Physical drivers of pelagic sargassum bloom interannual variability in the Central West Atlantic over 2010–2020

Abstract Since 2011, unprecedented pelagic sargassum seaweed blooms have occurred across the tropical North Atlantic, with severe socioeconomic impacts for coastal populations. To investigate role of physical drivers in post-2010 Central West Atlantic (CWA), conditions are examined wider using ocean and atmospheric re-analyses satellite-derived datasets. Of particular consequence growth drift patterns seasonality winds currents. Results suggest that years exceptionally large (2015, 2018), Intertropical Convergence Zone (ITCZ), an area maximum wind convergence where naturally accumulates, shifted southward, towards nutrient-rich waters Amazon River plume equatorial upwelling zone further stimulating growth. These changes associated modes natural variability notably a negative phase Meridional Mode (AMM) 2015 2018, positive Niño 2018. Negative AMM these 2 is also stronger trade enhanced northwest Africa upwelling, probably resulting southwestward nutrient transport into eastern part CWA. Moreover, contrast most years, important secondary winter took place both 2018 northern CWA, excessive wind-driven anomalously strong northwestward transport.