Global and Full-depth Oceanic Heat Uptake from Argo and Repeat Hydrography

The early 21^st century's (2004-2014) warming trend of the global ocean is assessed from a blend of Argo and ship-board hydrography data, respectively used to diagnose the upper and lower half of the water column. The surface-to-bottom temperature change corresponds to a heat uptake of 0.66 ± 0.07 W m^-2, 90% of it being found above 2000m depth. The Argo-derived warming primarily reflects a large-scale downward migration of isopycnals in the southern hemisphere's extratropics and in the intermediate layers of the North Atlantic, augmented by an intrinsic warming of water masses in the tropical zone and around Antarctica. Below 2000m depth, repeat hydrography sections capture a warming rate of 0.07 ± 0.005 W m^-2, also related to significant heave motions in the southern hemisphere and North Atlantic basins, and slightly compensated for by a widespread intrinsic cooling of water masses.

Overall, the global picture of the early 21^st century changes highlights a close relationship between heave motions and oceanic heat storage, and a smaller impact of water mass property changes. One may assume this impact to increase along with the length of the observing time series, still relatively short to average out dynamical adjustments of the large-scale circulation, and to capture the timescale of 10-100 years associated with the mixing and advection of water masses from the surface layer to the ocean interior.