Parameterization of Submesoscale Mixed Layer Restratification under Sea Ice
- 1 March 2022
- journal article
- research article
- Published by American Meteorological Society in Journal of Physical Oceanography
- Vol. 52 (3), 419-435
- https://doi.org/10.1175/jpo-d-21-0024.1
Abstract
Commonly used parameterization of mixed layer instabilities in general circulation models (Fox-Kemper and Ferrari 2008a) was developed for temperate oceans and does not take into account the presence of sea ice in any way. However, the ice-ocean drag provides a strong mechanical coupling between the sea ice and the surface ocean currents and hence may affect mixed layer restratification processes. Here we use idealized simulations of mixed layer instabilities to demonstrate that the sea ice dramatically suppresses the eddy-driven overturning in the mixed layer by dissipating the eddy kinetic energy generated during instabilities. Considering the commonly-used viscous-plastic sea ice rheology, we developed an improvement to the existing mixed layer overturning parameterization, making it explicitly dependent on sea ice concentration. Below the critical sea ice concentration of about 0.68, the internal sea ice stresses are very weak and the conventional parameterization holds. At higher concentrations, the sea ice cover starts acting as a nearly-immobile surface lid, inducing strong dissipation of submesoscale eddies and reducing the intensity of the restratification streamfunction up to a factor of 4 for a fully ice-covered ocean. Our findings suggest that climate projection models might be exaggerating the restratification processes under sea ice, which could contribute to biases in mixed layer depth, salinity, ice-ocean heat fluxes, and sea ice cover. Commonly used parameterization of mixed layer instabilities in general circulation models (Fox-Kemper and Ferrari 2008a) was developed for temperate oceans and does not take into account the presence of sea ice in any way. However, the ice-ocean drag provides a strong mechanical coupling between the sea ice and the surface ocean currents and hence may affect mixed layer restratification processes. Here we use idealized simulations of mixed layer instabilities to demonstrate that the sea ice dramatically suppresses the eddy-driven overturning in the mixed layer by dissipating the eddy kinetic energy generated during instabilities. Considering the commonly-used viscous-plastic sea ice rheology, we developed an improvement to the existing mixed layer overturning parameterization, making it explicitly dependent on sea ice concentration. Below the critical sea ice concentration of about 0.68, the internal sea ice stresses are very weak and the conventional parameterization holds. At higher concentrations, the sea ice cover starts acting as a nearly-immobile surface lid, inducing strong dissipation of submesoscale eddies and reducing the intensity of the restratification streamfunction up to a factor of 4 for a fully ice-covered ocean. Our findings suggest that climate projection models might be exaggerating the restratification processes under sea ice, which could contribute to biases in mixed layer depth, salinity, ice-ocean heat fluxes, and sea ice cover.Keywords
Funding Information
- National Science Foundation (1829969)
This publication has 84 references indexed in Scilit:
- Eddy-Driven Stratification Initiates North Atlantic Spring Phytoplankton BloomsScience, 2012
- The Arctic’s rapidly shrinking sea ice cover: a research synthesisClimatic Change, 2011
- Friction, Frontogenesis, and the Stratification of the Surface Mixed LayerJournal of Physical Oceanography, 2008
- Characteristics of sea ice floe size distribution in the seasonal ice zoneGeophysical Research Letters, 2006
- Thin and thinner: Sea ice mass balance measurements during SHEBAJournal of Geophysical Research: Oceans, 2003
- Nonlinear stratified spin-upJournal of Fluid Mechanics, 2002
- Ekman layers and two‐dimensional frontogenesis in the upper oceanPublished by American Geophysical Union (AGU) ,2000
- Gravitational, Symmetric, and Baroclinic Instability of the Ocean Mixed LayerJournal of Physical Oceanography, 1998
- Baroclinic Jets in Confluent Flow*Journal of Physical Oceanography, 1997
- Oceanic vertical mixing: A review and a model with a nonlocal boundary layer parameterizationReviews of Geophysics, 1994