The link between isopycnal mixing and meridional overturning in a channel model of the ACC

Many recent studies have emphasized the spatially-varying geography of lateral eddy mixing in the Southern Ocean. While this topic is certainly interesting in its own right, in the large-scale context of the general circulation of the ocean, lateral /isopycnal mixing is important because of its connection to the eddy-induced meridional overturning circulation, a.k.a. the bolus transport. With accurate knowledge of eddy mixing coefficients, the bolus transport can theoretically be inferred from the mean hydrographic fields. In this study, we describe and compare various diagnostics of eddy mixing in an a numerical, eddy-resolving channel model of the ACC: flux-gradient-derived diffusivities for Ertel PV, QGPV, and buoyancy; Nakamura diffusivity; Lagrangian-based Taylor diffusivity; and estimates of diffusivity based on mixing-length arguments. The point of this exercise is to identify which diagnostics are most useful for inferring the "true" bolus transport, which is known in the model but impossible to directly observe in the real ocean.