Modeling plankton ecosystem functioning and nitrogen fluxes in the oligotrophic waters of the Beaufort Sea, Arctic Ocean: a focus on light-driven processes
- 1Laboratoire d'Océanographie de Villefranche, BP 8, CNRS UMR7093 & Université Pierre et Marie Curie, 06238 Villefranche-sur-Mer Cedex, France
- 2Université du Sud Toulon-Var, CNRS/INSU, IRD, Mediterranean Institute of Oceanography (MIO), UM 110, 83957 La Garde, France
- 3Institut des sciences de la mer de Rimouski, Université du Québec à Rimouski, 310, allée des Ursulines, C.P. 3300 Rimouski (Quebec) G5L 3A1, Canada
- 4Aix-Marseille Université, CNRS/INSU, IRD, Mediterranean Institute of Oceanography (MIO), UM 110, 13288 Marseille, France
- 5Laboratoire d'Océanographie Microbienne, CNRS UMR7621 & Université Pierre et Marie Curie, 66650 Banyuls-sur-Mer, France
- 6Takuvik Joint International Laboratory, Université Laval (Canada) & Centre National de la Recherche Scientifique (France), Département de Biologie, 1045, Avenue de la Médecine, Quebec (Quebec), G1V 0A6, Canada
Abstract. The Arctic Ocean (AO) undergoes profound changes of its physical and biotic environments due to climate change. In some areas of the Beaufort Sea, the stronger haline stratification observed in summer alters the plankton ecosystem structure, functioning and productivity, promoting oligotrophy. A one-dimension (1-D) physical–biological coupled model based on the large multiparametric database of the Malina project in the Beaufort Sea was used (i) to infer the plankton ecosystem functioning and related nitrogen fluxes and (ii) to assess the model sensitivity to key light-driven processes involved in nutrient recycling and phytoplankton growth. The coupled model suggested that ammonium photochemically produced from photosensitive dissolved organic nitrogen (i.e., photoammonification process) was a necessary nitrogen source to achieve the observed levels of microbial biomass and production. Photoammonification directly and indirectly (by stimulating the microbial food web activity) contributed to 70% and 18.5% of the 0–10 m and whole water column, respectively, simulated primary production (respectively 66% and 16% for the bacterial production). The model also suggested that variable carbon to chlorophyll ratios were required to simulate the observed herbivorous versus microbial food web competition and realistic nitrogen fluxes in the Beaufort Sea oligotrophic waters. In face of accelerating Arctic warming, more attention should be paid in the future to the mechanistic processes involved in food webs and functional group competition, nutrient recycling and primary production in poorly productive waters of the AO, as they are expected to expand rapidly.