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We studied ice algae utilization by benthic fauna from the northern Bering and Chukchi Seas using highly branched isoprenoid (HBI) biomarkers. We assessed whether various food acquisition strategies influence the observed HBI signatures. The proportion of phytoplankton to ice algae-sourced HBIs was determined through the H-Print approach that is presumed to reflect the percentage of sea ice organic carbon (iPOC) incorporated into tissues, relative to phytoplankton organic carbon. Cluster analysis separated 3 groups based on location and feeding strategy that were significantly influenced by annual sea ice persistence. Ice algae utilization was most significant in the northeast Chukchi Sea, where seasonal sea ice was present the longest. General feeding strategy was determined to be a significant factor in the degree of ice algae utilization. Predominant deposit feeders (both surface and subsurface) used more ice algae relative to suspension feeders. Organic carbon incorporated by predominant suspension feeders was primarily phytoplankton-based. The vast majority of all organisms sampled (~90%) incorporated a measurable quantity of iPOC. Sipunculids and brittle stars had the highest relative dependence on ice algae, while other taxa displayed plastic dietary responses, including the suspension/surface deposit feeder Macoma calcarea. This study indicates that ice algae are widely utilized in Pacific Arctic benthic food webs, but most benthic organisms displayed flexibility in consuming the available food sources. The elevated utilization of ice algae by deposit feeders may prove to be a disadvantage for these organisms if they cannot adapt to the ongoing decline of iPOC as seasonal sea ice declines.

Spatial and temporal trends of remotely sensed sea-ice cover, sea surface temperatures, chlorophyll-aconcentration and primary production in the Baffin Bay, Davis Strait and Labrador Sea were analyzed for the 1998–2017 period. We found spatial variability in the trends of these cryospheric, biologic and oceanographic phenomena. For example, in the northern Baffin Bay, we observed decreases in annual sea-ice persistence, yet increases along the Labrador Sea-ice edge during winter, with the latter having significant correlations with broader atmospheric patterns. In general, we observed increases in summer sea surface temperatures across the study region, except a small area of cooling along the southern Greenlandic coast. We also found significant negative trends in April chlorophyll-aand primary production followed by significant positive trends for both biological phenomena in May, owing to anomalously high values in 2014 and 2015. Notably, we found a significant positive correlation between days of monthly sea ice presence in April with May primary production quantities. Finally, we found a significant positive trend in total annual primary production over the study period. This novel finding suggests an important relationship between the timing of breakup along the sea-ice edge and peaks in biological production.

Decreased sea ice cover in the northern Bering Sea has altered annual phytoplankton phenology owing to an expansion of open water duration and its impact on ocean stratification. Limitations of satellite remote sensing such as the inability to detect bloom activity throughout the water column, under ice, and in cloudy conditions dictate the need for shipboard based measurements to provide more information on bloom dynamics. In this study, we adapted remote sensing land cover classification techniques to provide a new means to determine bloom stage from shipboard samples. Specifically, we used multiyear satellite time series of chlorophyll a to determine whether in-situ blooms were actively growing or mature (i.e., past-peak) at the time of field sampling. Field observations of chlorophyll a and pheophytin (degraded and oxidized chlorophyll products) were used to calculate pheophytin proportions, i.e., (Pheophytin/(Chlorophyll a + Pheophytin)) and empirically determine whether the bloom was growing or mature based on remotely sensed bloom stages. Data collected at 13 north Bering Sea stations each July from 2013–2019 supported a pheophytin proportion of 28% as the best empirical threshold to distinguish a growing vs. mature bloom stage. One outcome was that low vs. high sea ice years resulted in significantly different pheophytin proportions in July; in years with low winter-to-spring ice, more blooms with growing status were observed, compared to later stage, more mature blooms following springs with abundant seasonal sea ice. The detection of growing blooms in July following low ice years suggests that changes in the timing of the spring bloom triggers cascading effects on mid-summer production.

The Distributed Biological Observatory (DBO) is a change detection array for select ecosystem variables along eight sampling transects in the Pacific Arctic Region (PAR). The overall objective of the DBO is to provide for the detection and consistent monitoring of the biophysical responses to major reductions in seasonal sea ice and concomitant increases in seawater temperatures observed across the region. A key uncertainty is how the PAR marine ecosystem is responding to these shifts in the timing of spring sea-ice retreat and/or delays in fall sea-ice formation. Variations in upper ocean hydrography, stratification, light penetration, planktonic production, pelagic-benthic coupling, and sediment carbon cycling are all influenced by sea ice and temperature changes. Observations of reduced sea ice extent/duration and seawater warming are linked to shifts in species composition and abundance, as well as northward range expansions in some upper trophic predators (e.g. humpback whales and commercially harvested fish), generally with negative impacts on ice-dependent species such as ice-associated seals and walruses. Some distributional shifts may be driven by changes in lower trophic level productivity that directly cascade into upper trophic levels. This special issue is a result of the international effort by participating scientists to implement a coordinated DBO that will meet these needs to understand the ecosystem responses to changing sea ice and thermal regimes. The key geographical focus is on the biologically productive waters in the PAR that are influenced by the inflow of North Pacific water through Bering Strait. Papers in this volume are based upon selected biological measurements at multiple trophic levels, together with appropriate hydrographic surveys and satellite observations. The DBO is developing into a significant national and international change detection resource for the identification and consistent monitoring of marine biophysical responses to climate change, with ongoing plans to expand into a pan-Arctic biological observing network.

