The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system

Clark, DR; Widdicombe, CE; Rees, AP; Woodward, EMS. 2016 The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system. Biogeosciences, 13. 2873-2888. 10.5194/bg-13-2873-2016

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Abstract/Summary

The Lagrangian progression of a biological community was followed in a filament of the Mauritanian upwelling system, north-west Africa, during offshore advection. The inert dual tracers sulfur hexafluoride and helium-3 labelled a freshly upwelled patch of water that was mapped for 8 days. Changes in biological, physical, and chemical characteristics were measured, including phytoplankton productivity, nitrogen assimilation, and regeneration. Freshly upwelled water contained high nutrient concentrations but was depleted in N compared to Redfield stoichiometry. The highest rate of primary productivity was measured on the continental shelf, associated with high rates of nitrogen assimilation and a phytoplankton community dominated by diatoms and flagellates. Indicators of phytoplankton abundance and activity decreased as the labelled water mass transited the continental shelf slope into deeper water, possibly linked to the mixed layer depth exceeding the light penetration depth. By the end of the study, the primary productivity rate decreased and was associated with lower rates of nitrogen assimilation and lower nutrient concentrations. Nitrogen regeneration and assimilation took place simultaneously. Results highlighted the importance of regenerated NHC 4 in sustaining phytoplankton productivity and indicate that the upwelled NO3 pool contained an increasing fraction of regenerated NO3 as it advected offshore. By calculating this fraction and incorporating it into an f ratio formulation, we estimated that of the 12:38Tg C of annual regional production, 4:73Tg C was exportable.

Item Type: Publication - Article
Subjects: Chemistry
Ecology and Environment
Marine Sciences
Divisions: Plymouth Marine Laboratory > Science Areas > Marine Biochemistry and Observations
Depositing User: Darren Clark
Date made live: 25 May 2016 14:29
Last Modified: 06 Jun 2017 16:16
URI: http://plymsea.ac.uk/id/eprint/7051

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