Sea Ice Decline Research Articles

Disentangling the coupling between sea ice and tundra productivity in Svalbard

The rapid decline in Arctic sea ice poses urgent questions concerning its ecological effects, such as on tundra terrestrial productivity. However, reported sea ice/terrestrial productivity linkages have seldom been constrained, and the mechanism governing them remains elusive, with a diversity of spatial scales and metrics proposed, at times in contradiction to each other. In this study, we use spatially explicit remotely sensed sea ice concentration and high-resolution terrestrial productivity estimates (Normalised Difference Vegetation Index, NDVI) across the Svalbard Archipelago to describe local/sub-regional and large-scale components of sea ice/terrestrial productivity coupling. Whereas the local/sub-regional component is attributed to sea breeze (cold air advection from ice-covered ocean onto adjacent land during the growing season), the large-scale component might reflect co-variability of sea ice and tundra productivity due to a common forcing, such as large-scale atmospheric circulation (North Atlantic Oscillation, NAO). Our study clarifies the range of mechanisms in sea ice/terrestrial productivity coupling, allowing the generation of testable hypotheses about its past, present, and future dynamics across the Arctic.

Warming in the Nordic Seas, North Atlantic storms and thinning Arctic sea ice

Arctic sea ice over the last few decades has experienced a significant decline in coverage both in summer and winter. The currently warming Atlantic Water layer has a pronounced impact on sea ice in the Nordic Seas (including the Barents Sea). More open water combined with the prevailing atmospheric pattern of airflow from the southeast, and persistent North Atlantic storms such as the recent extremely strong Storm Frank in December 2015, lead to increased energy transport to the high Arctic. Each of these storms brings sizeable anomalies of heat to the high Arctic, resulting in significant warming and slowing down of sea ice growth or even melting. Our analysis indicates that the recently observed sea ice decline in the Nordic Seas during the cold season around Svalbard, Franz Joseph Land and Novaya Zemlya, and the associated heat release from open water into the atmosphere, contributed significantly to the increase in the downward longwave radiation throughout the entire Arctic. Added to other changes in the surface energy budget, this increase since the 1960s to the present is estimated to be at least 10 W m−2, which can result in thinner (up to at least 15–20 cm) Arctic ice at the end of the winter. This change in the surface budget is an important contributing factor accelerating the thinning of Arctic sea ice.

Arctic sea-ice decline weakens the Atlantic Meridional Overturning Circulation

The ongoing decline of Arctic sea ice exposes the ocean to anomalous surface heat and freshwater fluxes, resulting in positive buoyancy anomalies that can affect ocean circulation. In this study, we use an optimal flux perturbation framework and comprehensive climate model simulations to estimate the sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to such buoyancy forcing over the Arctic and globally, and more generally to sea-ice decline. It is found that on decadal timescales, flux anomalies over the subpolar North Atlantic have the largest impact on the AMOC, while on multi-decadal timescales (longer than 20 years), flux anomalies in the Arctic become more important. These positive buoyancy anomalies spread to the North Atlantic, weakening the AMOC and its poleward heat transport. Therefore, the Arctic sea-ice decline may explain the suggested slow-down of the AMOC and the ‘Warming Hole’ persisting in the subpolar North Atlantic. Sea-ice loss has exposed the Arctic Ocean to anomalous heat and freshwater. Climate model experiments suggest that these changes, particularly on multi-decadal timescales, may explain the observed slow-down in the Atlantic Meridional Overturning Circulation.

The role of diminishing Arctic sea ice in increased winter snowfall over northern high-latitude continents in a warming environment

Large parts of North America, Europe, Siberia, and East Asia have experienced cold snaps and heavy snowfalls for the past few winters, which have been linked to rapid decline of Arctic sea ice. Although the role of reduction in Arctic sea ice in recent cold and snowy winters is still a matter of debate, there is considerable interest in determining whether such an emerging climate feedback will persist into the future in a warming environment. Here we show that increased winter snowfall would be a robust feature throughout the 21st century in the northeastern Europe, central and northern Asia and northern North America as projected by current-day climate model simulations under the medium mitigation scenario. We argue that the increased winter snowfall in these regions during the 21st century is due primarily to the diminishing autumn Arctic sea ice (largely externally forced). Variability of the winter Arctic Oscillation (dominant mode of natural variability in the Northern Hemisphere), in contrast, has little contribution to the increased winter snowfall. This is evident in not only the multi-model ensemble mean, but also each individual model (not model-dependent). Our findings reinforce suggestions that a strong sea ice-snowfall feedback might have emerged, and would be enhanced in coming decades, increasing the chance of heavy snowfall events in northern high-latitude continents.