Lakes in permafrost regions are dynamic landscape components and play an important role for climate change feedbacks. Lake processes such as mineralization and flocculation of dissolved organic carbon (DOC), one of the main carbon fractions in lakes, contribute to the greenhouse effect and are part of the global carbon cycle. These processes are in focus of climate research but studies so far are limited to specific study regions. In our synthesis, we analysed 2,167 water samples from 1,833 lakes across the Arctic in permafrost regions of Alaska, Canada, Greenland, and Siberia to provide first pan-Arctic insights for linkages between DOC concentrations and the environment. Using published data and unpublished datasets from the author team we report regional DOC differences linked to latitude, permafrost zones, ecoregions, geology, near-surface soil organic carbon contents, and ground ice classification of each lake region. The lake DOC concentrations in our dataset range from 0 mg L−1 to 1,130 mg L−1 (10.8 mg L−1 median DOC concentration). Regarding the permafrost regions of our synthesis, we found median lake DOC concentrations of 12.4 mg L−1 (Siberia), 12.3 mg L−1 (Alaska), 10.3 mg L−1 (Greenland), and 4.5 mg L−1 (Canada). Our synthesis shows a significant relationship of lake DOC concentration and ecoregion of the lake. We found higher lake DOC concentrations in boreal permafrost sites compared to tundra sites. About 22 % of the lakes in our extensive dataset are located in regions with ice-rich syngenetic permafrost deposits (yedoma). Yedoma contains large amounts of easily erodible organic carbon and we found significantly higher DOC concentrations in yedoma lakes compared to non-yedoma lakes. Compared to previous studies we found a weak significant relationship of soil organic carbon content and lake DOC concentration as well as between ground-ice content and lake DOC. Our pan-Arctic dataset shows that the DOC concentration of a lake strongly depends on its environmental properties, especially on permafrost extent and ecoregion, as well as vegetation, which is the most important driver of lake DOC in this study. This new dataset will be fundamental to quantify a pan-Arctic lake DOC pool for estimations of the impact of lake DOC on the global carbon cycle and climate change.

We investigated the change in terminus position between 1985 and 2015 of 17 marine-terminating glaciers that drain into Disko and Uummannaq Bays, West Greenland, by manually digitizing over 5000 individual frontal positions from over 1200 Landsat images. We find that 15 of 17 glacier termini retreated over the study period, with ~80% of this retreat occurring since 2000. Increased frequency of Landsat observations since 2000 allowed for further investigation of the seasonal variability in terminus position. We identified 10 actively retreating glaciers based on a significant positive relationship between glaciers with cumulative retreat >300 m since 2000 and their average annual amplitude (seasonal range) in terminus position. Finally, using the Detecting Breakpoints and Estimating Segments in Trend (DBEST) program, we investigated whether the 2000–2015 trends in terminus position were explained by the occurrence of change points (significant trend transitions). Based on the change point analysis, we found that nine of 10 glaciers identified as actively retreating also underwent two or three periods of change, during which their terminus positions were characterized by increases in cumulative retreat. Previous literature suggests potential relationships between our identified change dates with anomalous ocean conditions, such as low sea ice concentration and high sea surface temperatures, and our change durations with individual fjord geometry.

Permafrost-region lakes are dynamic landscape systems and play an important role for climate change feedbacks. Lake processes such as mineralization and flocculation of DOC, one of the main carbon fraction in lakes, contribute to the global carbon cycle. These processes are in focus of climate research but studies have been limited in geographic extent. We synthesized published datasets and unpublished datasets from the author team totaling 1,691 water samples from 1,387 lakes across the Subarctic and Arctic in permafrost regions of Alaska, Canada, Siberia, and Greenland to provide first insights for linkages between DOC concentration to the basin. In our synthesis, we find regional differences in DOC concentration of permafrost-region lakes. We focussed on relations between lake DOC concentration and latitude, permafrost zones, ecoregions, lake surrounding deposit type, and ground ice classification of each lake basin. Additionally, we analysed the lake surrounding soil organic carbon content from 0-100 cm depth and 0-300 cm depth. Individual lake DOC concentrations of our dataset range from below detection limit assigned to 0 mg L-1 (North Slope, Alaska) to 1,130 mg L-1 (Yukon Flats, Alaska). We found regional median lake DOC concentrations of 18.8 mg L-1 (Greenland, n=25), 12.2 mg L-1 (Alaska, n= 1,135), 9.6 mg L-1 (Siberia, n=252), and 7.2 mg L-1 (Canada, n=279). Lakes in the isolated permafrost zone had the highest median DOC concentration compared to lakes in the sporadic, discontinuous, and continuous permafrost zones. Our synthesis shows increasing lake DOC concentration with decreasing latitude and, due to a larger availability of biomass and organic carbon, a significant relationship of lake DOC concentration and ecoregion of the lake. We found higher lake DOC concentrations in boreal permafrost sites compared to tundra sites. About 22 % of lakes in our dataset are located in regions with ice-rich syngenetic permafrost deposits (yedoma). Because yedoma contains large amounts of organic carbon, we assumed to find higher DOC concentrations in yedoma lakes compared to non-yedoma lakes. Our analysis shows a significant relationship of lake DOC concentration and surrounding deposit type but not a higher DOC concentration in yedoma lakes compared to non-yedoma lakes. Finally, we found a relationship of soil organic carbon content from 0-100 cm depth and lake DOC concentration. In contrast, a comparison of soil organic carbon content from 0-300 cm depth and lake DOC concentration shows no significant correlation. This was also found for ground-ice content and lake DOC concentration. Our dataset of lakes across the Arctic shows that the DOC concentration of a lake strongly depends on its environmental properties. This dataset will be fundamental to establish a pan-Arctic lake DOC pool for estimations of the impact of lake DOC on the global carbon cycle and further on climate change.

