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The most significant factors currently affecting the Pacific walrus ( Odobenus rosmarus divergens) population are climate change and consequent changes in sea-ice morphology and dynamics. This paper integrates recent physical sea-ice change in the Bering Sea with biological and ecological conditions of walruses in their winter-spring reproductive habitat. Historically, walrus in winter-spring depended on a critical mass of sea-ice habitat to optimize social networking, reproductive fitness, feeding behavior, migration, and energetic efficiency. During 2003-2013, our cross-disciplinary, multiscale analysis from shipboard observations, satellite imagery, and ice-floe tracking, reinforced by information from indigenous subsistence hunters, documented change of sea-ice structure from a plastic continuum to a 'mixing bowl' of ice floes moving more independently. This fragmentation of winter habitat preconditions the walrus population toward dispersal mortality and will also negatively affect the availability of resources for indigenous communities. We urge an expanded research and management agenda that integrates walrus natural history and habitat more completely with changing sea-ice morphology and dynamics at multiple scales, while also meeting the needs of local communities. [ABSTRACT FROM AUTHOR]

Farley, E. V., Starovoytov, A., Naydenko, S., Heintz, R., Trudel, M., Guthrie, C., Eisner, L., Guyon, J. R. 2011. Implications of a warming eastern Bering Sea for Bristol Bay sockeye salmon. – ICES Journal of Marine Science, 68: 1138–1146.Overwinter survival of Pacific salmon (Oncorhynchus sp.) is believed to be a function of size and energetic status they gain during their first summer at sea. We test this notion for Bristol Bay sockeye salmon (O. nerka), utilizing data from large-scale fisheries and oceanographic surveys conducted during mid-August to September 2002–2008 and from February to March 2009. The new data presented in this paper demonstrate size-selective mortality for Bristol Bay sockeye salmon between autumn and their first winter at sea. Differences in the seasonal energetic signatures for lipid and protein suggest that these fish are not starving, but instead the larger fish caught during winter apparently are utilizing energy stores to minimize predation. Energetic status of juvenile sockeye salmon was also strongly related to marine survival indices and years with lower energetic status apparently are a function of density-dependent processes associated with high abundance of juvenile sockeye salmon. Based on new information regarding eastern Bering Sea ecosystem productivity under a climate-warming scenario, we hypothesize that sustained increases in spring and summer sea temperatures may negatively affect energetic status of juvenile sockeye salmon, potentially resulting in increased overwinter mortality. [ABSTRACT FROM PUBLISHER]

By compiling boreal summer (June to October) CO2 measurements from 1989 to 2019 on the Bering and eastern Chukchi Sea shelves, we find that the study areas act as a CO2 sink except when impacted by river runoff and wind‐driven upwelling. The CO2 system in this area is seasonally dominated by the biological pump especially in the northern Bering Sea and near Hanna Shoal, while wind‐driven upwelling of CO2‐rich bottom water can cause episodic outgassing. Seasonal surface ΔfCO2 (oceanic fCO2 – air fCO2) is dominantly driven by temperature only during periods of weak CO2 outgassing in shallow nearshore areas. However, after comparing the mean summer ΔfCO2 during the periods of 1989–2013 and 2014–2019, we suggest that temperature does drive long‐term, multi‐decadal patterns in ΔfCO2. In the northern Chukchi Sea, rapid warming concurrent with reduced seasonal sea‐ice persistence caused the regional summer CO2 sink to decrease. By contrast, increasing primary productivity caused the regional summer CO2 sink on the Bering Sea shelf to increase over time. While additional time series are needed to confirm the seasonal and annual trajectory of CO2 changes and ocean acidification in these dynamic and spatially complex ecosystems, this study provides a meaningful mechanistic analysis of recent changes in inorganic carbonate chemistry. As high‐resolution time series of inorganic carbonate parameters lengthen and short‐term variations are better constrained in the coming decades, we will have stronger confidence in assessing the mechanisms contributing to long‐term changes in the source/sink status of regional sub‐Arctic seas. Plain Language Summary: The ocean performs an essential function for the planet by removing carbon dioxide (CO2) from the atmosphere, providing an important limit on climate change and global warming. Hence it is critical to understand how much CO2 can be absorbed by the ocean surface in different regions and at different times of the year. On the Bering and Chukchi Sea shelves, ocean plants and temperature control how much CO2 can be absorbed by the ocean, especially during summer (June to October), and both are changing as our climate warms. Using 30 years of field data, we find that, on average, ocean plants help take up a substantial amount of CO2 on the shelves during summer. Over time, ocean plants on the Bering Sea shelf have been taking up more and more CO2 each summer; however, on the Chukchi Sea shelf, warming ocean temperatures have resulted in less CO2 uptake each summer. While our study shows that climate change can impact CO2 uptake by changing ocean temperatures and ocean plant activity, it is unclear if these changes are permanent or temporary. More data and research are essential to better understand these trends. Key Points: The Bering and eastern Chukchi Sea shelves act as summer CO2 sinks, except when impacted by river runoff and wind‐driven overturningThe summer surface CO2 is driven by primary productivity, while summer warming is only apparent in shallow nearshore areasRapid summer warming decreased the Chukchi sea shelf CO2 sink, while increasing primary productivity increased the Bering Sea shelf CO2 sink [ABSTRACT FROM AUTHOR]