Sensitivity and nonlinearity of Eurasian winter temperature response to recent Arctic sea ice loss

The recent decline in the Arctic sea ice has coincided with more cold winters in Eurasia. It has been hypothesized that the Arctic sea ice loss is causing more mid-latitude cold extremes and cold winters, yet there is lack of consensus in modeling studies on the impact of Arctic sea ice loss. Here we conducted modeling experiments with Community Atmosphere Model Version 5 (CAM5) to investigate the sensitivity and linearity of Eurasian winter temperature response to the Atlantic sector and Pacific sector of the Arctic sea ice loss. Our experiments indicate that the Arctic sea ice reduction can significantly affect the atmospheric circulation by strengthening the Siberian High, exciting the stationary Rossby wave train, and weakening the polar jet stream, which in turn induce the cooling in Eurasia. The temperature decreases by more than 1°C in response to the ice loss in the Atlantic sector and the cooling is less and more shifts southward in response to the ice loss in the Pacific sector. More interestingly, sea ice loss in the Atlantic and Pacific sectors together barely induces cold temperatures in Eurasia, suggesting the nonlinearity of the atmospheric response to the Arctic sea ice loss.

An Arctic predator-prey system in flux: climate change impacts on coastal space use by polar bears and ringed seals.

Climate change is impacting different species at different rates, leading to alterations in biological interactions with ramifications for wider ecosystem functioning. Understanding these alterations can help improve predictive capacity and inform management efforts designed to mitigate against negative impacts. We investigated how the movement and space use patterns of polar bears (Ursus maritimus) in coastal areas in Svalbard, Norway, have been altered by a sudden decline in sea ice that occurred in 2006. We also investigated whether the spatial overlap between polar bears and their traditionally most important prey, ringed seals (Pusa hispida), has been affected by the sea-ice decline, as polar bears are dependent on a sea-ice platform for hunting seals. We attached biotelemetry devices to ringed seals (n=60, both sexes) and polar bears (n=67, all females) before (2002-2004) and after (2010-2013) a sudden decline in sea ice in Svalbard. We used linear mixed-effects models to evaluate the association of these species to environmental features and an approach based on Time Spent in Area to investigate changes in spatial overlap between the two species. Following the sea-ice reduction, polar bears spent the same amount of time close to tidal glacier fronts in the spring but less time in these areas during the summer and autumn. However, ringed seals did not alter their association with glacier fronts during summer, leading to a major decrease in spatial overlap values between these species in Svalbard's coastal areas. Polar bears now move greater distances daily and spend more time close to ground-nesting bird colonies, where bear predation can have substantial local effects. Our results indicate that sea-ice declines have impacted the degree of spatial overlap and hence the strength of the predator-prey relationship between polar bears and ringed seals, with consequences for the wider Arctic marine and terrestrial ecosystems. Shifts in ecological interactions are likely to become more widespread in many ecosystems as both predators and prey respond to changing environmental conditions induced by global warming, highlighting the importance of multi-species studies.

Connections between north‐central United States summer hydroclimatology and Arctic sea ice variability

