From high above Earth, satellites have captured a sight so extraordinary that scientists initially thought it was a camera malfunction. Across the deep blue expanse of the Atlantic Ocean stretches a colossal brown ribbon, twisting and turning for more than 8,850 kilometres. This is not a living serpent or a strange current, but a vast bloom of brown seaweed known as Sargassum. The mass, officially called the Great Atlantic Sargassum Belt (GASB), is the largest recurring bloom of its kind ever recorded. Extending from the coast of West Africa to the Gulf of Mexico, this phenomenon has earned the nickname “The Brown Snake of the Atlantic.” A study published in Nature explores the causes of its limitless expansion.
The Great Atlantic Sargassum Belt: Causes, effects, and human influence
The Great Atlantic Sargassum Belt did not appear by chance. Its formation is the result of changes in both ocean chemistry and human activity. In recent decades, the Atlantic Ocean has received a growing amount of nutrients from land-based sources. Fertilisers used in agriculture, untreated wastewater, and urban runoff flow into rivers such as the Amazon, Congo, and Mississippi. These rivers carry nitrogen and phosphorus into the sea, acting as fertiliser for the growth of Sargassum. In addition, fine dust blown from the Sahara Desert enriches the ocean with iron, further fuelling the seaweed’s rapid expansion.Ocean circulation patterns also play an essential role in the story. Around 2010, shifts in the North Atlantic Oscillation altered wind directions and current movements, transporting Sargassum from its usual home in the Sargasso Sea into warmer, nutrient-rich tropical waters. These new conditions allowed the seaweed to grow at an unprecedented rate. Carried by the Gulf Stream and tropical trade winds, the seaweed spread across vast regions, forming the immense brown belt now visible from space. This combination of nutrient enrichment and altered ocean dynamics transformed a once-stable marine ecosystem into a sprawling, mobile seaweed mass.
From habitat to hazard: How the Sargassum invasion disrupts oceans and communities
In moderate amounts, Sargassum is a vital part of the ocean ecosystem. It provides food and shelter for fish, turtles, and other marine life. However, when the Great Atlantic Sargassum Belt grows excessively, it becomes a serious environmental problem. As enormous mats of seaweed drift towards coastlines, they block sunlight from reaching coral reefs and seagrass beds. This prevents photosynthesis, reduces oxygen in the water, and suffocates marine habitats.Once the Sargassum washes ashore, the problems multiply. As it decomposes, it releases gases such as hydrogen sulphide, ammonia, and methane. These gases produce strong odours that affect nearby communities and can irritate the eyes and lungs. Tourism-dependent regions, particularly in the Caribbean, Mexico, and parts of West Africa, suffer significant economic losses when beaches become covered in decaying seaweed. Clean-up operations are costly and ongoing, often requiring heavy machinery and continuous labour. For many coastal communities, what was once a symbol of marine life has turned into an environmental and economic burden that disrupts daily life and livelihoods.
How climate change is supercharging the Great Atlantic Sargassum Belt
The continuous expansion of the Great Atlantic Sargassum Belt is closely linked to global climate change. Rising sea surface temperatures across the tropical Atlantic have created ideal conditions for Sargassum to thrive. Warm waters accelerate its growth and reproduction, while shifting wind and current patterns affect how and where the seaweed spreads. Climate systems such as the Intertropical Convergence Zone and the Atlantic Meridional Mode influence these changes, determining the intensity and direction of the seaweed’s movement.Increased rainfall and stronger river flows caused by climate change also contribute more nutrients to the ocean. This excess nutrient input feeds further Sargassum growth. When the massive blooms die and decompose, they release greenhouse gases like methane and carbon dioxide into the atmosphere. These gases contribute to global warming, creating a repeating cycle in which climate change promotes Sargassum growth, and the decaying Sargassum feeds climate change in return. Scientists emphasise that this connection makes the Great Atlantic Sargassum Belt not only an environmental issue but also a climate concern. It highlights the direct link between human activity on land and the health of marine ecosystems thousands of kilometres away.
Turning a problem into potential: How science is finding uses for the Atlantic’s Sargassum bloom
Modern technology has transformed how researchers study the Great Atlantic Sargassum Belt. Satellites now provide near-real-time data on the size, distribution, and density of the Sargassum blooms. This has made it possible to track changes across entire ocean basins and to issue early warnings to coastal communities. By combining satellite observations with computer models of ocean currents, scientists can predict where the seaweed is likely to accumulate.Field researchers complement these satellite studies by collecting samples and analysing the chemical make-up of the Sargassum. This research helps trace nutrient sources, confirming the influence of river runoff and desert dust. Such insights are essential for understanding how human activity contributes to the problem. Predictive tools and early-warning systems now allow local authorities and tourism operators to prepare for possible beach landings before they occur.Efforts are also being made to find beneficial uses for the large quantities of collected Sargassum. Researchers are exploring its potential for biofuel production, organic fertilisers, and even biodegradable packaging materials. Some Caribbean nations have begun experimenting with sustainable harvesting methods to reduce the negative impact while turning the problem into an economic opportunity. However, large-scale management remains a challenge that requires international cooperation. Because the Great Atlantic Sargassum Belt crosses multiple national boundaries, its control and study demand shared responsibility among Atlantic nations.Also Read | Mount Everest visible from Bihar: NASA astronaut shares breathtaking image of the Himalayas from space
