2020). [ABSTRACT FROM AUTHOR]

Subglacial discharge has significant impacts on water circulation, material transport, and biological productivity in proglacial fjords of Greenland. To help clarify the fjord water properties and the effect of subglacial discharge, we investigated the properties of vertical water mass profiles of Bowdoin Fjord in northwestern Greenland based on summer hydrographic observations, including turbidity, in 2014 and 2016. We estimated the fraction of subglacial discharge from the observational data and interpreted the observed differences in subglacial plume behavior between two summer seasons with the numerical model results. At a depth of 15–40 m , where the most turbid water was observed, the maximum subglacial discharge fractions near the ice front were estimated to be ∼6 % in 2014 and ∼4 % in 2016. The higher discharge fraction in 2014 was likely due to stronger stratification, as suggested by the numerical experiments performed with different initial stratifications. Turbidity near the surface was higher in 2016 than in 2014, suggesting a stronger influence of turbid subglacial discharge. The higher turbidity in 2016 could primarily be attributed to a greater amount of subglacial discharge, as inferred from the numerical experiments forced by different amounts of discharge. This study suggests that both fjord stratification and the amount of discharge are important factors in controlling the vertical distribution of freshwater outflow. [ABSTRACT FROM AUTHOR]

We provide high-resolution datasets of Greenland hydrologic outlets, basins, and streams, and a 1979 through 2017 time series of Greenland liquid water runoff for each outlet. Outlets, basins, and streams are derived from traditional hydrologic routing algorithms over the surface of a 100 m ArcticDEM digital elevation model (DEM) twice: Once to the ice margin and once to the coast. We then partition liquid water runoff from both ice and land from two regional climate models (RCMs; MAR and RACMO) into each basin and at each outlet location. The data include 18903 ice basins and outlets (614 basins greater than 10 km2), 30241 land basins and outlets (958 basins greater than 10 km2), major streams in each basin, and daily runoff water volume flow rate at each outlet from each of two RCMs. We perform a sensitivity study of outlet location change for every ice sheet location over a range of hydrologic routing assumptions and data sets. Annual runoff from the ice ranges from ~136 km3 in 1992 to ~785 km3 in 2012. Daily maximum ice runoff from one basin is as large as 4380 m3 s-1. Both ice runoff magnitude and variability increase over the time series. Land runoff contributes an additional ~ 35 % to the ice runoff. Comparison with 9 basins instrumented with stream gauges shows a range of (dis)agreement from poor to excellent between our estimated discharge and observations. As part of the journal's living archive option, and our goal to make an operational product, all input data, code, and results from this study will be updated as needed (when new input data are available, as new features are added, or to fix bugs) and made available at https://doi.org/10.22008/promice/data/freshwater%5Frunoff/v01 (Mankoff, 2020) and at http://github.com/mankoff/freshwater. [ABSTRACT FROM AUTHOR]

In Greenland, tidewater glaciers discharge turbid subglacial freshwater into fjords, forming plumes near the calving fronts, and these areas serve as an important foraging habitat for seabirds. To investigate the effect of subglacial discharge on the foraging assemblages of surface feeders and divers in a glacial fjord, we conducted boat-based seabird surveys, near-surface zooplankton samplings, and hydrographic measurements at Bowdoin Fjord, northwestern Greenland in July. Foraging surface feeders (black-legged kittiwake Rissa tridactyla , glaucous gull Larus hyperboreus , and northern fulmar Fulmarus glacialis) aggregated within a plume-affected area in front of Bowdoin Glacier. This area was characterized by highly turbid subglacial meltwater and abundant large-sized zooplankton including Calanus hyperboreus , chaetognaths, and ctenophores near the surface. Surface feeders fed on these aggregated prey presumably transported to the surface by strong upwelling of subglacial meltwater. In contrast, divers (little auk Alle alle , thick-billed murre Uria lomvia , and black guillemot Cepphus grylle) foraged outside the fjord, where turbidity was low and jellyfish and Calanus copepods dominated under the influence of Atlantic water. Our study indicates spatial segregation between surface feeders and divers in a glacial fjord; surface feeders are not hindered by turbidity if taking prey at the surface, whereas divers need clear water. [ABSTRACT FROM AUTHOR]

