Indo-Pacific Deep Water Pathways and Transports in the South Australian Basin

Abstract

A key component of the ocean's global overturning circulation is the return of deep water from the Indian and Pacific Oceans to the Southern Ocean transporting heat, carbon, and nutrients poleward and toward the ocean surface. Indian Deep Water (IDW) and Pacific Deep Water (PDW) traverse the South Australian basin as they bring high-carbon, low-oxygen water to upwell in the Southern Ocean. Historically, limited sampling of this basin has made characterizing this circulation difficult. Here, we use 20 years of data from the Biogeochemical and Core Argo arrays to identify the upper portion of deep water above 2,000 m in this basin. We map time-mean potential vorticity, oxygen, temperature, and salinity. We combine Argo profiles with trajectory data to calculate time-mean geostrophic velocities. These property and velocity maps indicate three branches of flow on isopycnals between 1,400 and 2,000 dbar: a deep eastern boundary current (DEBC) carrying warm salty IDW along the continental slope, a central southeastward pathway carrying IDW through the center of the basin, and a westward pathway carrying fresher, cooler PDW into the basin. These pathways transport 0.3 ± 0.3 Sv, 3.6 ± 2.3 Sv, and 3.4 ± 0.9 Sv, respectively, between σ₁ = 32.2 and 32.3 kg/m³ where σ₁ is the potential density referenced to 1,000 dbar. Over the full deep water layer, we estimate the transport of the deep eastern boundary current as 2.2 ± 2.1 Sv, the southeast IDW as 27 ± 17 Sv, and the westward PDW as 18 ± 6 Sv.