Bering Sea | Climate and Oceanography
Biophysical processes influencing nutrient dynamics from the Gulf of Alaska to the Chukchi Sea Presenter: Calvin Mordy , mordy@uw.edu, CICOES, University of Washington / NOAA PMEL
Shaun Bell , shaun.bell@noaa.gov, NOAA Pacific Marine Environmental Laboratory Lisa Eisner , lisa.eisner@noaa.gov, Alaska Fisheries Science Center, NOAA Fisheries jeanette Gann , jeanette.gann@noaa.gov, NOAA Alaska Fisheries Science Center Noel Pelland , noel.pelland@noaa.gov, CICOES, University of Washington / NOAA AFSC Peter Proctor , peter.proctor@noaa.gov, CICOES, University of Washington / NOAA PMEL Phyllis Stabeno , phyllis.stabeno@noaa.gov, NOAA Pacific Marine Environmental Laboratory David Strausz , david.strausz@noaa.gov, CICOES, University of Washington / NOAA PMEL Eric Wisegarver , eric.wisegarver@noaa.gov, NOAA Pacific Marine Environmental Laboratory
The Gulf of Alaska (GOA) is the last stop on the global ocean conveyor belt which brings intermediate and deep waters from the Atlantic Ocean through the Indian Ocean and into the north Pacific Ocean, a transit during which nutrient concentrations slowly increase. Deeper water enters the Bering Sea basin through Kamchatka Strait contributing to the “sea of silica”. Shallower water that flows over the eastern Bering Sea (EBS) shelf enters through the eastern and central Aleutian Passes. As water flows over the EBS shelf, nutrient content is greatly modified through numerous physical and biological mechanisms, and these modified shelf waters eventually flow through Bering Strait and into the Chukchi Sea. These mechanisms include: the growth and retreat of seasonal sea ice; shelf-slope exchange; mixing; the diversity, abundance and seasonality of phytoplankton; and benthic respiration and denitrification. Drawing upon a compendium of nutrient data collected over 20 years in the GOA, Bering Sea, and Chukchi Sea, we map nutrient content in Alaskan waters and identify seasonal and interannual trends in nutrients in relation to these mechanisms. Discussion points include: mixing and primary production in the Aleutian Passes; the “sea of silica” in the Bering Sea basin; seasonality, anomalies, and trends of nutrients on the EBS shelf; net community production (NCP); transitory uncoupling of the marine nitrogen cycle leading to extraordinary, albeit temporary, levels of nitrite; and the spatial and temporal extent of denitrification on the shelf. While nutrients are non-conservative properties, we nevertheless use these properties as tracers of water masses and quantification including refining water types and physical processes (e.g., mixing, horizontal advection). The Bering and Chukchi Seas are extremely productive ecosystems due to the large nutrient concentrations that enter the shelf and flow northward. For instance, the magnitude of nutrients in the northeast Chukchi Sea depends upon the magnitude of nutrients in the northern Bering Sea, and on the magnitude of northward transport. Both are necessary to support nutrient flux into the Chukchi Sea. Variability we observe in the Bering and Chukchi Seas determines the extent of primary production in these regions, and primary producers serve as the energy source for the marine environment through the conversion of nutrients and sunlight into a food base that ultimately sustains all marine life.
Alaska Marine Science Symposium 2023 113
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