We present a 3-year record of seasonal variations in ice speed and frontal ablation of 10 marine-terminating outlet glaciers along the coast of Prudhoe Land in northwestern Greenland. The glaciers showed seasonal speedup initiated between late May and early June, and terminated between late June and early July. Ice speed subsequently decreased from July to September. The timing of the speedup coincided with the onset of the air temperature rise to above freezing, suggesting an influence of meltwater availability on the glacier dynamics. No clear relationship was found between the speedup and the terminus position or the sea-ice/ice-mélange conditions. These results suggest that the meltwater input to the glacier bed triggered the summer speedup. The excess of summer speed (June–August) over the mean for the rest of the year accounted for 0.5–13% of the annual ice motion. Several glaciers showed seasonal frontal variations, i.e. retreat in summer and advance in winter. This was not due to ice-speed variations, but was driven by seasonal variations in frontal ablation. The results demonstrate the dominant effect of glacier surface melting on the seasonal speedup, and the importance of seasonal speed patterns on longer-term ice motion of marine-terminating outlet glaciers in Greenland. [ABSTRACT FROM AUTHOR]

Subglacial discharge has significant impacts on water circulation, material transport, and biological productivity in proglacial fjords of Greenland. To help clarify the fjord water properties and the effect of subglacial discharge, we investigated the water mass structures of Bowdoin Fjord in northwestern Greenland based on summer hydrographic observations, including turbidity, in 2014 and 2016. We estimated the fraction of subglacial discharge from the observational data and interpreted the observed differences in subglacial discharge behavior between two summer seasons with the numerical model results. At a depth of 60-80 m, temperature profiles were distinctively different in 2014 and 2016, and a larger fraction of submarine meltwater was detected in 2014. At a depth of 15-40 m, where the most turbid water was observed, the maximum subglacial discharge fractions near the ice front were estimated to be ~6 % in 2014 and ~4 % in 2016. The higher discharge fraction in 2014 was due to the stronger stratification, as suggested by numerical experiments performed with different initial stratifications. Turbidity near the surface was higher in 2016 than in 2014, suggesting a stronger influence of turbid subglacial discharge. The higher turbidity in 2016 could primarily be attributed to a greater amount of subglacial discharge, as inferred from the numerical experiments forced by different amounts of discharge. This study indicates that ambient fjord stratification difference is an important factor controlling the vertical distribution of subglacial discharge, together with its amount. [ABSTRACT FROM AUTHOR]

We use the full-Stokes model Elmer/Ice to investigate the present dynamics of Bowdoin Glacier, a marine-terminating outlet glacier in northwestern Greenland. Short-term speed variations of the glacier were observed, correlating with air temperature and precipitation, and with the semi-diurnal ocean tides. We use a control inverse method to determine the distribution of basal friction. This reveals that most of the glacier area is characterized by near-plug-flow conditions, while some sticky spots are also identified. We then conduct experiments to test the sensitivity of the glacier flow to basal lubrication and tidal forcing at the calving front. Reduction of the basal drag by 10–40% produces speed-ups that agree approximately with the observed range of speed-ups that result from warm weather and precipitation events. In agreement with the observations, tidal forcing and surface speed near the calving front are found to be in anti-phase (high tide corresponds to low speed, and vice versa). However, the amplitude of the semi-diurnal variability is underpredicted by a factor ~ 3, which is likely related to either inaccuracies in the surface and bedrock topographies or mechanical weakening due to crevassing. [ABSTRACT FROM AUTHOR]

