Antarctic Bottom Water Warming and Circulation Slowdown in the Argentine Basin From Analyses of Deep Argo and Historical Shipboard Temperature Data Geophysical Research Letters

A decadal warming trend of 2.1 (±0.2) m°C yr−1 in Antarctic Bottom Water within the western Argentine Basin is found by comparing Deep Argo temperature profiles from 2021 to 2022 to nearby historical shipboard data from 1972 to 1998. This trend is similar in magnitude, but about 10 times more certain, than a previously published trend in the eastern Argentine Basin estimated using repeat hydrographic section data (World Ocean Circulation Experiment Section A16S) from 1989, 1995, and 2014. The present analysis also detects a warming rate in the coldest water entering the basin about double that in the interior. The observed reduction in deep meridional temperature gradient indicates a reduction in geostrophic shear, consistent with a reduced flow rate, and transport, of the coldest, deepest water entering the basin. The falling isotherms in the basin are consistent with an 0.6 × 106 m−3 s−1 reduction in inflow of the coldest waters to the basin.