February 1st to 5th 2016
Olhão, Portugal
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The impact of Amazon and Orinoco river plumes on the eutrophication of Caribbean coral reefs

Oral Presentation
Natural Resources
Wednesday, February 3, 2016 -
16:45 to 17:00

Mannoni, P-A. 1 Bouchon, C. 2

1UMR 7300 ESPACE; CNRS/University of Nice Sophia Antipolis
2UMR BOREA ; CNRS-7208/MNHN/UPMC/IRD-207/UCBN/UA

In the Caribbean, eutrophication has long been identified as a major factor of coral reefs degradation and loss of biodiversity. This nutrient enrichment is usually attributed to local anthropogenic sources, but considering that eutrophication is triggered above a threshold of nitrogen and phosphorus concentration and identified by chlorophyll concentration, the background concentration of these variables is a key element to determine the sensitivity of coral reef ecosystems to nutrient inputs.For this reason, long term biogeochemical time series have proven to be crucial for investigating these ecosystems changes supporting that satellites monitoring the oceans are a valuable tool. The Aqua satellite with its MODIS spectrometer is collecting data regularly since 2002 providing concentration on a 1 to 2 day basis. Although nitrogen and phosphorus are not directly measured, the variables available give indications on nutrients levels and include chlorophyll, particulate organic carbon, particulate inorganic carbon and absorption due to gelbstoff and detrital material. The analysis of these times series sampled upstream from the 3 islands of Martinique, Guadeloupe and St-Martin and the observation of dynamic scenes focused on the Caribbean Arch and the North Brazil Current confirm that ocean background concentrations at these locations are directly influenced by the Amazon and Orinoco river plumes. Background concentrations vary seasonally, occasionally reaching levels over eutrophication thresholds proving that local nutrient inputs are not the only factors responsible for these events. The rivers plumes, observed as precise spatio-temporal structures, fluctuate according to the seasonal cycles of the North Brazil Current, forcing the plumes along the South American coast in winter and allowing the plume to travel with the North Brazil Current rings as far as the north end of the Lesser Antilles in the warm season.
keywords: 
Coral reef eutrophication, Caribbean, North Brazil Current, Amazon, Orinoco, river plume

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