Abstract In Greenland, tidewater glaciers discharge turbid subglacial freshwater into fjords, forming plumes near the calving fronts. To evaluate the effects of this discharge on the zooplankton community in the fjords, we collected sea surface zooplankton samples in Bowdoin Fjord in north-western Greenland during the summer of 2016 and made microscopic, OPC and ZooScan analyses. Within the three quantitative methods, ZooScan has advantages that can evaluate various parameters (e.g., abundance, biomass, size and taxonomic information) simultaneously and has the ability to eliminate abiotic particles, such as silt and sediment, which are abundant in samples. Based on taxonomic biomass data, the zooplankton community is clustered into three groups, which varied spatially: inner, middle and outer fjord groups. Jellyfish dominated the outer fjord group, and barnacle cypris larvae dominated the middle fjord group. For the inner fjord group, large-sized Calanus spp. and chaetognaths were abundant. Since these species are characterized with oceanic taxa, they would intrude through the deep fjord water and subsequently be upwelled through entrainment of glacially modified plume water. From the NBSS analysis on zooplankton size spectra, the steep slope of NBSS in the middle fjord community suggests that the high productivity was caused by the addition of meroplanktonic cypris larvae. [ABSTRACT FROM AUTHOR]

Satellite images were analyzed to measure the frontal positions and ice speeds of 19 marine-terminating outlet glaciers along the coast of Prudhoe Land, northwestern Greenland from 1987 to 2014. All the studied glaciers retreated over the study period at a rate of between 12 and 200 m a−1, with a median (mean) retreat rate of 30 (40) m a−1. The glacier retreat began in the year ~2000, which coincided with an increase in summer mean air temperature from 1.4 to 5.5 °C between 1996 and 2000 in this region. Ice speed near the front of the studied glaciers ranged between 20 and 1740 m a−1 in 2014, and many of them accelerated in the early 2000s. In general, the faster retreat was observed at the glaciers that experienced greater acceleration, as represented by Tracy Glacier, which experienced a retreat of 200 m a−1 and a velocity increase of 930 m a−1 during the study period. A possible interpretation of this observation is that flow acceleration induced dynamic thinning near the termini, resulting in enhanced calving and rapid retreat of the studied glaciers. We hypothesize that atmospheric warming conditions in the late 1990s triggered glacier retreat in northwestern Greenland since 2000. [ABSTRACT FROM AUTHOR]

To better understand the processes controlling recent mass loss of peripheral glaciers and ice caps in northwestern Greenland, we measured surface mass balance (SMB), ice velocity and near-surface ice temperature on Qaanaaq Ice Cap in the summers of 2012–16. The measurements were performed along a survey route spanning the terminus of an outlet glacier to the upper reaches (243–968 m a.s.l.). The ice-cap-wide SMB ranged from −1.10 ± 0.29 to −0.13 ± 0.26 m w.e. a−1 for the years from 2012/13 to 2015/16. Mass balance showed substantially large fluctuations over the study period under the influence of summer temperature and snow accumulation. Ice velocity showed seasonal speedup only in the summer of 2012, suggesting an extraordinary amount of meltwater penetrated to the bed and enhanced basal ice motion. Ice temperature at a depth of 13 m was −8.0°C at 944 m a.s.l., which was 2.5°C warmer than that at 243 m a.s.l., suggesting that ice temperature in the upper reaches was elevated by refreezing and percolation of meltwater. Our study provided in situ data from a relatively unstudied region in Greenland, and demonstrated the importance of continued monitoring of these processes for longer timespans in the future. [ABSTRACT FROM AUTHOR]

In this paper, we analyse the calving activity of the Bowdoin Glacier, north-western Greenland, in 2015 by combining satellite images, UAV (unmanned aerial vehicle) photogrammetry and ice flow modelling. In particular, a highresolution displacement field is inferred from UAV orthoimages taken immediately before and after the initiation of a large fracture, which induced a major calving event. A detailed analysis of the strain rate field allows us to accurately map the path taken by the opening crack. Modelling results reveal (i) that the crack was more than half-thickness deep, filled with water and getting irreversibly deeper when it was captured by the UAV and (ii) that the crack initiated in an area of high horizontal shear caused by a local basal bump immediately behind the current calving front. The asymmetry of the bed at the front explains the systematic calving pattern observed in May and July-August 2015. As a corollary, we infer that the calving front of the Bowdoin Glacier is currently stabilized by this bedrock bump and might enter into an unstable mode and retreat rapidly if the glacier keeps thinning in the coming years. Beyond this outcome, our study demonstrates that the combination of UAV photogrammetry and ice flow modelling is a promising tool to horizontally and vertically track the propagation of fractures responsible for large calving events. [ABSTRACT FROM AUTHOR]

