The Sargasso Sea is a unique body of water situated in the middle of the North Atlantic Ocean. Unlike every other sea on Earth, it is not bordered by any landmass. This distinct area is instead defined entirely by the ocean currents that circulate around it, which creates a massive, enclosed pool of water within the open ocean. The classification of this area as a “sea” is rooted in the physical and biological characteristics that set its water mass apart from the surrounding Atlantic.
The Unique Definition of the Sargasso Sea
The definition of the Sargasso Sea relies on its hydrographic properties rather than continental geography. While most seas are classified as marginal seas partially enclosed by land, this region is a vast, open-ocean area approximately 1,100 kilometers wide by 3,200 kilometers long. Its water possesses a distinct set of characteristics, including a noticeably deep blue color and exceptional clarity, with underwater visibility reaching up to 60 meters.
The water mass within this region is also characterized by higher salinity and warmer temperatures compared to the surrounding North Atlantic waters. These differences are maintained by the sluggish movement of the water trapped within the circulatory system. Although its boundaries are fluid and shift slightly with the seasons, the unique physical properties of the water column are consistent enough to warrant its designation as a distinct sea. It is roughly located off the east coast of North America and west of the Azores.
The North Atlantic Gyre as a Boundary
The specific mechanism that contains the Sargasso Sea is the massive, clockwise-circulating system of ocean currents known as the North Atlantic Gyre. This gyre acts as a dynamic, continuous boundary, effectively isolating the central water mass from the rest of the Atlantic Ocean. The slow rotation of the gyre ensures that the water within the sea remains relatively calm and centralized.
Four major currents define the four sides of this oceanic enclosure. The powerful Gulf Stream forms the western boundary, while the North Atlantic Current flows along the northern edge. The eastern side is marked by the Canary Current, and the North Equatorial Current completes the circulation along the southern perimeter. This constant, circular movement traps surface waters for extended periods, estimated in some models to be up to 50 years, concentrating material and maintaining the sea’s singular conditions.
Sargassum and the Sea’s Namesake
The final element justifying the name is the unique biological feature that gives the sea its identity: the free-floating brown algae of the genus Sargassum. This seaweed is holopelagic, meaning it lives and reproduces exclusively while floating in the open ocean. It forms vast, dense mats on the surface that can extend for kilometers, creating a visible difference from the surrounding clear blue water.
These floating rafts of Sargassum provide an entire ecosystem, acting as a nursery habitat for an amazing variety of marine life. Species such as sea turtles, shrimp, and several types of fish rely on the seaweed for shelter and food during their early life stages. The name itself was given by Portuguese sailors, who encountered the floating masses and were reminded of a small grape known in their language as sargaço. The seaweed’s small, air-filled bladders, which keep it afloat, resembled the berries of the grape, leading to the designation of the area as the Sargasso Sea.