Dear all

Apparently, from a paper by Jim Gower

Gower, J., et al. (2013). "Satellite images suggest a new Sargassum source region in 2011." Remote Sensing Letters 4(8): 764-773.

there might be a new origin for the Sargassum that arrived in the Lesser
Antilles and north of south America in 2011. Their assumption is that
the Amazon river might be the cause of large nutrient inputs that could
favour Sargassum development. [...]