Inverse Modeling of the Deep Brazil Basin Circulation

Abstract

The pathways of seawater through the deepest parts of the world ocean are relatively unknown but critical to understanding how the ocean distributes heat that is taken up at the surface. The deep and abyssal circulation across 30°S in the Brazil Basin is inferred from multiple decades of full-depth CTD data by a potential vorticity and salt conserving inverse model which parameterizes diapycnal mixing as a function of bathymetric roughness. The basin exhibits strong diapycnal mixing especially towards its boundaries, and weak lateral mixing. The largest transport outside of boundary currents across 30°S is the southward flow of Antarctic Bottom Water (AABW) at a rate of ~10 10 kg s -1 . AABW flows northward through the Vema Channel and southward in the interior of the basin creating a cyclonic circulation around the Rio Grande Rise. Flow along -30°S is westward in the Antarctic Intermediate Water (AAIW) and Upper Circumpolar Deep Water (UCDW), and eastward in the North Atlantic Deep Water (NADW).