An assessment of the production, distribution and fate of highly branched isoprenoid (HBI) biomarkers produced by sea ice and pelagic diatoms is necessary to interpret their detection and proportions in the northern Bering and Chukchi Seas. HBIs measured in surface sediments collected from 2012 to 2017 were used to determine the distribution and seasonality of the biomarkers relative to sea ice patterns. A northward gradient of increasing ice algae deposition was observed with localized occurrences of elevated IP25 (sympagic HBI) concentrations from 68-70°N and consistently strong sympagic signatures from 71-72.5°N. A declining sympagic signature was observed from 2012 to 2017 in the northeast Chukchi Sea, coincident with declining sea ice concentrations. HBI fluxes were investigated on the northeast Chukchi shelf with a moored sediment trap deployed from August 2015 to July 2016. Fluxes of sea ice exclusive diatoms (Nitzschia frigida and Melosira arctica) and HBI-producing taxa (Pleurosigma, Haslea and Rhizosolenia spp.) were measured to confirm HBI sources and ice associations. IP25 was detected year-round, increasing in March 2016 (10 ng m-2 d-1) and reaching a maximum in July 2016 (1331 ng m-2 d-1). Snowmelt triggered the release of sea ice algae into the water column in May 2016, while under-ice pelagic production contributed to the diatom export in June and July 2016. Sea ice diatom fluxes were strongly correlated with the IP25 flux, however associations between pelagic diatoms and HBI fluxes were inconclusive. Bioturbation likely facilitates sustained burial of sympagic organic matter on the shelf despite the occurrence of pelagic diatom blooms. These results suggest that sympagic diatoms may sustain the food web through winter on the northeast Chukchi shelf. The reduced relative proportions of sympagic HBIs in the northern Bering Sea are likely driven by sea ice persistence in the region.

The timing of seasonal snowmelt in high-latitude tundra has implications ranging from local biological productivity to global atmospheric circulation, yet remains difficult to quantify, particularl...

Recent declines in sea ice extent and warming seawater temperatures in the Arctic have the potential to impact regional and pan-Arctic marine ecosystems. To investigate marine biological response to these key drivers and other environmental factors, we undertook a robust trend analysis of benthic macrofaunal populations and environmental drivers in the Bering Strait region. Our focus was on the waters of the northern Bering and southern Chukchi Seas, which are shallow (

As high-latitudes warm, permafrost thaws, and the hydrological cycle accelerates, ground-based monitoring of riverine organic matter may be supplemented by satellite remote sensing during ice-free conditions. Recent programs, namely the Arctic Great Rivers Observatory, have established methodologically consistent sampling across the hydrograph, and shared the resulting data publicly. However, these efforts are limited by frequency, funding, and length of record. Satellite remote sensing can be used to estimate chromophoric dissolved organic matter (CDOM) as a riverine constituent that influences optical properties in surface waters. In this study, daily CDOM absorption was first estimated using discharge-constituent regression-based models for 2000–2013. We then regressed these discharge-based CDOM estimates against Landsat TM and ETM+ surface reflectance data from Google Earth Engine for the six largest rivers draining the pan-Arctic watershed (the Kolyma, Lena, Mackenzie, Ob', Yenisey, and Yukon rivers). These CDOM results were converted to dissolved organic carbon (DOC), using the strong relationship (R2 = 0.88) between direct measurements of the two constituents. Using river-specific remote sensing models, R2 could be as high as 0.84. Grouping all rivers into a single “universal” regression reduced R2 and increased root mean square errors, such as in the Yenisey River where R2 dropped by 0.63, and RMSE rose by 1.1 m−1. Seasonally varying discharge drove much of the variation in satellite-derived CDOM and DOC, corroborating recent studies. Satellite imagery can increase the frequency of monitoring observations, particularly during summer and fall when riverine CDOM absorption may be most sensitive to thawing permafrost.

In this paper, we demonstrate that climate change is critically important for the current and future status of mining activity and its impacts on surrounding communities and environments. We illustrate this through examples from Latin America, including a spatial analysis of the intersection between projected climate changes and existing mining operations. We then elaborate a framework to identify and investigate the relationships among mining, climate change, and public and private responses to them. The framework also notes the importance of political economy and learning processes to the forms taken by these relationships. Our paper then reports on a focused review of peer-reviewed publications that aims to identify the extent to which a core research literature on mining and climate change currently exists. We show that this literature is still very limited, but that the analysis that does exist can be encapsulated by the main elements of our framework. This enables us to describe the current structure of both peer-reviewed and policy research on mining and climate change, and identify areas for future research. In particular, we note the chronic absence of research on this relationship for the vast majority of developing countries, where some of the most serious vulnerabilities to climate change exist.

The expected reduction of ice algae with declining sea ice may prove to be detrimental to the Pacific Arctic ecosystem. Benthic organisms that rely on sea ice organic carbon (iPOC) sustain benthic predators such as the Pacific walrus (Odobenus rosmarus divergens). The ability to track the trophic transfer of iPOC is critical to understanding its value in the food web, but prior methods have lacked the required source specificity. We analyzed the H-Print index, based on biomarkers of ice algae versus phytoplankton contributions to organic carbon in marine predators, in Pacific walrus livers collected in 2012, 2014 and 2016 from the Northern Bering Sea (NBS) and Chukchi Sea. We paired these measurements with stable nitrogen isotopes (δ15N) to estimate trophic position. We observed differences in the contribution of iPOC in Pacific walrus diet between regions, sexes, and age classes. Specifically, the contribution of iPOC to the diet of Pacific walruses was higher in the Chukchi Sea (52%) compared to the NBS (30%). This regional difference is consistent with longer annual sea ice persistence in the Chukchi Sea. Within the NBS, the contribution of iPOC to walrus spring diet was higher in females (~45%) compared to males (~30%) for each year (p < 0.001), likely due to specific foraging behavior of females to support energetic demands associated with pregnancy and lactation. Within the Chukchi Sea, the iPOC contribution was similar between males and females, yet higher in juveniles than in adults. Despite differences in the origin of organic carbon fueling the system (sea ice versus pelagic derived carbon), the trophic position of adult female Pacific walruses was similar between the NBS and Chukchi Sea (3.2 and 3.5, respectively), supporting similar diets (i.e. clams). Given the higher quality of organic carbon from ice algae, the retreat of seasonal sea ice in recent decades may create an additional vulnerability for female and juvenile Pacific walruses and should be considered in management of the species.