Abstract: This paper examines how climate variations influence the boundaries of suitable ocean habitat, and how these changes affect the spatial distribution and interactions between forage fishes in the southeastern Bering Sea shelf. The study focuses on the summer distributions of forage fish age-0 and age-1 walleye pollock, Theragra chalcogramma, and capelin, Mallotus villosus, observed during National Marine Fisheries Service summer acoustic trawl, surface trawl and bottom trawl surveys conducted in the Bering Sea between 2004 and 2009. We compare the responses of these forage fish to climate-induced shifts in ocean habitats. Habitat boundaries were defined using key explanatory variables including depth, bottom temperature and surface temperature, using general additive models. Bathymetry, bottom temperature and frontal zones formed boundaries between different groups of forage fishes. Age-0 pollock were dispersed throughout the middle domain (50–100m depth) in well-stratified regions. In cold years the highest densities of age-0s were found in the southern regions of the middle domain waters in waters warmer than approximately 1°C. In contrast, age-1 pollock were observed on the sea floor over the middle domain and in midwater in the northern outer domain in cold years and more broadly dispersed across the middle and outer domain in warm years. The demersal concentrations of age-1 pollock in the middle domain shows age-1 pollock tolerate a wide range of bottom temperatures. Midwater and demersal distributions of age-1 pollock exhibited a patchier distribution than age-0 pollock. Midwater concentrations of age-1 pollock tended to be associated with the outer domain and regions where higher levels of lower trophic level production are expected. Capelin were concentrated in the inner domain, a well-mixed region. The overlap of age-1 pollock and capelin was higher in cold years than in warm years. [Copyright &y& Elsevier]

Abstract: As part of a project comparing the structure and function of four marine ecosystems off Norway and the United States, this paper examines the oceanographic responses to climate forcing, with emphasis on recent changes. The four Northern Hemisphere ecosystems include two in the Pacific Ocean (Bering Sea and Gulf of Alaska) and two in the Atlantic Ocean (Georges Bank/Gulf of Maine and the Barents/Norwegian Seas). Air temperatures, wind forcing and heat fluxes over the four regions are compared as well as ocean hydrography and sea-ice conditions where seasonal sea ice is found. The long-term interannual variability in air temperatures, winds and net heat fluxes show strong similarity between adjacent ecosystems and within subregions of an ecosystem, but no significant correlations between Pacific and Atlantic ecosystems and few across the Atlantic. In spite of the lack of correlation between climate forcing and ocean conditions between most of the ecosystems, recent years have seen record or near record highs in air and sea temperatures in all ecosystems. The apparent causes of the warming differ. In the Atlantic, they appear to be due to advection, while in the Pacific temperatures are more closely linked to air-sea heat exchanges. Advection is also responsible for the observed changes in salinity in the Atlantic ecosystems (generally increasing salinity in the Barents and Norwegian Seas and decreasing in the Gulf of Maine and Georges Bank) while salinity changes in the Gulf of Alaska are largely related to increased local runoff. [Copyright &y& Elsevier]

Analyses of climate effects often ignore differences in life history for individual species. We analyzed a 34-year time series of eastern Bering Sea fish surveys to evaluate changes in distribution by length and between cold and warm shelf-wide average water temperatures for 20 species over inhabited depth, temperature, and location. All species showed evidence of ontogenetic migration. Differences in distribution between years with warm and years with cold shelf-wide water temperatures varied among species and within species at different lengths. For species where shelf-wide temperature effects were detected, the mid-sized fish were most active in changing spatial distribution. For aquatic organisms ontogenetic migration occurs because life history stages have different environmental requirements. This study illustrates the need to consider species responses to climate change over different life history stages, and that studies on ecosystem responses should take ontogenetic differences into consideration when assessing impacts. [ABSTRACT FROM AUTHOR]

Records of past warm periods are essential for understanding interglacial climate system dynamics. Marine Isotope Stage 11 occurred from 425 to 394 ka, when global ice volume was the lowest, sea level was the highest, and terrestrial temperatures were the warmest of the last 500 kyr. Because of its extreme character, this interval has been considered an analog for the next century of climate change. The Bering Sea is ideally situated to record how opening or closing of the Pacific-Arctic Ocean gateway (Bering Strait) impacted primary productivity, sea ice, and sediment transport in the past; however, little is known about this region prior to 125 ka. IODP Expedition 323 to the Bering Sea offered the unparalleled opportunity to look in detail at time periods older than had been previously retrieved using gravity and piston cores. Here we present a multi-proxy record for Marine Isotope Stages 12 to 10 from Site U1345, located near the continental shelf-slope break. MIS 11 is bracketed by highly productive laminated intervals that may have been triggered by flooding of the Beringian shelf. Although sea ice is reduced during the early MIS 11 laminations, it remains present at the site throughout both glacials and MIS 11. High summer insolation is associated with higher productivity but colder sea surface temperatures, which implies that productivity was likely driven by increased upwelling. Multiple examples of Pacific-Atlantic teleconnections are presented including laminations deposited at the end of MIS 11 in synchrony with millennial-scale expansions in sea ice in the Bering Sea and stadial events seen in the North Atlantic. When global eustatic sea level was at its peak, a series of anomalous conditions are seen at U1345. We examine whether this is evidence for a reversal of Bering Strait throughflow, an advance of Beringian tidewater glaciers, or a turbidite. [ABSTRACT FROM AUTHOR]

