Abyssal Mixing in the Southwest Pacific Basin

The Southwest Pacific Basin is an important pathway for the northward transport of cold, dense Antarctic Bottom Water (AABW) into the North Pacific Ocean. Here we examine and steady and non-steady state heat budget to quantify diapycnal and advective heat fluxes into the abyssal Southwest Pacific Basin. We find that the total deep northward mass transport into the basin between 1992 and 2017 has remained relatively constant below ϒⁿ=28.1 kg m^-3 ranging from 14.6 x10⁹ kg/s to 15.3x10⁹ kg/s, however a reduction in the northward advective heat flux below the 0.75^oC isotherm driven by the disappearance of the coldest isotherms over the last three decades is observed. The vertical diffusive heat flux derived from the heat budget agree within error estimates of diffusive heat fluxes calculated from CTD-mounted χ-pod temperature microstructure measurements, finescale strain parameterization, and vertical kinetic energy (VKE) parameterization estimated for a single zonal ship-based transect across the basin over most warmer abyssal temperature classes but diverge outside the error estimate estimates in the cold isotherms in contact with the bottom. This broad agreement of large-scale mixing estimates from abyssal heat budgets to microstructure and finescale parameterization estimates from ship-based hydrographic sections across abyssal basins is encouraging for our ability to make sustained measurements and diagnose changes in the abyssal mixing and the deep overturning circulation.