Massive sargassum blooms are spreading across the Atlantic, impacting coastlines and ecosystems. Research suggests excess nutrients from human activities are fuelling this growth, with the Amazon River playing a significant role.
A new study shows that large amounts of floating seaweed, known as sargassum, are spreading across the Atlantic Ocean. This was once a rare occurrence but has now become a widespread and recurring event that spans thousands of miles, impacting coastlines, marine ecosystems, and even tourism. The research was led by scientists at Florida Atlantic University (FAU).
What is Sargassum?
Sargassum is a type of brown seaweed that floats on the ocean’s surface. It provides shelter and food to various sea creatures. Previously, scientists believed that sargassum mainly stayed in a specific region called the Sargasso Sea, located in the centre of the North Atlantic Ocean. However, recent studies suggest that sargassum has expanded far beyond the Sargasso Sea and that’s concerning. It now stretches from West Africa all the way to the Gulf of Mexico, forming what is called the Great Atlantic Sargassum Belt.
The Problem of Sargassum
This growing problem was first noticed in 2011. Since then, it has returned almost every year, except for 2013, and continues to increase. In May of this year, the sargassum belt reached a record high of 37.5 million tonnes, not including the 7.3 million tonnes that remain in the Sargasso Sea.
Removing this seaweed is expensive and it can affect tourism, fishing, and local wildlife. When it washes up on beaches, it can build up in thick layers, emit an unpleasant smell, and pose health risks. Researchers believe both natural ocean processes and human activities are contributing to this sudden increase in sargassum.
The review from FAU combines over 40 years of research, satellite images, and water chemistry data to better understand the situation. The findings indicate that excess nutrients, primarily nitrogen and phosphorus, are fuelling the growth of sargassum, allowing it to expand faster and reach greater sizes than before. These nutrients often come from sources on land, such as fertilizer, sewage and wastewater, industrial pollution, airborne particles from burning fossil fuels.
How Quickly Can Sargassum Grow?
Under ideal conditions, like warm, nutrient-rich water, it can double its size in just 11 days. Over the past few decades, the nitrogen content in sargassum has increased by more than 50%. It shows the significant impact of human pollution on the bloom. At the same time, phosphorus levels have remained the same or even slightly decreased.
Major Contributors
One important contributor is the Amazon River. It releases a large amount of nutrients into the ocean, particularly during flood seasons. Scientists found that when the Amazon floods, sargassum blooms often increase the following year. While some of the sargassum bloom may have been influenced by natural climate patterns, like the North Atlantic Oscillation in 2009-2010, scientists say the main driver behind its continued growth is human-caused pollution.
Finding Solutions
These massive sargassum blooms impact coastal communities, harm marine life, and cost millions of dollars in cleanup and lost tourism. Some piles of sargassum can also release gases that may affect human health. The researchers hope to study the causes of this issue to find solutions to reduce nutrient pollution and manage the effects of these seaweed blooms.