ABSTRACTArctic sea ice has been shrinking at unprecedented rates over the past three decades. These cryospheric changes have coincided with greater incidence of global extreme weather conditions, including increased severity and frequency of summer heatwaves and extreme rainfall events. Recent studies identify potential physical mechanisms related to Rossby wave and resonance theories that may attribute the observed changes in extreme summer weather patterns to Arctic sea ice decline. This study explores the linkages between summer Arctic sea ice variability and hydroclimate of the north‐central United States (US) during the 1979 to 2013 period. Since 1979, summers with low sea ice conditions have coincided with significant increases in mean, minimum, maximum, and dew point air temperatures. Also apparent are increases in seasonal precipitation, the number of wet days, heavy (>95th percentile) precipitation days, and accumulated precipitation over the region. These moisture changes coincide with atmospheric patterns typically observed during anomalously wet summers, known to prompt flooding across the Upper Mississippi River Valley (UMRV) region. Low sea ice summers have coincided with (1) enhanced southerly air flow and increased activity of the Great Plains Low Level Jet (GPLLJ) over the study area, (2) increased occurrence of moist tropical air masses over the UMRV region, and (3) amplified 500 hPa flow over the Pacific‐North American region with a ridge situated over the central‐eastern portions of the North American continent emanating from Greenland and the central Arctic basin. The results suggest summer Arctic sea ice variability has been associated with recent hydroclimate anomalies of the north‐central United States and the UMRV region and add to our growing knowledge of the connections between a changing Arctic environment and concurrent mid‐latitude climate variability.

Sea ice origin and sea ice retreat as possible drivers of variability in Arctic marine protist composition

The ongoing decrease in sea ice thickness and extent is expected to have significant implications for protists in the Arctic Ocean. We analyzed protist community composition and diversity in water and sea ice samples to elucidate the impact of sea ice retreat and sea ice origin. Samples were collected during 2 summer periods with contrasting sea ice concentrations (2011 and 2012). The results are based on a combination of ARISA and sequencing of the 18S rRNA V4 gene region. We show for the first time that the regions of ice floe origin play a fundamental role in structuring the sea ice community. Community structure of pelagic protists correlated signifi- cantly with sea ice concentrations, water masses and sampling regions. Both habitats differed in protist diversity and composition between years and were less diverse during the recorded sea ice minimum year 2012. A reduction in protist diversity was especially true for rare sea ice algae in 2012, which suggests that sea ice algae might be more vulnerable to climate change. In the future Arctic, changes in protist diversity can be expected due to sea ice decline and a temporal and spatial shift in sea ice formation

Atmospheric circulation patterns which promote winter Arctic sea ice decline

The impact of winter atmospheric blocking over the Ural Mountains region (UB) coincident with different phases of the North Atlantic Oscillation (NAO) on the sea ice variability over the Barents and Kara Seas (BKS) in winter is investigated. It is found that the UB in conjunction with the positive phase of the NAO (NAO+) leads to the strongest sea ice decline. During this phase composites and trajectory analyses reveal an efficient moisture pathway to the BKS from the mid-latitude North Atlantic near the Gulf Stream Extension region where water vapor is abundant due to high sea surface temperatures. The NAO+-UB combination is an optimal circulation pattern that significantly increases the BKS water vapor that plays a major role in the BKS warming and sea ice reduction, while the increased sensible and latent heat fluxes play secondary roles. By contrast, much fewer dramatic impacts on the BKS are observed when the UB coincides with the neutral or negative phases of the NAO.Our results present new insights into the complex processes involved with Arctic sea ice reduction and warming. The mechanisms highlighted here potentially offer a perspective into the mechanisms behind Arctic multi-decadal climate variability.

Changing seasonality of panarctic tundra vegetation in relationship to climatic variables

Potential climate drivers of Arctic tundra vegetation productivity are investigated to understand recent greening and browning trends documented by maximum normalized difference vegetation index (NDVI) (MaxNDVI) and time-integrated NDVI (TI-NDVI) for 1982–2015. Over this period, summer sea ice has continued to decline while oceanic heat content has increased. The increases in summer warmth index (SWI) and NDVI have not been uniform over the satellite record. SWI increased from 1982 to the mid-1990s and remained relatively flat from 1998 onwards until a recent upturn. While MaxNDVI displays positive trends from 1982–2015, TI-NDVI increased from 1982 until 2001 and has declined since. The data for the first and second halves of the record were analyzed and compared spatially for changing trends with a focus on the growing season. Negative trends for MaxNDVI and TI-NDVI were more common during 1999–2015 compared to 1982–1998.Trend analysis within the growing season reveals that sea ice decline was larger in spring for the 1982–1998 period compared to 1999–2015, while fall sea ice decline was larger in the later period. Land surface temperature trends for the 1982–1998 growing season are positive and for 1999–2015 are positive in May–June but weakly negative in July–August. Spring biweekly NDVI trends are positive and significant for 1982–1998, consistent with increasing open water and increased available warmth in spring. MaxNDVI trends for 1999–2015 display significant negative trends in May and the first half of June.Numerous possible drivers of early growing season NDVI decline coincident with warming temperatures are discussed, including increased standing water, delayed spring snow-melt, winter thaw events, and early snow melt followed by freezing temperatures. Further research is needed to robustly identify drivers of the spring NDVI decline.

