Steady models of Arctic shelf-basin exchange

Abstract

Efforts to understand the Arctic system have recently focused on the role in local and global circulation of waters from the Arctic shelf seas. In this study, steady-state exchanges between the Arctic shelves and the central basins are estimated using an inverse box model. The model accounts for data uncertainty in the estimates, and quantifies the solution uncertainty. Other features include resolution of the two-basin Arctic hydrographic structure two-way shelf-basin exchange in the surface mixed layer, the capacity for shelfbreak upwelling, and recognition that most inflows enter the Arctic via the shelves. Aggregate estimates of all fluxes across the Arctic boundary, with their uncertainties, are generated from flux estimates published between 1975 and 1997. From the aggregate estimates, mass-, heat-, and salt-conserving boundary flux estimates are derived, which imply a net flux of water from the shelves to the basins of 1.2±0.4 Sv. Due primarily to boundary flux data uncertainty, constraints of mass, heat, and salt conservation alone cannot determine how much shelf-basin exchange occurs via dense overflows, and how much via the surface mixed layer. Adding δ180 constraints, however, greatly reduces the uncertainty. Dense water flux from the shelves to the basins is necessary for maintaining steady state, but shelfbreak upwelling is not required. Proper representation of external sources feeding the shelves, rather than the basins, is important to obtain the full range of plausible steady solutions. Implications of the results for the study of Arctic change are discussed.