Understanding Regional Trends in Southern Ocean Eddy Kinetic Energy

There is some evidence, based on relatively simple but high-resolution and eddy-resolving models, that increasing wind energy input will cause an increase in eddy kinetic energy (EKE) instead of overall transport over the Southern Ocean. This has become known as the eddy-saturation theory. However, due to sparsity of available measurements, quantifying and understanding EKE changes in the Southern Ocean is a major scientific challenge. Although a previous study using large area averages of satellite altimetry data suggests EKE has increased in the Pacific and Indian Ocean, more work is needed to verify this.

In this study, we first conduct a sampling experiment using a high-resolution HYCOM reanalysis run to show that EKE calculated from TOPEX/Poseidon and Jason-1,2,3 crossovers accurately represents yearly-averaged EKE changes over the Southern Ocean. We then examine the EKE changes over 15⁰ longitudinal sectors banded with by north-south boundaries determined from where EKE exceeds 94.5 cm²s^-2 and occurrence frequency is higher than 35%.

Our results suggest that there is no coherent increase in EKE over the entire Southern Ocean, which one would expect from the theory. Instead, there are only few regions where EKE is significantly increasing, which are just downstream of major topographic features where the Antarctic Circumpolar Current (ACC) jets become more turbulent. In other regions where there is no interaction of ACC jets with bathymetry, EKE does not change significantly.