Southern Chukchi Sea Research Articles

A unique warm–water oasis in the Siberian Arctic’s Chaun Bay sustained by hydrothermal groundwater discharge

Chaun Bay, located on the fringe of the East Siberian Sea, has been described since the mid-20th century to support a unique marine ecosystem that is atypical for the local Siberian Arctic. Here we use ship-board physical, biogeochemical and geological measurements taken in October 2020, along with hydrographic observations taken from land-fast ice in April 2023, to demonstrate that these warm-water biological communities are supported by hydrothermal submarine groundwater discharge that delivers heat, salinity, nutrients, and trace elements to the bay. We identify a cyclonic eddy that mixes the warm nutrient-rich groundwater with oxygen-rich surface water, resulting in a water mass within Chaun Bay that has similar physical and chemical properties to the highly productive waters of the North Pacific and Southern Chukchi Sea. The bay showed elevated concentrations of chlorophyll-a and zooplankton, and the abundance and species diversity of epibenthos significantly exceeded values observed elsewhere in the East Siberian Sea. The benthic communities contained a number of boreal species that are not typically found in the Arctic Ocean. We also observed Thysanoessa krill populations, a pelagic species generally considered an expatriate in Arctic waters.

Characterization of pelagic communities in the Pacific sector of the Arctic Ocean using a broadband acoustic system, net samplers, and optical instruments

Rising Arctic temperatures are causing substantial declines in sea ice, altering ice retreat and formation in the Pacific Arctic and impacting marine communities. Despite the significant challenges facing the Pacific Arctic, there are still gaps in our understanding of the environmental impacts on pelagic communities, particularly sound scattering layers (SSLs), and their distributions in the southern Chukchi Sea (SCS), northern Chukchi Sea (NCS), and East Siberian Sea (ESS). This study utilized a wideband autonomous transceiver, net samplers, and optical instruments to explore SSLs in the Pacific Arctic, detailing their relationships with hydrographic properties. The findings indicated a greater vertical distribution of pelagic communities in the SCS than in the NCS and ESS. Significant differences in frequency spectra patterns were observed between the SCS and both the NCS and the ESS, though not between the NCS and the ESS. The correlations between the broadband acoustic and hydrographic values were generally weak to moderate. Elevated acoustic values in the SCS were linked to higher water temperature, dissolved oxygen, and chlorophyll and lower salinity. This study also revealed the behavioral properties of individual pelagic animals and identified Ctenophores and Copepods as the most abundant classes based on camera images and net samples. This research offers crucial insights into the distribution and interactions of pelagic communities with environmental factors, laying the groundwork for understanding climate change impacts. Additionally, this paper presents the first findings of frequency spectra from a broadband system in the Arctic Ocean.

Precious Metals in the Holocene Sediments of the Chukchi Sea

Abstract ––We studied the distribution of gold, silver, and platinum group elements (Pd, Pt, Rh, Ir, and Ru) in two bottom sediment cores of the southern Chukchi Sea. It is shown that the Holocene pelite–silty sediments with an age of up to 4.0 ka BP are significantly enriched in these elements, except for Ru and Rh, relative to their clarkes. Native silver minerals were found in all samples by probe microanalysis, whereas gold minerals were revealed only in the surface layer of the sediment core closest to the Chukchi Sea coast. Multicomponent statistical analysis of the chemical composition and grain size of the sediments and the content of organic matter in them has led to the conclusion about the accumulation of clastogenic and chemogenic forms of precious metals. The abnormally high content of gold (0.3 ppm) in the recent sediments near the Chukchi Peninsula coast might be due to its additional removal from the continent as a result of the placer mining there.

Sediment-water fluxes of inorganic carbon and nutrients in the Pacific Arctic during the sea ice melt season

