The Only Sea Without a Coast

The Sargasso Sea is the only sea in the world without a coastline. Unlike most seas that are bounded by land, the Sargasso Sea lies entirely within the North Atlantic Ocean, defined not by continental boundaries but by ocean currents. It is an area of calm, clear, warm water surrounded by circulating currents that form a vast, elliptical gyre.

Geographic Location

• Location: North Atlantic Ocean
• Approximate Coordinates: Between 20°N and 35°N latitude, and 40°W to 70°W longitude
• Area: Around 3.5 million square kilometres (1.4 million square miles)
• Boundaries: Defined by four major ocean currents forming the North Atlantic Subtropical Gyre:
  1. North Atlantic Current (to the north)
  2. Canary Current (to the east)
  3. North Equatorial Current (to the south)
  4. Gulf Stream (to the west)

These currents create a slowly rotating system that isolates the Sargasso Sea from the rest of the Atlantic, giving it its distinctive calm and stable waters.

Origin of the Name

The sea takes its name from the abundant Sargassum, a type of free-floating brown seaweed (Sargassum natans and Sargassum fluitans), that drifts on its surface. Early sailors, including Christopher Columbus, encountered the dense mats of seaweed while crossing the Atlantic and named the region after it.

Physical Characteristics

1. No Coastline: The Sargasso Sea is unique because it is entirely enclosed by ocean currents, not landmasses. Its “boundaries” are fluid and defined by water movement rather than geography.
2. Colour and Clarity: The waters are famous for their deep blue colour and exceptional transparency, allowing visibility up to 60 metres (200 feet).
3. Temperature: The sea maintains relatively warm surface temperatures, typically ranging from 20°C to 28°C (68°F to 82°F).
4. Currents and Stability: The circular motion of surrounding currents traps water within the gyre, resulting in slow movement, minimal turbulence, and accumulation of floating material such as seaweed and debris.

Ecology and Marine Life

Although relatively nutrient-poor compared to coastal waters, the Sargasso Sea supports a specialised ecosystem:

• Sargassum Seaweed: Provides shelter and food for numerous marine organisms.
• Fauna: Includes species such as the Sargassum fish, flying fish, juvenile sea turtles, crabs, and eels.
• Eel Migration: The Sargasso Sea is the spawning ground for both the European eel (Anguilla anguilla) and the American eel (Anguilla rostrata), which migrate thousands of kilometres from European and North American rivers to reproduce here.

This unique biological activity makes the Sargasso Sea an important site for global marine biodiversity.

Oceanographic Importance

1. Gyre System: The Sargasso Sea is located at the centre of the North Atlantic Subtropical Gyre, one of the Earth’s major oceanic circulation systems that influences global climate and marine nutrient transport.
2. Carbon Sequestration: The calm waters and planktonic activity contribute to the ocean carbon cycle, playing a role in absorbing atmospheric carbon dioxide.
3. Drift Accumulation Zone: The sea is also known as a convergence zone where floating materials, including plastics and organic matter, tend to accumulate due to the circular currents.

Historical and Cultural Significance

• Exploration: Christopher Columbus crossed the Sargasso Sea during his 1492 voyage, noting its strange calm and thick seaweed mats, which made sailors fearful of becoming trapped.
• Sailing Lore: Early mariners referred to it as a “dead sea” due to the weak winds and sluggish waters that could delay ships for weeks.
• Literature and Science: The Sargasso Sea has inspired numerous literary references and studies of oceanic ecology and navigation.

Environmental Concerns

The Sargasso Sea, despite its isolation, faces environmental threats:

• Plastic Pollution: Modern ocean currents trap not only natural seaweed but also floating plastic debris, forming a concentration zone similar to the “garbage patches” found in other gyres.
• Climate Change: Rising sea temperatures and changing ocean currents may disrupt its delicate ecological balance.
• Overfishing: Migratory species like eels and turtles are affected by declining populations due to global overfishing and habitat loss.