As a major gateway from the Pacific to the open Arctic Ocean, biogeochemical transformations of nutrients in the Chukchi Sea are important for understanding the Arctic ecosystem as a whole. This study examines the biogeochemical cycling of the macronutrient phosphorus (P) relative to carbon (C) and nitrogen (N) in the eastern Chukchi Sea during the ICESCAPE mission. Sea ice and water column dissolved and particulate P samples were collected during summer expeditions in 2010 ( n =543) and 2011 ( n =553). Nearly all forms of P were higher in Pacific Winter Waters (PWW), indicating the potential importance of PWW to Chukchi Sea nutrient pools. Annual means of P concentrations in all its forms in the offshore waters throughout the Chukchi Sea were also consistently higher (TP 2010 =1.56±0.61 µM, TP 2011 =1.67±0.68 µM) relative to waters inshore and within the Alaska Coastal Current (ACC), suggesting coastal inputs were relatively minor during our sampling. Rather, biological modification of P pools dominated, with 30–40% of the total dissolved P pool (TDP) and nearly 50% of the total particulate P pool (TPP) comprised of organic P. Nutrient analyses of first year sea ice suggest that sea ice melt contains highly variable P concentrations that span an order of magnitude depending on particulate matter content. As such, sea ice melt may contribute significant nutrients to summer waters on a transient basis. Low N:P ratios (

Retrospective analysis of apparent freshwater isotopic end-members through use of salinity– δ 18 O mixing lines for 15 research cruises from 1990 to 2012 indicates that the freshwater contributed by melted seasonal sea ice does not directly reflect the large change in seasonal sea ice extent in the Chukchi Sea observed over the past several decades. Instead the freshwater that appears to be contributed by melting sea ice relative to runoff is highly dependent upon cruise track (e.g. proximity to runoff) and sampling capabilities in sea ice (icebreakers sample waters with less melted sea ice). Although under certain circumstances, including later seasonal sampling and recurrent cruise tracks between years, increased melted sea ice in surface waters can be readily detected. This suggests a more ephemeral influence of melted sea ice on ecosystem properties despite the significant decadal changes in sea ice extent. As a recent case study, the freshwater component present in waters within an under-ice bloom in the Chukchi Sea reported by Arrigo et al. (2012) , included a significant fraction (~10% or more) of freshwater, primarily from melted sea ice. These results suggest that this under-ice bloom, which extended more than 60 km under solid ice still might be reasonably interpreted as being part of a continuum with other ice melt-associated blooms and not independent of sea ice retreat and dissolution.

We construct mass-balance based estimates of carbon (C) export fractions from the water column across the Chukchi Sea shelf. Export is calculated as the difference between phytoplankton drawdown of dissolved inorganic C (DIC) and the accumulation of autochthonous particulate and dissolved organic C in the water column. Organic carbon (Corg) exports of >50% of DIC drawdown are ubiquitous across the shelf, even during, or shortly after, phytoplankton blooms, suggesting widespread and strong pelagic-benthic coupling. Export fractions on the shelf were generally greater in the less-productive Alaska Coastal Water than in the more productive Bering Shelf-Anadyr Water. Additionally, export fractions were greater in 2011 than in 2010, highlighting the significant spatial and inter-annual variability of the fate of Corg in this ecologically and biogeochemically important, and rapidly changing, ecosystem.

We investigated chromophoric dissolved organic matter (CDOM) in sea ice and the underlying water column in the Chukchi and Beaufort seas of the Pacific Arctic region and its relationship with both physical and biogeochemical parameters. Sea ice, water and melt pond samples were collected as sea ice melted in June–July 2010 and 2011. CDOM absorption was found to be significantly lower in sea ice compared to under-ice waters. In particular, the average CDOM absorption coefficient at 254 nm was approximately four times greater in the underlying water column than in the overlying ice. This indicates that melting sea ice did not contribute to net CDOM at this point in the melt season, but rather diluted CDOM in the under-ice water column. In the 2011 under-ice water column samples, the average CDOM absorption coefficients at 440 nm were twice as high along a transect associated with high phytoplankton biomass, which may have been contributed through subsequent microbial generation of CDOM. Less extensive sea ice cover with melt ponds may also have increased the presence of CDOM owing to increases in light transmission, leading to under-ice phytoplankton blooms and associated microbial production. However, oxygen isotope analysis of these waters with high under-ice phytoplankton biomass also indicates the presence of prior sea ice melt, including potentially sea ice algae and microbes, which could have also contributed to this anomalously high CDOM. These observations suggest that while melting sea ice may not necessarily contribute to increased CDOM concentrations, there are circumstances where CDOM in underlying waters may be higher than expected, either due to enhanced light transmission and higher under-ice production, and/or prior ice melt that provided significant contributions to under-ice CDOM.