The Bering and Chukchi Seas are important oceanic regions of carbon dioxide (CO2) uptake owing to enhanced gas solubility in cold surface waters and highly productive spring phytoplankton blooms. Over the past several decades, sea ice extent in the Arctic Ocean has decreased and the ice-melt season has started earlier in the year, but the biogeochemical impacts of these systematic changes are unclear. As these marginal seas of the Arctic Ocean are quite shallow (mostly <60 m depth) there is extensive interaction across air-sea-sediment boundaries, and export production rates are high during the spring bloom, delivering organic carbon to the sediments. However, the subsequent transformations and fluxes of carbon in Bering and Chukchi Sea sediments have not been directly quantified. In May–June 2021, we collected sediment cores at 5 stations spanning the eastern Bering Sea and southern and eastern Chukchi Sea. These stations encompassed a range of surface water ice coverage history, from greater than one month to less than one day of ice-free conditions. In the Chukchi Sea, dissolved nutrient and inorganic carbon (DIC) effluxes from the sediments decreased northward. The highest and most variable DIC fluxes were observed in the southern Chukchi Sea, north of the Bering Strait, ranging from 2.0 to 21.5 mmol m−2 d−1, while the lowest DIC fluxes were observed at the northernmost Chukchi Sea station near Cape Lisburne, ranging from 1.1 to 2.3 mmol m−2 d−1. Moving northward, the surface water had greater sea ice concentrations, inhibiting surface productivity and air-sea exchange of CO2. The reduced export of labile carbon to the seafloor likely resulted in decreased benthic respiration and thus a lower flux of remineralization products from the sediments to the water column. Some duplicate core measurements were highly heterogeneous, especially in the Bering Sea, illustrating the dynamic nature of this macrofauna-dominated benthic environment and the range of fluxes under different rates of infaunal activity. Core replicates with relatively higher effluxes of remineralization products also had high fluxes of radon-222, a proxy for bio-irrigation in sediments, illustrating the dominant role of benthic macrofauna in benthic-pelagic coupling in this region. While these observations serve as a seasonal reference, they may also demonstrate how sedimentary fluxes will evolve under future conditions wherein sea ice retreats earlier in the season.

A note on observations of gray whales in the southern Chukchi and northern Bering Seas, August-November, 1980-89

A total of 176 sightings of 488 gray whales (Eschrichtius robustus) were made during 85.6 hours of aerial surveys in the southern Chukchi Sea and northern Bering Sea, east of the International Date Line, from August to early November 1980-1989. Surveys were flown infrequently and effort varied considerably between years and geographic areas. Gray whales were sighted in all areas where surveys were flown, with the exceptions of Kotzebue Sound and Norton Sound. Abundance indices of whales per unit effort (WPUE) in the northern Bering Sea were higher than those in the southern Chukchi Sea during every month except September, when survey coverage was inadequate for abundance calculations, indicating comparatively higher overall use of that area or suggesting the onset of the southbound migration. Most gray whales were feeding (57%, n = 276). Incidental sightings of gray whales observed in and near the study area by other researchers were reviewed to better assess gray whale activity and migration patterns.

Response of nutrients and primary production to high wind and upwelling-favorable wind in the Arctic Ocean: A modeling perspective

Both remote sensing and numerical models revealed increasing net primary production (NPP) in the Arctic Ocean due to declining sea ice cover and increasing ice-free days. The NPP increases in some parts of the Arctic Ocean are also hypothesized to link to high wind (&amp;gt;10 m/s) and upwelling-favorable wind, however, the mechanism remains unclear. Using Regional Arctic System Model (RASM) to investigate the relationship between NPP and wind, we found that the seasonal NPP are statistically correlated to high wind frequency (HWF) in the Barents (Br) and Southern Chukchi Seas (SC) due to their high subsurface nutrients in the 20-50 m layer. Five high and five low HWF years along a zonally averaged section were chosen to understand the spatial variation of the correlation between HWF, NO3, and NPP in the SC. During high HWF years, the decrease in subsurface NO3 exceeds its increase in surface, implying the utilization by biological productivity. A more positive response of NPP to HWF in north SC than south was also found because more subsurface nutrients were entrained into the surface by higher HWF. The NPP are statistically correlated to easterly wind frequency (EWF) in the Beaufort and Canada Basin (BC), where the stronger EWF-induced upwelling could bring up higher nutrients from &amp;gt;100 m depth. While the nutrients and NPP in the south BC are normally higher than in the north, an increase of EWF can further enhance the nutrients and NPP in the south much more than those in the north. Differences between five high and five low EWF years reveal that the increase of EWF is most important around the shelf break region, where NO3 and NPP are also most enhanced. The enhancement of NPP by higher HWF in the Br and SC is less than that by higher ice-free days ratio (IFR), while the enhancement of NPP by higher EWF in BC is of similar magnitude to that by IFR. As the trend of declining sea ice cover continues, it’s necessary to advance our understanding on the nutrients and NPP response to changing wind regimes in different Arctic regions.

