Direct numerical simulations of diffusive staircases in the Arctic

Abstract

The vertical transport of heat by the diffusive layer in the Arctic thermocline is a critical element of the high-latitude climate, and yet, after decades of research, the extant estimates remain highly controversial. Laboratory-based estimates of vertical heat fluxes originating from the thermohaline staircases of the thermocline are typically on the order of 0.1W/m2. This study suggests that these laboratory experiments underestimate the vertical heat fluxes and exceed their calculations by nearly an order of magnitude. We first quantify the typical density ratio, step height and temperature gradient within the diffusive staircases of the Beaufort Gyre. Then, these characteristics are used as an input into a numerical model, which simulates the vertical heat fluxes driven by the double diffusive processes. The series of two-dimensional simulation runs consistently calculated heat fluxes on the order of 1W/m2. In addition, analysis of a three-dimensional simulation suggests that the three-dimensional fluxes substantially exceed their two-dimensional counterparts. A detailed analysis of the laboratory measurements suggests that the empirical coefficients estimated scaling factors from these experiments are inconsistent with the corresponding numerical simulations. These findings suggest that laboratory derived flux laws cannot be directly applied to the Arctic Ocean and that further investigations into double-diffusive convective processes are warranted.