Regional Sea Ice Research Articles

Bearded seal (Erignathus barbatus) birth mass and pup growth in periods with contrasting ice conditions in Svalbard, Norway

AbstractGlobal climate warming has caused major reductions in sea ice in the Arctic, posing a serious threat to ice‐associated marine mammals. Herein, novel data on birth mass and pup growth rates over a 15‐year period (1993–2007; 10 years with growth data) are reported for bearded seals, as well as initial behavioral responses by this species to major, local declines in sea‐ice in Svalbard, Norway. In total, 205 pups were captured; 64 of which were recaptured, some repeatedly, producing 85 growth intervals for nursing pups. Average birth mass of pups was 37.1 ± 3.8 (SD) kg (range 33–47 kg, n = 25); birth mass before vs. after the sea ice collapse (2006 onward) were not found to differ. Pups grew at a rate of 3.0 ± 0.7 kg/day (1.8–4.8 kg/day, n = 64) during the nursing period. LME models suggest that ice concentration did not affect the growth rate of pups. Most females shifted from traditional first‐year ice floes to glacier‐ice pieces for birthing and nursing their young, following the regional sea ice collapse. However, retraction of tidal glaciers will likely eliminate this replacement birthing and nursing habitat for bearded seals in Svalbard in the coming decades.

The Value of Sustained Ocean Observations for Sea Ice Predictions in the Barents Sea

ABSTRACT Dynamical prediction systems have shown potential to meet the emerging need for seasonal forecasts of regional Arctic sea ice. Observationally constrained initial conditions are a key source of skill for these predictions, but the direct influence of different observation types on prediction skill has not yet been systematically investigated. In this work, we perform a hierarchy of observing system experiments with a coupled global data assimilation and prediction system to assess the value of different classes of oceanic and atmospheric observations for seasonal sea ice predictions in the Barents Sea. We find notable skill improvements due to the inclusion of both sea surface temperature (SST) satellite observations and subsurface conductivity–temperature–depth (CTD) measurements. The SST data are found to provide the crucial source of interannual variability, whereas the CTD data primarily provide climatological and trend improvements. Analysis of the Barents Sea ocean heat budget suggests that ocean heat content anomalies in this region are driven by surface heat fluxes on seasonal time scales.

Attributing Greenland Warming Patterns to Regional Arctic Sea Ice Loss

AbstractObserved and model‐projected sea ice loss enhances warming in the Arctic. We investigate to what extent warming on Greenland can be attributed to changes in the sea ice cover in different parts of the Arctic. Using Climate Model Intercomparison Project phase 5 model projections of the future, we perform multilinear regressions to separate the simulated warming on Greenland in two parts; one following global warming and one following regional sea ice changes. This reveals the magnitude and spatial pattern of warming on Greenland, which can be attributed to sea ice loss in different Arctic regions. The results indicate that the impact of sea ice loss is largely confined to the coastal parts of Greenland. We find the strongest links to sea ice loss in adjacent regions; remote regions only have a limited impact. Overall, warming attributable to sea ice variability is a minor contribution but can be a dominant signal locally in coastal regions.

Winter Sea Ice Export From the Beaufort Sea as a Preconditioning Mechanism for Enhanced Summer Melt: A Case Study of 2016

AbstractDuring September 2016 an ice‐free Beaufort Sea was observed for only the second time. Like previous regional sea ice minima (1998, 2008, and 2012), seasonal preconditioning of the ice pack toward younger, thinner ice types contributed to premature breakup that accelerated the ice‐albedo feedback and enhanced summer melt. In 2016, anomalously high sea ice export and ice pack divergence during February and April promoted the unusual widespread formation of new ice within the Beaufort. Thin ice types reached a peak regional concentration of 30% in March, when the ice cover is typically dominated by thick first‐year and multiyear sea ice. Combined CryoSat‐2 and Soil Moisture and Ocean Salinity (SMOS) data indicate that the regional ice volume plateaued from December to March as export offset ice growth and ultimately culminated in a −30% volume anomaly in April 2016. This atypically thin ice cover broke up 7 weeks earlier than average, with open water forming not only within coastal flaw leads but also within the offshore pack ice. By July 2016, vast areas of open water within the highly fractured ice cover accelerated the ice‐albedo feedback and led to rapid melt. Though maintaining a partial ice cover during summer throughout the observational record, significant negative trends in September sea ice area within the Beaufort are now punctuated by two recent ice‐free Septembers (2012 and 2016). As the Beaufort transitions toward a seasonally ice‐free sea, we examine the role of winter preconditioning through sea ice transport and its growing importance within an increasingly seasonal and mobile Arctic ice cover.