To quantify recent thinning of marine-terminating outlet glaciers in northwestern Greenland, we carried out field and satellite observations near the terminus of Bowdoin Glacier. These data were used to compute the change in surface elevation from 2007 to 2013 and this rate of thinning was then compared with that of the adjacent land-terminating Tugto Glacier. Comparing DEMs of 2007 and 2010 shows that Bowdoin Glacier is thinning more rapidly (4.1 ± 0.3 m a−1) than Tugto Glacier (2.8 ± 0.3 m a−1). The observed negative surface mass-balance accounts for <40% of the elevation change of Bowdoin Glacier, meaning that the thinning of Bowdoin Glacier cannot be attributable to surface melting alone. The ice speed of Bowdoin Glacier increases down-glacier, reaching 457 m a−1 near the calving front. This flow regime causes longitudinal stretching and vertical compression at a rate of −0.04 a−1. It is likely that this dynamically-controlled thinning has been enhanced by the acceleration of the glacier since 2000. Our measurements indicate that ice dynamics indeed play a predominant role in the rapid thinning of Bowdoin Glacier. [ABSTRACT FROM AUTHOR]

A large number of glaciers and ice caps (GICs) are distributed along the Greenland coast, physically separated from the ice sheet. The total area of these GICs accounts for 5% of Greenland’s ice cover. Melt water input from the GICs to the ocean substantially contributed to sea-level rise over the last century. Here, we report surface elevation changes of six ice caps near Qaanaaq (77°28′N, 69°13′W) in northwestern Greenland based on photogrammetric analysis of stereo pair satellite images. We processed the images with a digital map plotting instrument to generate digital elevation models (DEMs) in 2006 and 2010 with a grid resolution of 500 m. Generated DEMs were compared to measure surface elevation changes between 2006 and 2010. Over the study area of the six ice caps, covering 1215 km 2 , the mean rate of elevation change was −1.1 ± 0.1 m a −1 . This rate is significantly greater than that previously reported for the 2003–2008 period (−0.6 ± 0.1 m a −1 ) for GICs all of northwestern Greenland. This increased mass loss is consistent with the rise in summer temperatures in this region at a rate of 0.12 °C a −1 for the 1997–2013 period. [ABSTRACT FROM AUTHOR]

Glacial meltwater discharge from the Greenland ice sheet and ice caps forms high turbidity water in the proglacial ocean off the Greenland coast. Although the timing and magnitude of high turbidity water export affect the coastal marine environment, for example, through impacts on biological productivity, little is known about the characteristics of this high turbidity water. In this paper, we therefore report on the spatial and temporal variations in high turbidity water off the Thule region in northwestern Greenland, based on remote sensing reflectance data at a wavelength of 555 nm (Rrs555). The high turbidity area, identified on the basis of high reflectivity (Rrs555 ≥ 0.0070 sr −1 ), was generally distributed near the coast, where many outlet glaciers terminate in the ocean and on land. The extent of the high turbidity area exhibited substantial seasonal and interannual variability, and its annual maximum extent was significantly correlated with summer air temperature. Assuming a linear relationship between the high turbidity area and summer temperature, annual maximum extent increases under the influence of increasing glacial meltwater discharge, as can be inferred from present and predicted future warming trends. [ABSTRACT FROM AUTHOR]

To better understand recent rapid recession of marine-terminating glaciers in Greenland, we performed satellite and field observations near the calving front of Bowdoin Glacier, a 3 km wide outlet glacier in northwestern Greenland. Satellite data revealed a clear transition to a rapidly retreating phase in 2008 from a relatively stable glacier condition that lasted for >20 years. Ice radar measurements showed that the glacier front is grounded, but very close to the floating condition. These results, in combination with the results of ocean depth soundings, suggest bed geometry in front of the glacier is the primary control on the rate and pattern of recent rapid retreat. Presumably, glacier thinning due to atmospheric and/or ocean warming triggered the initial retreat. In situ measurements showed complex short-term ice speed variations, which were correlated with air temperature, precipitation and ocean tides. Ice speed quickly responded to temperature rise and a heavy rain event, indicating rapid drainage of surface water to the bed. Semi-diurnal speed peaks coincided with low tides, suggesting the major role of the hydrostatic pressure acting on the calving face in the force balance. These observations demonstrate that the dynamics of Bowdoin Glacier are sensitive to small perturbations occurring near the calving front. [ABSTRACT FROM AUTHOR]

