14 Sep 2023
 | 14 Sep 2023
Status: this preprint is open for discussion.

Two-dimensional Numerical Simulations of Mixing under Ice Keels

Sam De Abreu, Rosalie M. Cormier, Mikhail G. Schee, Varvara E. Zemskova, Erica Rosenblum, and Nicolas Grisouard

Abstract. Changes in sea ice conditions directly impact the way the wind transfers energy to the Arctic Ocean. The thinning and increasing mobility of sea ice is expected to change the size and speed of ridges on the underside of ice floes, called ice keels, which cause turbulence and impact upper-ocean stratification. However, the effects of changing ice keel characteristics on below-ice mixing are difficult to determine from sparse observations and have not been directly investigated in numerical or laboratory experiments. Here, for the first time, we examine how the size and speed of an ice keel affect the mixing of various upper-ocean stratifications using 16 two-dimensional numerical simulations of a keel moving through a two-layer flow. We find that the irreversible ocean mixing and the characteristic depth over which mixing occurs each vary significantly across a realistic parameter space of keel sizes, keel speeds, and ocean stratifications. Furthermore, we find that mixing does not increase monotonically with ice keel depth and speed, but instead depends on the emergence and propagation of vortices and turbulence. These results suggest that changes to ice keel speed and depth may have a significant impact on below-ice mixing across the Arctic Ocean, and highlight the need for more realistic numerical simulations and observational estimates of ice keel characteristics.

Sam De Abreu et al.

Status: open (until 30 Oct 2023)

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Sam De Abreu et al.

Sam De Abreu et al.


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Short summary
Arctic sea ice is becoming more mobile and thinner, which will affect the upper Arctic ocean in unforeseen ways. Using numerical simulations, we find that mixing by ice keels (ridges underlying sea ice) depends significantly on their speeds and depths, and the density structure of the upper ocean. Large uncertainties in our results highlight the need for more realistic numerical simulations and better measurements of ice keel characteristics.