Collaborative Research: RAPID: Pilot observations of enhanced near-bottom equatorial turbulence

The low-latitude deep Pacific is known to be the locus of a critical abyssal upwelling branch of the overturning circulation. This upwelling requires diapycnal mixing of buoyancy downward from the less dense upper ocean. However, the diapycnal mechanisms driving this process are currently poorly understood and relatively poorly sampled. This project will leverage a funded mooring array at 140°W (part of the NSF project OCE-2048660 “Evaluating mechanisms for enhanced mixing below tropical instability waves”) to make the first full year, high-resolution equatorial observations of abyssal mixing. The funded moorings are scheduled to be deployed at the end of 2023. Instrumentation will be added to the mooring planned for 0.5 and 3°N latitutde to observe the bottom boundary layer, using point and profiling current meters and a dense positioning of temperature sensors. This pilot project will inform understanding of the low-latitude diffusive upwelling branch of the global circulation, a fundamental component of climate. The observations will be used to test several hypothesized abyssal equatorial turbulence mechanisms including: near-bottom wave trapping driven by the horizontal component of the Earth's rotation, topographic lee-wave- driven mixing, and inertial instability generated through wave-driven displacement of fluid away from the equator. The project will advance knowledge of deep equatorial dynamics and the overturning circulation to inform future observations of mixing in the deep equatorial Pacific. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.