Mechanisms Leading the Decadal Variability of the Oxygen Concentration in the Tropical Pacific Ocean

Previous studies found a negative trend in oxygen concentrations in tropical regions during the last decades. The mechanisms driving the low frequency oxygen variability in the tropical Pacifc Ocean have been identified in a coupled biogeochemical circulation model, by comparing experiments forced by interannual and climatological fields. Changes in the strength of advection alone play a dominant role in driving oxygen variability in the eastern boundary upwelling systems while in the equatorial Pacific Ocean both changes in the strength of advection and diapycnal diffusion drive the oxygen variability. Changes in circulation are linked with changes in the strength of the Subtropical - Tropical Cells (STC), where subtropical mode water recirculates. The observed and simulated slowdown of the STCs by 30% from the 1960s to the 1990s caused a decrease in oxygen transport to the tropics leading to an oxygen decrease. The observed recent strengthening of the STCs leads us to expect a pause in the oxygen decrease or even an increase of tropical Pacific oxygen values in the near future.