Heat transport into the interior ocean induced by water-mass subduction

The subduction of oceanic water masses provides a crucial pathway for anthropogenic heat to enter the subsurface ocean, thereby shaping deep-reaching warming signatures. Analyzing data from eight ocean and atmosphere reanalysis datasets, we show that the average annual subduction rate of the global ocean (excluding 10° S–10° N) is 312.4 ± 27.9 Sv, resulting in a mean heat transport of 20.2 ± 2.1 PW towards the subsurface ocean. This subduction-driven heat transport has exhibited an increase of 0.09 ± 0.08 PW/decade since 1970. The increase predominantly stems from the overall enhancement of subduction within the latitudes of 30° S–50° S, dictated by intensified westerly winds that lead to the deepening of the local mixed layer depth. Our findings underscore the essence of wind-driven changes in the Southern Ocean subduction, which wield considerable influence over the global climate by regulating the vertical transport of heat and carbon from the sea surface to the deep waters.