MixED Layer hEterogeneitY

Informations

Funding country

Norway

Acronym

-

URL

-

Start date

1/1/2020

End date

12/31/2023

Budget

547,473 EUR

Fundings

Abstract

The surface of the ocean is continuously influenced by the wind, which produces waves, stirring and mixing the uppermost part of the ocean. This continuous stirring creates a surface layer in the ocean where properties such as temperature, salinity, and nutrients are uniform across the whole layer. This so-called mixed layer is a hot spot for biology and a central part of heat and momentum transfer between the ocean and the atmosphere. Properly capturing the physics of the mixed layer is, however, challenging. Today's ocean and climate models struggle to correctly reproduce the mean state of the mixed layer, such as its depth. In most cases, they don't capture this variability well enough. In the models, the mixed-layer depth and other characteristics change slowly in space, giving an overly smooth - or not heterogeneous enough - representation of this important feature of the surface ocean. The over-arching goal of MEDLEY is to investigate the heterogeneity of the mixed layer and how better to reproduce that in models. Nowhere is this heterogeneity of the mixed layer more pronounced than in the Arctic, and nowhere do our models fail as badly at reproducing it. In MEDLEY, we propose that the reason is that the sea-ice models used generally don't simulate narrow openings in the ice, called leads. The Norwegian partner in MEDLEY is the Nansen Center and the Center's sea-ice modelling group. This group has developed a new sea-ice model that reproduces leads much better than traditional models. In the project, we have used the new sea-ice model coupled with an ocean model to investigate the effects leads have on the ice and ocean. We have used the new model to gain insights into the role of leads in sea-ice formation in winter. We have shown that between 20 and 30% of the ice formed in winter is formed in leads. This fits well with observational estimates, but our estimate has the added value of showing also an increasing trend in this over the last 20 years. This localised ice formation is expected to impact the mixed layer substantially. Investigations of this aspect are currently underway. We have also used the model to understand better how the oldest Arctic sea ice is lost due to climate change. This information will also be valuable concerning the mixed layer because we expect the mixed layer to behave differently under multi-year ice compared to first-year ice. This is related to the difference in thickness between the two ice types but also difference in salinity.