A variational inverse method for the reconstruction of general circulation fields in the northern Bering Sea

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Abstract
The knowledge of the dynamical structures associated with the general circulation in the Northern Bering Sea and Bering Strait is improving as numerical models together with in situ observing systems become more and more sophisticated. The ultimate objective being the design of a realistic model, it is fundamental to confront the results stemming from numerical simulations with the extensive set of hydrographic data collected since the beginning of the century. A variational inverse model has been developed for the study of continental seas with the aim of reconstructing, on the basis of local measurements (such as CTD profiles carried out at isolated hydrographic stations), continuous fields of the state variables representative of the general circulation. A numerical inverse methodology based on a variational principle and a finite element discretization has been designed to generate dynamically consistent patterns, providing a practical tool for the visualization and the mathematical interpretation of observations. Horizontal distributions of temperature, salinity, nutrients, chlorophyll and other chemical tracers, as well as the horizontal transport of water are reconstructed by using synoptic data collected from the ISHTAR NSF Research Project. Among the three water masses that can be distinguished in the region, the Anadyr Stream is obviously the main source of nutrients for the whole basin. The trace of a permanent upwelling located close to the Siberian coast can be detected on a series of general circulation patterns representative of various tracers. The strong vertical motions resulting from this upwelling allow an intensive primary productivity and determine the particularly fertile conditions for the development of the ecosystem in the Chukchi Sea.

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