Sea ice directs changes in bowhead whale phenology through the Bering Strait

BackgroundClimate change is warming the Arctic faster than the rest of the planet. Shifts in whale migration timing have been linked to climate change in temperate and sub-Arctic regions, and evidence suggests Bering–Chukchi–Beaufort (BCB) bowhead whales (Balaena mysticetus) might be overwintering in the Canadian Beaufort Sea.MethodsWe used an 11-year timeseries (spanning 2009–2021) of BCB bowhead whale presence in the southern Chukchi Sea (inferred from passive acoustic monitoring) to explore relationships between migration timing and sea ice in the Chukchi and Bering Seas.ResultsFall southward migration into the Bering Strait was delayed in years with less mean October Chukchi Sea ice area and earlier in years with greater sea ice area (p = 0.04, r2 = 0.40). Greater mean October–December Bering Sea ice area resulted in longer absences between whales migrating south in the fall and north in the spring (p < 0.01, r2 = 0.85). A stepwise shift after 2012–2013 shows some whales are remaining in southern Chukchi Sea rather than moving through the Bering Strait and into the northwestern Bering Sea for the winter. Spring northward migration into the southern Chukchi Sea was earlier in years with less mean January–March Chukchi Sea ice area and delayed in years with greater sea ice area (p < 0.01, r2 = 0.82).ConclusionsAs sea ice continues to decline, northward spring-time migration could shift earlier or more bowhead whales may overwinter at summer feeding grounds. Changes to bowhead whale migration could increase the overlap with ships and impact Indigenous communities that rely on bowhead whales for nutritional and cultural subsistence.

Composition of Late Holocene Deposits in the Southern Chukchi Sea

Composition of Late Holocene Deposits in the Southern Chukchi Sea

Infaunal community structure, diversity, and function in Pacific-Arctic shelf sediments: a comparison of meiofaunal- and macrofaunal-sized nematodes

Meiofauna, and nematodes in particular, perform essential roles in benthic ecosystems and serve as bioindicators of disturbance and environmental change. In the Pacific Arctic, a region experiencing rapid environmental change, this component of the fauna has received little attention, and the role of meiofauna in ecosystem processes is poorly understood. We collected multi-core samples at 10 stations in the northern Bering and southern Chukchi Seas in June 2018 and characterized the sedimentary environment. We also assessed meiofauna community structure and abundance at higher taxonomic levels and evaluated genus-level nematode composition in meiofaunal (63-500 µm) and macrofaunal (&gt;500 µm) size fractions. Nematodes were classified by feeding type and life-history strategies. Total meiofauna abundance and biomass varied greatly, with 1449-12875 ind. 10 cm-2 and 373-2325 µg dry weight 10 cm-2 for the upper 5 cm of sediment. Estimated production of meiofaunal-sized nematodes was 5-28 g C m-2 yr-1. Four distinct communities of meiofaunal-sized nematodes were identified in different sub-regions reflecting food availability and substrate type. The meiofaunal- and macrofaunal-sized nematodes represented 2 distinct communities. The unique taxonomic composition and large standing stock of the macrofaunal-sized nematodes (22 ± 15% of total nematode biomass) suggest they are critical components of the infauna and merit further research to assess their role in critical ecosystem functions. This study provides the first genus-level characterization of nematodes and some of the first measurements of meiofauna standing stock in the region, contributing important data for assessing ecosystem function in a rapidly changing Arctic.

Trait-based assessment of polychaete assemblages distinguishes macrofaunal community structure among four distinct benthic eco-regions on a shallow arctic shelf