The interaction between island geomorphology and environmental parameters drives Adélie penguin breeding phenology on neighboring islands near Palmer Station, Antarctica.

Despite many studies on Adélie penguin breeding phenology, understanding the drivers of clutch initiation dates (CIDs, egg 1 lay date) is limited or lacks consensus. Here, we investigated Adélie penguin CIDs over 25 years (1991–2016) on two neighboring islands, Torgersen and Humble (<1 km apart), in a rapidly warming region near Palmer Station, Antarctica. We found that sea ice was the primary large‐scale driver of CIDs and precipitation was a secondary small‐scale driver that fine‐tunes CID to island‐specific nesting habitat geomorphology. In general, CIDs were earlier (later) when the spring sea ice retreat was earlier (later) and when the preceding annual ice season was shorter (longer). Island‐specific effects related to precipitation and island geomorphology caused greater snow accumulation and delayed CIDs by ~2 days on Torgersen compared to Humble Island. When CIDs on the islands were similar, conditions were mild with less snow across breeding sites. At Torgersen Island, the negative relationship between CID and breeding success highlights detrimental effects of delayed breeding and/or snow on penguin fitness. Past phenological studies reported a relationship between air temperature and CID, assumed to be related to precipitation, but we found air temperature was more highly correlated to sea ice, revealing a misinterpretation of temperature effects. Finally, contrasting trends in CIDs based on temporal shifts in regional sea ice patterns revealed trends toward earlier CIDs (4–6 day advance) from 1979 to 2009 as the annual ice season shortened, and later CIDs (7–10 day delay) from 2010 to 2016 as the annual ice season lengthened. Adélie penguins tracked environmental conditions with flexible breeding phenology, but their life history remains vulnerable to subpolar weather conditions that can delay CIDs and decrease breeding success, especially on landscapes where geomorphology facilitates snow accumulation.

United States Heat Wave Frequency and Arctic Ocean Marginal Sea Ice Variability

AbstractRecent studies point to a significant rise in the number of summer extreme weather events that correspond with the presence of amplified, quasistationary midtropospheric planetary waves, weakened atmospheric circulation in the Northern Hemisphere, and coincide with reduced summer Arctic sea ice cover. This study explores potential connections between 1979 and 2016 summer heat wave frequency across the USA and regional Arctic sea ice extent (SIE) in various Arctic basins. Most notable SIE interannual relationships exist across the southern Plains and southeastern US during low Hudson Bay summer SIE. Locally increased frequencies of summer heat waves coincide with unseasonably warm conditions developed and sustained by the presence of an omega blocking pattern situated over the southern US throughout summer. The block appears following anomalous atmospheric warming and reduced mean zonal winds observed throughout spring (March–May) over northeastern Canada, the northwestern Atlantic basin, and Greenland. Spring preconditioning of summer ice melt is favored by the presence of strong negative phase of the North Atlantic Oscillation and positive Greenland Blocking Index. Summer synoptic flow related to Hudson Bay ice melt over North America appears to be influenced by the background state of atmospheric variability, namely, the positive phase of the Atlantic Multidecadal Oscillation. Antecedent local humidity, soil moisture, and precipitation conditions are shown to influence the “flavor” of the heat waves, which are more likely to be oppressive in the southeastern US and extreme across the southern Plains during summers experiencing low Hudson SIE.

Local snow melt and temperature-but not regional sea ice-explain variation in spring phenology in coastal Arctic tundra.

