Reconstruction of the Eastern Bering Ice-Ocean System by Variational Assimilation of the BEST-BSIERP Data

PI: Jinlun Zhang

Tremendous amounts of in situ and satellite data have been collected for the eastern Bering sea since 2007 in the framework of the Bering Sea Ecosystem STudy (BEST) and the Bering Sea Integrated Ecosystem Research Program (BSIERP) funded by the National Science Foundation (NSF) and the North Pacific Research Board. The rich collection of BEST-BSIERP observations and other sources of data provide an excellent opportunity for synthesis through modeling and data assimilation to improve understanding of changes in the physical forcings of the Bering ecosystem in response to climate change.

This project will include the following three major goals. The first goal is to maximize the
impact of BEST-BSIERP research by synthesizing the BEST-BSIERP data and data from other sources via modeling and data assimilation. Two joint data assimilation (DA) systems will be applied to reconstruct the eastern Bering ice-ocean system for the 2007-2010 period, to conduct quality control of the reconstructed ice-ocean system, and to provide the BEST-BSIERP researchers and general scientific community with gridded sea ice and ocean parameters for Bering ecosystem studies. The first DA system will be configured for the eastern Bering Sea with a resolution of 18 km. The goal of applying this DA system is to reconstruct the large-scale circulation in the eastern Bering Sea and to accurately describe the large-scale processes in the South Eastern Bering Sea Shelf (SEBSS). The second DA will be configured
for the eastern Bering Sea Shelf with an eddy-permitting resolution of 5-10km. This system will explicitly resolve eddy and tidal dynamics, and thus will lead to a better understanding of the nonlinear interaction processes between the deep basin and the shelf region of the eastern Bering Sea.

The second goal of this project is to analyze the obtained data sets for the eastern Bering Sea and the SEBSS, and identify the processes important for causing the observed changes. In particular, the variability of the SEBSS state during the investigated period will be studied and compared with results obtained using high-resolution mean climate state from the Oceanographic Atlas of the Bering Sea.

The third goal of this project is to determine the impact of assimilating data with different origins on the estimation of near-surface transports of volume, momentum, heat, and material. This goal will be accomplished through adjoint sensitivity analysis and a conventional DA experiment. An interactive adjoint sensitivity analysis webpage will also be developed to help optimize Bering Sea mooring observations in future studies.

This research will improve understanding of observed climate changes and interactions between sea ice and ocean processes in the Bering Sea. Heat and freshwater balance in the region and water mass transformation along the Pacific Water pathway will be analyzed. Statistical and empirical orthogonal function (EOF) analyses of the reconstructed circulation patterns will help to identify the different circulation regimes and will link them to the latest environmental changes in the Bering Sea.