Arrowtooth flounder (Atheresthes stomias) are an important predator of juvenile walleye pollock (Gadus chalcogramus) in the eastern Bering Sea (EBS) shelf and have increased 3-fold in biomass from 1977 to 2014. Arrowtooth flounder avoid the summer "cold pool" (bottom water ≤2°C) and variability in cold pool size and location has affected their spatial overlap with juvenile walleye pollock. Developing a method to account for the relationship between climate change and pollock mortality can highlight ecosystem dynamics and contribute to better assessments for fisheries management. Consequently, spatially resolved predation mortality rateswere estimated within an age-structuredwalleye pollock stock assessment population model (based on spatial information on diet and abundance from trawl surveys), along with the effect of sea surface temperature (SST) on pollock recruitment. Projections of SST and cold pool area to 2050 were obtained (or statistically downscaled) from nine global climate models and used within an age-structure population model to project pollock abundance given estimated relationships between environmental variables and predator and prey spatial distributions, pollock recruitment, and maximum rate of arrowtooth flounder consumption. The climate projections showa wide range of variability but an overall trend of increasing SSTand decreasing cold pool area. Projected pollock biomass decreased largely due to the negative effect of increased SST on pollock recruitment. A sensitivity analysis indicated that the decline in projected pollock biomass would be exacerbated if arrowtooth flounder increased their relative distribution in the EBS northwest middle shelf (an area of relatively high density of juvenile pollock) in warm years. [ABSTRACT FROM AUTHOR]

Dramatic multiyear fluctuations in water temperature and seasonal sea ice extent and duration across the Bering-Chukchi continental shelf have occurred in this century, raising a pressing ecological question: Do such environmental changes alter marine production processes linking primary producers to upper trophic-level predators? We examined this question by comparing the blubber fatty acid (FA) composition and stable carbon isotope ratios of individual FA (δ13CFA) of adult ringed seals ( Pusa hispida), bearded seals ( Erignathus barbatus), spotted seals ( Phoca largha), and ribbon seals ( Histriophoca fasciata), collectively known as 'ice seals,' sampled during an anomalously warm, low sea ice period in 2002-2005 in the Bering Sea and a subsequent cold, high sea ice period in 2007-2010. δ13CFA values, used to estimate the contribution to seals of carbon derived from sea ice algae (sympagic production) relative to that derived from water column phytoplankton (pelagic production), indicated that during the cold period, sympagic production accounted for 62-80% of the FA in the blubber of bearded seals, 51-62% in spotted seals, and 21-60% in ringed seals. Moreover, the δ13CFA values of bearded seals indicated a greater incorporation of sympagic FAs during the cold period than the warm period. This result provides the first empirical evidence of an ecosystem-scale effect of a putative change in sympagic production in the Western Arctic. The FA composition of ice seals showed clear evidence of resource partitioning among ringed, bearded, and spotted seals, and little niche separation between spotted and ribbon seals, which is consistent with previous studies. Despite interannual variability, the FA composition of ringed and bearded seals showed little evidence of differences in diet between the warm and cold periods. The findings that sympagic production contributes significantly to food webs supporting ice seals, and that the contribution apparently is less in warm years with low sea ice, raise an important concern: Will the projected warming and continuing loss of seasonal sea ice in the Arctic, and the associated decline of organic matter input from sympagic production, be compensated for by pelagic production to satisfy both pelagic and benthic carbon and energy needs? [ABSTRACT FROM AUTHOR]

The Bering Sea and Gulf of Alaska support a number of commercially important flatfish fisheries. These high latitude ecosystems are predicted to be most immediately impacted by ongoing ocean acidification, but the range of responses by commercial fishery species has yet to be fully explored. In this study, we examined the growth responses of northern rock sole (Lepidopsetta polyxystra) eggs and larvae across a range of CO2 levels (ambient to 1500 µatm) to evaluate the potential sensitivity to ocean acidification. Laboratory-spawned eggs and larvae were reared at 8°C in a flow-through culture system in which CO2 levels were maintained via computer-controlled injection of CO2 into a seawater conditioning tank. Overall, we observed only minor effects of elevated CO2 level on sizes of northern rock sole larvae. Size at hatch differed among offspring from four different females, but there was no significant effect of CO2 level on egg survival or size at hatch. In three separate larval growth trials, there was little effect of CO2 level on growth rates through the first 28 d post-hatch (DPH). However, in the one trial extended to 60 DPH, fish reared at the highest CO2 level had lower condition factors after 28 DPH, suggesting that larvae undergoing metamorphosis may be more sensitive to environmental hypercapnia than earlier pre-flexion stages. These results suggest that while early life stages of northern rock sole are less sensitive to ocean acidification than previously examined flatfish, they may be more sensitive to elevated CO2 levels than a previously studied gadid with a similar geographic range. [ABSTRACT FROM AUTHOR]

The recent cooling in the eastern Bering Sea resulted in a series of cold years (2008–2010) marked by extensive ice coverage and late ice retreat. In the present study, we examined the spatial and temporal variability of three predominant euphausiid species Thysanoessa raschii , Thysanoessa inermis , and Thysanoessa longipes in the summers of 2008–2010. Simple box-and-whisker plots as well as generalized additive models (GLMs) were applied to examine habitat selection for three euphausiid species. The coefficients of dispersion were calculated for three species to examine potential changes in spatial patterns. Results showed that T. raschii was broadly distributed in the inner and middle domains. The abundance of T. raschii was related to water temperature, salinity and chlorophyll a concentration. T. inermis was primarily distributed in the middle domain and was related to water temperature and salinity. T. longipes was mostly distributed in the outer domain and was only related to salinity. The proportion of T. raschii , a coastal species in the inner and middle domains, showed large interannual variation with the highest in 2008 and the lowest in 2009 (a >50% decline). This same species did not show large interannual variation in the spatial distribution. T. longipes , a shelf species in the outer domain, did not show large interannual variation in abundance, but the center of mass distribution consistently shifted northward and offshore from 2008 to 2010. T. inermis , a coastal species in the middle and coastal domains, did not show large interannual variation in abundance and spatial distribution. In summary, euphausiid populations showed large spatial and temporal variability among cold years. Different species could be affected by different processes in the southeastern Bering Sea. [ABSTRACT FROM AUTHOR]

