Reconciling estimates of the ratio of heat and salt fluxes at the ice-ocean interface

Abstract

The heat exchange between floating ice and the underlying ocean is determined by the interplay of diffusive fluxes directly at the ice–ocean interface and turbulent fluxes away from it. In this study, we examine this interplay through direct numerical simulations of free convection. Our results show that an estimation of the interface flux ratio based on direct measurements of the turbulent fluxes can be difficult because 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. This approach allows us to reconcile previous estimates of the ice–ocean interface conditions. We find that the ratio of heat and salt fluxes directly at the interface is 83–100 rather than 33 as determined by previous turbulence measurements in the outer layer. This can cause errors in the estimated ice‐ablation rate from field measurements of up to 40% if they are based on the three‐equation formulation.

Topography generation by melting and freezing in a turbulent shear flow

“…Capturing three-dimensional topographical features, such as scallops, which do affect momentum and heat transfers (Bushuk et al. 2019), in coupled fluid–solid simulations would be a major achievement, which could complement fluid-only simulations at planar ice boundaries (Gayen, Griffiths & Kerr 2016; Keitzl, Mellado & Notz 2016 a , b ; Mondal et al. 2019; Vreugdenhil & Taylor 2019).…”

The Sensitivity of the Antarctic Ice Sheet to a Changing Climate: Past, Present, and Future

“…Beyond the diffusive layer (further away from the ice interface), fluxes are usually dominated by turbulent processes in the outer layer which has a thickness in the order of 10 m. The turbulence is due to a combination of natural convection from buoyant melt water, strong shear ambient flows, internal waves, and ocean tides (Cenedese & Gatto, 2016; Gayen et al, 2016; Keitzl et al, 2016). Next to the ice face, meltwater is positively buoyant compared to the ambient seawater and forms a convective plume.…”

Numerical Simulations of Melt-Driven Double-Diffusive Fluxes in a Turbulent Boundary Layer beneath an Ice Shelf

“…In the Martin and Kauffman (1977) experiments the density was dominated by the cooled temperature profile beneath the salt boundary layer, causing a peak in density that triggered convection. The velocity field was not examined in these experiments, however a numerical study of a melting boundary was conducted by Keitzl et al (2016), where similar convection was observed. The Keitzl et al (2016) simulations showed convective plumes descending from a region immediately below the salt boundary layer, although here the far-field temperatures were larger, varying between 10 • C and 24 • C. Martin and Kauffman (1977) did not observe staircase formation, however their experimental set-up had no ambient stratification.…”

“…The velocity field was not examined in these experiments, however a numerical study of a melting boundary was conducted by Keitzl et al (2016), where similar convection was observed. The Keitzl et al (2016) simulations showed convective plumes descending from a region immediately below the salt boundary layer, although here the far-field temperatures were larger, varying between 10 • C and 24 • C. Martin and Kauffman (1977) did not observe staircase formation, however their experimental set-up had no ambient stratification. Turner (1968) observed the progressive formation of staircases when heating a stable salt stratification from below, suggesting staircases may form in a stable stratification when double-diffusive convection is forced by a destabilising flux at the boundary.…”