The effect of a salinity gradient on the dissolution of a vertical ice face

Abstract

We investigate experimentally the effect of stratification on a vertical ice face dissolving into cold salty water. We measure the interface temperature, ablation velocity and turbulent plume velocity over a range of salinity gradients and compare our measurements with results of similar experiments without a salinity gradient We observe that stratification acts to reduce the ablation velocity, interface temperature, plume velocity and plume acceleration. We define a stratification parameter, S = N 2 Q/Φ o , that describes where stratification will be important, where N is the Brunt-Väisälä frequency, Q is the height-dependent plume volume flux and Φ o is the buoyancy flux per unit area without stratification. The relevance of this stratification parameter is supported by our experiments, which deviate from the homogeneous theory at approximately S = 1. Finally, we calculate values for the stratification parameter at a number of ice shelves and conclude that ocean stratification will have a significant effect on the dissolution of both the Antarctic and Greenland ice sheets.

Testing a common ice‐ocean parameterization with laboratory experiments

“…A series of laboratory investigations have recently been reported that examined the ablation of a vertical ice face into a cold, salty ambient fluid [ Kerr and McConnochie , ; McConnochie and Kerr , ]. The experiments had a typical far‐field temperature of around C, far‐field salinity of 35 g/kg, and depth of 1.1 m. Measurements were made of the ablation velocity (melt rate), the temperature at the ice‐saltwater interface, and the maximum velocity in the rising meltwater plume as a function of height.…”

“…McConnochie and Kerr [] conducted experiments that included a stable salinity gradient in the far‐field fluid. Stratification was seen to reduce the ablation velocity, the plume velocity, and the interface temperature [ McConnochie and Kerr , ].…”

“…McConnochie and Kerr [] conducted experiments that included a stable salinity gradient in the far‐field fluid. Stratification was seen to reduce the ablation velocity, the plume velocity, and the interface temperature [ McConnochie and Kerr , ]. With stratification the ablation velocity decreases with height while the plume velocity increases with height, albeit at a slower rate than in the case of a homogeneous ambient fluid.…”

“…The effects of a fjord-scale circulation [Sciascia et al, 2014], the distance between two subglaical discharge sources [Cenedese and Gatto, 2016a], and the strength of a subglacial discharge flux [Cenedese and Gatto, 2016b] on the melt rate of an ice block have been investigated in this two-layer environment. A second series of experiments has examined the melt rate and meltwater plume velocity in uniform far-field conditions including a homogeneous ambient fluid [Kerr and McConnochie, 2015;McConnochie and Kerr, 2016a], a uniformly stratified ambient fluid [McConnochie and Kerr, 2016b], and a homogeneous ambient fluid with an external buoyancy source [McConnochie and Kerr, 2017]. Here we use the results from the second series of laboratory experiments to test specific assumptions of the numerical parameterization.…”

Boundary layers in turbulent vertical convection at high Prandtl number

“…This matches the prediction of who used GL theory to estimate the transition. Over such large vertical distances, other physical phenomena are likely to play an important role in the dynamics, such as ambient stratification (McConnochie & Kerr 2016) or the pressure dependence of the melt condition at the boundary of the ice (Hewitt 2020). It is therefore unlikely that a shear-driven boundary layer would develop at an ice face solely due to natural convection, without some external forcing such as subglacial discharge or a mean horizontal current.…”