The Sargasso Sea Is the Only One of Its Kind and Not Because Its Waters Are So Blue

In the vast expanse of Earth’s oceans, the Sargasso Sea stands as a unique and enigmatic entity, distinguished not only by its mesmerizing azure waters but by a myriad of fascinating features that set it apart from any other marine region on the planet.

Seas, smaller in size compared to oceans, are commonly situated at the interface of land and ocean. They are typically partially surrounded by land. Well, typically – except for one.

Named after the genus of seaweed that floats on its surface, the Sargasso Sea is the only sea in the world that has no land boundaries, and is defined entirely by ocean currents. It is located in the North Atlantic Ocean, and is surrounded by a clockwise-circulating system of currents called the North Atlantic Gyre. These currents are the Gulf Stream on the west, the North Atlantic Current on the north, the Canary Current on the east, and the North Atlantic Equatorial Current on the south.

As boundary currents define this region, its borders are dynamic (changing) and generally correlate with the Azores High Pressure Center – a large subtropical semi-permanent center of high atmospheric pressure typically found south of the Azores in the Atlantic Ocean.

While these currents contribute marine plants, debris, and lately, trash, to the sea, the ocean water in the Sargasso Sea stands out due to its deep blue hue and remarkable clarity, providing underwater visibility of up to 60 meters (200 feet). In fact, it’s the gyre surrounding the sea that makes for this excellent visibility as the sea itself is characterized by weak currents. On its surface, the seaweed Sargassum forms a distinctive brown layer that covers large areas of the sea, and creates a rich habitat for many marine animals.

The Sargasso Sea is not only remarkable for its blue waters and its seaweed, but also for its history and its role in marine ecology. It is known for capturing the public imagination, and is featured in numerous literary and artistic works, as well as in popular culture.

The first written mention of the Sargasso Sea is from Christopher Columbus in 1492, when he encountered it during his voyage to the New World. He noticed that the wind was very calm in this region, which made sailing difficult. However, the presence of the seaweed indicated the nearness of land, motivating Columbus to persist. That said, many early navigators harbored an (unjustified) apprehension of getting ensnared in the expanse of drifting vegetation, or that it would hide shallow waters that could damage their vessel.

Columbus was not the first to discover the Sargasso Sea. Some scholars believe that ancient mariners, such as the Phoenicians and the Carthaginians, knew about it and used it as a navigational reference. There is also evidence that Arab explorers reached this sea in the 12th century, also describing it as a place covered by seaweed.

The Sargasso Sea became a source of mystery and legend for many centuries. Some stories claimed that it was haunted by ghost ships, such as the Flying Dutchman, or that it was inhabited by monstrous creatures, such as sea serpents and giant octopuses. Some writers, such as Jules Verne and Edgar Allan Poe, used the Sargasso Sea as a setting for their novels, adding to its mystique and allure.

The Sargasso Sea also attracted scientific interest and exploration. In the 17th century, naturalists began to study the seaweed and its associated fauna. In the 19th century, oceanographers mapped the currents and depths of the sea. In the 20th century, biologists discovered that the Sargasso Sea was the spawning ground for several species of now threatened and endangered eels, which migrate thousands of kilometers from Europe and North America to reproduce there. The Sargasso Sea also became a site for deep-sea diving and observation, as well as for oceanographic data collection.

The Sargasso Sea is one of the most productive and diverse ecosystems in the ocean. Sargassum, the seaweed that dominates its surface, is a type of brown macroalgae that provides food, shelter, and nursery grounds for many animals, such as fish, crustaceans, mollusks, turtles, birds, and mammals. Some of these animals are endemic to the Sargasso Sea, meaning they are found nowhere else in the world. The Great Atlantic Sargassum Belt located at the sea’s southern currents is the largest such mass and the largest macroalgae bloom in the world.

These days, however, there appears to be too much sargassum in the water from time to time. In 2015, numerous Caribbean islands faced an invasion of sargassum, which, when washed ashore, causes environmental and economic concerns, with residents expressing worries about its impact on both the environment and their health.

This proliferation of sargassum actually serves as a defense mechanism against the mistreatment inflicted by humans on marine and coastal ecosystems. It is a clear warning to curtail or eliminate anthropogenic actions that harm marine organisms.

The Sargasso Sea is also a vital corridor for many migratory species, such as whales, sharks, dolphins, tuna, marlin, and birds. These animals use the sea as a feeding ground or a resting place during their long journeys across the ocean. Some of these species are endangered or threatened by overfishing, pollution, or climate change.

Indeed, the Sargasso Sea faces many challenges and risks in the 21st century, despite its importance and beauty. One of them is pollution. In fact, the North Atlantic Gyre, and in it, the sea is home to the North Atlantic garbage patch, measuring hundreds of kilometers across, with a density of more than 200,000 pieces of debris per square kilometer. Sadly, the seaweed accumulates plastic debris and other garbage that are carried by the currents from different parts of the world. This can harm or kill animals that ingest or get entangled in the trash.

The seaweed also absorbs chemicals and metals that are released into the ocean by human activities, such as agriculture, industry, or mining. These pollutants can affect the health and reproduction of the seaweed and its associated organisms.

Another threat is climate change. The rising temperatures and changing patterns of wind and precipitation can alter the distribution and abundance of the seaweed and its inhabitants. The increased levels of carbon dioxide in the atmosphere can also make the ocean more acidic, which can reduce the growth and survival of some organisms, such as corals and shellfish.

A third threat is the lack of legal protection and management for the Sargasso Sea. Because it has no land boundaries, it falls outside the jurisdiction of any country. This means that it is subject to exploitation and damage by various activities, such as fishing, shipping, tourism, or research. There is no international agreement or organization that regulates or monitors these activities, or that ensures the conservation and sustainable use of the sea’s resources. That’s something to be changed, as it is our responsibility to protect and preserve this beautiful and unique sea for the benefit of ourselves and future generations.

Sources: 1, 2, 3, 4, 5, 6, 7, 8