Forecasting seasonal sargassum events across the tropical Atlantic: Overview and challenges

Abstract

Proliferation of sargassum across the tropical Atlantic since 2011 has motivated a range of forecasting methods. Statistical methods based on basin-scale satellite data are used to address seasonal timescales. Other methods involve explicit Lagrangian calculations of trajectories for particles that are representative of drifting sargassum over days-months. This computed sargassum drift is attributed to the combined action of surface currents, winds and waves, individually or in various combinations. Such calculations are undertaken with both observed surface drift and simulated currents, each involving strengths and weaknesses. Observed drift implicitly includes the action on sargassum of winds and waves, assumed equivalent between drifters and sargassum mats. Simulated currents provide large gridded datasets that facilitate computation of ensembles, enabling some quantification of the uncertainty inherent in an eddy-rich ocean, further subject to interannual variability. A more limited number of forecasts account for in situ growth or loss of sargassum biomass, subject to considerable uncertainty. Forecasts provide either non-dimensional indices or quantities of sargassum, accumulated in specified areas or counted across specified transects over a given time interval. Proliferation of different forecast methodologies may reduce uncertainty, if predictions for given seasons are consistent in broad terms, but there is scope to coordinate different approaches with common geographical foci and predicted variables, to facilitate direct inter-comparisons. In an example of forecasting westward sargassum flux into the Caribbean during the first half of 2022, challenges and opportunities are highlighted. In conclusion, prospects for closer alignment of complementary forecasting methods, and implications for sargassum management, are identified.

Seasonal variation in morphotype composition of pelagic Sargassum influx events is linked to oceanic origin

“…aspx). Forecasts from the Outlook bulletin are well suited for monitoring Sargassum within the Lesser Antilles and are in close agreement with observed influxes 56 .…”

Skillful Seasonal Forecast of Sargassum Proliferation in the Tropical Atlantic

“…This forecast extends the current Sargassum observation and forecasting services (Marsh et al., 2022; Triñanes et al., 2021; Wang & Hu, 2017), and is freely available at https://www.legos.omp.eu/sargassum/. While there are several companies or national agencies that provide short‐term forecasts or inundation reports ( Sargassum Inundation Risk weekly reports by the National Oceanic and Atmospheric Administration [https://cwcgom.aoml.noaa.gov/SIR]; monthly outlook bulletin by the University of the West Indies [https://www.cavehill.uwi.edu/cermes/research-projects/sargassum/outlook-bulletin.aspx]; SAMtool forecast by Collecte Localisation Satellites [https://datastore.cls.fr/products/samtool-sargassum-detection/]), seasonal forecasting initiatives are scarce.…”

Science and policy lessons learned from a decade of adaptation to the emergent risk of sargassum proliferation across the tropical Atlantic

“…This is further delaying development of operational monitoring frameworks. In a recent review of current seasonal forecasts of sargassum, the considerable scope for improvement in large scale monitoring and forecasting, using data from multiple sources at multiple scales, was highlighted [47].…”