Abstract
The holopelagic macroalgae sargassum has proliferated across the tropical Atlantic since 2011, of consequence for coastal populations from West Africa to the Caribbean with limited early warning of major beaching events. As part of an interdisciplinary project, ‘Teleconnected SARgassum risks across the Atlantic: building capacity for TRansformational Adaptation in the Caribbean and West Africa’ (SARTRAC), an ensemble forecast system, SARTRAC-EFS, is providing seasonal predictions of sargassum drift. An eddy-resolving ocean model hindcast provides the winds and currents necessary to generate ensemble members. Ensemble forecasts are then obtained for different combinations of ‘windage’, the fractional influence of winds on sargassum mats, and in situ rates of growth, mortality, and sinking. Forecasts for north and south of Jamaica are evaluated with satellite-observed distributions, associated with beaching events in specific years of heavy inundation, 2015 and 2018-20. These seasonal forecasts are evaluated, on lead times of up to 180 days. Forecasts are subject to leading modes of tropical climate variability, in particular the Atlantic Meridional Mode (AMM). More accurate forecasts for a given year are obtained with ensemble members from hindcast years with a similar spring AMM-index. This is most clearly evident during negative AMM phases in spring of 2015 and 2018, when positive sea surface temperature anomalies and anomalously weak trade winds were established across the northern tropics. On this evidence, SARTRAC-EFS is potentially useful in providing early warning of high sargassum prevalence. Extended to sargassum drift off West Africa, extensive cloud cover limits availability of the satellite data needed for full application and evaluation of SARTRAC-EFS in this region, although experimental forecasts off the coast of Ghana are found highly sensitive to the windage that is associated with strong onshore winds during boreal summer. Alongside other forecast systems, SARTRAC-EFS is providing useful early warnings of sargassum inundation at seasonal timescale.
Highlights
In recent years, holopelagic sargassum macroalgae has been increasingly recorded far beyond the Sargasso Sea – named after the prevalent seaweed – in the western subtropical gyre in the North Atlantic (Fidai et al, 2020)
Initializing Sargassum to Forecast Selected Peak Events Accounting for the limits on seasonal prediction, we focus on the four peak events around Jamaica (Figure 5) to test predictions over the second and third quarters of 2015, 2018, and 2020, and over the first and second quarters of 2019
To provide an example of a summary SARTRAC-EFS forecast, we show in Figure 14 and Supplementary Table 5 the graphical and tabulated “dashboard” information that can be provided to stakeholders
Summary
Holopelagic sargassum macroalgae (seaweed) has been increasingly recorded far beyond the Sargasso Sea – named after the prevalent seaweed – in the western subtropical gyre in the North Atlantic (Fidai et al, 2020). Large quantities of sargassum notably appeared across the tropical Atlantic during the summer of 2011 (Franks et al, 2012). Proliferation of sargassum in most years since 2011 has been consequential, as it accumulates and decomposes on beaches, causing damage to ecosystems (van Tussenbroek et al, 2017) and adversely impacting human health and livelihoods (UNEP, 2018). A wide range of uses for sargassum has been identified, providing business opportunities (Desrochers et al, 2020). The unpredictable supply of sargassum is identified as one of five challenges that face stakeholders concerned with potential opportunities for sargassum reuse and valorisation (Oxenford et al, 2021). For resilient adaptation to this environmental challenge, we need to better understand and predict the annual influxes of sargassum to beaches throughout the tropical Atlantic
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