An acoustic study of sea ice behavior in a shallow, Arctic bay

Recent acceleration of sea ice decline observed in the Arctic Ocean draws attention to environmental factors driving this phenomenon. One of the main conclusions is a growing need for better understanding of sea ice drift, deformation, and fracturing. In response to that call, several ambient noise recordings were carried out in the coastal zone of Hornsund Fjord, Spitsbergen, in spring 2015 to study underwater acoustic signatures of sea ice behavior. The noise levels varied significantly with sea ice type and intensity of external forces. Low-frequency signatures were strongly related to tidal cycle, which manifested in much higher SPL values at low water. Compacted ice cover is periodically deformed and crushed, representing a significant contribution to the ambient noise field in the study site. Average noise levels at frequencies above 1 kHz are, in turn, considerably higher in front of marine-terminating glacier than in the neighboring, non-glacial bay. These differences, expanding with the rise of water temperature, are associated with melting of the ice cliff and generally unaffected by the presence of sea ice. [Work funded by the Polish National Science Centre, Grant No. 2013/11/N/ST10/01729.]

Arctic sea ice decline and continental cold anomalies: Upstream and downstream effects of Greenland blocking

AbstractThe influence of Greenland blocking on continental cold anomalies in the Northern Hemisphere is examined. It is found that westward moving Greenland blocking (WGB) events in the recent decade are more strongly related to the sea ice decline over the Baffin Bay, Davis Strait, and Labrador Sea (BDL), while the quasi‐stationary Greenland blocking (QGB) events are more strongly related to the negative phase of the North Atlantic Oscillation. The frequency of WGB events is significantly increased owing to reduced mid‐high‐latitude westerly winds in the North Atlantic and its upstream region because of intensified Arctic warming related to the large BDL sea ice decline. It is further revealed that North American low temperatures are more sensitive to the WGB, while European low temperatures are more sensitive to the QGB. For the WGB, an intense cold anomaly is seen over the eastern North America. But for the QGB, strong cold anomalies appear over the North Europe and eastern Asia. Thus, it is concluded that more winter cold air outbreaks should occur over the eastern North America, if large BDL sea ice decline continues in the recent decade.

Weakening and shift of the Arctic stratospheric polar vortex: Internal variability or forced response?

AbstractRecent studies have proposed that the Arctic stratospheric polar vortex has weakened and shifted away from the North Pole during the past three decades. Some of these studies suggest that this trend has been driven by a decline in Arctic sea ice leading to enhanced zonal wave number 1 waves propagating into the stratosphere and that it has in turn contributed to a recent wintertime surface cooling over North America and some parts of Eurasia. Here trends in several measures of the location and strength of the stratospheric polar vortex from 1980 to 2016 are examined in two reanalysis products. All measures show weakening and equatorward shift trends, but only one measure, the vortex centroid latitude, has a trend which is statistically significant at the 95% level in both reanalyses. By comparing large ensembles of historical simulations with preindustrial control simulations for two coupled climate models, the ensemble mean response of the vortex is found to be small relative to internal variability. There is also no relationship between sea ice decline and trends in either vortex location or strength. Despite this, individual ensemble members are found to have vortex trends similar to those observed, indicating that these trends may be primarily a result of natural internally generated climate variability.

