Transport of Antarctic Bottom Water Entering the Brazil Basin in a Planetary Geostrophic Inverse Model

Abstract

To understand the deep ocean's role in climate change, it is critical to understand how heat and CO 2 , absorbed at the surface, make their way throughout the deep ocean over decades to centuries, transported by complex current systems and modified by deep ocean mixing. This understanding should be grounded in an observational description of existing deep ocean circulation, something that is currently unavailable, except in limited areas. Given the impracticality of directly measuring the weak, time-mean deep ocean interior currents, inverse techniques have been more widely applied. Here, an inverse method is used to study the broad interior flow of Antarctic Bottom Water (AABW) in the western subtropical South Atlantic, both in the northern part of the Argentine Basin, and as it enters the broader Brazil Basin across 30°S (Figure 1). In particular, this study adds to a well-developed and somewhat contradictory discussion of circulation in this area.The inverse model flow fields offer a new perspective on two unresolved oceanographic questions. The first question (Section 3.1) is whether some of the densest AABW, flowing northward through the Vema and Hunter channels, is sourced from the eastern Argentine Basin or supplied along a deep western boundary current (DWBC) route (e.g., see the discussion in Zenk & Visbeck, 2013). Although the eastern pathway is suggested by mudwave and tracer data (Flood & Shor, 1988) observations in this area have been limited. In their overall scheme for the Argentine Basin circulation, Coles et al. (1996) suggested a deep cyclonic recirculation in the Argentine Abyssal Plain located south and west of the Zappiola Rise at nominal 45°S, 45°W (see also Wienders et al., 2000), but were unable to definitively connect it to northward flow in the eastern Argentine Basin. McDonagh et al. (2002) examined just the northern Argentine Basin. Their conclusions emphasize flow supplying the Vema Channel from the more traditional DWBC route, and they also show a band of eastward flow south of the Rio Grande Rise (RGR) at 36°W that would argue against an eastern route.

The South Atlantic Circulation Between 34.5°S, 24°S and Above the Mid‐Atlantic Ridge From an Inverse Box Model

“…In addition to the total mass constraints, eight regional constraints across several longitude and depth ranges were introduced to reduce this underdetermined system (Table 1). These constraints have been previously applied in earlier studies of the South Atlantic Ocean as in other inverse models (Table 1; Hogg et al., 1982; Warren & Speer, 1991; Zenk et al., 1999), although the recent study of Finucane and Hautala (2022) suggested that the bottom transport estimated in the Hunter Channel by Zenk et al. (1999) could be overestimated.…”

“…In addition to the total mass constraints, eight regional constraints across several longitude and depth ranges were introduced to reduce this underdetermined system (Table 1). These constraints have been previously applied in earlier studies of the South Atlantic Ocean as in other inverse models (Table 1; Hogg et al, 1982;Warren & Speer, 1991;Zenk et al, 1999), although the recent study of Finucane and Hautala (2022) suggested that the bottom transport estimated in the Hunter Channel by Zenk et al (1999) could be overestimated. We have also included new constraints for 34.5°S from recent studies by Chidichimo et al (2021), Kersalé et al (2019), and Meinen et al (2017) using data from the moored arrays deployed along this section as part of the South Atlantic MOC Basin-wide Array (SAMBA) (Ansorge et al, 2014;Meinen et al, 2013Meinen et al, , 2017Meinen et al, , 2018.…”