In a rapidly changing Arctic, effects of taxonomic and functional composition of infaunal benthic communities on ecosystem function are poorly characterized for many areas of the continental shelf environment. Infaunal macrobenthos perform essential ecosystem services in soft-sediment habitats, including sediment oxygenation, organic-matter burial, and nutrient regeneration. Changes in the distribution and composition of infauna are likely to impact these important processes. We investigated spatial patterns in macrofauna on the northern Bering and southern Chukchi Sea continental shelves in conjunction with a suite of environmental variables as part of the Arctic Shelf Growth, Advection, Respiration, and Deposition (ASGARD) project. Depth-stratified macrofauna samples (>500 μm) were collected from multi-cores in June 2017 and 2018. Abundance and biomass were recorded for broad taxonomic categories (phylum or class). Polychaetes were identified to family to capture well-described functional-trait information. Functional guilds were assigned to polychaete families, reflecting feeding mode, motility, and feeding structures. Macrofauna exhibited no significant spatial patterns when examined at higher taxonomic levels; however, analysis of polychaete families yielded three distinct station groups, and polychaete functional guilds yielded four distinct groups. These groups were aligned with variations in key habitat characteristics and suggest variation in ecosystem function across the study area. At sandy stations, tube-dwelling, particle-selective suspension and surface deposit feeders were relatively abundant, reflecting an advective system with moderate current speeds and low deposition. Sites with gravelly substrate and moderate levels of organic matter in deeper sediment layers likely experience sporadic organic-matter deposition and disturbance from scouring and were inhabited by larger-bodied species, including bivalves and subsurface deposit-feeding or carnivorous polychaetes. Muddy, offshore stations in the southern Chukchi Sea also contained large bivalves and large carnivorous polychaetes, with evidence of high bioturbation. At more coastal Chukchi Sea stations, macrofauna were dominated by small, motile polychaetes concentrated in the 1-cm surface layer, with indications of anaerobic conditions below. Overall, polychaete functional traits and vertical distribution reflected the quality and quantity of organic matter input and the depositional environment inferred from grain size and current speed, with implications for biogeochemical cycling in sediments.

Benthic bacteria and archaea in the North American Arctic reflect food supply regimes and impacts of coastal and riverine inputs

Benthic bacteria and archaea can be considered biogeochemical engineers as they play a major role in organic matter (OM) degradation and nutrient cycling. As such, prokaryotic community structure, yielded from 16S rRNA amplicon sequencing, can reflect environmental conditions such as OM composition and quantity, nutrient availability, redox conditions, and natural/anthropogenic contaminants (e.g. petroleum hydrocarbons). To assess prokaryotic community structure, we sequenced marine sediments in the upper 10-cm layer on the northern Bering and southern Chukchi Sea shelves, a high-latitude region undergoing rapid environmental change. We then explored broader spatial patterns in community structure for surface sediments (upper 1 cm), incorporating samples from the Northeast Chukchi and Beaufort Seas in relation to environmental variables. Three assemblages were characterized at distinct depth horizons in the upper 10-cm sediment layer from the Northern Bering and Southern Chukchi benthos. One assemblage was exclusively found in sediments at greater than 1 cm sediment depth and contained a relatively higher proportion of anaerobic taxa (e.g. Anaerolineaceae, Desulfobulbaceae, and Desulfosarcinaceae). Overall, community distribution in the upper 10-cm reflected sediment grain size, OM quantity and composition, and possibly the influence of bioturbation. Two assemblages were characterized in surface sediments (upper 1 cm) across the broader Northern Bering and Chukchi Sea study area. A relatively high abundance of anaerobic taxa (e.g. SEEP-SRB4, Subgroup 23, and R76-B128) in one assemblage suggested comparatively suboxic sediments, and the other suggested allochthonous input of phytodetritus based on high abundance of diatom/particle associated microbes (e.g. Polaribacter, Dokdonia, and Ulvibacter), combined with high sediment Chl-a concentration. This latter assemblage may reflect depositional areas influenced by hydrographic patterns. Prokaryotic community structure across the North American Arctic highlights regional differences in environmental controls, with food-supply regimes influencing structure on the Bering-Chukchi inflow shelves, in contrast to the Beaufort interior shelves where nearshore heterogeneity (riverine input and terrigenous material) are major drivers of sediment prokaryote communities.

Recent Changes of Phytoplankton Bloom Phenology in the Northern High‐Latitude Oceans (2003–2020)

AbstractEighteen years (2003–2020) of data on remotely‐sensed ocean color in high northern latitudes show a significant increase (0.56% yr−1) in double blooms of phytoplankton. Starting in 2015 the rate of increase rose to 1.10% yr−1. Double blooms have become especially prevalent in regions north of 50°N in the North Atlantic, Gulf of Alaska and southern Chukchi Sea. Our correlation analysis suggests that double bloom occurrences are dependent on latitude and seasonal changes in both sea surface temperature (SST) and mixed layer depth (MLD), particularly in the subpolar North Pacific (SNP) and polar oceans (65°–75°N), although we cannot attribute the increased double blooms to specific causes. Single blooms indicated by Chlorophyll a (Chl a) dominate in subpolar‐polar waters and occur close to the timing of the Particulate Inorganic Carbon (PIC) peak (i.e., June–August). In the SNP single bloom, Chl a peaks occur earlier than PIC peaks. This interval was shorter during 2016–2020, which is associated with warming anomalies. In the southern part of the Chukchi Sea, however, we found that PIC peaks occur earlier than Chl a peaks, suggesting a potentially different succession pattern between calcifiers and other functional groups. We speculate that in the near future double blooms of phytoplankton will become a prevalent feature in high‐latitude oceans with concurrent changes in the timing of blooms and seasonal phytoplankton succession in the surface ocean due to climate change.

