Nitrogen and Phosphorus Budgets in the Northwestern Mediterranean Deep Convection Region. Issue 12 (5th December 2017)

• Record Type: Journal Article
• Authors: Kessouri, Faycal; Ulses, Caroline; Estournel, Claude; Marsaleix, Patrick; Severin, Tatiana; Pujo‐Pay, Mireille; Caparros, Jocelyne; Raimbault, Patrick; Pasqueron de Fommervault, Orens; D'Ortenzio, Fabrizio; Taillandier, Vincent; Testor, Pierre; Conan, Pascal
• Is Part Of: Journal of geophysical research. Volume 122:Issue 12(2017)
• Page Start: 9429
• Page End: 9454
• Publication Date: 2017-12-05
• Subjects: Mediterranean Sea -- physical‐biogeochemical modeling -- nutrient seasonal dynamics -- nitrate and phosphate budget -- N:P stoichiometry; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2016JC012665
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: The aim of this study is to understand the biogeochemical cycles of the northwestern Mediterranean Sea (NW Med), where a recurrent spring bloom related to dense water formation occurs. We used a coupled physical‐biogeochemical model at high resolution to simulate realistic 1 year period and analyze the nitrogen (N) and phosphorus (P) cycles. First, the model was evaluated using cruises carried out in winter, spring, and summer and a Bio‐Argo float deployed in spring. Then, the annual cycle of meteorological and hydrodynamical forcing and nutrients stocks in the upper layer were analyzed. Third, the effect of biogeochemical and physical processes on N and P was quantified. Fourth, we quantified the effects of the physical and biological processes on the seasonal changes of the molar NO3 :PO4 ratio, particularly high compared to the global ocean. The deep convection reduced the NO3 :PO4 ratio of upper waters, but consumption by phytoplankton increased it. Finally, N and P budgets were estimated. At the annual scale, this area constituted a sink of inorganic and a source of organic N and P for the peripheral area. NO3 and PO4 were horizontally advected from the peripheral regions into the intermediate waters (130–800 m) of the deep convection area, while organic matter was exported throughout the whole water column toward the surrounding areas. The annual budget suggests that the NW Med deep convection constitutes a major source of nutrients for the photic zone of the Mediterranean Sea. Key Points: Modeling of annual nitrogen and phosphorus cycles in the northwestern Mediterranean deep convection region for the period 2012–2013 The deep convection area was a sink of inorganic matter and a source of organic matter for the surrounding area over the period 2012–2013 The N:P ratio in the surface layer is submitted to drastic variations during deep convection and bloom transition periods