Southern Ocean drivers of Equatorial Pacific O2 changes over the 21st century in a large ensemble suite with GFDL's ESM2M earth system model

Future evolution of the degree of oxygenation of the ocean expected to have important implications for future ocean ecosystem health. Recently published analyses of changes in ocean oxygen inventories in the current generation of earth system models reveal important projected differences in the equatorial Pacific (EQPAC; 15°N-15°S) oxygen inventories in response to 21^stcentury climate perturbations. For the EQPAC, there is disagreement in not only the amplitude of oxygen response, but also the sign of response. This degree of uncertainty in model-derived projections underscores the need for improved understanding of the oceanic controls of oxygen inventories in the EQPAC.

Here we consider the mechanistic controls on EQPAC oxygen inventories using a large 30-member ensemble suite with GFDL’s ESM2M under historical/RCP8.5 forcings over 1950-2100. Our main finding is that 21^st century oxygen perturbations within the EQPAC are dominated by deep ocean changes, reflecting non-local perturbations over the Southern Ocean that are propagated into the low latitudes with planetary waves. The role of coastal and equatorial Kelvin waves in a teleconnected EQPAC response from the Southern Ocean is consistent with the fact that projected decreases in oxygen concentrations and inventories occurs for waters whose ventilation timescale is significantly longer than the duration of the historical/RCP8.5 perturbations. Five members of the full suite of 30 runs exhibit polynyas centered near the year 2000, and these polynya members exhibit a decreased rate of de-oxygenation in the EQPAC region relative to the 25 non-polynya members. The polynya response in the tropics also manifests itself through the propagation of planetary waves from the Southern Ocean into the EQPAC region.