Enhanced Diapycnal Mixing Between Water Masses in the Western Equatorial Pacific

Abstract

AbstractDiapycnal mixing of momentum and heat is crucially important to ocean dynamics, as it affects the state of the ocean and its interactions with the atmosphere. For realistic climate and circulation predictions, the magnitude and distribution of diapycnal mixing must be accurately represented in ocean models. Based on full‐depth microstructure data obtained in the western equatorial Pacific, we demonstrate that there is an enhanced diapycnal diffusivity layer nested below the thermocline of the western equatorial Pacific. Diapycnal diffusivities in this layer range from 5×10−6 to 5× 10−4 m2 s−1, one to two orders of magnitude higher than those predicted by the wave‐wave interaction theory (5 ×10−7−5×10−6 m2 s−1). These enhanced diapycnal mixings are strongly related to the South Pacific Tropical Water intrusion. Stratification is largely weakened by the South Pacific Tropical Water intrusion; thus, the shear can easily trigger shear instabilities and induce strong diapycnal mixing. This enhanced diapycnal diffusivity layer occupies the water column between ~250 and 750 m and spans from the equator to 10°N. Such widespread enhanced diapycnal mixing related to water mass intrusions may play an important role in the dynamics of the equatorial ocean, and it should be taken into account in ocean models.