Intense Observation of the Deep Convection in the North-Western Mediterranean Sea with a SEAEXPLORER Glider Fleet

A deep sea convection process particularly intense in early 2018 has been observed in the Northwestern Mediterranean Sea. The Laboratoire d’Océanographie de Villefranche-sur-Mer (LOV) and ALSEAMAR have been jointly deploying in the NiceCalvi area a fleet of SEAEXPLORER glides over several months in order to monitor this phenomenon.

In February-March 2018, intense winds and cold air temperature induced a strong evaporation and heat loss increasing the density of the surface layer until it sinks via convection to an intermediate depth. This intense mixing, revealed by a deep mixed layer, occurred in the Ligurian Sea at 50-80 km off Nice (Fig.1). Due to this intense dilution, the Levantine Intermediate Water (LIW), usually characterized by a maximum of T and S and a minimum of O2 at 300-700m lost its characteristics becoming less warm, less salty and more oxygenated. In addition to this O2 supply, the deep mixed layer induces usually a replenishment of nutrients to the surface waters which determines the onset of the following spring bloom.

The SEAEXPLORER gliders used for this campaign are equipped with Sea-Bird’s GPCTD and SBE 43F dissolved oxygen sensor, as well as other sensors such as Nortek’s AD2CP current profiler and WET Labs ECO Puck measuring chlorophyll-a, turbidity and CDOM. Among the gliders operating are some of the SEAEXPLORER X2, the second generation of SEAEXPLORER glider which has a 1000 m depth capability.