Deep chlorophyll maximum and upper ocean structure interactions: Case of the Guinea Thermal Dome.

Duteil, Olaf , Lazar, Alban, Dandonneau, Yves, Wainer, Ilana and Menkes, Christophe (2009) Deep chlorophyll maximum and upper ocean structure interactions: Case of the Guinea Thermal Dome. Open Access Journal of Marine Research, 67 (2). pp. 239-271. DOI 10.1357/002224009789051191.

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Deep Chlorophyll Maximum (DCM) modifies the upper ocean heat capture distribution and thus impacts water column temperature and stratification, as well as biogeochemical processes. This energetical role of the DCM is assessed using a 1 m-resolution 1D physical-biogeochemical model of the upper ocean, using climatological forcing conditions of the Guinea Dome (GD). This zone has been chosen among others because a strong and shallow DCM is present all year round. The results show that the DCM warms the seasonal thermocline by +2°C in September/October and causes an increase of heat transfer from below into the mixed layer (ML) by vertical diffusion and entrainment, leading to a ML warming of about 0.3°C in October. In the permanent thermocline, temperature decreases by up to 2°C. The result is a stratification increase of the water column by 0.3°C m−1 which improves the thermocline realism when compared with observations. At the same time, the heating associated with the DCM is responsible for an increase of nitrate (+300%, 0.024 μM), chlorophyll (+50%, 0.02 μg l−1) and primary production (+45%: 10 mg C m−2 day−1) in the ML during the entrainment period of October. The considered concentrations are small but this mechanism could be potentially important to give a better explanation of why there is a significant amount of nitrate in the ML. The mechanisms associated with the DCM presence, no matter which temperature or biogeochemical tracers are concerned, are likely to occur in a wide range of tropical or subpolar regions; in these zones a pronounced DCM is present at least episodically at shallow or moderate depths. These results can be generalized to other thermal dome regions where relatively similar physical and biogeochemical structures are encountered. After testing different vertical resolutions (10 m, 5 m, 2.5 m, 1 m and 0.5 m), we show that using at least a 1 m vertical resolution model is mandatory to assess the energetical importance of the DCM.

Document Type: Article
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BM Biogeochemical Modeling
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1357/002224009789051191
ISSN: 0022-2402
Projects: Future Ocean
Date Deposited: 29 May 2012 08:31
Last Modified: 21 Mar 2018 10:47

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