Seasonal and interannual variability of the pelagic ecosystem and of the organic carbon budget in the Rhodes Gyre (eastern Mediterranean): influence of winter mixing
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Published:2023-08-04
Issue:15
Volume:20
Page:3203-3228
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Habib JoelleORCID, Ulses Caroline, Estournel Claude, Fakhri Milad, Marsaleix Patrick, Pujo-Pay Mireille, Fourrier MarineORCID, Coppola Laurent, Mignot Alexandre, Mortier Laurent, Conan PascalORCID
Abstract
Abstract. The Rhodes Gyre is a cyclonic persistent feature of the general circulation of the Levantine Basin in the eastern Mediterranean Sea. Although it is
located in the most oligotrophic basin of the Mediterranean Sea, it is a relatively high primary production area due to strong winter nutrient
supply associated with the formation of Levantine Intermediate Water. In this study, a 3D coupled hydrodynamic–biogeochemical model
(SYMPHONIE/Eco3M-S) was used to characterize the seasonal and interannual variability of the Rhodes Gyre's ecosystem and to estimate an annual
organic carbon budget over the 2013–2020 period. Comparisons of model outputs with satellite data and compiled in situ data from cruises and
Biogeochemical-Argo floats revealed the ability of the model to reconstruct the main seasonal and spatial biogeochemical dynamics of the Levantine
Basin. The model results indicated that during the winter mixing period, phytoplankton first progressively grow sustained by nutrient supply. Then,
short episodes of convection driven by heat loss and wind events, favoring nutrient injections, organic carbon export, and inducing light limitation
on primary production, alternate with short episodes of phytoplankton growth. The estimate of the annual organic carbon budget indicated that the
Rhodes Gyre is an autotrophic area, with a positive net community production in the upper layer (0–150 m) amounting to
31.2 ± 6.9 gCm-2yr-1. Net community production in the upper layer is almost balanced over the 7-year period by
physical transfers, (1) via downward export (16.8 ± 6.2 gCm-2yr-1) and (2) through lateral transport towards the
surrounding regions (14.1 ± 2.1 gCm-2yr-1). The intermediate layer (150–400 m) also appears to be a source of
organic carbon for the surrounding Levantine Sea (7.5 ± 2.8 gCm-2yr-1) mostly through the subduction of Levantine
Intermediate Water following winter mixing. The Rhodes Gyre shows high interannual variability with enhanced primary production, net community
production, and exports during years marked by intense heat losses and deep mixed layers. However, annual primary production appears to be only
partially driven by winter vertical mixing. Based on our results, we can speculate that future increase of temperature and stratification could
strongly impact the carbon fluxes in this region.
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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