Preprints
https://doi.org/10.5194/bg-2021-82
https://doi.org/10.5194/bg-2021-82

  06 Apr 2021

06 Apr 2021

Review status: a revised version of this preprint is currently under review for the journal BG.

Particulate organic carbon budget of the Gulf of Lion shelf (NW Mediterranean) using a coupled hydrodynamic-biogeochemical model

Gaël Many1, Caroline Ulses1,2, Claude Estournel1,2, and Patrick Marsaleix2 Gaël Many et al.
  • 1Laboratoire d’Aérologie, Université de Toulouse, CNRS, UPS, 14 Avenue Edouard Belin, 31400 Toulouse, France
  • 2LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, 14 Avenue Edouard Belin, 31400 Toulouse, France

Abstract. The Gulf of Lion shelf (NW Mediterranean) is one of the most productive areas in the Mediterranean Sea. A 3D coupled hydrodynamic-biogeochemical model is used to study the mechanisms that drive the particulate organic carbon (POC) budget over the shelf. A set of observations, including temporal series from a coastal station, remote sensing of surface chlorophyll-a, and a glider deployment, is used to validate the distribution of physical and biogeochemical variables from the model. The model reproduces well the time and spatial evolution of temperature, chlorophyll, and nitrate concentrations and shows a clear annual cycle of gross primary production and respiration. Knowing the physical and biogeochemical inputs and outputs terms, the annual budget of the POC in the Gulf of Lion is estimated and discussed. We estimate an annual net primary production of ~200 104 tC yr−1 at the scale of the shelf. The primary production is marked by a coast-slope increase with maximal values in the eastern region. Our results show that the primary production is favored by the inputs of nutrients imported from offshore waters, representing 3 and 15 times the inputs of the Rhône in terms of nitrate and phosphate. Besides, the EOFs decomposition highlights the role of solar radiation anomalies and continental winds that favor upwellings, and inputs of the Rhône River, on annual changes in the net primary production. Annual POC deposition (19 104 tC yr−1) represents 10 % of the net primary production. The delivery of terrestrial POC favored the deposition in front of the Rhône mouth and the mean cyclonic circulation increases the deposition between 30 and 50 m depth from the Rhône prodelta to the west. Mechanisms responsible for POC export (24 104 tC yr−1) to the open sea are discussed. The export off the shelf in the western part, from the Cap de Creus to the Lacaze-Duthiers canyon, represented 37 % of the total POC export. Maximum values were obtained during shelf dense water cascading events and marine winds. Considering surface waters only, the POC was mainly exported in the eastern part of the shelf through shelf waters and Rhône inputs, which spread to the Northern Current during favorable continental wind conditions. The Gulf of Lion shelf appears as an autotrophic ecosystem with a positive Net Ecosystem Production and as a source of POC for the adjacent NW Mediterranean basin. The undergoing and future increase in temperature and stratification induced by climate change could impact the trophic status of the GoL shelf and the carbon export towards the deep basin. It is crucial to develop models to predict and assess these future evolutions.

Gaël Many et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-82', Anonymous Referee #1, 22 May 2021
    • AC1: 'Reply on RC1', Gaël Many, 11 Jun 2021
  • RC2: 'Comment on bg-2021-82', Anonymous Referee #2, 23 May 2021
    • AC2: 'Reply on RC2', Gaël Many, 11 Jun 2021

Gaël Many et al.

Gaël Many et al.

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Short summary
The Gulf of Lion shelf is one of the most productive areas in the Mediterranean. A model is used to study the mechanisms that drive the particulate organic carbon (POC). The model reproduces well the annual cycle of primary production. The shelf appears as an autotrophic ecosystem with a high production and as a source of POC for the adjacent basin. The increase in temperature induced by climate change could impact the trophic status of the shelf.
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