Are near-inertial waves and instabilities with the North Equatorial Countercurrent responsible for moderate sea surface temperatures in the tropical North Atlantic?

Observational and modelling studies of the tropical ocean mixed layer have shown a dominate role of the vertical diffusive heat flux due to turbulent mixing for maintaining sea surface temperature in the tropical Atlantic. Progress has been made in identifying ocean processes responsible for enhancing turbulent mixing in the upper stratified ocean. E.g., at the equator, the vertically sheared large-scale equatorial circulation provides an energy source that can overcome stratification and drive turbulence known as deep cycle turbulence. North of the equator, near-inertial waves and Tropical Instability Waves contribute to elevated shear at the base of the mixed layer which enhances turbulent vertical diffusive heat flux out of the mixed layer. In this contribution we exploit a large observational data base (22 month-long cruises) of upper-ocean turbulence, velocity, hydrographic and wind measurements to determine the seasonal variability of turbulent vertical diffusive heat flux due to near-inertial waves in the tropical eastern North Atlantic. We find that the average mixed-layer heat loss due to near inertial waves is 35 W/m^2 with larger heat loss during boreal summer and discuss the near-inertial energy budget. Additionally, we show that enhanced upper-ocean turbulence and mixed layer heat loss also occurs due to instabilities within the North Equatorial Countercurrent during boreal summer and autumn.