Presenter: Boer Zhang (Harvard University)

Description:
Both isopycnal and diapycnal mixing in the ocean play an important role in the ventilation of deep water, which impacts the climate system through the uptake of heat and carbon. However, observational estimates of mixing rates in the ocean interior still have large uncertainties. This research aims to explore a novel method, adapted from a framework recently developed for the stratospheric dynamics (Linz et al., 2016),  quantifying mixing rates in the ocean from the distribution of the idealized age tracer.  Based on the mathematical properties of idealized age tracer, Linz et al. found in the stratosphere that the strength of the diabatic circulation can be diagnosed from the meridional gradient of age tracer along isentropic surfaces, while the mixing along isentropic surfaces can be quantified by the gradient of age tracer across isentropic surfaces. In this research, we quantify oceanic mixing rates following the premise that along-isopycnal gradients in age are related to the diapycnal transport, while diapycnal gradients in age are related to isopycnal mixing. We examine the age tracer distribution in a MITgcm ocean-only simulation, configured in an idealized domain that includes a single basin and a zonally reentrant channel. By varying the parameterized mixing rate and examining the resulting tracer distributions in the model, we evaluate the skill of our framework in recovering the specified mixing parameters.   Linz, M., Plumb, R. A., Gerber, E. P., & Sheshadri, A. (2016). The Relationship between Age of Air and the Diabatic Circulation of the Stratosphere, Journal of the Atmospheric Sciences, 73(11), 4507-4518.