Abstract:
socioeconomic impacts for coastal populations. To investigate the role of physical drivers in post-2010 sargassum blooms
in the Central West Atlantic (CWA), conditions are examined across the wider tropical North Atlantic, using ocean and
atmospheric re-analyses and satellite-derived datasets. Of particular consequence for the growth and drift of sargassum
are patterns and seasonality of winds and currents. Results suggest that in years of exceptionally large sargassum blooms
(2015, 2018), the Intertropical Convergence Zone (ITCZ), an area of maximum wind convergence where sargassum naturally
accumulates, shifted southward, towards nutrient-rich waters of the Amazon River plume and the equatorial upwelling
zone further stimulating sargassum growth. These changes are associated with modes of natural variability in the tropical
Atlantic, notably a negative phase of the Atlantic Meridional Mode (AMM) in 2015 and 2018, and a positive phase of the
Atlantic Niño in 2018. Negative AMM in these 2 years is also associated with stronger trade winds and enhanced northwest
Africa upwelling, probably resulting in stronger southwestward nutrient transport into the eastern part of CWA. Moreover,
in contrast with most years, important secondary winter blooms took place in both 2015 and 2018 in the northern part of
CWA, associated with excessive wind-driven equatorial upwelling and anomalously strong northwestward nutrient transport.
