Spatiotemporal Variability of Nutrients and Chlorophyll in the Chukchi Sea

Calvin Mordy, NOAA Pacific Marine Environmental Laboratory, Seattle, WA, United States, Phyllis J Stabeno, NOAA Pacific Marine Environmental Lab, Seattle, WA, United States, Carol A Ladd, NOAA Seattle, Seattle, WA, United States and Lisa B Eisner, NOAA - Alaska Fisheries Science Center, Ecosystem Monitoring and Assessment, Seattle, WA, United States
Although the Chukchi Sea is the conduit for flow from the Pacific to the Arctic basin, there is considerable heterogeneity due to variable endmembers and seasonal modification. The spatiotemporal variability of water types and associated nutrients and chlorophyll were examined using satellite-tracked drifters (drogued at ~30 m), moorings, and hydrographic data that was collected during the past 6 years (2010-2015) through multiple field programs (CHAOZ, CHAOZ-Extension, ArcWEST, EIS, and RUSALCA). Seasonal changes in bottom water nutrients and chlorophyll were observed off of Icy Cape and Wainwright from 4 years of mooring deployments. This includes nutrient replenishment throughout the winter concurrent with increasing salinity, and increased chlorophyll fluorescence along the bottom during ice retreat, most likely due to the deposition of ice algae. Associated with this event was a temporary decrease or loss of PAR, a decrease in nitrate concentrations, and oxygen super-saturation. In summer, ~40 satellite-tracked drifter trajectories and 6 repeat hydrographic transects between Point Hope and Barrow Canyon clearly delineate the pattern of flow and the boundary between the nutrient-poor Alaska Coastal Current, and the nutrient-rich water to the west (Bering Sea water and Anadyr water). In addition, higher nutrients were observed on the northern flank of Barrow Canyon. In Russian waters, chlorophyll concentrations were an order of magnitude higher than east of 168°W, and silicate limitation was common in the bottom water. These results are used to project the response of the lower trophic level to reductions in sea-ice.