Preprints
https://doi.org/10.5194/bg-2018-306
https://doi.org/10.5194/bg-2018-306
02 Aug 2018
 | 02 Aug 2018
Status: this discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The manuscript was not accepted for further review after discussion.

Potential effects of deep seawater discharge by an Ocean Thermal Energy Conversion plant on the marine microorganisms in oligotrophic waters

Mélanie Giraud, Véronique Garçon, Denis De La Broise, Stéphane L'Helguen, Joël Sudre, and Marie Boye

Abstract. Installation of an Ocean Thermal Energy Conversion pilot plant (OTEC) off the Caribbean coast of Martinique is expected to use approximately 100 000 m3 h−1 of deep seawater for its functioning. This study examined the potential effects of the cold nutrient-rich deep seawater discharge on the phytoplankton community before the installation of the pilot plant. Thermal effect induced by the deep seawater upwelled by the OTEC was described using the Regional Ocean Modeling System. Numerical simulations of deep seawater discharge showed that a 3.0 °C temperature change, considered as a critical threshold for temperature impact, was never reached during an annual cycle on the top 150 m of the water column on two considered sections centered on the OTEC. The thermal effect should be limited, less than 1 km2 on the area exhibited a temperature difference of 0.3 °C (absolute value). The impact on phytoplankton of the resulting mixed deep and surface seawater was evaluated by in situ microcosm experiments. Two scenario of water mix ratio (2 % and 10 % of deep water) were tested at two incubation depths (deep chlorophyll-a maximum: DCM and bottom of the euphotic layer: BEL). The larger impact was obtained at DCM for the highest deep seawater addition (10 %), with a development of diatoms, whereas 2 % addition induced only a limited change of the phytoplankton community. This study suggested that the OTEC plant would significantly modify the phytoplankton assemblage only in the case of a discharge affecting the DCM and would be restricted to a local scale.

Mélanie Giraud, Véronique Garçon, Denis De La Broise, Stéphane L'Helguen, Joël Sudre, and Marie Boye
 
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Mélanie Giraud, Véronique Garçon, Denis De La Broise, Stéphane L'Helguen, Joël Sudre, and Marie Boye
Mélanie Giraud, Véronique Garçon, Denis De La Broise, Stéphane L'Helguen, Joël Sudre, and Marie Boye

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Short summary
Associated to transitional blue energies, first investigation of the environmental impact on the marine microorganisms of an Ocean Thermal Energy Conversion (OTEC) pilot plant before its installation, using numerical simulation and in situ experimentations. No environmental standards are available yet. Microbiodiversity can be impacted in one scenario of the OTEC functioning. Give the basis for anticipating the long-term effects of renewable marine thermal energies on the environment.
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