The contrasted phytoplankton dynamics across a frontal system in the southwestern Mediterranean Sea
|Author(s)||Tzortzis Roxane1, Doglioli Andrea M.1, Barrillon Stéphanie1, Petrenko Anne A.1, Izard Lloyd2, Zhao Yuan3, D'Ovidio Francesco2, Dumas Franck4, Gregori Gérald1|
|Affiliation(s)||1 : Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, 13288, Marseille, France
2 : Sorbonne Université, CNRS, IRD, MNHN, Laboratoire d’Océanographie et du Climat: Expérimentations et Approches Numériques (LOCEAN-IPSL), Paris, France
3 : CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, People’s Republic of China
4 : SHOM, Service Hydrographique et Océanographique de la Marine, 13 rue de Chatellier, CS592803, 29228 Brest, CEDEX 2, France
|Source||Biogeosciences (1726-4189) (Copernicus GmbH), 2023 , Vol. 20 , N. 16 , P. 3491-3508|
Phytoplankton plays a major role in the ocean, being the basis of the marine food web and controlling the biogeochemical cycles. Numerical simulation have shown that finescale structures such as fronts are often suitable places for the generation of vertical velocities, transporting subsurface nutrients to the euphotic zone and thus modulating phytoplankton abundance and community structure. Since several years, observations have concentrated on nutrient fluxes along these structures. Instead, direct in situ estimations of the phytoplankton growth rates are much less numerous; although difficult to obtain, they provide a precious information on the ecosystem functioning. Here, we consider the case of a front separating two water masses characterized by several phytoplankton groups with different abundances, in the southwestern Mediterranean Sea. In order to estimate possible differences in growing rates, we used an adaptive and Lagrangian sampling strategy to measure the phytoplankton diurnal cycle in these two water masses. The use of a size-structured population model was then applied to these data to estimate the growth and division rates for each phytoplankton groups identified by flow cytometry, showing that these two population parameters are significantly different on the two sides of the front, and consistent with the relative abundances. Our results introduce a general method for estimating growth rates at frontal systems, paving the way to in situ exploration of finescale biophysical scenarios.