In the continuous permafrost zone, unfrozen ground may exist beneath large lakes and streams. Sub-lake taliks that extend through permafrost provide a potential conduit for subpermafrost groundwater to reach the surface, increasing dissolved ion concentrations in lake water. Twenty-eight lakes on the Arctic Coastal Plain of northern Alaska were sampled in 2013–14 to determine whether a difference in ionic concentration could be detected between lakes with and without through taliks. A thermal model originally developed by J. Ross Mackay indicated that 20 of the lakes may have a talik that penetrates the permafrost. Lake water samples were analysed for a variety of ions and geochemical properties. Generally, there was little interannual variation in ion concentration, pH and specific conductivity of lake water. Proximal lakes tended to have similar chemical signatures, but there were large variations across the study region. Local factors appeared largely to control lake water chemistry. Lakes with suspected through taliks did not demonstrate a hydrochemical signature distinct from nearby lakes lacking a through talik. This suggests that either: (1) there is no hydrological connection with subpermafrost groundwater due to aquicludes in the subsurface; (2) the flux of groundwater is too small to have a measurable impact on lake water chemistry; or (3) the steady-state condition for talik configuration assumed in the thermal model is not justified. Copyright © 2016 John Wiley & Sons, Ltd.

The Kolyma River in northeast Siberia is among the six largest Arctic rivers and drains a region underlain by vast deposits of Holocene-aged peat and Pleistocene-aged loess known as yedoma, most of which is currently stored in ice-rich permafrost throughout the region. These peat and yedoma deposits are important sources of dissolved organic matter (DOM) to inland waters that in turn play a significant role in the transport and ultimate remineralization of organic carbon to CO2 and CH4 along the terrestrial flow-path continuum. The turnover and fate of terrigenous DOM during offshore transport largely depends upon the composition and amount of carbon released to inland and coastal waters. Here, we measured the ultraviolet-visible optical properties of chromophoric DOM (CDOM) from a geographically extensive collection of waters spanning soil pore waters, streams, rivers, and the Kolyma River mainstem throughout a ∼ 250 km transect of the northern Kolyma River basin. During the period of study, CDOM absorption coefficients were found to be robust proxies for the concentration of DOM, whereas additional CDOM parameters such as spectral slopes (S) were found to be useful indicators of DOM quality along the flow path. In particular, the spectral slope ratio (SR) of CDOM demonstrated statistically significant differences between all four water types and tracked changes in the concentration of bioavailable DOC, suggesting that this parameter may be suitable for clearly discriminating shifts in organic matter characteristics among water types along the full flow-path continuum across this landscape. However, despite our observations of downstream shifts in DOM composition, we found a relatively constant proportion of DOC that was bioavailable ( ∼ 3–6 % of total DOC) regardless of relative water residence time along the flow path. This may be a consequence of two potential scenarios allowing for continual processing of organic material within the system, namely (a) aquatic microorganisms are acclimating to a downstream shift in DOM composition and/or (b) photodegradation is continually generating labile DOM for continued microbial processing of DOM along the flow-path continuum. Without such processes, we would otherwise expect to see a declining fraction of bioavailable DOC downstream with increasing residence time of water in the system. With ongoing and future permafrost degradation, peat and yedoma deposits throughout the northeast Siberian region will become more hydrologically active, providing greater amounts of DOM to fluvial networks and ultimately to the Arctic Ocean. The ability to rapidly and comprehensively monitor shifts in the quantity and quality of DOM across the landscape is therefore critical for understanding potential future feedbacks within the Arctic carbon cycle.

Sea ice is a dynamic physical element of the greater Arctic marine system, one that has myriad connections to human systems on a variety of spatial and temporal scales. Changes to the spatial extent of sea ice simultaneously permits and endangers maritime operations, as well as impacts current debates over maritime boundaries, presenting an interesting challenge for international law. Sea ice is not a stationary object; it moves through time and space in response to the physical forces of wind, ocean currents, and heating. It has a tangible, material and substantive role in contestations over territory, resources and marine boundaries in both the Beaufort and Bering Seas. We suggest here that sea ice’s material nature in these marine regions continuously challenges stationary conceptions of law in complex and sometimes contradictory ways. Building on recent work on the human geographies of sea ice, the dynamic field of legal geography and recent contributions in ocean-space geography, we outline how the dynamism of sea ice could influence notions of boundary, resources and climate change in ocean-spaces of the greater Arctic region.

Ice shelves modulate Antarctica’s contributions to sea-level rise. Regional-climate-model simulations and observations suggest historical ice melt intensification before collapse of Antarctic peninsula shelves, and project future melt evolution.

Over the past three decades of the observed satellite record, there have been significant changes in sea ice cover across the Bering, Chukchi, and Beaufort seas of the Pacific Arctic Region (PAR). Satellite data reveal that patterns in sea ice cover have been spatially heterogeneous, with significant declines in the Chukchi and Beaufort seas, yet more complex multi-year variability in the Bering Sea south of St. Lawrence Island. These patterns in the Chukchi and Beaufort seas have intensified since 2000, indicating a regime shift in sea ice cover across the northern portion of the PAR. In particular, satellite data over 1979–2012 reveal localized decreases in sea ice presence of up to −1.64 days/year (Canada Basin) and −1.24 days/year (Beaufort Sea), which accelerated to up to −6.57 days/year (Canada Basin) and −12.84 days/year (Beaufort Sea) over the 2000–2012 time period. In contrast, sea ice in the Bering Sea shows more complex multi-year variability with localized increases in sea ice presence of up to +8.41 days/year since 2000. The observed increases in sea ice cover since 2000 in the southern Bering Sea shelf region are observed in wintertime, whereas sea ice losses in the Canada Basin and Beaufort Sea have occurred during summer. We further compare sea ice variability across the region with the National Centers for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR) wind and air temperature fields to determine the extent to which this recent variability is driven by thermal vs. wind-driven processes. Results suggest that for these localized areas that are experiencing the most rapid shifts in sea ice cover, those in the Beaufort Sea are primarily wind driven, those offshore in the Canada Basin are primarily thermally driven, and those in the Bering Sea are influenced by elements of both. Sea ice variability (and its drivers) across the PAR provides critical insight into the forcing effects of recent shifts in climate and its likely ultimate profound impacts on ecosystem productivity across all trophic levels.

