Quantifying Antarctic Bottom Water and North Atlantic Deep Water volumes

A near-global census of Antarctic Bottom Water (AABW) and North Atlantic Deep Water (NADW) is essayed through a nonnegative least squares analysis of conservative and quasi-conservative seawater properties. AABW thickness generally decreases from south to north, modulated by ocean bathymetry. Likewise, NADW thickness generally decreases from north to south in the Atlantic Ocean. NADW dominates below the thermocline of the Atlantic Ocean at least as far south as the subtropical gyre of the South Atlantic, with a lesser, but still significant, influence around the entire Antarctic Circumpolar Current, in the Indian Ocean, and in the Pacific Ocean. However, in the Pacific and Indian oceans, AABW dominates below the thermocline. In addition, measurable quantities of AABW reach into the abyssal North Atlantic on both sides of the mid-Atlantic Ridge. The census results suggest that AABW occupies roughly twice the volume of NADW in the three main oceans, and that AABW is in contact with roughly twice the area of the deep main ocean floor compared with NADW. However, these results are somewhat sensitive to choices of water masses, their values of seawater properties, and the weightings of the seawater properties used in the analysis.