During the last glacial termination, the upper North Pacific Ocean underwent dramatic and rapid changes in oxygenation that lead to the transient intensification of oxygen minimum zones (OMZs), recorded by the widespread occurrence of laminated sediments on circum-Pacific continental margins. We present a new laminated sediment record from the mid-depth (1100 m) northern Bering Sea margin that provides insight into these deglacial OMZ maxima with exceptional, decadal-scale detail. Combined ultrahigh-resolution micro-X-ray-fluorescence (micro-XRF) data and sediment facies analysis of laminae reveal an alternation between predominantly terrigenous and diatom-dominated opal sedimentation. The diatomaceous laminae are interpreted to represent spring/summer productivity events related to the retreating sea ice margin. We identified five laminated sections in the deglacial part of our site. Lamina counts were carried out on these sections and correlated with the Bolling-Allerad and Preboreal phases in the North Greenland Ice Core (NGRIP) oxygen isotope record, indicating an annual deposition of individual lamina couplets (varves). The observed rapid decadal intensifications of anoxia, in particular within the Bølling-Allerød, are tightly coupled to short-term warm events through increases in regional export production. This dependence of laminae formation on warmer temperatures is underlined by a correlation with published Bering Sea sea surface temperature records and δ18O data of planktic foraminifera from the Gulf of Alaska. The rapidity of the observed changes strongly implies a close atmospheric teleconnection between North Pacific and North Atlantic regions. We suggest that concomitant increases in export production and subsequent remineralization of organic matter in the Bering Sea, in combination with oxygen-poor waters entering the Being Sea, drove down oxygen concentrations to values below 0.1 mLL-1 and caused laminae preservation. Calculated benthic-planktic ventilation ages show no significant variations throughout the last deglaciation, indicating that changes in formation rates or differing sources of North Pacific mid-depth waters are not prime candidates for strengthening the OMZ at our site. The age models established by our correlation procedure allow for the determination of calendar age control points for the Bolling-Allerad and the Preboreal that are independent of the initial radiocarbon-based chronology. Resulting surface reservoir ages range within 730-990 yr during the Bølling-Allerød, 800-1100yr in the Younger Dryas, and 765-775yr for the Preboreal. [ABSTRACT FROM AUTHOR]

Climate change in the last century was associated with spectacular growth of many wild Pacific salmon stocks in the North Pacific Ocean and Bering Sea, apparently through bottom-up forcing linking meteorology to ocean physics, water temperature, and plankton production. One species in particular, pink salmon, became so numerous by the 1990s that they began to dominate other species of salmon for prey resources and to exert top-down control in the open ocean ecosystem. Information from long-term monitoring of seabirds in the Aleutian Islands and Bering Sea reveals that the sphere of influence of pink salmon is much larger than previously known. Seabirds, pink salmon, other species of salmon, and by extension other higher-order predators, are tightly linked ecologically and must be included in international management and conservation policies for sustaining all species that compete for common, finite resource pools. These data further emphasize that the unique 2-y cycle in abundance of pink salmon drives interannual shifts between two alternate states of a complex marine ecosystem. [ABSTRACT FROM AUTHOR]

The Bering Sea Sub-Network, a Community-Based Observation Network, was initiated to improve knowledge of environmental changes occurring in the Bering Sea and to enable scientists, Arctic communities and governments to predict, plan and respond. Climate change can affect the health of the social-ecological system of Indigenous communities through negative effects to travel and changes to biological resources used for subsistence. Harvesters are perceptive of, and often have multigenerational knowledge about, the environmental conditions which subsistence activities are dependent upon. Community monitoring can detect local level environmental changes, and provide society with examples of adaptation strategies. Semi-structured interviews, with a participatory mapping component, were used to collect data on marine subsistence activity in Indigenous communities bordering the Bering Sea, in the Russian Federation and Alaska, USA. Spatial data allow exploration of human responses to change over time. In the Yup'ik village of Togiak, Alaska a shift has occurred in recent years in where residents harvest walrus, while seasonal regulations remain static. This may cause residents to travel farther in more dangerous conditions. The co-management system in place could be an effective forum to deal with change as it was structured to incorporate local input in adaptive management. [ABSTRACT FROM PUBLISHER]

Pinchuk, A. I., Coyle, K. O., Farley, E. V., and Renner, H. M. 2013. Emergence of the Arctic Themisto libellula (Amphipoda: Hyperiidae) on the southeastern Bering Sea shelf as a result of the recent cooling, and its potential impact on the pelagic food web. – ICES Journal of Marine Science, 70: 1244–1254.The eastern Bering Sea shelf experienced a sequence of warm years after a regime shift in the late 1970s. Following a series of unusually warm years in the early 2000s, the climate shifted again in 2007 to a series of extremely cold years that were marked by intense ice coverage and late ice retreat. Spatial and temporal variability in zooplankton communities during the recent cold period was investigated as part of the collaborative BEST-BSIERP program. An increasing presence of the Arctic hyperiid Themisto libellula, which had not been reported from the southeastern Bering Sea since the 1970s, was observed in the Middle Shelf Domain, indicating a developing structural shift in the zooplankton community in response to continuous cold conditions. Simultaneously, T. libellula became an increasingly dominant prey in the diets of zooplanktivorous fish and seabirds, demonstrating the important role for T. libellula in the pelagic food web. Our analysis suggests that T. libellula is capable of controlling copepod populations, thus it may become a potential contributor to top-down regulation of Calanus spp. in the eastern Bering Sea. [ABSTRACT FROM PUBLISHER]

