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The Bering Sea has some of the highest concentrations of inorganic nutrients of any marine system. In the Bering Sea, eukaryotic microbes interface inorganic nutrient sequestration and cycling processes that drive one of the most productive ecosystems globally. Historical surveys of eukaryotic microbial diversity in the Bering Sea have relied on microscopy and culturing-dependent analyses to assess microbial diversity patterns. In this study, we used high-throughput sequencing (Illumina MiSeq) of the 18S rRNA gene to explore general patterns of eukaryotic microbial diversity from six regions in the Bering Sea and surrounding Subarctic Pacific. The greatest richness was found in the Shelikof Strait and at the marginal ice zone. The lowest richness was found in the deep water basin south of the Aleutian Islands. Ordination analysis of our sequences revealed nearly identical community structures between our Shelikof Strait and the deep water basin sites. Operational taxonomic unit analysis revealed that water samples from the Bering Sea sites shared more OTUs with the Shelikof Strait site than with the sea ice sample, despite the existence of sea ice in the Bering Sea, reflecting known circulation patterns out of the Gulf of Alaska. Richness increased with increasing latitude and decreasing temperature, suggesting that the base of food webs is susceptible to temperature perturbations. [ABSTRACT FROM AUTHOR]

Abstract: Icebreaker-based sampling in the northern Bering Sea south of St. Lawrence Island in March of 2008, 2009, and 2010 has provided new data on overall ecosystem function early in the annual productive cycle. While water-column chlorophyll concentrations (<25mgm−2 integrated over the whole water column) are two orders of magnitude lower than observed during the spring bloom in May, sea-ice algal inventories of chlorophyll are high (up to 1g m−3 in the bottom 2-cm of sea-ice). Vertical fluxes of chlorophyll as measured in sediment traps were between 0.3 and 3.7mgm−2 d−1 and were consistent with the recent deposition (days’ to weeks’ time scale) of chlorophyll to the surface sediments (0–25mgm−2 present at 0–1cm). Sediment oxygen respiration rates were lower than previous measurements that followed the spring bloom, but were highest in areas of known high benthic biomass. Early spring release of sedimentary ammonium occurs, particularly southeast of St. Lawrence Island, leading to bottom-water ammonium concentrations of >5µM. These data, together with other physical, biological, and nutrient data, are presented here in conjunction with observed sea-ice dynamics and the distribution of an apex predator, the Spectacled Eider (Somateria fischeri). Sea-ice dynamics in addition to benthic food availability, as determined by sedimentation processes, play a role in the distribution of spectacled eiders, which cannot always access the greatest biomass of their preferred bivalve prey. Overall, the data and observations indicate that the northern Bering Sea is biologically active in late winter, but with strong atmospheric and hydrographic controls. These controls pre-determine nutrient and chlorophyll distributions, water-column mixing, as well as pelagic–benthic coupling. [Copyright &y& Elsevier]

Abstract: Seasonal patterns in the partitioning of phytoplankton carbon during receding sea ice conditions in the eastern Bering Sea water column are presented using rates of 14C net primary productivity (NPP), phototrophic plankton carbon content, and POC export fluxes from shelf and slope waters in the spring (March 30–May 6) and summer (July 3–30) of 2008. At ice-covered and marginal ice zone (MIZ) stations on the inner and middle shelf in spring, NPP averaged 76±93mmolCm−2 d−1, and in ice-free waters on the outer shelf NPP averaged 102±137mmolCm−2 d−1. In summer, rates of NPP were more uniform across the entire shelf and averaged 43±23mmolCm−2 d−1 over the entire shelf. A concomitant shift was observed in the phototrophic pico-, nano-, and microplankton community in the chlorophyll maximum, from a diatom dominated system (80±12% autotrophic C) in ice covered and MIZ waters in spring, to a microflagellate dominated system (71±31% autotrophic C) in summer. Sediment trap POC fluxes near the 1% PAR depth in ice-free slope waters increased by 70% from spring to summer, from 10±7mmolCm−2 d−1 to 17±5mmolCm−2 d−1, respectively. Over the shelf, under-ice trap fluxes at 20m were higher, averaging 43±17mmolCm−2 d−1. POC export over the shelf and slope estimated from 234Th deficits averaged 11±5mmolCm−2 d−1 in spring and 10±2mmolCm−2 d−1 in summer. Average e-ratios calculated on a station-by-station basis decreased by ∼30% from spring to summer, from 0.46±0.48 in ice-covered and MIZ waters, to 0.33±0.26 in summer, though the high uncertainty prevents a statistical differentiation of these data. [Copyright &y& Elsevier]