Reconciling heat-flux and salt-flux estimates at a melting ice-ocean interface

TL;DR

This study uses direct numerical simulations to accurately determine the heat-salt flux ratio at melting ice-ocean interfaces, revealing it is significantly higher than previous estimates and impacts melt rate calculations.

Contribution

It provides a new, more accurate flux ratio derived from simulations, improving ice-ocean interaction modeling and addressing limitations of field measurements.

Findings

Flux ratio at the interface is three times larger than previous estimates.

Interface salinities and melt rates are overestimated by up to 40% using older models.

Flux ratio depends weakly on far-field flow conditions.

Abstract

The ratio of heat and salt flux is employed in ice-ocean models to represent ice-ocean interactions. In this study, this flux ratio is determined from direct numerical simulations of free convection beneath a melting, horizontal, smooth ice-ocean interface. We find that the flux ratio at the interface is three times as large as previously assessed based on turbulent-flux measurements in the field. As a consequence, interface salinities and melt rates are overestimated by up to 40\% if they are based on the three-equation formulation. We also find that the interface flux ratio depends only very weakly on the far-field conditions of the flow. Lastly, our simulations indicate that estimates of the interface flux ratio based on direct measurements of the turbulent fluxes will be difficult because at the interface the diffusivities alone determine the mixing and the flux ratio varies with depth. As an alternative, we present a consistent evaluation of the flux ratio based on the total heat and salt fluxes across the boundary layer and reconcile the determinations of the ice-ocean interface conditions.