The Arctic is undergoing dramatic environmental change with rapidly rising surface temperatures, accelerating sea ice decline and changing snow regimes, all of which influence tundra plant phenology. Despite these changes, no globally consistent direction of trends in spring phenology has been reported across the Arctic. While spring has advanced at some sites, spring has delayed or not changed at other sites, highlighting substantial unexplained variation. Here, we test the relative importance of local temperatures, local snow melt date and regional spring drop in sea ice extent as controls of variation in spring phenology across different sites and species. Trends in long-term time series of spring leaf-out and flowering (average span: 18years) were highly variable for the 14 tundra species monitored at our four study sites on the Arctic coasts of Alaska, Canada and Greenland, ranging from advances of 10.06days per decade to delays of 1.67days per decade. Spring temperatures and the day of spring drop in sea ice extent advanced at all sites (average 1°C per decade and 21days per decade, respectively), but only those sites with advances in snow melt (average 5days advance per decade) also had advancing phenology. Variation in spring plant phenology was best explained by snow melt date (mean effect: 0.45days advance in phenology per day advance snow melt) and, to a lesser extent, by mean spring temperature (mean effect: 2.39days advance in phenology per °C). In contrast to previous studies examining sea ice and phenology at different spatial scales, regional spring drop in sea ice extent did not predict spring phenology for any species or site in our analysis. Our findings highlight that tundra vegetation responses to global change are more complex than a direct response to warming and emphasize the importance of snow melt as a local driver of tundra spring phenology.

Predicting Which Species Succeed in Climate-Forced Polar Seas

Understanding the mechanisms which determine the capacity of any species to adapt to changing environmental conditions is one of the foremost requirements in accurately predicting which populations, species and clades are likely to survive ongoing, rapid, climate change. The polar oceans are amongst the most rapidly changing environments on earth with reduced regional sea ice duration and extent, and their faunas expected sensitivity to warming and acidification. These changes potentially pose a significant threat to a number of polar fauna. There is, therefore, a critical need to assess the vulnerability of a wide range of species to determine the tipping points, or weak links in marine assemblages. Knowledge of the effect of multiple stressors on polar marine fauna has advanced over the last 40 years, but there are still many data gaps. This study applies ecological risk assessment techniques to the increasing knowledge of polar species’ physiological capacities to identify their exposure to climate change and their vulnerability to this exposure. This relatively rapid, semi-quantitative assessment, provides a layer of vulnerability on top of climate envelope models, until such times as more extensive physiological data sets can be produced. The risk assessment identified more species that are likely to benefit from the near future predicted change (the winners), especially predators and deposit feeders. Fewer species were scored at risk (the losers), although animals that feed on krill were consistently as under the most risk.

An assessment of regional sea ice predictability in the Arctic ocean

Arctic sea ice plays a central role in the Earth’s climate. Changes in the sea ice on seasonal-to-interannual timescales impact ecosystems, populations and a growing number of stakeholders. A prerequisite for achieving better sea ice predictions is a better understanding of the underlying mechanisms of sea ice predictability. Previous studies have shown that sea ice predictability depends on the predictand (area, extent, volume), region, and the initial and target dates. Here we investigate seasonal-to-interannual sea ice predictability in so-called “perfect-model” 3-year-long experiments run with six global climate models initialized in early July. Consistent with previous studies, robust mechanisms for reemergence are highlighted, i.e. increases in the autocorrelation of sea ice properties after an initial loss. Similar winter sea ice extent reemergence is found for HadGEM1.2, GFDL-CM3 and E6F, while a long sea ice volume persistence is confirmed for all models. The comparable predictability characteristics shown by some of the peripheral regions of the Atlantic side illustrate that robust similarities can be found even if models have distinct sea ice states. The analysis of the regional sea ice predictability in EC-Earth2.3 demonstrates that Arctic basins can be classified according to three distinct regimes. The central Arctic drives most of the pan-Arctic sea ice volume persistence. In peripheral seas, we find predictability for the sea ice area in winter but low predictability throughout the rest of the year, due to the particularly unpredictable sea ice edge location. The Labrador Sea stands out among the considered regions, with sea ice predictability extending up to 1.5 years if the oceanic conditions upstream are known.

