Regional Trends in Southern Ocean Eddy Kinetic Energy

Abstract Previous model‐based studies and observation‐based studies suggest that increasing wind energy input into the Southern Ocean will primarily cause increases in eddy kinetic energy (EKE) with no significant change in the mean circulation, a result that has been named the “eddy‐saturation” hypothesis. However, due to the sparsity of the available observations, quantifying and understanding regional EKE changes in the Southern Ocean is challenging. In this study, we examine regional trends in the Southern Ocean EKE using altimetry crossover measurements and an ocean reanalysis product to quantify if undersampling by altimetry will bias EKE trend estimates and to test if previously observed EKE trends are homogenous throughout the Southern Ocean or concentrated in a few regions. To verify that the EKE computed from altimetry crossovers accurately represents yearly averaged EKE over the Southern Ocean, we first conduct a sampling experiment with the HYCOM Global Ocean Forecasting System 3.1 ocean reanalysis. We find that the crossover sampling is sufficient to represent the yearly averaged EKE when averaged over sectors of at least 30° of longitude. We find no coherent increase in EKE over the entire Southern Ocean from altimetry crossover measurements, but instead find significant EKE increase over only one region, primarily south of New Zealand and downstream of the Campbell Plateau. We conclude that the EKE change in the Southern Ocean is not as homogenous as implied by previous studies and more work is needed to understand if this is consistent with the “eddy‐saturation” hypothesis or related more to local dynamics.