A 4D Variational Reanalysis of the Bering Sea Circulation in 2007-2010

Gleb Panteleev, University of Alaska Fairbanks, Fairbanks, AK, United States, Max Yaremchuk, Naval Research Lab, Stennis Space Center, MS, United States, Oceana Puananilei Francis, University of Hawaii, Honolulu, United States, Phyllis J Stabeno, NOAA Pacific Marine Environmental Laboratory, Seattle, WA, United States, Thomas Weingartner, University of Alaska Fairbanks, College of Fisheries and Ocean Sciences, Fairbanks, AK, United States and Jinlun Zhang, University of Washington, Seattle, WA, United States
Abstract:
A two-way nested 4d-variational data assimilation system is implementedin the Eastern Bering Sea (EBS) to investigate changes in circulation andthermodynamic state for a 3.8-year period. Assimilated observations includedata from 19 moorings deployed on the shelf and in the Bering Strait, 1705hydrographic stations occupied during eight surveys, and remotely sensedsea surface temperature and sea surface height (SSH) data. Validation ofthe presented 4dVar reanalysis against the output of two sequential data-assimilative systems (the Bering Ecosystem Study ice-ocean Modeling andAssimilation System (BESTMAS) and the Arctic Cap Nowcast-ForecastSystem (ACNFS)) has shown that the product is more consistent with theobserved transports in the Bering Strait and in the EBS interior both interms of their magnitude and time variability.Analysis of the data-optimized solution quantifies a sequence of wind-forced events that resulted in the anomalous heat and freshwater transportsthrough the Bering Strait, including a 28-day long flow reversal that occurredin November of 2009 and carried Siberian Coastal Current water as far asthe Gulf of Anadyr. Lagrangian study of the Arctic-bound Pacific watersindicates the extreme importance of the cross-shelf exchange along the pathof the Bering Slope Current and quantifies the spectrum of residence timesfor the waters entering EBS through Unimak Pass and through Aleutianpassages. Residence times in the EBS cold pool are diagnosed to be 2-3times longer than those in the surrounding waters.
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