The northern Bering and Chukchi Seas are areas in the Pacific Arctic characterized by high northward advection of Pacific Ocean water, with seasonal variability in sea ice cover, water mass characteristics, and benthic processes. In this review, we evaluate the biological and environmental factors that support communities of benthic prey on the continental shelves, with a focus on four macrofaunal biomass “hotspots.” For the purpose of this study, we define hotspots as macrofaunal benthic communities with high biomass that support a corresponding ecological guild of benthivorous seabird and marine mammal populations. These four benthic hotspots are regions within the influence of the St. Lawrence Island Polynya (SLIP), the Chirikov Basin between St. Lawrence Island and Bering Strait (Chirikov), north of Bering Strait in the southeast Chukchi Sea (SECS), and in the northeast Chukchi Sea (NECS). Detailed benthic macrofaunal sampling indicates that these hotspot regions have been persistent over four decades of sampling due to annual reoccurrence of seasonally consistent, moderate-to-high water column production with significant export of carbon to the underlying sediments. We also evaluate the usage of the four benthic hotspot regions by benthic prey consumers to illuminate predator–prey connectivity. In the SLIP hotspot, spectacled eiders and walruses are important winter consumers of infaunal bivalves and polychaetes, along with epibenthic gastropods and crabs. In the Chirikov hotspot, gray whales have historically been the largest summer consumers of benthic macrofauna, primarily feeding on ampeliscid amphipods in the summer, but they are also foraging further northward in the SECS and NECS hotspots. Areas of concentrated walrus foraging occur in the SLIP hotspot in winter and early spring, the NECS hotspot in summer, and the SECS hotspot in fall. Bottom up forcing by hydrography and food supply to the benthos influences persistence and composition of benthic prey that then influences the distributions of benthivorous upper trophic level populations.

Physical and morphological properties of sea ice in the Chukchi and western Beaufort seas were measured during the 2010 and 2011 June−July ICESCAPE (Impacts of Climate on the Eco-Systems and Chemistry of the Arctic Pacific Environment) missions aboard the USCGC Healy. Observations of ice conditions, including ice thicknesses, types, and concentrations of primary, secondary, and tertiary categories were reported at 2-h intervals while the ship was in transit using the Antarctic Sea ice Processes and Climate (ASPeCt) protocol. On-ice surveys of ice thickness, melt-pond depth, and ice properties (including profiles of internal temperature, salinity, and isotopic composition) were conducted at 21 total ice stations (12 in 2010 and 9 in 2011). Comparison to historical ship-based observations confirms a multi-decadal transition from a multiyear to thinner, first year -dominated seasonal sea-ice pack in the region, with much earlier ice retreat than in past decades. The ice encountered was predominantly (>98%) first year, with un-deformed ice thicknesses ranging from 0.73 to 1.2 m. Pond coverage was extensive, averaging 29% in 2010 and 19% in 2011, resulting in considerable light absorption in the ice and transmission of light to the ocean. Enhanced melting near the ice edge is consistent with transport of Pacific-origin heat and/or ice-albedo feedbacks. Sediment entrainment was visible in 7.5% and 10.9% of the ice in 2010 and 2011, respectively. Overall, the results indicate a regime shift in the characteristics of the ice cover has occurred in the region over recent decades, with substantive implications for thermodynamic forcing, light availability in the upper ocean, and biological and biogeochemical processes in the ice and water column beneath. The results presented have applications for the interpretation of optical and biological measurements in the Chukchi Sea and serve as record of ice conditions for assessing long-term change.

Arctic soils contain three times as much carbon (C) as all aboveground biomass distributed globally, much of which is stored in permafrost soils. Here, we (1) determine the predictability of estimating soil organic carbon (SOC) using different satellite data, classifications, and methods; (2) estimate the quantity and distribution of SOC for the top 10 cm for the Ambolikha River watershed (~121 km2) in northeast Siberia, a sub-watershed of the Kolyma River; and (3) produce a hybrid SOC map through data fusion, combining the strengths of each data type. Land cover maps were produced using a pixel-based classification with Landsat-5 Thematic Mapper (TM) data and an object-based classification using WorldView-2 data. Spectral mixture analysis (SMA) was performed on both data types to calculate the fraction of four vegetation types in each pixel, and land cover maps were combined with field measurements of SOC in the top 10 cm. The overall classification accuracy was 69% for Landsat, 81% for WorldView-2, and ...

The carbon dioxide (CO2)-carbonate chemistry of sea-ice melt and co-located, contemporaneous seawater has rarely been studied in sea-ice-covered oceans. Here, we describe the CO2–carbonate chemistry of sea-ice melt (both above sea-ice as "melt ponds" and below sea-ice as "interface waters") and mixed-layer properties in the western Arctic Ocean in the early summer of 2010 and 2011. At 19 stations, the salinity (∼0.5 to 1500 μatm) with the majority of melt ponds acting as potentially strong sources of CO2 to the atmosphere. The pH of melt pond waters was also highly variable ranging from mildly acidic (6.1 to 7) to slightly more alkaline than underlying seawater (>8.2 to 10.8). All of the observed melt ponds had very low (

The Hindu Kush-Himalayan (HKH) region epitomizes a geographic region where cryospheric processes coupled with hydrological regimes are under threat owing to a warming climate and shifts in climate extremes. In this study, we analyse global climate models in the Coupled Model Intercomparison Project phase 3 (CMIP3) and phase 5 (CMIP5) archives to investigate the qualitative aspects of change and trends in temperature and precipitation indices. Specifically, we examine and evaluate multi-model, multi-scenario climate change projections and seven extreme temperature and precipitation indices over the eastern Himalaya (EH) and western Himalaya-Karakoram (WH) regions for the 21st century. Density distribution plots of observed climate indices for meteorological stations and gridded indices are also analysed, which indicate significant negative trends in the annual number of frost days and significant increasing trends in warm nights in the EH region over the 1960-2000 period. Multi-model average (MMA) projections additionally indicate continued trends towards more extreme conditions consistent with a warmer, wetter climate. Precipitation projections indicate increased mean precipitation with more frequent extreme rainfall during monsoon season in the EH region, and a wetter cold season in the WH region. Time series of all MMA precipitation indices exhibit significant increasing trends over the 1901-2099 period. By comparison, time series of temperature indices show decreases in the intra-annual extreme temperature range and total number of frost days, as well as increases in warm nights. In general, these future projections point towards increases in summertime temperatures and modifications in precipitation across both regions.

