Title: Elevated Diapycnal Mixing by a Subthermocline Eddy in the Western Equatorial Pacific

Journal: Geophysical Research Letters, 46: 2628-2636

Authors: ZHANG Z. -W., Z. -Y. Liu, K. Richards, S. Gong, W. Zhao*, J. -W. Tian, X. -D. Huang, and C. Zhou

Abstract: Diapycnal mixing plays an important role in modulating upper‐ocean heat content of the western equatorial Pacific (WEP) that profoundly impacts the global climate. Given the sparsity of long‐term in situ observations, the mechanisms driving thermocline mixing in the WEP remain poorly understood. Here, based on yearlong mooring measurements in the WEP, we first report that the occurrence of shear instability was significantly enhanced by an anticyclonic subthermocline eddy (STE). As a result of strong subinertial velocity shear and weakened stratification associated with the STE, the Richardson number was decreased below 1/4 and the estimated diapycnal diffusivity was increased by 400%. Moreover, contrary to surface‐intensified anticyclonic eddies, the STE appeared to act as a dynamic barrier for downward penetration of wind-generated near-inertial energy, which may also fertilize mixing near the upper thermocline. Given the frequent occurrence of STEs, they may play a pivotal role in driving thermocline mixing in the WEP.