Shifts in climate regime are prominent features of the physical environment of the eastern Bering Sea and in recent years have been documented in approximately 1977 and 1989. Average snow crab ( Chionoecetes opilio) recruitment decreased sharply after the 1989 fertilization year. Models in which control of snow crab recruitment shifts between drivers dependent on climate 'regime' are presented. These models are evaluated using cross-validation and retrospective analysis, both of which indicate that the relationships are relatively robust to varying levels of information. Larval survival as influenced by food availability in the pelagic phase and advection to suitable nursery grounds are the hypothesized mechanisms driving recruitment dynamics. [ABSTRACT FROM AUTHOR]

An assessment of the potential for 17 fish or shellfish stocks or stock groups to move from the sub- Arctic areas into the Arctic Ocean was conducted. A panel of 34 experts was convened to assess the impact of climate change on the potential movement of the 17 stocks or stock groups. The panel considered the exposure of species to climate change, the sensitivity of species to these changes and the adaptive capacity of each stock or stock group. Based on expert opinions, the potential for expansion or movement into the Arctic was qualitatively ranked (low potential, potential, high potential). It is projected that the Arctic Ocean will become ice-free during the summer season, and when this happens new areas will open up for plankton production, which may lead to new feeding areas for fish stocks. Five stocks had a low potential to move to, or expand in, the high Arctic. Six species are considered as potential candidate species to move to, or expand in, the high Arctic. Six stocks had a high potential of establishing viable resident populations in the region. These six stocks exhibit life history characteristics that allow them to survive challenging environmental conditions that will continue to prevail in the north. This study suggests that several life history factors should be considered when assessing the potentiality of a species moving in response to changing climate conditions. [ABSTRACT FROM AUTHOR]

In recent years coastal oceanographers have suggested using the "Strouhal" number or its inverse, the "Stokes" number, to describe the effect of bottom boundary layer turbulence on the vertical structure of both density and currents. These are defined as the ratios of the frictional depth (δ) to the water column depth (h) or vice versa. Although many researchers have mentioned that the effects of the earth's rotation should be important, they have tended to omit it. Rotation may have an important influence on tidal currents, as the frictional depth from a fully cyclonic to a fully anticyclonic tidal ellipse can vary by up to an order of magnitude at mid latitudes. The Stokes number might appear smaller for cyclonic current ellipses (larger for anticyclonic) than it is without rotation, resulting in frictional effects being underestimated (overestimated). Here, a way to calculate a Stokes number is proposed, in which the effect of the earth's rotation is taken into account. The standard Stokes and the rotational Stokes numbers are used as predictors for the position of the tidal mixing fronts in the Irish Sea. Results show that use of the rotational number improves the predictions of fronts in shallow cyclonic areas of the eastern Irish Sea. This suggests that the effect of rotation on the water column structure will be more important in shallow shelf seas and estuaries with strong rotational currents. [ABSTRACT FROM AUTHOR]

Statistical relationships between future and historical model runs in multimodel ensembles (MMEs) are increasingly exploited to make more constrained projections of climate change. However, such emergent constraints may be spurious and can arise because of shared (common) errors in a particular MME or because of overly influential models. This study assesses the robustness of emergent constraints used for Arctic warming by comparison of such constraints in ensembles generated by the two most recent Coupled Model Intercomparison Project (CMIP) experiments: CMIP3 and CMIP5. An ensemble regression approach is used to estimate emergent constraints in Arctic wintertime surface air temperature change over the twenty-first century under the Special Report on Emission Scenarios (SRES) A1B scenario in CMIP3 and the Representative Concentration Pathway (RCP) 4.5 scenario in CMIP5. To take account of different scenarios, this study focuses on polar amplification by using temperature responses at each grid point that are scaled by the global mean temperature response for each climate model. In most locations, the estimated emergent constraints are reassuringly similar in CMIP3 and CMIP5 and differences could have easily arisen from sampling variation. However, there is some indication that the emergent constraint and polar amplification is substantially larger in CMIP5 over the Sea of Okhotsk and the Bering Sea. Residual diagnostics identify one climate model in CMIP5 that has a notable influence on estimated emergent constraints over the Bering Sea and one in CMIP3 that that has a notable influence more widely along the sea ice edge and into midlatitudes over the western North Atlantic. [ABSTRACT FROM AUTHOR]