Processes Controlling Arctic and Antarctic Sea Ice Predictability in the Community Earth System Model

AbstractSea ice predictability is a rapidly growing area of research, with most studies focusing on the Arctic. This study offers new insights by comparing predictability between the Arctic and Antarctic sea ice anomalies, focusing on the effects of regional differences in ice thickness and ocean dynamics. Predictability in simulated regional sea ice area and volume is investigated in long control runs of an Earth system model. Sea ice area predictability in the Arctic agrees with results from other studies, with features of decaying initial persistence and reemergence because of ocean mixed layer processes and memory in thick ice. In pan-Arctic averages, sea ice volume and the area covered by thick ice are the best predictors of September area for lead times greater than 2 months. In the Antarctic, area is generally the best predictor of future area for all times of year. Predictability of area in summer differs between the hemispheres because of unique aspects of the coupling between area and volume. Generally, ice volume only adds to the predictability of summer sea ice area in the Arctic. Predictability patterns vary greatly among different regions of the Arctic but share similar seasonality among regions of the Antarctic. Interactive ocean dynamics influence anomaly reemergence differently in the Antarctic than the Arctic, both for the total and regional area. In the Antarctic, ocean dynamics generally decrease the persistence of area anomalies, reducing predictability. In the Arctic, the presence of ocean dynamics improves ice area predictability, mainly through mixed layer depth variability.

Arctic Climate Changes Based on Historical Simulations (1900‒2013) with the CAMS-CSM

The Chinese Academy of Meteorological Sciences Climate System Model (CAMS-CSM) is a newly developed global climate model that will participate in the Coupled Model Intercomparison Project phase 6. Based on historical simulations (1900‒2013), we evaluate the model performance in simulating the observed characteristics of the Arctic climate system, which includes air temperature, precipitation, the Arctic Oscillation (AO), ocean temperature/salinity, the Atlantic meridional overturning circulation (AMOC), snow cover, and sea ice. The model‒data comparisons indicate that the CAMS-CSM reproduces spatial patterns of climatological mean air temperature over the Arctic (60°‒90°N) and a rapid warming trend from 1979 to 2013. However, the warming trend is overestimated south of the Arctic Circle, implying a subdued Arctic amplification. The distribution of climatological precipitation in the Arctic is broadly captured in the model, whereas it shows limited skills in depicting the overall increasing trend. The AO can be reproduced by the CAMS-CSM in terms of reasonable patterns and variability. Regarding the ocean simulation, the model underestimates the AMOC and zonally averaged ocean temperatures and salinity above a depth of 500 m, and it fails to reproduce the observed increasing trend in the upper ocean heat content in the Arctic. The large-scale distribution of the snow cover extent (SCE) in the Northern Hemisphere and the overall decreasing trend in the spring SCE are captured by the CAMS-CSM, while the biased magnitudes exist. Due to the underestimation of the AMOC and the poor quantification of air–sea interaction, the CAMS-CSM overestimates regional sea ice and underestimates the observed decreasing trend in Arctic sea–ice area in September. Overall, the CAMS-CSM reproduces a climatological distribution of the Arctic climate system and general trends from 1979 to 2013 compared with the observations, but it shows limited skills in modeling local trends and interannual variability.

Habitats and movement patterns of white whales Delphinapterus leucas in Svalbard, Norway in a changing climate

