Isopycnal Mixing Controls Deep Ocean Tracer Distributions

C Spencer Jones, Lamont -Doherty Earth Observatory, Palisades, United States and Ryan Abernathey, Lamont-Doherty Earth Observatory, Palisades, United States
Abstract:
In coarse-resolution models, isopycnal mixing by mesoscale eddies is often parameterized using Redi’s 1982 scheme, in which an isopycnal-mixing coefficient, Kredi, is multiplied by a diffusion operator that acts in the isopycnal direction. The magnitude of Kredi is uncertain, with observational estimates ranging from 10 m2/s to 10,000 m2/s. In an idealized-geometry ocean model, Kredi is varied across a similar range without allowing the circulation to change: this leads to large changes in the ventilation of the deep ocean. Passive tracers are used to assess how Kredi influences water mass distributions, both in the modern ocean and at the LGM. In the modern ocean, increasing Kredi from 50 m2/s to 5000 m2/s leads to a 63% reduction in the amount of North Atlantic Deep Water and a doubling in the amount of Antarctic Bottom Water in the deep Pacific ocean. The effect of spatial variations in Kredi is explored.