To study the glaciological processes controlling the mass budget of Greenland's peripheral glaciers and ice caps, field measurements were carried out on Qaanaaq ice cap, a 20 km long ice cap in northwestern Greenland. In the summer of 2012, we measured surface melt rate, ice flow velocity and ice thickness along a survey route spanning the ice margin (200ma.s.l.) to the ice-cap summit (1110ma.s.l.). Melt rates in the ablation area were clearly influenced by dark materials covering the ice surface, where degree-day factors varied from 5.44mmw.e. K-1 d-1 on a clean surface to 8.26mmw.e. K-1 d-1 in the dark regions. Ice velocity showed diurnal variations, indicating the presence of surface-meltwater induced basal sliding. Mean ice thickness along the survey route was 120 m, with a maximum thickness of 165 m. Ice velocity and temperature fields were computed using a thermomechanically coupled numerical glacier model. Modelled ice temperature, obtained by imposing estimated annual mean air temperature as the surface boundary condition, was substantially lower than implied by the observed ice velocity. This result suggests that the ice dynamics and thermodynamics of the ice cap are significantly influenced by heat transfer from meltwater and changing ice geometry. [ABSTRACT FROM AUTHOR]

Environments along the coast of Greenland are rapidly changing under the influence of a warming climate in the Arctic. To better understand the changes in the coastal environments, we performed researches in the Qaanaaq region in northwestern Greenland as a part of the ArCS (Arctic Challenge for Sustainability) Project. Mass loss of ice caps and marine-terminating outlet glaciers were quantified by field and satellite observations. Measurements and sampling in fjords revealed the important role of glacial meltwater discharge in marine ecosystems. Flooding of a glacial stream in Qaanaaq and landslides in a nearby settlement were investigated to identify the drivers of the incidents. Our study observed rapid changes in the coastal environments, and their critical impact on the society in Qaanaaq. We organized workshops with the residents to absorb local and indigenous knowledge, as well as to share the results and data obtained in the project. Continuous effort towards obtaining long-term observations requiring involvement of local communities is crucial to contribute to a sustainable future in Greenland. [ABSTRACT FROM AUTHOR]

Glacial meltwater discharge is increasing in Greenland under recent warming climate. As a consequence, floods and damages on infrastructures are reported at outlet streams of land terminating glaciers. For example, discharge from Qaanaaq Glacier in northwestern Greenland rapidly increased on 21 July 2015, leading to a flood of a proglacial stream and destruction of a road between a settlement and Qaanaaq Airport. Another flood on 2 August 2016 caused even more serious damage. These events occurred after an intensive melt period and a heavy rain storm, suggesting a risk of similar disaster increases in the future under warming and wetter conditions in the Arctic. To better understand the mechanisms causing the flood events at Qaanaaq Glacier, we investigated meteorological conditions during the 2015 and 2016 events, and performed field measurements in the summer 2017 and 2018.Before the flood on 21 July 2015, high temperature was continuously observed for 5 days. Daily mean temperature rose above 5 ℃ in the accumulation area (944 m a.s.l.), causing intensive melting over the entire glacier. The most likely interpretation of the flood was that meltwater accumulated in snowpack and suddenly drained from the glacier when it reached saturation. The flood on 2 August 2016 was due to extraordinary heavy rainfall with daily precipitation of 90 mm. In addition to a clear influence of the precipitation on the stream discharge, we assume that a snow-free glacier surface condition enhanced rapid increase in glacier runoff. From 7 July to the date of the flood, daily mean air temperature at 944 m a.s.l. remained above freezing for the entire period, resulting in disappearance of snow on the glacier below 950 m a.s.l.. Snowline elevation on the day of the rain storm was significantly higher than usually observed in late summer. Largely exposed ice surface has no capacity to store water, thus helped immediate runoff of a large amount of rainwater. These analyses suggested that retention and saturation of meltwater within a snow layer play a key role in the flood events in 2015 and 2016. Discharge from Qaanaaq Glacier was measured from 21 July to 3 August 2017. Melt and runoff from the glacier was estimated by repeating surveys of snow depth, density, stratifications, ice melt and meteorological conditions along a route spanning the terminus to the accumulation area (243–968 m a.s.l.). Stream discharge rapidly increased in late July, leading to a peak value of 8.11 m³ s⁻¹ on 28 July 2017. Estimated total glacier melt accounted for only 60 % of the runoff measured before the peak discharge, indicating the rest of meltwater remained on the glacier. From 21 to 28 July, snowline elevation rose from 500 to 650 m a.s.l. after intensive melting. Our data suggested that meltwater stored in snowpack reached saturation, and rapidly released during the period of rapid melting and upglacier snowline migration. Together with data in 2018, we conclude that saturation and disappearance of snowpack are the key to predict rapid increase in stream discharge and following flood. [ABSTRACT FROM AUTHOR]