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Pfeiffer, L., and Haynie, A. C. 2012. The effect of decreasing seasonal sea-ice cover on the winter Bering Sea pollock fishery. – ICES Journal of Marine Science, 69: .The winter fishing season for eastern Bering Sea pollock (Theragra chalcogramma) is during the period of maximum seasonal sea-ice extent, but harvesters avoid fishing in ice-covered waters. Global climate models predict a 40% reduction in winter ice cover by 2050, with potential implications for the costs incurred by vessels travelling to and around their fishing grounds and the value of their catch. Additionally, it may open entirely new areas to fishing. Using retrospective data from 1999 to 2009, a period of extensive annual climate variation, the variation in important characteristics of the fishery is analysed. When ice is present, it restricts a portion of the fishing grounds, but in general, ice-restricted areas have lower expected profits at the time of restriction than the areas left open. Some areas show a change in effort in warm years relative to cold, but the global redistribution of effort attributable to ice cover is small. This is largely because the winter fishery is driven by the pursuit of roe-bearing fish whose spawning location is stable in the southern part of the fishing grounds. [ABSTRACT FROM PUBLISHER]

Since 1997, ocean color satellite images have revealed large-scale blooms of the coccolithophorid Emiliania huxleyi in the eastern Bering Sea. The blooms are often sustained over several months and have caused ecosystem changes in the Arctic Ocean, as well as in the Bering Sea. We examined continental shelf sediment profiles of alkenone, a biomarker for E. huxleyi, covering the past ∼70 years. The alkenone records suggest that large E. huxleyi blooms are a novel feature in the Bering Sea as they have occurred only since the late 1970s. Recent changes in alkenone content were closely related to the 1976-77 climatic regime shift in the North Pacific, implying that warming and freshening of Bering Sea waters promoted E. huxleyi blooms. The production rate of diatoms (total valves in sediment samples), the dominant primary producers in the Bering Sea, also increased during the past several decades. However, the ratio of alkenone content to total diatom valves in the sediments increased as E. huxleyi production increased, suggesting that the increase in the E. huxleyi production rate frequently exceeded the increase in the diatom production rate. Overall, our results indicate a possible subarctic region ecosystem shift driven by climate change. [ABSTRACT FROM AUTHOR]

Hunt, G. L., Coyle, K. O., Eisner, L. B., Farley, E. V., Heintz, R. A., Mueter, F., Napp, J. M., Overland, J. E., Ressler, P. H., Salo, S., and Stabeno, P. J. 2011. Climate impacts on eastern Bering Sea foodwebs: a synthesis of new data and an assessment of the Oscillating Control Hypothesis. – ICES Journal of Marine Science, 68: 1230–1243.Walleye pollock (Theragra chalcogramma) is an important component of the eastern Bering Sea ecosystem and subject to major fisheries. The Oscillating Control Hypothesis (OCH) predicted that recruitment of pollock year classes should be greatest in years with early ice retreat and late blooms in warm water, because more energy would flow into the pelagic (vs. benthic) community. The OCH further predicted that, with pollock population growth, there should be a shift from bottom-up to top-down regulation. New data support the predictions that in those years with early ice retreat, more primary production accrues to the pelagic compartment and that large numbers of age-0 pollock survive to summer. However, in these years, production of large crustacean zooplankton is reduced, depriving age-0 pollock of lipid-rich prey in summer and autumn. Consequently, age-0 pollock energy reserves (depot lipids) are low and predation on them is increased as fish switch to age-0 pollock from zooplankton. The result is weak recruitment of age-1 recruits the following year. A revised OCH indicates bottom-up constraints on pollock recruitment in very warm periods. Prolonged warm periods with decreased ice cover will likely cause diminished pollock recruitment and catches relative to recent values. [ABSTRACT FROM PUBLISHER]

Concern about impacts of climate change in the Bering Sea prompted several research programs to elucidate mechanistic links between climate and ecosystem responses. Following a detailed literature review, Hunt et al. (2011) (Deep-Sea Res. II, 49, 2002, 5821) developed a conceptual framework, the Oscillating Control Hypothesis (OCH), linking climate-related changes in physical oceanographic conditions to stock recruitment using walleye pollock ( Theragra chalcogramma) as a model. The OCH conceptual model treats zooplankton as a single box, with reduced zooplankton production during cold conditions, producing bottom-up control of apex predators and elevated zooplankton production during warm periods leading to top-down control by apex predators. A recent warming trend followed by rapid cooling on the Bering Sea shelf permitted testing of the OCH. During warm years (2003-06), euphausiid and Calanus marshallae populations declined, post-larval pollock diets shifted from a mixture of large zooplankton and small copepods to almost exclusively small copepods, and juvenile pollock dominated the diets of large predators. With cooling from 2006-09, populations of large zooplankton increased, post-larval pollock consumed greater proportions of C. marshallae and other large zooplankton, and juvenile pollock virtually disappeared from the diets of large pollock and salmon. These shifts in energy flow were accompanied by large declines in pollock stocks attributed to poor recruitment between 2001 and 2005. Observations presented here indicate the need for revision of the OCH to account for shifts in energy flow through differing food-web pathways due to warming and cooling on the southeastern Bering Sea shelf. [ABSTRACT FROM AUTHOR]

