Ocean eddies. Image: NASA/GSFC Scientific Visualization Studio
Just like atmospheric fronts and vortices, which are the high and low-pressure areas depicted in meteorological maps influencing weather conditions, similar features exist in the ocean. Mesoscale eddies (the “little” swirls you see in the picture above) are known as the “weather” of the ocean. Eddies are found almost everywhere in the ocean, they result from many causes, including wind blowing over the water's surface, upwelling along coasts, etc. Some of the largest eddies emerge from instabilities of strongly horizontally sheared motions, particularly in boundary currents such as the Gulf Stream and frontal currents such as the Antarctic Circumpolar Current. The size of ocean mesoscale features (such as eddies) ranges from ~100 kilometres near the equator to a ~few kilometres closer to the poles and can last from a few weeks to months.
Eddies have relevance to our climate as they transport properties such as heat, salt, carbon, etc around the ocean. In many regions, including the Southern Ocean, mesoscale eddy heat transport is the dominant mechanism. Furthermore, they regulate exchanges of energy, moisture, and carbon between key climate system components (i.e., the ocean, atmosphere, and cryosphere). Our oceans absorb large amounts of anthropogenic heat and carbon and act as a strong buffer for anthropogenic climate change (A recent study about increasing ocean heat). Mesoscale eddies play the role of a “gatekeeper” for ocean heat uptake and therefore it is important to understand the mesoscale processes and how they might change in the future.
Earth system models simulate physical, chemical, and biological processes and how these work together, integrating the interactions of atmosphere, ocean, land, ice, and biosphere to estimate climate under various conditions. Due to computational expense and limitations, so far Earth system models were of coarser resolution that did not resolve mesoscale processes. The ambitious EU-funded EERIE project will develop improved Earth system models, that will help to unravel the mysteries of the mesoscale ocean processes. EERIE stands for European Eddy RIch Earth System Models. The project has 17 partners from 9 countries across Europe and Africa including the Université catholique de Louvain (UCLouvain) from Belgium, where I’m work.
Our team at UCLouvain will focus on investigating the ocean mesoscale processes in the polar regions. Previous research from UCLouvain using a regional model (not a global Earth System model) has shown that mesoscale ocean eddies play an important role in the interaction between ocean, sea ice, and atmosphere in Antarctica. Anticyclonic and cyclonic eddies have contrasting effects on sea ice and the atmosphere above, acting to freeze and sustain more sea ice or melt sea ice faster. Through the EERIE project, these processes will be investigated further at a larger scale in both the Arctic and the Antarctic and also evaluate how the mesoscale processes in the polar regions have an impact on global climate.
-Written by Stephy Libera
Further reading:
NOAA: Ocean Mesoscale Eddies [https://www.gfdl.noaa.gov/ocean-mesoscale-eddies/#:~:text=Ocean%20mesoscale%20eddies%20are%20the,2C%20squirts%20and%20spirals%20(Fig.]
Science Direct: Mesoscale Eddy [https://www.sciencedirect.com/topics/earth-and-planetary-sciences/mesoscale-eddy]
EERIE video: https://www.youtube.com/watch?v=x9sMObYqark