Local increase of anticyclonic wave activity over northern Eurasia under amplified Arctic warming

AbstractIn an attempt to resolve the controversy as to whether Arctic sea ice loss leads to more midlatitude extremes, a metric of finite‐amplitude wave activity is adopted to quantify the midlatitude wave activity and its change during the period of the drastic Arctic sea ice decline in both ERA Interim reanalysis data and a set of Atmospheric Model Intercomparison Project‐type of model experiments. Neither the ensemble mean response to the trend in the SST nor that to the declining trend of Arctic sea ice can replicate the sizable midlatitude‐wide increase in the total wave activity (Ae) observed in the reanalysis, leaving its explanation to the atmospheric internal variability. On the other hand, both the diagnostics of the flux of the local anticyclonic wave activity (LAWA) and atmospheric general circulation model experiments lend evidence to a possible linkage between the sea ice loss near the Barents and Kara Seas and the increasing trend of LAWA over the northern part of the central Eurasia and the associated impacts on the frequency of temperature extremes.

Ural Blocking as an Amplifier of the Arctic Sea Ice Decline in Winter

In this paper, the lead–lag relationship between the Arctic sea ice variability over the Barents–Kara Sea (BKS) and Ural blocking (UB) in winter (DJF) ranging from 1979/80 to 2011/12 is examined. It is found that in a regressed DJF-mean field an increased UB frequency (days) corresponds to an enhanced sea ice decline over the BKS, while the high sea surface temperature over the BKS is accompanied by a significant Arctic sea ice reduction. Lagged daily regression and correlation reveal that the growth and maintenance of the UB that is related to the positive North Atlantic Oscillation (NAO+) through the negative east Atlantic/west Russia (EA/WR−) wave train is accompanied by an intensified negative BKS sea ice anomaly, and the BKS sea ice reduction lags the UB pattern by about four days. Because the intensified UB pattern occurs together with enhanced downward infrared radiation (IR) associated with the intensified moisture flux convergence and total column water over the BKS, the UB pattern contributes significantly to the BKS sea ice decrease on a time scale of weeks through intensified positive surface air temperature (SAT) anomalies resulting from enhanced downward IR. It is also found that the BKS sea ice decline can persistently maintain even when the UB has disappeared, thus indicating that the UB pattern is an important amplifier of the BKS sea ice reduction. Moreover, it is demonstrated that the EA/WR− wave train formed by the combined NAO+ and UB patterns is closely related to the amplified warming over the BKS through the strengthening (weakening) of mid-to-high-latitude westerly wind in the North Atlantic (Eurasia).

On the discrepancy between observed and CMIP5 multi-model simulated Barents Sea winter sea ice decline

This study aims to understand the relative roles of external forcing versus internal climate variability in causing the observed Barents Sea winter sea ice extent (SIE) decline since 1979. We identify major discrepancies in the spatial patterns of winter Northern Hemisphere sea ice concentration trends over the satellite period between observations and CMIP5 multi-model mean externally forced response. The CMIP5 externally forced decline in Barents Sea winter SIE is much weaker than that observed. Across CMIP5 ensemble members, March Barents Sea SIE trends have little correlation with global mean surface air temperature trends, but are strongly anti-correlated with trends in Atlantic heat transport across the Barents Sea Opening (BSO). Further comparison with control simulations from coupled climate models suggests that enhanced Atlantic heat transport across the BSO associated with regional internal variability may have played a leading role in the observed decline in winter Barents Sea SIE since 1979.

The transitional climate of the late Miocene Arctic: Winter-dominated precipitation with high seasonal variability

The late Miocene (11.6–5.3 Ma) was an important transitional period following the greenhouse conditions of the Eocene. In order to gain insight into the Arctic paleoclimate of the time, we performed high-resolution intraring δ 13 C analyses on fossil wood collected from the late Miocene Khapchansky sediments of northeastern Siberia (∼69°N). From these data we quantified the ratio of summer to winter precipitation (Ps/Pw) and compared it to current values for the region determined from modern wood samples and instrumental records. We observed much greater frequency of winter-dominated precipitation (Ps/Pw < 1) and much greater variability in Ps/Pw during the Miocene than today. Specifically, years with Ps/Pw < 1 occurred three times more often, and years with at least three times as much precipitation in summer or winter (0.33 < Ps/Pw < 3.0) occurred approximately twice as often during the Miocene than today. We attribute the high interannual variability in precipitation to an inconsistent moisture source associated with the relatively unstable and incomplete ice cover in the Arctic Ocean during the late Miocene. Our result highlights the potential for enhanced variability in Arctic precipitation in response to Arctic sea ice decline caused by anthropogenic, CO 2 -induced warming.

