Changes in Antarctic Bottom Water properties in the western South Atlantic in the late 1980s

Abstract

Data collected in 1988–1989, as part of the South Atlantic Ventilation Experiment, have been combined with the historical database to study the circulation and water mass variability of the abyssal water in the Argentine Basin. A map of potential temperature at 4000 m used as an indication of geostrophic shear defines a south and western intensified crescent‐shaped abyssal recirculation. Within this recirculation, and its northward extension to the Brazil Basin, Antarctic Bottom Water (AABW) properties have undergone two modifications during the 1980s: (1) The water mass cooled (0.05°C) and freshened (0.008 in salinity ratio) on surfaces of constant density. (2) The densest layer of AABW was altered to less dense water through mixing or advection out of the study area. This water mass change does not appear to have affected the flow pattern. Data collected in 1983 and 1988 to the north in the Brazil Basin show penetration of the freshwater mass in the deep western boundary current to between 18°S and 10°S, indicating very rapid propagation of the anomaly from the Argentine Basin into the Brazil Basin as a deep western boundary current. It is suggested that open ocean convective events within the Weddell Sea contributed to the change in AABW documented here.

Assimilation of Radiocarbon and Chlorofluorocarbon Data to Constrain Deep and Bottom Water Transports in the World Ocean

“…The deep water flow directions of the model in the South Atlantic are also consistent with the 3 He distributions of Rüth et al (2000), which indicate westerly flow over the Mid-Atlantic Ridge at 30°S, and little net zonal flows at 19°and 11°S. In the Argentine Basin the bottom water circulation resembles the patterns found by Peterson (1992) and Coles et al (1996).…”

Characteristics and causes of Deep Western Boundary Current transport variability at 34.5° S during 2009–2014

“…There is no question; however, that AABW is observed further north, reaching at least the subtropical North Atlantic in the western half of the Atlantic basin (e.g., Frajka-Williams et al, 2011). The hydrographic observations reported by Coles et al (1996) provide a possible answer to this conundrum, suggesting a possible interior pathway that would bring AABW to the Vema Channel along the western flank of the MidAtlantic Ridge, which would be offshore of the PIES array presented here. The bottom topography contours at AABW depth levels are nearly parallel to the PIES array, which may also complicate capturing an accurate assessment of the deepest flow layers.…”

Sensitivity of Antarctic Bottom Water to Changes in Surface Buoyancy Fluxes

“…Observations suggest a warming trend within the bottom water of the Argentine basin and Brazil basins (Coles et al 1996;Johnson and Doney 2006;Johnson et al 2014); however, there is evidence of cooling and freshening on AABW density surfaces having occurred during the 1980s in the Argentine region (Coles et al 1996). Further, while a warming trend is evident from 1989 or 1995 to 2014 in the Argentine basin, no significant warming is observed from 2005 to 2014 (Johnson et al 2014).…”