nterannual variability of Ocean Heat Content (OHC) is intimately linked to ocean water mass changes. Water mass characteristics are imprinted at the ocean surface and are modulated by climate variability on interannual to decadal time scales. In this study, we investigate the water mass change and their variability using an isopycnal decomposition of the OHC. For that purpose, we address the thickness and temperature changes of these water masses using both individual temperature‐salinity profiles and optimal interpolated products from Argo data. Isopycnal decomposition allows us to characterize the water masses interannual variability and decadal trends of volume and OHC. During the last decade (2006–2015), much of interannual and decadal warming is associated with Southern Hemisphere Subtropical Mode Water (STMW) and Subantarctic Mode Water (SAMW), particularly in the South Pacific Eastern Subtropical Mode Water (SPESTMW), the Southeastern Indian Subantarctic Mode Water (SEISAMW) and the Southern Pacific SAMW (SPSAMW). In contrast, Antarctic Intermediate Water (AAIW) in the Southern Hemisphere and North Atlantic STMW (NASTMW) in the Northern Hemisphere have cooled. This OHC interannual variability is mainly explained by volume (or mass) changes of water masses related to the isopycnal heaving. The forcing mechanisms and interior dynamics of water masses are discussed in the context of the wind stress change and ocean adjustment occurring at interannual time scale.

Key points

Upper global Ocean mode water are the hot spots of 2006‐2015 ocean heat trend

Southern hemisphere mode water gained volume and buoyancy over 2006‐2015

Wind forcing and oceanic adjustment may partly explain the interannual mode water volume change