So far, no study has been able to confirm the reason for this new migration pattern of Sargassum algae and these massive strandings in the Caribbean. Initial hypotheses were put forward in 2011 and have evolved as new data has become available (2). Various explanations have been proposed by the scientific community.
Changes in Ocean Currents
One theory behind this significant increase in Sargassum in the Caribbean arc is that, for various reasons, ocean currents are changing, leading to a greater release of Sargassum from the Sargasso Sea, which would eventually end up in the Caribbean (2).
Oil Spill in the Gulf of Mexico and Dispersant Discharge
In 2010, one year before the first massive influxes of Sargassum into the Caribbean, the «Deepwater Horizon» incident occurred. The dispersants used to combat the oil spill caused by the explosion of the oil rig are believed to have increased nutrient levels, which in turn may have triggered the proliferation of Sargassum. The algae may have subsequently traveled to the Caribbean archipelago via ocean currents. This possibility has not been proven and remains a hypothesis (2).
DEAL Map of Guadeloupe: http://www.ifrecor.com/documents/2014-note-sargasses-fmazeas-deal-unite-biodiversite-marine-maj-5fev2015.pdf
The Small Sargasso Sea
The most plausible cause would be the formation of a new «mini Sargasso Sea» in northern Brazil, which has been observed via satellite imagery (2). The emergence of this recent accumulation and proliferation is believed to be due to two factors.
A significant amount of nutrients that promote the growth of Sargassum algae is believed to have accumulated in the North Equatorial Recirculation Region (NERR), located between Brazil and Africa (2). The Congo, Amazon, and Orinoco rivers, in addition to dust from the Sahara Desert, are believed to have contributed to the accumulation of these nutrients in this area (6).
In 2010, erratic weather conditions may have contributed to the formation of this «little Sargasso Sea.» Low atmospheric pressure over the Portuguese islands of the Azores reduced the strength of westerly winds, moderated the frequency of storms in the Atlantic Ocean, and warmed the ocean waters of the NERR. As a result, the NERR is believed to have been less turbulent, which would have allowed nutrients to accumulate in that area, thereby promoting the proliferation of Sargassum algae (2).
In conclusion
Based on studies conducted by the NOAA (National Oceanic and Atmospheric Administration), scientists believe that this new phenomenon of massive sargassum algal blooms in the Caribbean arc may be the result of global warming and that it will continue in the coming years (7).
Mariska Desmarquis
References
1- French National Agency for Food, Environmental and Occupational Health & Safety (ANSES), 2017. Exposure to fumes from decomposing Sargassum seaweed in the French West Indies and French Guiana. [Online PDF]: https://www.anses.fr/fr/system/files/AIR2015SA0225Ra.pdf Page accessed on March 27, 2018.
2- FLORENNE, T. and et al., 2016. The Phenomenon of Sargassum Drift in the Caribbean and French Guiana. French Government. [Online PDF]: http://cgedd.documentation.developpement-durable.gouv.fr/documents/cgedd/010345-01_rapport.pdf Page accessed on March 27, 2018.
3- French Institute of the Sea, Toulon-Provence-Corsica Committee, 2016. Sargassum Seaweed: A Menace or an Opportunity? [Online PDF]: http://www.ifmer.org/assets/documents/files/documents_ifm/Les-algues-sargasses.pdf Page accessed on March 27, 2018.
