Connections between surface fluxes and the deep circulation in the Sea of Japan

Abstract

The extent to which seasonably variable surface fluxes and bottom friction can exert a control on the abyssal circulation above localized bottom topography is analyzed in the Japan Sea region through the use of a three‐dimensional eddy‐resolving ocean model. Our simulations show that the bottom friction exerts a first‐order control on the magnitude of the eddy‐driven deep circulation over f/H geostrophic contours, which is inversely dependent on the bottom drag, in accordance with theory. Seasonal surface flux variability acts as a modifier to this theory, depending on the timescale of active forcing relative to bottom friction spin‐down time. Possible physical mechanisms for a varying bottom drag coefficient are proposed. Winter ventilation of isopycnals during deep convection is followed by enhanced drain energy to small‐scale turbulence and strong energy dissipation in intermediate layers leading to a weakening of deep circulation that contradicts the classic ventilation theory.