The match-mismatch hypothesis (MMH) predicts that marine fish larvae will have their highest rate of growth and survival when they overlap with their prey. However, Pacific cod (Gadus macrocephalus) and other gadids continue to thrive in the Bering Sea despite delayed prey production resulting from warming and loss of sea ice. In this study, we examined how temperature mediates growth and survival of Pacific cod larvae under varying match-mismatch conditions. Cod larvae were reared at two temperatures (3 °C and 8 °C) and exposed to one of five different food treatments over a 6-week period: (i) high food (HF) (match); (ii) low food (LF); (iii) HF then LF (HF-LF); and (iv) LF then HF (LF-HF) (2-4 mismatch); and (v) no food (NF) (complete mismatch). Results showed that cold environments allow Pacific cod larvae to bridge gaps in prey availability (i.e., timing and magnitude), but negatively impact survival over longer periods. Under warmer conditions, mismatches in prey significantly impacted growth and survival. However, both yolk reserves and compensatory growth mechanisms reduced the severity of mismatches occurring in the first 3 weeks of development. Our results demonstrate a clear need to incorporate the direct effects of temperature on fish larvae in food limitation models. L'hypothèse de l'appariement-mésappariement (MMH, match-mismatch hypothesis) prédit que les larves de poissons marins possèdent une croissance et une survie maximales lorsqu'il y un chevauchement entre elles et leurs proies. Cependant, la morue du Pacifique (Gadus macrocephalus) et d'autres gadidés continuent de prospérer dans la mer de Béring malgré la production retardée de proies causée par le réchauffement et la perte de glace de mer. Nous examinons dans notre étude comment la température contrôle la croissance et la survie de la morue du Pacifique sous diverses conditions d'appariement-mésappariement. Nous avons élevé des larves de morue à deux températures (3 °C et 8 °C) et les avons exposées à l'un de cinq traitements alimentaires durant une période de 6 semaines: (i) nourriture abondante (HF) (appariement), (ii) nourriture restreinte (LF), (iii) HF puis LF (HF-LF), (iv) LF puis HF (LF-HF) (2-4 mésappariements) et (v) absence de nourriture (NF) (mésappariement complet). Nos résultats montrent que les environnements froids permettent aux larves de morues du Pacifique de surmonter des interruptions dans la disponibilité des proies (c'est-à-dire le moment et l'intensité de la pénurie); mais cela affecte négativement la survie sur des périodes plus longues. Dans des conditions plus chaudes, les mésappariements des proies affectent significativement la croissance et la survie. Cependant, les réserves de vitellus et les mécanismes compensatoires de la croissance réduisent tous deux la sévérité des mésappariements qui se produisent durant les trois premières semaines du développement. Nos résultats démontrent clairement la nécessité d'incorporer les effets directs de la température sur les larves de poissons dans les modèles de restriction de nourriture. [ABSTRACT FROM AUTHOR]

The southeastern shelf of the Bering Sea is one of the ocean's most productive ecosystems and sustains more than half of the total US fish landings annually. However, the character of the Bering Sea shelf ecosystem has undergone a dramatic shift over the last several decades, causing notable increases in the dominance of temperate features coupled to the decline of arctic species and decreases in the abundance of commercially important organisms. In order to assess the current state of primary production in the southeastern Bering Sea, we measured the spatio-temporal distribution and controls on dissolved inorganic carbon (DIC) concentrations in spring and summer of 2008 across six shelf domains defined by differing biogeochemical characteristics. DIC concentrations were tightly coupled to salinity in spring and ranged from ∼1900 μmol kg-1 over the inner shelf to ∼2400 μmol kg-1 in the deeper waters of the Bering Sea. In summer, DIC concentrations were lower due to dilution from sea ice melt and primary production. Concentrations were found to be as low ∼1800 μmol kg-1 over the inner shelf. We found that DIC concentrations were drawn down 30-150 μmol kg-1 in the upper 30m of the water column due to primary production between the spring and summer occupations. Using the seasonal drawdown of DIC, estimated rates of net community production (NCP) on the inner, middle, and outer shelf averaged 28±10 mmol C m-2 d-1. However, higher rates of NCP (40-47 mmol C m-2 d-1) were observed in the "Green Belt" where the greatest confluence of nutrient-rich basin water and iron-rich shelf water occurs. We estimated that in 2008, total productivity across the shelf was on the order of ∼105 Tg C yr-1. Due to the paucity of consistent, comparable productivity data, it is impossible at this time to quantify whether the system is becoming more or less productive. However, as changing climate continues to modify the character of the Bering Sea, we have shown that NCP can be an important indicator of how the ecosystem is functioning. [ABSTRACT FROM AUTHOR]

Stomach content data from 798 Pacific walruses ( Odobenus rosmarus divergens) collected during 1952–1991 were analyzed using a method that evaluates the stage of digestion of prey remains. Non-molluscan prey taxa were not well represented in previous interpretations of walrus diet due to digestion biases. Stomach contents least affected by digestion (fresh stomachs) contained more prey taxa than stomachs of an unknown or more digested state. Bivalves, gastropods, and polychaete worms were the most frequent prey items in both the Bering and Chukchi seas, although bivalves occurred more frequently in stomachs from the Bering Sea and gastropods occurred more frequently in stomachs from the Chukchi Sea. Male and female walruses consumed essentially the same prey when in the same location. Using only fresh stomachs collected between 1975 and 1985, there was no significant difference between the proportion that contained mostly bivalves and the proportion that contained non-bivalve prey items. Earlier interpretations of a change in walrus diet in this period compared to the prior two decades may have been due to digestion as well as sampling biases. Current climatic changes may affect walrus's access to diverse, productive shallow water feeding areas. [ABSTRACT FROM AUTHOR]