Annual and spatial variation in the condition and lipid storage of juvenile Chukchi Sea gadids during a recent period of environmental warming (2012 to 2019).

The Arctic is undergoing dramatic environmental change with decreasing sea-ice extent and increasing summer temperatures. The late summers of 2017 and 2019 on the eastern Chukchi Sea were anomalously warm, nearly 4 °C warmer than the previous 30-year average. Increased ocean temperatures can affect the energetics of North Pacific fish by increasing their metabolic demands and via shifting fish prey assemblages. Here we describe the total lipids as well as fatty acid (FA) trophic markers in juveniles of two Arctic gadids (polar cod, Boreogadus saida and saffron cod, Eleginus gracilis) as well as two sub-Arctic gadids (walleye pollock, Gadus chalcogrammus and Pacific cod, Gadus macrocephalus) collected on recent ecosystem surveys spanning the north Bering and Chukchi seas. Fifty percent of the variance in the lipid composition of gadids was accounted for by species-specific differences, while ecosystem measurements such as bottom temperature, large > C3 stage Calanus abundance, and surface temperature were found to independently account for 25%, 12% and 10%, respectively. Allometric relationships in lipid storage revealed that polar cod have a different lipid profile than other gadids, suggesting a species-specific life-history strategy for high lipid storage that is an adaptation to Arctic environments. Both polar cod and saffron cod had reduced lipid storage in 2017 compared to fish collected in earlier years. Polar cod in 2017 were significantly lower in total lipid, triacylglycerols (TAG), diatom- (16:1n-7/16:0) and Calanus-sourced (∑C20+ C22) FAs over the Chukchi Shelf. Juvenile gadids showed interspecific differences in the spatial distribution of high lipid individuals, with polar cod having the highest lipids in the northern ice-associated regions of the Chukchi Sea and walleye pollock in the southern Chukchi Sea. In 2019, polar cod's distribution had shifted north such that they were only abundant in the northern Chukchi Sea, where they maintained higher region-specific lipid storage than in 2017. It is concerning that reduced lipid content in polar cod was associated with elevated water temperatures, given predicted continued warming in the Chukchi Sea. Energetic changes in juvenile gadids may be associated with future increased natural mortality rates for regional populations (e.g. overwintering) and unstable foraging value for birds and mammals in the Arctic.

The Forgotten Coast: A Synthesis of Current Knowledge of Southern Chukchi Sea Lagoon Ecosystems

In the Southern Chukchi Sea Region (SCSR) of the Alaskan Arctic, approximately 40% of the coastline consists of freshwater-brackish lagoons and the gravel spits that separate them from the ocean. These lagoons are important rearing, feeding, and spawning habitats for diverse fish and invertebrate assemblages composed of freshwater, diadromous, and marine taxa. Many of these species are prey for a suite of marine mammals and avian predators in addition to being important to the food security of subsistence users from the surrounding region. Despite recognition of the ecological and cultural importance of these habitats from as far back as the 1950s, the body of knowledge surrounding lagoons of the SCSR contains many knowledge gaps and fails to comprehensively capture the dynamic nature of both biotic and abiotic factors that define the functional ecology of these habitats. This report synthesizes the available knowledge of SCSR lagoons, including geomorphology, hydrology, food web structure, and local knowledge. We also recommend avenues of future study, such as characterizing the basal trophic levels of lagoon food webs. Only by constructing a more detailed and comprehensive knowledge base of SCSR lagoon ecology will management and conservation efforts in the region be able to address and mitigate potential threats resulting from expanding infrastructure and global climate change, while simultaneously supporting the diverse portfolio of lagoon habitats that have a vital role in regional subsistence practices and food security.

Seasonal Water Mass Evolution and Non-Redfield Dynamics Enhance CO2 Uptake in the Chukchi Sea.

