The Guiana current: a fast-lane to the Caribbean for holopelagic Sargassum contaminated in arsenic and cadmium

To date, little key information about inorganic arsenic (iAs) and cadmium (Cd) has been promulgated to help manage the massive influxes of pelagic Sargassum that have inundated the Caribbean coasts since 2011 and are causing significant environmental, health and economic impacts. In particular, the levels of iAs and Cd, which often exceed regulatory levels and limit the seaweed valorization, have not been linked to an origin or route. By analyzing a large number of samples collected at different times in Guadeloupe and Martinique, we have highlighted for the first time a route that rapidly traces back through the Guiana, North-Brazil and equatorial currents, bringing Sargassum to the Lesser Antilles in <3 months from the equator. All the Sargassum morphotypes from this problematic fast track displayed high levels of iAs and Cd, very often exceeding 40 ppm and 1 ppm, respectively. The other routes, which bring Sargassum more slowly, either from the Cape Verde basin or from the North Brazil Retroflection area, have low or intermediate levels of iAs and Cd. Following an in-depth examination of the cadmium-phosphorus relationship in the tropical Atlantic Ocean, we provide here for the first time an overview of the spatial disparities in the Cd and P composition of Sargassum.