Arctic sea ice decline has led to an amplification of surface warming and is projected to continue to decline from anthropogenic forcing, although the exact timing of ice-free summers is uncertain owing to large natural variability. Sea ice reductions affect surface heating patterns and the atmospheric pressure distribution, which may alter midlatitude extreme weather patterns. Increased light penetration and nutrient availability during spring from earlier ice breakup enhances primary production in the Arctic Ocean and its adjacent shelf seas. Ice-obligate marine mammals may be losers, whereas seasonally migrant species may be winners from rapid sea ice decline. Tundra greening is occurring across most of the Arctic, driven primarily by warming temperatures, and is displaying complex spatial patterns that are likely tied to other factors. Sea ice changes are affecting greenhouse gas exchanges as well as halogen chemistry in the Arctic. This review highlights the heterogeneous nature of Arctic change, which is vital for researchers to better understand.

The climate of West Antarctica is strongly influenced by remote forcing from the tropical Pacific. For example, recent surface warming over West Antarctica reflects atmospheric circulation changes over the Amundsen Sea, driven by an atmospheric Rossby wave response to tropical sea surface temperature (SST) anomalies. Here, it is demonstrated that tropical Pacific SST anomalies also influence the source and transport of marine-derived aerosols to the West Antarctic Ice Sheet. Using records from four firn cores collected along the Amundsen coast of West Antarctica, the relationship between sea ice–modulated chemical species and large-scale atmospheric variability in the tropical Pacific from 1979 to 2010 is investigated. Significant correlations are found between marine biogenic aerosols and sea salts, and SST and sea level pressure in the tropical Pacific. In particular, La Niña–like conditions generate an atmospheric Rossby wave response that influences atmospheric circulation over Pine Island Bay. Seasonal regression of atmospheric fields on methanesulfonic acid (MSA) reveals a reduction in onshore wind velocities in summer at Pine Island Bay, consistent with enhanced katabatic flow, polynya opening, and coastal dimethyl sulfide production. Seasonal regression of atmospheric fields on chloride (Cl−) reveals an intensification in onshore wind velocities in winter, consistent with sea salt transport from offshore source regions. Both the source and transport of marine aerosols to West Antarctica are found to be modulated by similar atmospheric dynamics in response to remote forcing. Finally, the regional ice-core array suggests that there is both a temporally and a spatially varying response to remote tropical forcing.

Inland water systems are generally supersaturated in carbon dioxide (CO 2 ) and are increasingly recognized as playing an important role in the global carbon cycle. The Arctic may be particularly important in this respect, given the abundance of inland waters and carbon contained in Arctic soils; however, a lack of trace gas measurements from small streams in the Arctic currently limits this understanding.We investigated the spatial variability of CO 2 evasion during the summer low-flow period from streams and rivers in the northern portion of the Kolyma River basin in north-eastern Siberia. To this end, partial pressure of carbon dioxide ( p CO 2 ) and gas exchange velocities ( k ) were measured at a diverse set of streams and rivers to calculate CO 2 evasion fluxes. We combined these CO2 evasion estimates with satellite remote sensing and geographic information system techniques to calculate total areal CO 2 emissions. Our results show that small streams are substantial sources of atmospheric CO 2 owing to high p CO 2 and k , despite being a small portion of total inland water surface area. In contrast, large rivers were generally near equilibrium with atmospheric CO 2 . Extrapolating our findings across the Panteleikha-Ambolikha sub-watersheds demonstrated that small streams play a major role in CO 2 evasion, accounting for 86% of the total summer CO 2 emissions from inland waters within these two sub-watersheds. Further expansion of these regional CO 2 emission estimates across time and space will be critical to accurately quantify and understand the role of Arctic streams and rivers in the global carbon budget. Keywords: Arctic streams and rivers; CO 2 evasion; inland water surface area; Kolyma River; p CO 2 ; Siberia (Published: 5 December 2013) Citation: Polar Research 2013, 32 , 19704, http://dx.doi.org/10.3402/polar.v32i0.19704

Previous studies have drawn attention to substantial hydrological changes taking place in mountainous watersheds where hydrology is dominated by cryospheric processes. Modelling is an important tool for understanding these changes but is particularly challenging in mountainous terrain owing to scarcity of ground observations and uncertainty of model parameters across space and time. This study utilizes a Markov Chain Monte Carlo data assimilation approach to examine and evaluate the performance of a conceptual, degree-day snowmelt runoff model applied in the Tamor River basin in the eastern Nepalese Himalaya. The snowmelt runoff model is calibrated using daily streamflow from 2002 to 2006 with fairly high accuracy (average Nash-Sutcliffe metric approx. 0.84, annual volume bias

We present a new algorithm for retrieving sea ice concentration from the AMSR-E data, the dual-polarized ratio (DPR) algorithm. The DPR algorithm is developed using vertically and horizontally polarized brightness temperatures at the same channel of 36.5 GHz. It depends on the ratio of dual-polarized emissivity, α, which is determined empirically at about 0.92 by remotely sensed brightness temperature in winter and used for the other seasons as well. The ice concentration retrieved by the DPR is compared with those by the NT2 and ABA algorithms. Since the main difference among these algorithms takes place in marginal ice zones, 17 marginal ice zones are chosen. The retrieved ice concentrations in these zones are examined by the ice concentration obtained by the MODIS data. The mean error, root-mean-square error and mean absolute error of the DPR algorithm are relatively better than those from the other two algorithms. The results of this study illustrate that the DPR algorithm is a more accurate algorithm for retrieving sea ice concentration from the AMSR-E brightness temperature, and can be used for operational purposes.