The Chukchi Sea is an increasing CO2 sink driven by rapid climate changes. Understanding the seasonal variation of air-sea CO2 exchange and the underlying mechanisms of biogeochemical dynamics is important for predicting impacts of climate change on and feedbacks by the ocean. Here, we present a unique data set of underway sea surface partial pressure of CO2 (pCO2) and discrete samples of biogeochemical properties collected in five consecutive cruises in 2014 and examine the seasonal variations in air-sea CO2 flux and net community production (NCP). We found that thermal and non-thermal effects have different impacts on sea surface pCO2 and thus the air-sea CO2 flux in different water masses. The Bering summer water combined with meltwater has a significantly greater atmospheric CO2 uptake potential than that of the Alaskan Coastal Water in the southern Chukchi Sea in summer, due to stronger biological CO2 removal and a weaker thermal effect. By analyzing the seasonal drawdown of dissolved inorganic carbon (DIC) and nutrients, we found that DIC-based NCP was higher than nitrate-based NCP by 66%-84% and attributable to partially decoupled C and N uptake because of a variable phytoplankton stoichiometry. A box model with a non-Redfield C:N uptake ratio can adequately reproduce observed pCO2 and DIC, which reveals that, during the intensive growing season (late spring to early summer), 30%-46% CO2 uptake in the Chukchi Sea was supported by a flexible stoichiometry of phytoplankton. These findings have important ramification for forecasting the responses of CO2 uptake of the Chukchi ecosystem to climate change.

North‐South Differences in Under‐Ice Primary Production in the Chukchi Sea From 1988 to 2018

AbstractAs Arctic sea ice has thinned and begun to retreat earlier in the year, there have been substantial changes in the timing and magnitude of regional net primary production (NPP). Most notably, field, remote sensing, and model‐based studies have demonstrated that massive under‐ice phytoplankton blooms (UIBs) contribute substantially to annual NPP and can even drive increases in sedimentary nitrogen recycling and loss through coupled partial nitrification‐denitrification. In this study, we used a 1‐D biogeochemical model (CAOS‐GO) to compare the magnitude of NPP associated with UIBs in the northern and southern Chukchi Sea between 1988 and 2018. While UIBs were critical in driving interannual variation and secular increases in annual NPP and sedimentary nitrification and denitrification in the northern Chukchi Sea, UIBs were far less important at our southern site. As the length of the under‐ice (UI) period diminished between 1988 and 2018 in the southern Chukchi Sea, there was a decrease in the amount of NPP produced during the UI period. Despite higher rates of both annual NPP and denitrification at the southern site, there were no secular trends in these rates over time. Our results indicate that, as sea ice continues to retreat earlier, the impact of UIBs on the biogeochemistry of the Chukchi Sea is likely to diminish.

Species composition, structure and biomass of zooplankton in the Chukchi Sea in August-September 2019

Plankton survey was conducted in the Chukchi Sea in August-September 2019 by two research vessels: RV Professor Levanidov in the western part of the sea and RV Ocean Starr in its eastern part. Parasagitta elegans dominated everywhere in zooplankton. Beside these arrowworms, species of the arctic and arctic-boreal complex were abundant in the northwestern Chukchi Sea, as Calanus glacialis and other species typical for the adjacent East-Siberian Sea. C. glacialis was numerous in the northeastern Chukchi Sea, too, together with species of the Arctic waters and the Beaufort Sea. The southern Chukchi Sea was occupied by the waters invaded from the Bering Sea, so species of the Bering Sea complex were abundant there, as Eucalanus bungii and Neocalanus plumchrus/flemingeri, at Alaska coast together with neritic species typical for the Alaska coastal water mass. The zooplankton community structure corresponded to the spring phase of seasonal succession in the northern area, whereas to the summer phase in the southern area. Total density of zooplankton was estimated as 65 t/km2 for the northwestern part of the sea, presented mostly by large-sized fraction (56 t/km2) including arrowworms (35 t/km2) and copepods (13 t/km2), and as 48 t/km2 for the southwestern part of the sea, also mostly large-sized fraction (40 t/km2). So high zooplankton density in the western Chukchi Sea is considered as result of the Bering Sea waters advection (previously such abundance was observed in 2008 — 40 and 36 t/km2, when the advection was also active). In the eastern Chukchi Sea, the total density of zooplankton was 44 t/km2 in the northeastern area (including 29 t/km2 of large-sized fraction) and 43 t/km2 in the southeastern area, that was higher than in 2017 (15 t/km2) but lower than in 2007 (49 t/km2). However, different phases of seasonal succession should be noted: summer season in 2019, spring season in 2017, and late-summer season in 2007.

