Antarctic Bottom Water Warming in the Brazil Basin: 1990s Through 2020, From WOCE to Deep Argo

A warming trend of 2.1 (±0.4) m °C yr −1 in bottom waters (4,500 to 5,900 dbar) spreading north from Antarctica through the Brazil Basin is quantified by comparing 2019–2020 data from a new Deep Argo regional pilot array to 1989–1995 data from full‐depth zonal and meridional hydrographic sections occupied across the basin before and during the World Ocean Circulation Experiment (WOCE). Additionally, float temperatures are about 0.046°C warmer than those from a long‐term climatology in those same bottom waters. Lower North Atlantic Deep Water in the basin shows no detectable warming, but Upper North Atlantic Deep Water exhibits evidence of warming in both analyses. The bottom‐intensified warming results in a reduction in vertical density stratification between the bottom and deep waters of about 1% per decade. This change is in contrast with the effects of surface‐intensified warming, which tends to increase vertical density stratification.