BackgroundThe Arctic is experiencing rapid reductions in sea ice and in some areas tidal glaciers are melting and retracting onto land. These changes are occurring at extremely rapid rates in the Northeast Atlantic Arctic. The aim of this study was to investigate the impacts of these environmental changes on space use by white whales (Delphinapterus leucas) in Svalbard, Norway. Using a unique biotelemetry data set involving 34 animals, spanning two decades, habitat use and movement patterns were compared before (1995–2001) and after (2013–2016) a dramatic change in the regional sea ice regime that began in 2006.ResultsWhite whales were extremely coastal in both study periods, remaining near the islands within the Svalbard Archipelago, even when winter sea ice formation pushed them offshore somewhat (later in the year in the recent period), into areas with drifting sea ice (concentrations up to 90%). In both periods, the whales followed the same basic patterns seasonally; they occupied the west coast in summer and shifted to the east coast as winter approached. However, space use did change between the two periods, with the whales spending less time close to tidal glacier fronts in the second period compared to the first (2nd-36% vs 1st-51%), a habitat characterized by low swimming speeds and high turning angles, and more time out in the fjords (2nd-26% vs1st-10%). Use of coastal transit corridors remained the same in both periods; the whales appear to minimize time spent moving between fjords.ConclusionsGlacier fronts have previously been shown to be important foraging areas for white whales in Svalbard and the movement metrics documented in this study confirms that this is still the case. However, use of the Fjords habitat in summer and fall (frequency of occupancy and movement metrics) seen in the recent period suggests that the white whales might now also be feeding on Atlantic prey that is increasingly common in the fjords, concomitant with influxes of Atlantic Water along the west coast of Svalbard. Such behavioural flexibility, if confirmed by further diet studies, would likely be important for white whales in adapting to new conditions in Svalbard.

Predicting regional and pan-Arctic sea ice anomalies with kernel analog forecasting

Predicting Arctic sea ice extent is a notoriously difficult forecasting problem, even for lead times as short as one month. Motivated by Arctic intraannual variability phenomena such as reemergence of sea surface temperature and sea ice anomalies, we use a prediction approach for sea ice anomalies based on analog forecasting. Traditional analog forecasting relies on identifying a single analog in a historical record, usually by minimizing Euclidean distance, and forming a forecast from the analog's historical trajectory. Here an ensemble of analogs are used to make forecasts, where the ensemble weights are determined by a dynamics-adapted similarity kernel, which takes into account the nonlinear geometry on the underlying data manifold. We apply this method for forecasting pan-Arctic and regional sea ice area and volume anomalies from multi-century climate model data, and in many cases find improvement over the benchmark damped persistence forecast. Examples of success include the 3--6 month lead time prediction of pan-Arctic area, the winter sea ice area prediction of some marginal ice zone seas, and the 3--12 month lead time prediction of sea ice volume anomalies in many central Arctic basins. We discuss possible connections between KAF success and sea ice reemergence, and find KAF to be successful in regions and seasons exhibiting high interannual variability.

Paleoproductivity and Stratification Across the Subarctic Pacific Over Glacial‐Interglacial Cycles

AbstractIn the Subarctic Pacific, variability in productivity on glacial‐interglacial timescales is often attributed to changes in stratification and nutrient delivery to the surface, but the mechanisms driving this relationship are poorly constrained. Records extending beyond the last glacial maximum from both the open ocean and the marginal seas are required to investigate the timing and magnitude of different influential processes through the full glacial cycle. In this study we generated 231Pa/230Th over 210,000 years in order to capture two full glacial cycles of paleoproductivity on the Juan de Fuca Ridge in the East Subarctic Pacific. The sedimentary 231Pa/230Th ratios are always equal to or greater than the seawater production ratio (0.093), consistent with enhanced biological scavenging in this region. The temporal pattern of 231Pa/230Th burial is remarkably coherent with changes in climate, with high values (0.20) during peak interglacial periods descending to low values (0.10) during peak glacial conditions, consistent with other long productivity records from this region. We investigate the possible contributions of temperature, sea ice formation, Bering Strait closure, wind strength, upwelling, and subsurface nutrient concentrations as possible mechanisms by which physical and/or chemical stratification emerged during glacial periods. Due to the low sea surface salinity in the North Pacific, cooling actually weakens the density gradient in surface (0–200 m) waters. To create the steep density profiles that characterize physical stratification, additional processes to reduce the salinity of surface waters must occur during glacial periods. We suggest that regional sea ice formation and Bering Strait closure may have contributed to freshening surface waters and enhancing physical stratification during glacial periods. Additionally, simulated weak winds in this region due to the southward shift of the glacial westerlies may have further reduced surface mixing depths in the Subarctic Pacific. Finally, previous model simulations suggest strong glacial wind stress curl in the Subarctic Pacific, but enhanced Ekman divergence of nutrient‐poor subsurface waters would have little impact on stimulating productivity in surface waters of the Subarctic Pacific. We therefore suggest that the combined effects of surface freshening, weak winds, and lower subsurface nutrient concentrations may all have contributed to lower productivity during glacial periods in the Subarctic Pacific.

