Sailing through the Sargasso Sea

At the beginning of March 2023, piles of seaweed appeared on the sea surface. The photo at the top was taken by Captain Seidl March 1, and the following day he wrote this in his log.

- The piles have increased in size now and can be mistaken for small islands.

Statsraad Lehmkuhl is on its way into the Sargasso Sea, which got its name from this floating seaweed, Sargassum. The Sargasso Sea is a large eddy, bounded by the Gulf Stream to the west, the North Atlantic Current to the north, the Canary Current to the east and the Atlantic Equatorial Current to the south.

The eddy rotates clockwise, and little exchange of water makes the Sargasso Sea warmer, saltier and more nutrient-poor than the rest of the Atlantic. It provides perfect conditions for the seaweed.

Floating

Sargassum is similar to the seaweed that grows along our coasts, but this species of brown algae does not stick to the seafloor as our local seaweed does. The meter-long branches, full of floating bubbles, just drift around, and gather in large clusters. If a branch is torn in two, the two parts grow further, and that is how this species reproduces.

Seaweed that drifts ashore brings nutrients, and is important for the ecosystems on the islands in this otherwise nutrient-poor oecan.

The amount of seaweed varies, and since 2011, at intervals of two or three years, such large quantities have drifted ashore that it has become a problem. As the seaweed rots, oxygen is consumed at the same time as toxic gases are produced, which kills fish and makes life difficult for people along the coast.

The cause of these blooms is not known in detail, but the scientists assume that it is due to more nutrients in water in the Amazon River and in the waters of the Gulf of Mexico than before, together with more nutrient-rich water surfacing from the depths off West Africa.

The large eddy doesn't just collect seaweed, the Sargasso Sea is one of the ocean areas where the most plastic floats around.

The european eel

The European eel, which is also found throughout Norway, starts life in the Sargasso Sea. After the eggs have hatched, the larvae drift with the ocean currents towards the coast from the very north of Africa to Iceland and Finnmark.

There, the eel migrates into rivers and lakes. After 10-15 years, the eel has grown from a half to one and a half meters long, the females the largest. When the eel has reached spawning age, which can take 20 years, they swim back to sea, and begin the long journey back to the Sargasso Sea, where it spawns.

The eel is a highly endangered species, and on the red list.