Full life-cycle observations of a deep-reaching summer submesoscale vortex

We report on novel observations of deep-reaching submesoscale eddy (SME). Open-ocean SMEs typically appear as mixed layer eddies (MLEs), with signatures rapidly decaying beneath the mixed layer depth. The observed eddy is, like MLEs, top-intensified, but its signature reaches to 300 m, over 10 times the mixed layer depth. Moreover, the eddy was detected in summer in shallow (20 m) mixed layer conditions, i.e., where relatively weak mixed layer instability is expected. Despite this, the eddy Rossby number and Richardson number are measured as O(1), and the eddy radius is 7 km, all in accordance with submesoscale flows. The vortex was detected in the East Mediterranean Sea at the foot of the continental slope offshore of Israel and was monitored via multiple in-situ platforms and via remote sensing for its full lifetime of three weeks. Based on satellite imagery, we attribute the anomalous deep-signature of the eddy to a different formation mechanism than mixed layer instability, namely formation from a meander in the regional boundary current, which has a similar depth signature. Finally, we note multiple similar events in the satellite record and discuss the border implications, including on cross-shelf material transport.