Modulation of Sea Ice Melt Onset and Retreat in the Laptev Sea by the Timing of Snow Retreat in the West Siberian Plain

AbstractRecent years have seen growing interest in improving seasonal predictions of Arctic sea ice conditions, including the timing of ice melt onset and retreat, especially on the regional scale. This paper investigates potential links between regional sea ice melt onset and retreat in the southern Laptev Sea and retreat of terrestrial snow cover. Past studies have shown that variability of snow extent over Eurasia can substantially impact regional atmospheric circulation patterns over the North Pacific and Arctic Oceans. It is shown here that for the Laptev Sea, earlier melt onset and retreat of sea ice are encouraged by earlier retreat of snow cover over the West Siberian Plain. Earlier snow retreat in spring encourages greater ridging (e.g., at 500 hPa) over the East Siberian Sea through the summer. This results in more frequently southerly flow of warm, moist air over the Laptev Sea. This relationship could provide modest improvements to predictive skill for sea ice melt onset and retreat in the southern Laptev Sea at lead times of approximately 50 and 90 days, respectively. The detrended time series of snow retreat in the West Siberian Plain explains 26 and 29% of the detrended variance of the timing of sea ice melt onset and retreat in southern Laptev Sea, respectively.

Effects of Northern Hemisphere Atmospheric Blocking on Arctic Sea Ice Decline in Winter at Weekly Time Scales

In this study, the effects of the Northern Hemisphere atmospheric blocking circulation on Arctic sea ice decline at weekly time scales are examined by defining four key regions based on observational data analysis. Given the regression analysis, the frequently occurring atmospheric patterns related to the sea ice decline in four key sea regions (Baffin Bay, Barents-Kara Seas, Okhotsk Sea and Bering Sea) are found to be Greenland blocking (GB), Ural blocking (UB), western Pacific blocking (PB-W) and eastern Pacific blocking (PB-E), respectively. The results show that the regional blocking frequency is higher (lower) in lower (higher) sea ice winters for each key region. Moreover, composite analysis indicates that blocking evolution is usually accompanied by significant sea ice decline at weekly time scales during the blocking life cycle for each key region. In addition, the intensified surface downward infrared radiation (IR) anomaly and the precipitable water for the entire atmosphere (PWA) in each key region are found to make significant contributions to the positive surface air temperature (SAT) anomaly, which is beneficial for the reduction in sea ice. The approximate quantitative analysis of different surface energy fluxes induced by blocking is also applied. Further analysis shows that the blocking event and the associated changes in SAT and radiation anomalies for each key region lead the sea ice decline by approximately 3~6 days. This result indicates that regional blocking can contribute to regional sea ice decline at weekly time scales through surface warming associated with enhanced water vapor and associated IR variations. Further quantitative estimates indicate that regional blocking can reduce regional sea ice cover (SIC) by 49.6%, 49.4%, 52.2% and 49.5% for Baffin Bay, Barents-Kara Seas, Okhotsk Sea and Bering Sea, respectively, during the blocking life cycle. Finally, a physical process diagrammatic sketch is given to illustrate how blocking affects SIC decline.

A method for correcting seal-borne oceanographic data and application to the estimation of regional sea ice thickness

Abstract The high-latitude oceans surrounding Antarctica are substantially undersampled compared to lower latitudes. Mammal based instruments such as Conductivity-Temperature-Depth Satellite Relay Data Loggers (CTD-SRDLs) present one possible solution. Unfortunately, these are subject to instrument-dependent offsets in absolute salinity. This study investigates a set of satellite-transmitted data collected by CTD-SRDLs mounted on Weddell seals (Leptonychotes weddellii) in the South-western Ross Sea in 2011. The uncorrected salinity offset between devices was found to be up to 1.4 g kg−1, making the data unsuitable for some oceanographic studies without correction. Here, a correction method was developed that uses profiles from pairs of CTD-SRDLs that are considered to be co-located and to sample the same body of water if they occur within defined time and space windows. Using least squares, a best-fit solution to the matrix of offsets in co-located pairs was found that reduces salinity offsets between the CTD-SRDLs. These offsets are smaller than the original offsets by a factor of 10. A calibrated reference instrument, that was co-located with some of the devices, provided further improvement in the absolute accuracy of all the CTD-SRDLs. Using the corrected CTD-SRDL data we estimate the rejection of salt into the water column by sea ice formation, and derived the time evolution of sea ice thickness in the South-western Ross Sea. Our estimates of regional sea ice thickness are in agreement with direct sea ice thickness measurements taken over a limited area in November 2011, providing further affirmation of our method.

