Estimates of vertical and lateral diffusivities of heat on the West Antarctic Peninsula shelf

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Once on the West Antarctic Peninsula (WAP) shelf, nutrient-rich upper circumpolar deep water (UCDW) is modified by mixing vertically with the overlying winter water and laterally with ambient modified circumpolar deep water.  12 years of concurrent shipboard CTD and ADCP observations reveal that cross-pycnocline mixing is weak (K_z ~ 10^-5 m²s^-1) over most of the WAP but elevated (10^-4 m²s^-1) over shoaling bathymetry. Intermittent high values capable of sustaining large heat fluxes (~7-35 W m^-2) are occasionally observed.  Laterally, a glider reveals strong attenuation of the T_max core along the advective path of intrusions.  A simple analytic solution to the advection-diffusion equation reveals that the glider data are consistent with a lateral eddy diffusivity of the same order as that predicted by mixing length arguments.  We hypothesize that shear dispersion and/or interleaving act to explain the effective diffusivity.