A variety of changes are occurring in the ecosystems of the North Pacific Ocean and Bering Sea, but information about the mechanisms of change has been relatively limited, due in part to the region’s remoteness and subarctic conditions. Any number of ecosystem components or indicators could be used to exemplify this dilemma, but here we point to the salmon shark ( Lamna ditropis, Lamnidae) as an example of a species that can potentially mediate considerable ecosystem change due to its high trophic level, but for which some basic information is lacking despite attracting some interesting research and widespread rumours and anecdotal evidence of increased abundance. Increases in the abundance of sharks such as salmon sharks in this region during the 1990s, if true, may help explain other observed changes such as declines in ocean survival rates of Pacific salmon ( Oncorhynchus spp., Salmonidae) in the region and declines in some wild salmon stocks. Mechanisms that could cause salmon shark increases in Alaskan coastal waters include: (i) increases in sea temperature since the 1970s allowing distributional shifts of this species and changes in the abundance or distribution of their prey; (ii) the 1992 banning of high seas drift gillnets; and (iii) indirect fisheries effects such as competitive release of salmon sharks in the North Pacific transition region and towards the more southern geographic extent of their annual migration as the result of fishery-related reductions in blue sharks ( Prionace glauca, Carcharhinidae) and other pelagic predators. The relative plausibility of these alternative explanations can be evaluated using combinations of existing ecosystem models and empirical research and monitoring programmes including local and indigenous observations. [ABSTRACT FROM AUTHOR]

The last 10,000 years have been characterized by distinctly stable climates. For the earlier glacial period (up to 125,000 years ago), climate records show long-lasting large-amplitude oscillations, generally known as Dansgaard–Oeschger (D/O) or Heinrich events. These fluctuations are believed to be a result of freshwater anomalies in the North Atlantic which dramatically reduce the transport of the meridional overturning cell (MOC). They are followed by a recovery of the MOC.Here, we propose that such long lasting instabilities in the meridional circulation are only possible during glacial periods when the Bering Strait (BS) is closed. An analytical ocean model which includes both wind and thermohaline processes) is used to show that, during interglacial periods (when the BS is open) perturbations in North Atlantic Deep Water (NADW) formation are quickly damped out. This new mechanism involves the strong winds in the Southern Ocean (SO) which, with an open BS, quickly [O(1–10 years)] flush any large low salinity anomalies out of the Atlantic and into the Pacific Ocean. During glacial periods, the stabilizing effect is prevented by the closure of the BS which traps the anomalies within the Atlantic, causing long lasting perturbations. We also show that no continuous fresh-water flux is needed in order to keep the collapsed MOC from a recovery in the closed basin case, but a relatively large continuous flux of 0.19 Sv is required in order to keep the collapsed state in the open BS case. With a smaller freshwater transport, the open MOC quickly recovers. This also indicates that an open BS is more stable than the closed BS case.Process-oriented numerical simulations using idealized geometry in a two-layer ocean support our analytical solutions and show that the flushing mechanism is active even when the shallow BS sill is included. [Copyright &y& Elsevier]

In the summer of 1997, positive sea surface temperature anomalies (SSTA) extended across the Gulf of Alaska (GOA) and into the eastern Bering Sea (EBS). The SSTA in the EBS are at least in part due to atmospheric causes. Anomalously high 925 mb temperatures and 700 mb geopotential heights and low 925 mb relative humidities, and hence decreased low cloud cover, occurred over the region during April to August. This resulted in enhanced warming of the GOA and EBS owing to increased insolation. The anomalous solar heating was particularly great in the EBS from mid-May to mid-July. The pattern of positive 700 mb height anomalies for April to August 1997 is similar to its counterpart formed by compositing the April to August anomalies that occurred during previous El Niños. The positive equatorial SSTA for 1997 was one of the strongest on record for summer months. The existence of an equatorial/high-latitude connection and the strength of the summer equatorial SSTA in 1997 suggest an El Niño/Southern Oscillation (ENSO) influence in the GOA and EBS. The warming in the Bering Sea and North Pacific during summer 1997 appears to be due in part to the confluence of three meteorological factors which favoured clear skies. There was not only an El Niño influence, but also a decadal trend toward higher 700 mb geopotential heights and a particularly strong blocking ridge weather pattern over the Gulf of Alaska in May. [ABSTRACT FROM AUTHOR]

In 1997, the Bering Sea ecosystem, a productive, high-latitude marginal sea, demonstrated that it responds on very short time scales to atmospheric anomalies. That year, a combination of atmospheric mechanisms produced notable summer weather anomalies over the eastern Bering Sea. Calm winds, clear skies, and warm air temperatures resulted in a larger-than-normal transfer of heat to surface waters and the establishment of a shallow mixed layer. In spring, significant new production occurred below the shallow pycnocline over the Middle Shelf, depleting the subpycnocline nutrient reservoir that normally exists during summer. Following the depletion of nitrate and silicate from the system, a sustained (≥ 4 months) bloom of coccolithophores (Emiliania huxleyi) was observed – a phenomenon not previously documented in this region. Summer Middle Shelf Domain copepod concentrations were higher for some species in 1997 than in the early 1980s. Warmer surface water and lack of wind mixing also changed the basic distribution of hydrographic regimes on the south-eastern shelf and altered the strength and position of fronts or transition zones where apex predators seek elevated food concentrations. The Inner Front was well inshore of its normal position, and adult euphausiids (the primary prey of short-tailed shearwaters, Puffinus tenuirostris) were unavailable at, and shoreward of, the front in autumn. High shearwater mortality rates followed the period of low euphausiid availability. Some, but not all, of these anomalous conditions re-occurred in 1998. These observations are another demonstration that the structure and function of marine ecosystems are intimately tied to forcing from the atmosphere. Alteration of climatological forcing functions, expressed as weather, can be expected to have large impacts on this ecosystem and its natural resources. [ABSTRACT FROM AUTHOR]