Deep ocean cooling and freshening from Subpolar North Atlantic reaches Subtropics at 26.5°N

Deep water masses of the North Atlantic Ocean are formed in the subpolar regions through ocean-atmosphere interactions, imprinting unique climate signals like anomalous temperature and salinity on the deep waters that are exported to the Subtropical North Atlantic. Sustained hydrographic, mooring, and seafloor temperature surveys off Abaco Island, Bahamas at 26.5°N have illuminated significant cooling and freshening of the deep ocean (>2000 m) over the past four decades, challenging the paradigm of anticipated deep ocean warming in the Subtropical North Atlantic. Here, we discuss a linkage between the deep Subtropics and Subpolar North Atlantic, finding synchronicity between the observed freshening at 26.5°N and a multi-decadal freshening event in the subpolar basins occurring more than two decades prior. Findings hint at the likely onset of subtropical deep ocean warming and salinification in the near future, which could have notable impacts on deep ocean Atlantic heat content, circulation, and sea level changes. Over the past four decades, the deep western Atlantic Ocean at 26.5°N has experienced significant cooling and freshening, according to hydrographic observations.