Decreased Stratification in the Abyssal Southwest Pacific Basin and Implications for the Energy Budget

Abstract

As the abyssal oceans warm, stratification is also expected to change in response. This change may impact mixing and vertical transport by altering the buoyancy flux, internal wave generation, and turbulent dissipation. In this study, repeated surveys of three hydrographic sections in the Southwest Pacific Basin between the 1990s and 2010s are used to estimate the change in buoyancy frequency (Formula presented.). We find that below the (Formula presented.) °C isotherm, (Formula presented.) is on average reduced by a scaling factor of (Formula presented.), a 12% reduction, per decade that intensifies with depth. At (Formula presented.) °C, we observe the biggest change: (Formula presented.), or a 29% reduction per decade. Within the same period, the magnitude of vertical diffusive heat flux is also reduced by about (Formula presented.), although this estimate is sensitive to the choice of estimated diffusivity. Finally, implications of these results for the heat budget and global ocean circulation are qualitatively discussed.