Research into Balearic Sea eddies. A SOCIB-led study reveals new insights into the formation and impact of strong long-lived eddies

New research led by scientists from the Balearic Islands Coastal Observing and Forecasting System (SOCIB), in collaboration with researchers at the Mediterranean Institute for Advanced Studies (IMEDEA CSIC-UIB) and the Université de Liège, reveals new insights into mesoscale eddies in the Balearic Sea.

Research into Balearic Sea eddies. A SOCIB-led study reveals new insights into the formation and impact of strong long-lived eddies

Sea surface temperature (SST) (ºC) from satellite data on 17 December of 2017. SOCIB. 

Published in the Journal of Geophysical Research: Oceans, the study analyses the formation and intensification mechanisms, as well as the thermal impact associated with two of the most significant recent strong long-lived Balearic Sea eddies, occurring in 2010 and 2017. Results have shown that northwesterly wind events and the existence of the intense Pyrenees thermal front are both necessary for their formation. While the drivers for the eddy intensification differed between both years, these eddies both created warm temperature anomalies with the characteristics of local marine heat waves in the Balearic Sea.

The ocean is in perpetual motion, not only in the form of waves and tides but also through ocean currents transporting heat and other water properties around the globe and impacting Earth's climate. These currents sometimes create circular currents known as eddies. This is the case in the Balearic Sea, where mesoscale eddies are frequently identified with radius between 10 and 100 km and life time between a few days to several weeks.

According to researchers, anticyclonic mesoscale eddies—which rotates in a clockwise direction— are often observed toward the end of summer and autumn in the area between the Catalan and Balearic coast. “These eddies are important phenomena due to their capacity to produce vertical speeds towards the deep ocean as well as accumulation zones around them, which have important implications for the ecosystems. Furthermore, their presence can also affect the global circulation of the Mediterranean Sea, since they can prevent the flow of other currents. Indeed, in some years, they become strong and persistent, thus modifying the local water mass properties,” explains Joaquín Tintoré, director of the SOCIB and co-author of the study. This was the case in 2010 and 2017, when two eddies lasted around 2 and 4 months, with a radius varying between 40 and 75 km.

Now, the generation and intensification mechanisms of these long-lived anticyclonic eddies have been studied using the high-resolution circulation model WMOP (Western Mediterranean OPerational model), and altimetry and satellite-borne sea surface temperature observations. “Numerical models are valuable tools to analyze the details of the generation and growth of intense long-lived eddies. They provide a full description of eddy evolution that allows us to evaluate eddy-mean flow interactions, conduct sensitivity tests, and relate the simulated variability to external forcings,” highlights Baptiste Mourre, head of the Modelling and Forecasting Facility at SOCIB and co-author of the study.

Results have shown that these eddies were formed and intensified through intense northwesterly wind events and the presence of a summer thermal front between the Balearic Sea and the Gulf of Lion, as well as northward inflows of relatively lower salinity waters. “We have found that the intensification process varied between both events. While in 2010 it was driven by significant salinity gradients produced by northwards inflows, in 2017 it was produced by additional intense northwesterly winds,” says Eva Aguiar, leading author of the study. Furthermore, “both long-lived anticyclonic eddies in 2010 and 2017 created long-lasting surface temperature anomalies (reaching 2.5°C during winter 2017) which have characteristics of local marine heatwaves,” she adds.

Reference article

Aguiar, E., Mourre, B., Alvera-Azcárate, A., Pascual, A., Mason, E., & Tintoré, J. Strong long-lived anticyclonic mesoscale eddies in the Balearic Sea formation, intensification, and thermal impact. Journal of Geophysical Research: Oceans, e2021JC017589.