Bering Sea | Climate and Oceanography
Rate of change in bottom temperatures on the Bering and Chukchi Sea shelves and potential impact on fish assemblages Presenter: Phyllis Stabeno , phyllis.stabeno@noaa.gov, NOAA Pacific Marine Environmental Laboratory Shaun Bell , shaun.bell@noaa.gov, NOAA Pacific Marine Environmental Laboratory
Ben Laurel , ben.laurel@noaa.gov, NOAA Alaska Fisheries Science Center Calvin Mordy , calvin.w.mordy@noaa.gov, CICOES, University of Washington Thomas Van Pelt , tvanpelt@uw.edu
The Eastern Bering Sea (EBS) ecosystem is undergoing extensive warming and a reduction in the extent of winter sea ice. The summer “cold pool” (bottom temperature < 2°C) is a remnant of the prior winter’s sea ice and varies in location and extent from year to year. Changes in cold pool extent are associated with changes in the distribution of gadids in EBS, including Pacific cod ( Gadus macrocephalus ) and walleye pollock ( Gadus chalcogrammus ). The rate of bottom cooling may also have ecological impacts on these and other important fish populations. The evolution of the cold pool on the middle shelf (water depth 50 - 100 m) is straightforward. In mid-to-late fall, the water column becomes well mixed at 4-6°C in the south and 1-3°C in the north. The water column continues to cool. As winter progresses, strong northerly winds can advect ice southward. The leading edge of the ice melts, cooling and freshening the upper water column. Over a period of a week to approximately a month, the water column under the ice becomes well mixed and cools to the freezing point. Slow cooling of the bottom of the middle shelf may allow species to adapt to cold water or to retreat to warmer water. While many marine fish species can acclimate to prolonged cold-temperatures, the synthesis of antifreeze proteins can take months to build to sufficient levels ahead of winter. Consequently, acute daily drops in temperature (e.g., to < -0.6°C for gadids) are associated with large scale mortality events (aka ‘winter kills’) in species that might otherwise be considered cold-adapted. To assess how cooling rates vary across the region, we are using long-term mooring records in the Bering Sea (M2, M4, M5, M8 and M14) and the southern Chukchi Sea (C2) to quantify how rapidly the bottom cools after ice arrival. To give us a broader spatial understanding of rates of cooling, we also use data from ~35 moored bottom thermistors (PUFs) that were deployed in the last three years (2020-2022) on the EBS. The PUFs collected high-resolution data across the EBS shelf from fall through summer. In addition, PUFs were deployed in southern Chukchi in 2018 and 2020. We will present an analysis of the spatial dynamics in cold pool formation across the study region. Further research will include assimilation of the bottom temperature data into regional biophysical models, powering an improved understanding of cold pool dynamics and ecological consequences for sub-Arctic gadids now and in the future.
Alaska Marine Science Symposium 2023 37
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