## Abstract

We estimate transport of heat, CO<latex>$_{2}$</latex> and O<latex>$_{2}$</latex> by the Atlantic's thermohaline circulation using an approach based on differences in the chemical and physical characteristics of North Atlantic Deep Water (NADW), Antarctic Intermediate Water (AAIW), and the northward return flow across the equator. The characteristics of the return-flow waters are constrained by imposing conservation of phosphate in the North Atlantic as a whole. Based on a total equatorial return flow of 13 <latex>$\times $</latex> 10<latex>$^{6}$</latex> m<latex>$^{3}$</latex> s<latex>$^{-1}$</latex>, we find that the Atlantic north of the equator is a source of 7.7 <latex>$\pm $</latex> 1.4 <latex>$\times $</latex> 10<latex>$^{14}$</latex> W to the atmosphere, a sink of 0.51 <latex>$\pm $</latex> 0.21 <latex>$\times $</latex> 10<latex>$^{14}$</latex> mol of O<latex>$_{2}$</latex>, and preindustrially was a sink of 0.33 <latex>$\pm $</latex> 0.15 <latex>$\times $</latex> 10<latex>$^{14}$</latex> mol of CO<latex>$_{2}$</latex>. Uptake of O<latex>$_{2}$</latex> and CO<latex>$_{2}$</latex> by the North Atlantic is driven mainly by thermal, as opposed to biological processes.