Monitoring a large Sargassum bloom subject to a major volcanic eruption (MONISARG)

Satellite observations reveal development in early April 2021 of a substantial bloom of the macroalgae Sargassum, centred on the Lesser Antilles, coincident with a major volcanic eruption on the island of St Vincent, which began on 9 April. Since 2011, Sargassum has proliferated across the tropical Atlantic in summer months, of consequence for coastal populations through the region as it accumulates and decomposes on beaches, causing damage to health and livelihoods. Blooms are highly variable from year to year, generally drifting westward across the tropical Atlantic with prevailing winds and currents. Despite rapid growth in research on Sargassum, there remains significant uncertainty with regard to the nature, extent, longevity, timing, and driving processes of major Sargassum bloom events. These Sargassum influxes have not been subject to a continuous combined ground-based and remote monitoring campaign. For the first time, UK researchers working with colleagues in the region are ready to monitor in real time a large Sargassum influx that is coincidentally subject to a major volcanic eruption - an unexpected and remarkable combination of natural events. Based on a prototype seasonal forecast system, we anticipate that substantial quantities of the Sargassum will beach along coastlines throughout the Caribbean during June-August of 2021, motivating our campaign to monitor the bloom at sea and along coasts, targeting waters and beaches around Barbados and Jamaica. We specifically plan to develop and use high-resolution satellite images that can reveal the extent of Sargassum, down to the detail of individual mats. Identifying where these Sargassum mats are prevalent in early summer, we will then deploy GPS trackers in offshore waters around Barbados and to the east of Jamaica, to track their movement through the Caribbean and in the vicinity of Jamaica specifically. Trajectory data from our trackers will be complemented with data from the Global Drifter Programme, identifying several drifters that are currently in, or approaching, the region. At selected beaches on the east coasts of Barbados and Jamaica, where Sargassum is known to accumulate, our Project Partners will systematically monitor the extent and landing of Sargassum, using drone surveys to complement in situ sampling. While we do not know the duration of the ongoing eruption, and how the growth or mortality of Sargassum may be affected, this is a serendipitous opportunity to monitor marine and coastal environments during simultaneous extreme events.