The study of extreme weather events and their impact is challenging due to the difficulty involved with collecting in situ data. However, recent research has pointed out the major influence of such physical forcing events on microbiological organisms. Moreover, the occurrence of such intense events may increase in the future in the context of global change. In May 2019, an intense storm occurred in the Ligurian Sea (NW Mediterranean Sea) and was captured during the FUMSECK cruise. In situ multi-platform (vessel-mounted ADCP, thermosalinometer, fluorometer, flow cytometer, moving vessel profiler, glider) measurements along with satellite data and a 3D atmospheric model were used to characterise the fine-scale dynamics occurring in the impacted oceanic zone. The most affected area was marked by a 1°C colder water, a factor of 2 increase in surface chlorophyll a, and a factor of 7 increase in the nitrate concentration, with strong gradients with respect to the surrounding waters. Our results show that this storm led to a deepening of the mixed-layer depth from 15 to 50 m and a dilution of the deep chlorophyll maximum. As a result, the surface biomass of most phytoplankton groups increased by up to a factor of 2. Conversely, their carbon/chlorophyll ratio decreased by a factor of 2, evidencing significant changes in the phytoplankton cell composition. These results suggest that the role of storms on the biogeochemistry of the Mediterranean Sea may be underestimated and highlight the need for high-resolution measurements during these events coupling physics and biology.

Primary Presenter: Stéphanie Barrillon, CNRS - MIO (stephanie.barrillon@mio.osupytheas.fr)

Authors:

Stéphanie Barrillon, Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110 , 13288, Marseille, France  (stephanie.barrillon@mio.osupytheas.fr)

Robin Fuchs, Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110 , 13288, Marseille, France and Aix Marseille Univ, CNRS, Centrale Marseille, I2M, Marseille, France  ()

Anne Petrenko, Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110 , 13288, Marseille, France  ()

Caroline Comby, Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110 , 13288, Marseille, France  ()

Anthony Bosse, Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110 , 13288, Marseille, France  ()

Christophe Yohia, Aix Marseille Univ., Université de Toulon, CNRS, IRD, OSU Pytheas UAR 3470 , 13288, Marseille, France  ()

Jean-Luc Fuda, Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110 , 13288, Marseille, France  ()

Nagib Bhairy, Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110 , 13288, Marseille, France  ()

Frédéric Cyr, Fisheries and Oceans Canada, Northwest Atlantic Fisheries Centre, St. John’s, Canada  ()

Andrea Doglioli, Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110 , 13288, Marseille, France  ()

Gérald Grégori, Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110 , 13288, Marseille, France  ()

Roxane Tzortzis, Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110 , 13288, Marseille, France  ()

Francesco D'Ovidio, LOCEAN, UMR CNRS / Université P. et M. Curie / IRD / MNHM, F-75005 Paris, France  ()

Melilotus Thyssen, Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110 , 13288, Marseille, France  ()