Improved estimates of global ocean circulation, heat transport and mixing from hydrographic data

Through its ability to transport large amounts of heat, fresh water and nutrients, the ocean is an essential regulator of climate(1,2). The pathways and mechanisms of this transport and its stability are critical issues in understanding the present state of climate and the possibilities of future changes. Recently, global high-quality hydrographic data have been gathered in the World Ocean Circulation Experiment (WOCE), to obtain an accurate picture of the present circulation. Here we combine the new data from high-resolution trans-oceanic sections and current meters with climatological wind fields, biogeochemical balances and improved a priori error estimates in an inverse model, to improve estimates of the global circulation and heat fluxes. Our solution resolves globally vertical mixing across surfaces of equal density, with coefficients in the range (3-12) x 10(-4) m(2) s(-1). Net deepwater production rates amount to (15 +/- 12) x 10(6) m(3) s(-1) in the North Atlantic Ocean and (21 +/- 6) x 10(6) m(3) s(-1) in the Southern Ocean. Our estimates provide a new reference state for future climate studies with rigorous estimates of the uncertainties.