As Caribbean economies reel from the impacts of multiple years of sargassum invasions, a new field of research has emerged to find out what is fueling the phenomenon. The Cayman Compass talked to scientists from Barbados to Florida as they track the sargassum back to the source.

Dr. Mengqiu Wang (right) and Dr Chuanmin Hu, of the University of South Florida, led a team of researchers that used satellite imagery to identify the source of the sargassum invasions afflicting the Caribbean.

When waves of thick brown sargassum swamped the eastern coast of Barbados in 2011, it was the first warning sign that something very strange was happening in the Atlantic Ocean.

The sticky brown algae had been seen in small teardrop-shaped mats around the Caribbean Sea for decades. Clumps of it were occasionally found on beaches on the windward coasts of islands throughout the region.

But the extraordinary volumes that inundated the eastern Caribbean that year were unprecedented in recorded history. White-sand beaches were buried, turquoise bays turned a gloopy chocolate brown and some hotels were forced to close their doors to tourists as the sulphur-tinged scent of rotting vegetation festered on the coast.

The 2011 incursion turned out to be the advance column of a sargassum invasion that now plagues beaches from Mexico to the west coast of Africa.

It has also sparked a scientific mystery that continues to unravel, more than eight years later. What brought such large quantities of the thick sticky weed so far south from its normal range in the Sargasso Sea around Bermuda? What was causing it to bloom in such large quantities? How long would the invasion last and could anything be done to stop it?

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Scientists are just beginning to answer some of those questions in a new strand of oceanography that has developed to explain and attempt to mitigate the invasion.

Ground Zero

At ground zero is Professor Hazel Oxenford, a fisheries scientist based at the Cave Hill campus of the University of the West Indies in Barbados. The impact of sargassum on the island, which declared a state of emergency last year in order to mobilise the military to clear its beaches, has fundamentally altered her job description.

The campus, with Oxenford as its principal mouthpiece, now acts as a clearing house for all sargassum-related queries in the region and is one of a number of groups investigating the phenomenon.

“Nobody knew it was coming so nobody was thinking about studying it,” says Oxenford.

“The university is expected to provide the answers.”

“The key drivers of climate change and ocean nutrification are not going away.”

Hazel Oxenford
University of the West Indies

One of the most significant findings thus far is that the problem is here to stay. The seasonal cycles of sargassum inundation depend on a variety of factors, including the intensity of ocean currents. But while some years may be better than others, scientists agree that this is the “new normal”.

The sargassum bloom has been linked to run-off from farms along the Amazon River, slowly flooding the ocean with excess nutrients. Upwellings of currents off the African coast, bringing nutrient-rich water from the deep ocean to the surface, have added another potent ingredient to the mix. None of that is expected to change any time soon.

“The key drivers of climate change and ocean nutrification are not going away,” Oxenford warns.

Chuanmin Hu

The ocean’s super highway

Some of the first detective work done by scientists was to trace the sargassum invasion back to the source. Using sophisticated models to back track a route along a well-documented super highway of ocean currents that circles through the Atlantic, researchers reached a surprising conclusion: The source of the sargassum was not the eponymous Sargasso Sea but a new “accumulation zone” between Brazil and West Africa.

According to Dr. Chuanmin Hu, of the University of South Florida, there has been a fundamental change in the ocean’s chemistry that has allowed this to happen.

Since 2011, Hu and his team of researchers have been using NASA satellites to track the volume of sargassum in the Atlantic Ocean.

The results of their research, published in Science Magazine earlier this year, culminated in the discovery of the largest bloom of macro algae in the world, which they have dubbed the “Great Atlantic Sargassum Belt”.

Sea of Trouble

The Caribbean was largely free of sargassum until 2011. This satellite map shows how abundant the seaweed was across the region in May this year.

Their analysis shows that sargassum, which barely registered on satellite imagery in the central Atlantic prior to 2010, exploded to the point where an estimated 20 million tons of it, spanning 5,500 miles of ocean, were recorded in 2018.

It is the North Equatorial Current that is sweeping that biomass in great floating mats towards the Caribbean.

Hu told the Cayman Compass that he believes the research of his team will just be the beginning of an emerging new field of study.

Sargassum in the Caribbean Sea And Central Atlantic Ocean

The University of South Florida research team’s analysis identified a tipping point around 2011 where sargassum went from being almost non-existent in the central Atlantic and the Caribbean to the point where it started showing up in large quantities detectable by analysis of satellite imagery. Despite seasonal peaks and troughs it appears to have been steadily increasing since then.

“The entire scientific community needs to better understand exactly why this happened. Even though we can’t go back, we can only go forward, we must put more effort to measure the chemistry of the ocean and find out what is driving this.”

Hu and his fellow researchers are working on modelling to predict where sargassum will show up and in what quantities.

But he warns they are a long way from being able to provide forecasts that may be useful to tourism boards attempting to mitigate the impact of the unwelcome visitor. Currently, he says, they can confidently predict the overall mass of sargassum within the Caribbean from around three months out. But the vagaries of local currents and wind conditions dictate if and when it shows up on island beaches.

Funding needed for research

Back in Barbados, Oxenford, and her team are attempting to combat a different problem – a lack of funding.

Scientists at the University of South Florida used satellite imagery to demonstrate that a new “accumulation zone” had developed. Their analysis shows that sargassum had exploded to the point where an estimated 20 million tons of it, spanning 5,500 miles of ocean, were recorded in 2018. They dubbed this new zone the “great Atlantic Sargassum Belt”.

Serious research is needed into the management and mitigation of the problem. But her small team is ill-equipped to answer all the questions pinging in her inbox from across the region. A couple of factors are starting to change that dynamic.

The impact on Mexico, which has 400 miles of windward coast, and faces the potential ruin of a large part of its tourism industry, has moved the matter up the list of priorities for international policy makers. Meanwhile, the link to climate change has opened up opportunities to bid for specialist grant funding.

“This is a huge regional problem, that needs regional funding,” she says.

Oxenford and her team are in the final stages of applying for a large chunk of funding that would enable them to explore and test the best methods to suppress and intercept sargassum and to utilise it when it washes ashore.

Golden Tides

Every solution brings its own set of questions.

Sargassum has been mooted as a potential food source for livestock or even humans. But preliminary studies in Mexico found levels of arsenic and other heavy metals in the seaweed beyond what is considered safe for human or animal consumption.

Using it as fertiliser for plants is another option. But the high salt content could ruin the soil.

Sargassum boats have been developed to collect it at sea.

But in its natural habitat, out in the ocean, it acts as a refuge for all kinds of life, including sea turtle hatchlings.

One area Oxenford and her team would like to investigate is how close to shore these creatures leave the sargassum mats. Is there a zone of opportunity, where the biodiversity effectively abandons a sinking ship?

Sargassum accumulates in large quantities in a wide stretch of ocean spanning from West Africa to Brazil. A well-mapped conveyer belt of currents sweeps it from the open ocean into the Caribbean Sea. Data supplied by the University of South Florida.

With so many unanswered questions, there is room for pessimism. But both Oxenford and Hu see room for hope amid the gloom.

“We have to treat sargassum not only as a threat but as an opportunity,” says Oxenford.

“Renewable energy, bio plastics, organic fertiliser. There are a ton of things that sargassum can be used for.”

Both scientists believe a new branch of research and development, funded by a growing number of impacted countries, could yet help communities transform those pungent brown waves of sargassum into golden tides of economic opportunity.

Animated view of sargassum density in the region

An animated graphic supplied by the University of South Florida shows the explosion of sargassum across the central Atlantic and Caribbean Sea since 2011.

View animation. (13MB)

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