Unveiling eddy subsurface evolution combining in situ and remote-sensing observation in Lagrangian tracking

Since the development of altimetric eddy detection, numerous studies assessed that mesoscale eddies have a strong signature in surface and subsurface properties, but also on ocean-atmosphere fluxes and biogeochemical variables. However previous studies largely used a composite approach, greatly inhibiting the temporal variability analysis. More recently, eddy Lagrangian tracking reveals marked temporal evolution in individual mesoscale structures. Seasonal variations in eddy-induced sea surface temperature (SST) anomalies were observed and linked with a modulation of the vertical mixing, while winter mixed layer depth (MLD) were observed to be strongly impacted by subsurface density anomalies. But this temporal evolution is complex, changing from one eddy to another, with interannual variability not yet properly documented. The DYNED atlas gathers altimetric eddy observations in Lagrangian tracks over the Mediterranean Sea, in addition to vertical measurements from Argo floats, high resolution SST (CMEMS 1/120⁰) and ERA5 reanalysis ERA5 (1/4°) offering a continuous and joint time series from 2008 to 2021. The colocation of in situ and remote-sensing data reveals that subsurface anticyclones remain cold in surface for a longer time in summer and on the other hand surface-intensified anticyclones are warmer in winter. Winter mixed layer inside-eddy is impacted by both atmospheric flux variability and subsurface density anomalies. Eddy winter SST anomaly evolution also appears as an interesting proxy for eddy MLD evolution. Mesoscale eddy subsurface evolution is complex, but the imbrication between air-sea fluxes, and heat content of the mixed layer offers a way to unveil eddy subsurface evolution. This is a further step in the retrieval of 3D structures at mesoscale, using only remote-sensing data and sparse Argo profiles.