Although data for temporal spring river ice breakup are available for a number of Arctic rivers, there is a paucity of information related to the type of breakup. The Arctic Climate Impact Assessment (ACIA) of 2005 predicted a transition from mechanical to thermal spring breakup of ice cover on arctic rivers, with this shift being greatest in exclusively Arctic watersheds where observed warming is most pronounced. We describe a rare instance of an entirely Arctic river with limited but well documented historical and recent data regarding the type of breakup. Time-series ground imagery of spring breakup from 1966, 1975, 1978, 2009, 2010 and 2012, in combination with interviews of local inhabitants, documents a shift from predominantly mechanical to predominantly thermal breakup after spring 1978 and by spring 2009 within the context of a locally and regionally warming Arctic. The resultant shift from predominantly mechanical to predominantly thermal breakup is predicted to result in significant changes to water, sediment, nutrient and organic carbon fluxes, as well as riparian ecology and human activities.

investigation of how regional SIC is recorded in the ice-sheet stratigraphy. Over the period 2002–2010 we find that the ice-sheet chemistry is significantly correlated with SIC variability within the AS and Pine Island Bay polynyas. Based on this result, we evaluate the use of icecore chemistry as a proxy for interannual polynya variability in this region, one of the largest and most persistent polynya areas in Antarctica. MSA concentrations correlate strongly with summer SIC within the polynya regions, consistent with MSA at this site being derived from marine biological productivity during the spring and summer. Cl – concentrations correlate strongly with winter SIC within the polynyas as well as some regions outside the polynyas, consistent with Cl – at this site originating primarily from winter sea-ice formation. Spatial correlations were generally insignificant outside of the polynya areas, with some notable exceptions. Ice-core glaciochemical records from this dynamic region thus may provide a proxy for reconstructing AS and Pine Island Bay polynya variability prior to the satellite era.

Arctic streams are likely to receive increased inputs of dissolved nutrients and organic matter from thawing permafrost as climate warms. Documenting how Arctic streams process inorganic nutrients is necessary to understand mechanisms that regulate watershed fluxes of permafrost-derived materials to downstream ecosystems. We report on summer nitrogen (N) and phosphorus (P) uptake in streams draining upland soils from the Pleistocene, and lowland floodplain soils from the Holocene, in Siberia’s Kolyma River watershed. Uptake of N and P differed between upland and floodplain streams, suggesting topographic variation in nutrient limitation. In floodplain streams, P uptake rate and uptake velocity were higher than N, while upland streams had similar values for all N and P uptake metrics. Phosphorus uptake velocity and size of the transient hydrologic storage zone were negatively related across all study streams, indicating strong influence of hydrologic processes on nutrient fluxes. Physical sorption of P was higher in floodplain stream sediments relative to upland stream sediments, suggesting more physically driven uptake in floodplain streams and higher biological activity in upland streams. Overall, these results demonstrate that high-latitude headwater streams actively retain N and P during summer base flows; however, floodplain and upland streams varied substantially in N and P uptake and may respond differently to inorganic nutrient and organic matter inputs. Our results highlight the need for a comprehensive assessment of N and P uptake and retention in Arctic streams in order to fully understand the impact of permafrost-derived materials on ecosystem processes, and their fate in continental drainage networks. Keywords: Arctic streams; nutrient uptake; hydrologic transient storage; phosphorus sorption; coupled N and P cycling. (Published: 6 June 2016) To access the supplementary material for this article, please see the supplementary files in the column to the right (under Article Tools). Citation: Polar Research 2016, 35 , 24571, http://dx.doi.org/10.3402/polar.v35.24571

The northern Bering Sea shelf is dominated by soft-bottom infauna and ecologically significant epifauna that are matched by few other marine ecosystems in biomass. The likely basis for this high benthic biomass is the intense spring bloom, but few studies have followed the direct sedimentation of organic material during the bloom peak in May. Satellite imagery, water column chlorophyll concentrations and surface sediment chlorophyll inventories were used to document the dynamics of sedimentation to the sea floor in both 2006 and 2007, as well as to compare to existing data from the spring bloom in 1994. An atmospherically-derived radionuclide, 7Be, that is deposited in surface sediments as ice cover retreats was used to supplement these observations, as were studies of light penetration and nutrient depletion in the water column as the bloom progressed. Chlorophyll biomass as sea ice melted differed significantly among the three years studied (1994, 2006, 2007). The lowest chlorophyll biomass was observed in 2006, after strong northerly and easterly winds had distributed relatively low nutrient water from near the Alaskan coast westward across the shelf prior to ice retreat. By contrast, in 1994 and 2007, northerly winds had less northeasterly vectors prior to sea ice retreat, which reduced the westward extent of low-nutrient waters across the shelf. Additional possible impacts on chlorophyll biomass include the timing of sea-ice retreat in 1994 and 2007, which occurred several weeks earlier than in 2006 in waters with the highest nutrient content. Late winter brine formation and associated water column mixing may also have impacts on productivity that have not been previously recognized. These observations suggest that interconnected complexities will prevent straightforward predictions of the influence of earlier ice retreat in the northern Bering Sea upon water column productivity and any resulting benthic ecosystem re-structuring as seasonal sea ice retreats in the northern Bering Sea.