We will quantify the export flux of organic carbon in the Eastern Bering Sea water column. We will also link arbon export to primary production and benthic oxygen utilization to assess the efficiency of pelagic-benthic coupling associated wtih seasonal and interannual changes in sea ice extent.
We will use a custom-built benthic digital imaging system at shallow stations in the Bering Sea. We will then analyze the imagery to determine grouping patterns of association between infaunal animals, bottom types and environmental factors.
We will document benthic infaunal community composition and biomass as a means to determine key indicator species that should be monitored to evaluate climate change impacts on the Bering Sea ecosystem. In addition, they will analyze sediment indicators of status and trends in ecosystem health, including sediment grain size, oxygen demand, chlorophyll inventories, organic carbon content and stable carbon isotope ratios of sediment organic carbon. These can be used as ecosystem indicators of recent particle deposition, sediment processing, and the overall fertility of overlying waters.
We will investigate how the production and partitioning of spring bloom organic carbon, phytoplankton community structure, export, and water column-benthic coupling varies spatially (north-south) and temporally (seasonally and from year to year), as a function of sea ice extent. These spatial and temporal patterns are hypothesized to affect the lower trophic levels (primary producers and zooplankton) as well as upper-trophic organisms (fish, marine birds, mammals) exploited by commercial fisheries and subsistence hunters.
We will measure new (nitrate) and regenerated nitrogen product ion directly with tracer incubation measurements in ice-impacted and ice-free regions of the eastern Bering Sea shelf. This project also will measure the natural isotopic ratios of both the nitrate supply (both 15N/14N and 18O/16O) and the forms of nitrogen produced (the 15N/14N of suspended and sinking particles, dissolved organic N and ammonium). These measurements provide a passive isotope approach that will reflect the intensity of nitrate assimilation and provide a new constraint on shelf new product ion.
Denitrification in shelf sediments of the southeastern Bering Sea is estimated to remove about one third of the total nitrate supply to the Bering Shelf. We will measure profiles and fluxes of oxygen, nitrate, ammonium, phosphate and silicate. We will also collect samples for measurement of 222Rn and 210Pb profiles, from which we will calculate sediment bioirrigation rates and bulk sedimentation rates, respectively. This combination of measurements will allow us to estimate sedimentary denitrification rates, overall benthic carbon oxidation rates, macrobenthic irrigation rates and organic-matter burial rates.
We will analyze spatial and temporal patterns of abundance, biomass, community composition and productivity of sea ice algae and phytoplankton just below the ice. We will measure salinity, temperature, and nutrient concentrations in ice cores and under-ice water, as well as ice thickness, snow cover and light regime. Sedimenting material, stable isotope ratios and algal community composition will be used as three lines of evidence to follow the fate of ice algal production through the pelagic and into the benthic food web of the Bering Sea. The combined data set will allow for a refined interpretation of the relevance of the sea ice produced organic matter for the food web structure in the Bering Sea.