Discrimination of volcanic and glacial seismic signals remains one of the key challenges for studies on volcano-glacier interactions. Here we show that even in the absence of any active volcano, interpretation of so-called Long-Period (LP) seismic events of glacial origin is truly challenging.Discoveries of LP seismic events in volcanic, tectonic and glacial environments have led to a decades-long debate on their source mechanisms, which could be either fluid-driven rupture or slow-slip. LP events in volcanic environments are of pivotal importance for eruption forecasting because they can provide information on fluid migration beneath the volcanic edifice. LP events in environments of fast glacier flow may also correspond to the resonance of fluid-filled cracks or represent sliding. However, other sources have to be ruled out before making such an assertion. Here we present observations from three comprehensive experiments at a tidewater Bowdoin Glacier, northwest Greenland, where thousands of apparently hybrid LP events were recorded. We conducted a detailed analysis of their properties by applying advanced seismological approaches and using a novel-to-glaciology GPS-stacking technique. The events are found to be highly repetitive, year-round events that are localized near the calving front, with tide-modulated amplitudes that increased with waiting time and an occurrence rate that exhibited a temporal dependence on ice speed. The emergent onset of the events is polarized, with a mixed polarity that is primarily in the horizontal plane. Taken together, the records suggest that the source of the LP events, which is sensitive to ice speed and meltwater supply, may correspond to localized slip with fluid resonance. However, further research is necessary to fully resolve the source mechanism of these LP events since we cannot dismiss the possibility of pure fluid-filled cracking due to a complex link between basal-water pressure and ice speed. [ABSTRACT FROM AUTHOR]

Snow grain size is indispensable property for evaluating surface albedo of ice sheets. Especially, information of ice sheet albedo in the past is necessary for improving climatic models and future prediction. Ice core samples have potential to provide these data. However, the most parts of ice core samples, are composed of firn and ice, which have already lost initial information of snow grain size after densification. From this reason, it is important to develop a new method to evaluate history of snow grain from ice core samples. There is a correlation between specific surface area (SSA) and near-infrared reflectance. Continuous SSA values of ice core samples can be obtained by near-infrared reflectance analysis. Here, we investigate SSA and density of ice core samples and suggest new proxy to reconstruct history of snow grain modification. We collected two ice cores from the southeastern (SE-Dome) and northwestern (SIGMA-A) Greenland. The ice core from SE-Dome clearly records about 60 years of seasonal variations and include few ice layers, which indicate it barely experienced melting/refreezing. In contrast, SIGMA-A ice sample includes a lot of ice layers, indicating influence of melting/refreezing process. Density and SSA data from these two ice cores are negatively correlated. These negative correlations show SSA values basically decrease with snow densification. On the other hand, SSA decreased as the grain size increased under a constant density. SSA values measured for some SE Dome summer samples are smaller than those estimated from density using approximation formula. This result indicates grain size growth or sintering were enhanced under higher air temperature during summer. Our study demonstrated a possibility to reconstruct grain size growth due to climate change based on a relationship between SSA and density of ice core samples. [ABSTRACT FROM AUTHOR]