Changes in gray whale phenology and distribution related to prey variability and ocean biophysics in the northern Bering and eastern Chukchi seas.

Changes in gray whale (Eschrichtius robustus) phenology and distribution are related to observed and hypothesized prey availability, bottom water temperature, salinity, sea ice persistence, integrated water column and sediment chlorophyll a, and patterns of wind-driven biophysical forcing in the northern Bering and eastern Chukchi seas. This portion of the Pacific Arctic includes four Distributed Biological Observatory (DBO) sampling regions. In the Bering Strait area, passive acoustic data showed marked declines in gray whale calling activity coincident with unprecedented wintertime sea ice loss there in 2017-2019, although some whales were seen there during DBO cruises in those years. In the northern Bering Sea, sightings during DBO cruises show changes in gray whale distribution coincident with a shrinking field of infaunal amphipods, with a significant decrease in prey abundance (r = -0.314, p<0.05) observed in the DBO 2 region over the 2010-2019 period. In the eastern Chukchi Sea, sightings during broad scale aerial surveys show that gray whale distribution is associated with localized areas of high infaunal crustacean abundance. Although infaunal crustacean prey abundance was unchanged in DBO regions 3, 4 and 5, a mid-decade shift in gray whale distribution corresponded to both: (i) a localized increase in infaunal prey abundance in DBO regions 4 and 5, and (ii) a correlation of whale relative abundance with wind patterns that can influence epi-benthic and pelagic prey availability. Specifically, in the northeastern Chukchi Sea, increased sighting rates (whales/km) associated with an ~110 km (60 nm) offshore shift in distribution was positively correlated with large scale and local wind patterns conducive to increased availability of krill. In the southern Chukchi Sea, gray whale distribution clustered in all years near an amphipod-krill 'hotspot' associated with a 50-60m deep trough. We discuss potential impacts of observed and inferred prey shifts on gray whale nutrition in the context of an ongoing unusual gray whale mortality event. To conclude, we use the conceptual Arctic Marine Pulses (AMP) model to frame hypotheses that may guide future research on whales in the Pacific Arctic marine ecosystem.

Spatial and Interannual Patterns of Epipelagic Summer Mesozooplankton Community Structures in the Western Arctic Ocean in 2016–2020

AbstractMesozooplankton play a crucial role as primary or secondary consumers in Arctic ecosystems and are sensitive indicators of environmental changes. This research is the first comprehensive Arctic zooplankton study covering the area ranging from the southern Chukchi Sea (SCS) and the northern Chukchi Sea (NCS) to the East Siberian Sea (ESS). Mesozooplankton samples were collected at 151 stations in the western Arctic Ocean each August from 2016 to 2020. The mesozooplankton abundance of the study area ranged from 9 to 6,172 ind. m−3, and the predominant group was copepods at 7–3,866 ind. m−3, of which Pseudocalanus spp. and Calanus glacialis were the most abundant copepods. In the SCS, small copepods and meroplankton, such as Pseudocalanus spp., Cirripedia larvae, Echinodermata larvae, and Centropages abdominalis were the predominant taxa. Especially in 2019, C. abdominalis dominated over meroplankton when water temperatures were high (maximum 12.5°C; sea surface temperature, SST). In the NCS and ESS, C. glacialis, Pseudocalanus spp., Metridia longa, Oithona similis, Parasagitta elegans, and Calanus hyperboreus were abundant. The distributions and structures of mesozooplankton communities indicated variability over large spatial scales in the western Arctic waters because of variations in multiple factors, such as water temperature, salinity, and sea ice; however, geographical effects cannot be ignored even during alterations in the physical properties. Our results suggest that these variable patterns of mesozooplankton communities fluctuate horizontally from south to north as warming progresses on a regional bathymetric basis, and can be used to infer the fate of mesozooplankton communities in the study area.

Annual variation of oceanographic conditions changed migration timing of bowhead whales Balaena mysticetus in the southern Chukchi Sea

Annual variation of oceanographic conditions changed migration timing of bowhead whales Balaena mysticetus in the southern Chukchi Sea