The Buoyancy-Driven Ocean Circulation with Realistic Bathymetry

The large scale ocean circulation is forced by buoyancy fluxes, winds and fresh water. The mechanisms controlling the circulation and its stability are critical issues in understanding the present state and future changes of the climate. Although the buoyancy fluxes at the surface, and most importantly the differential heating, are a crucial part of the mechanisms driving the large scale circulation, we lack a simple dynamical framework for rationalizing the buoyancy-driven circulation. Most of our intuition is based on numerical solutions, primarily in idealized basins.

Here we examine numerical solutions of the global circulation with realistic bathymetry, driven solely by surface buoyancy forcing. Explicit wind forcing is excluded, although vertical mixing is retained. The character of the resulting flow is consistent in many ways with the observed ocean circulation. There is inflow to and sinking in the Nordic Seas, baroclinic western boundary currents and an overturning streamfunction which closely resembles those obtained in full GCMs and in observations. We also examine the complex interplay between the basins, as well as the important sites for up and downwelling. Furthermore, the solutions share many features with solutions obtained with a linear analytical model , suggesting the latter may be conceptually useful, despite lacking bathymetry. We discuss these points, as well as implications for the climate system in general.