Changes in ocean water masses reveal accumulation of the climate's excess heat in the Atlantic Ocean

Ocean warming is central to understanding climate change, because it accounts for over 90% of the excess heat in the earth system in recent decades. Observations have revealed regional patterns of warming and cooling up to ten times the global average, in particular in the North Atlantic where sub-polar cooling has been contrasted with sub-tropical warming in recent decades. Patterns of warming representative of excess heat in the ocean may be being obscured by large and compensating patterns of redistributed heat due to ocean circulation change. Here we present a novel diagnosis of the ‘excess’ and ‘redistributed’ contributions to observed regional heat content change in the Atlantic based on water mass theory and observations over the Argo period. Southward redistribution of 40±10TW at 40^oN in the Atlantic can explain the sub-polar cooling pattern and substantial portion of the sub-tropical warming. Globally 0.4±0.08PW of excess heat is spread across all ocean basins with maxima in subtropical and tropical subduction regions. This warming is largest in the in the sub-tropical North Atlantic explaining a further 40±20TW of warming between 20^oN and 40^oN and represents the largest sink (per unit area) of excess heat in the climate system.