Seasonality of the Physical and Biogeochemical Hydrography in the Inflow to the Arctic Ocean Through Fram Strait

Eastern Fram Strait and the shelf slope region north of Svalbard is dominated by the advection of warm, salty and nutrient-rich Atlantic Water (AW). This oceanic heat contributes to keeping the area relatively free of ice. The last years have seen a dramatic decrease in regional sea ice extent, which is expected to drive large increases in pelagic primary production and thereby changes in marine ecology and nutrient cycling. In a concerted effort, we conducted five cruises to the area in winter, spring, summer and fall of 2014, in order to understand the physical and biogeochemical controls of carbon cycling, for the first time from a year-round point of view. We document (1) the offshore location of the wintertime front between salty AW and fresher Surface Water in the ocean surface, (2) thermal convection of Atlantic Water over the shelf slope, likely enhancing vertical nnutrient fluxes, and (3) the importance of ice melt derived upper ocean stratification for the spring bloom timing. Our findings strongly confirm the hypothesis that this ``Atlantification'', as it has been called, of the shelf slope area north of Svalbard resulting from the advection of AW alleviates both nutrient and light limitations at the same time, leading to increased pelagic primary productivity in this region.

Seasonal and Regional Manifestation of Arctic Sea Ice Loss

The Arctic Ocean is currently on a fast track toward seasonally ice-free conditions. Although most attention has been on the accelerating summer sea ice decline, large changes are also occurring in winter. This study assesses past, present, and possible future change in regional Northern Hemisphere sea ice extent throughout the year by examining sea ice concentration based on observations back to 1950, including the satellite record since 1979. At present, summer sea ice variability and change dominate in the perennial ice-covered Beaufort, Chukchi, East Siberian, Laptev, and Kara Seas, with the East Siberian Sea explaining the largest fraction of September ice loss (22%). Winter variability and change occur in the seasonally ice-covered seas farther south: the Barents Sea, Sea of Okhotsk, Greenland Sea, and Baffin Bay, with the Barents Sea carrying the largest fraction of loss in March (27%). The distinct regions of summer and winter sea ice variability and loss have generally been consistent since 1950, but appear at present to be in transformation as a result of the rapid ice loss in all seasons. As regions become seasonally ice free, future ice loss will be dominated by winter. The Kara Sea appears as the first currently perennial ice-covered sea to become ice free in September. Remaining on currently observed trends, the Arctic shelf seas are estimated to become seasonally ice free in the 2020s, and the seasonally ice-covered seas farther south to become ice free year-round from the 2050s.

Antarctic ice shelf disintegration triggered by sea ice loss and ocean swell.

Understanding the causes of recent catastrophic ice shelf disintegrations is a crucial step towards improving coupled models of the Antarctic Ice Sheet and predicting its future state and contribution to sea-level rise. An overlooked climate-related causal factor is regional sea ice loss. Here we show that for the disintegration events observed (the collapse of the Larsen A and B and Wilkins ice shelves), the increased seasonal absence of a protective sea ice buffer enabled increased flexure of vulnerable outer iceshelf margins by ocean swells that probably weakened them to the point of calving. This outer-margin calving triggered wider-scale disintegration of ice shelves compromised by multiple factors in preceding years, with key prerequisites being extensive flooding and outer-margin fracturing. Wave-induced flexure is particularly effective in outermost ice shelf regions thinned by bottom crevassing. Our analysis of satellite and ocean-wave data and modelling of combined ice shelf, sea ice and wave properties highlights the need for ice sheet models to account for sea ice and ocean waves.