Influence of high-latitude atmospheric circulation changes on summertime Arctic sea ice

The Arctic has seen rapid sea-ice decline in the past three decades, whilst warming at about twice the global average rate. Yet the relationship between Arctic warming and sea-ice loss is not well understood. Here, we present evidence that trends in summertime atmospheric circulation may have contributed as much as 60% to the September sea-ice extent decline since 1979. A tendency towards a stronger anticyclonic circulation over Greenland and the Arctic Ocean with a barotropic structure in the troposphere increased the downwelling longwave radiation above the ice by warming and moistening the lower troposphere. Model experiments, with reanalysis data constraining atmospheric circulation, replicate the observed thermodynamic response and indicate that the near-surface changes are dominated by circulation changes rather than feedbacks from the changing sea-ice cover. Internal variability dominates the Arctic summer circulation trend and may be responsible for about 30–50% of the overall decline in September sea ice since 1979. The Arctic is warming and sea ice is declining, but how the two link is unclear. This study shows changes in summertime atmospheric circulation and internal variability may have caused up to 60% of September sea-ice decline since 1979.

Comparing sea ice, hydrography and circulation between NEMO3.6 LIM3 and LIM2

Abstract. A set of hindcast simulations with the new version 3.6 of the Nucleus for European Modelling of the Ocean (NEMO) ocean–ice model in the ORCA1 configuration and forced by the DRAKKAR Forcing Set version 5.2 (DFS5.2) atmospheric data was performed from 1958 to 2012. Simulations differed in their sea-ice component: the old standard version Louvain-la-Neuve Sea Ice Model (LIM2) and its successor LIM3. Main differences between these sea-ice models are the parameterisations of sub-grid-scale sea-ice thickness distribution, ice deformation, thermodynamic processes, and sea-ice salinity. Our main objective was to analyse the response of the ocean–ice system sensitivity to the change in sea-ice physics. Additional sensitivity simulations were carried out for the attribution of observed differences between the two main simulations.In the Arctic, NEMO-LIM3 compares better with observations by realistically reproducing the sea-ice extent decline during the last few decades due to its multi-category sea-ice thickness. In the Antarctic, NEMO-LIM3 more realistically simulates the seasonal evolution of sea-ice extent than NEMO-LIM2. In terms of oceanic properties, improvements are not as evident, although NEMO-LIM3 reproduces a more realistic hydrography in the Labrador Sea and in the Arctic Ocean, including a reduced cold temperature bias of the Arctic Intermediate Water at 250 m. In the extra-polar regions, the oceanographic conditions of the two NEMO-LIM versions remain relatively similar, although they slowly drift apart over decades. This drift is probably due to a stronger deep water formation around Antarctica in LIM3.

Habitat degradation affects the summer activity of polar bears.

Understanding behavioral responses of species to environmental change is critical to forecasting population-level effects. Although climate change is significantly impacting species' distributions, few studies have examined associated changes in behavior. Polar bear (Ursus maritimus) subpopulations have varied in their near-term responses to sea ice decline. We examined behavioral responses of two adjacent subpopulations to changes in habitat availability during the annual sea ice minimum using activity data. Location and activity sensor data collected from 1989 to 2014 for 202 adult female polar bears in the Southern Beaufort Sea (SB) and Chukchi Sea (CS) subpopulations were used to compare activity in three habitat types varying in prey availability: (1) land; (2) ice over shallow, biologically productive waters; and (3) ice over deeper, less productive waters. Bears varied activity across and within habitats with the highest activity at 50-75% sea ice concentration over shallow waters. On land, SB bears exhibited variable but relatively high activity associated with the use of subsistence-harvested bowhead whale carcasses, whereas CS bears exhibited low activity consistent with minimal feeding. Both subpopulations had fewer observations in their preferred shallow-water sea ice habitats in recent years, corresponding with declines in availability of this substrate. The substantially higher use of marginal habitats by SB bears is an additional mechanism potentially explaining why this subpopulation has experienced negative effects of sea ice loss compared to the still-productive CS subpopulation. Variability in activity among, and within, habitats suggests that bears alter their behavior in response to habitat conditions, presumably in an attempt to balance prey availability with energy costs.