Sargasso Sea

The Sargasso Sea is the only sea on Earth without a coast: some 4.16 million km² of the North Atlantic, bounded not by land but by four currents turning clockwise around it, and holding on its surface a brown alga that never touches the seabed at any point in its life. Its reputation is that ships get caught in the weed and rot there. That reputation is traceable, and it is wrong. Columbus sailed through it in September 1492 and his log records the crew cheering, because they read the weed as a sign of land; on the day the sea seemed «curdled» with it the fleet still made thirteen leagues. Otto Krümmel's 1891 chart, the map on this page, grades the sea by the probability of meeting drifting Sargassum, and its darkest class is ten per cent. What actually becalms a ship here is the windless high of the horse latitudes — not the doldrums, which lie two thousand kilometres south. The real unsolved question is quieter: a century after the eels of Europe were traced to this water, nobody has ever found one spawning.

The Sargasso Sea is the one sea on Earth that nobody can stand beside. It has no coast. Its edges are four moving currents — the Gulf Stream to the west, the North Atlantic Current to the north, the Canary Current to the east, the North Atlantic Equatorial Current to the south — turning clockwise inside the North Atlantic subtropical gyre. Because those currents shift, so do the boundaries, which is why the sea has been given different dimensions by every authority that has tried. The Sargasso Sea Alliance settled the question pragmatically in 2011 by commissioning a map from current and eddy occurrence, satellite detection of weed and seabed topography: an area of roughly 4,163,499 km², extending between 22°–38°N and 76°–43°W and centred on 30°N, 60°W. That map was adopted three years later as Annex I of the Hamilton Declaration. Inside all that water there is exactly one piece of land: Bermuda. The name is Portuguese. Sargaço is the weed, and the weed is Sargassum, a brown alga that in this one place is holopelagic — it never touches the seabed at any point in its life, floating and dividing on the open ocean, which is what NOAA singles out as the sea's unique quality. The most quoted witness is Christopher Columbus, and the record does not say what the legend says it says. Columbus's own log is lost; what survives is the abstract made by Bartolomé de las Casas, and it can be read line by line. On Sunday 16 September 1492 the fleet begins to see "muchas manadas de hierba muy verde" — great herds of very green weed — and the reaction recorded is not dread but hope: "todos juzgaban que estaban cerca de alguna isla", everyone judged they were near some island. The next day there is more of it, they fish a live crab out of it and the Admiral keeps the crab as proof, and the entry ends with the whole fleet racing: "Iban muy alegres todos y los navíos quien más podía andar andaba por ver primero tierra." The fear that is actually written down is the opposite of the one the legend supplies. On Saturday 22 September, in Columbus's own words inside the abstract, a contrary wind is welcome: "Mucho me fue necesario este viento contrario, porque mi gente andaban muy estimulados, que pensaban que no ventaban estos mares vientos para volver a España." His men were not afraid of being held by weed and starving. They were afraid that in these seas no wind ever blew back — that they could sail out and never sail home. The following day the sea rose without wind and Columbus, in the same abstract, compares his relief to the parting of the waters for Moses. And the crossing itself can be checked with arithmetic. The heaviest weed of the whole voyage is logged on Friday 21 September, when "hallaron tanta hierba que parecía ser la mar cuajada de ella" — so much weed that the sea seemed curdled with it. They made thirteen leagues that day, slowed by calm, not by weed; the day after that, thirty. The weed thins out and by Friday 5 October the entry reads "hierba ninguna", none at all. Landfall came a week later. Nineteen days of intermittent weed and not one day stopped. The scientific career of the sea begins properly with Matthew Fontaine Maury's The Physical Geography of the Sea (1855), and it is worth noting where he put it: "Midway the Atlantic, in the triangular space between the Azores, Canaries, and the Cape de Verd Islands" — the eastern side of the ocean, not the western basin the name denotes today. In §13 Maury describes an area the size of the Mississippi valley "so thickly matted over with Gulf weed (fucus natans), that the speed of vessels passing through it is often much retarded", adds that "to the eye, at a little distance, it seems substantial enough to walk upon", and explains the accumulation with the image every later writer borrowed: cork in a basin of water given a circular motion gathers at the quiet centre. Measurement replaced impression in 1891, and the result is the picture at the head of this file. Otto Krümmel's plate for Petermanns Geographische Mitteilungen (Jahrgang 1891, Tafel 10; Gotha: Justus Perthes; scale 1:31,300,000) is titled "the North Atlantic Sargasso Sea, represented according to the frequency of weed occurrence". Krümmel had compiled ship reports and shaded the ocean in four probability classes. He also drew, as a separate dotted outline, the "Gebiet häufiger Windstillen im Sommer" — the area of frequent summer calms — and marked Alexander von Humboldt's Fucusbänke, the weed banks of the older literature. Krümmel's map keeps apart the two things the legend fuses. The botany was settled by Frank S. Collins in Rhodora in May 1917, whose conclusion is the sentence that ought to have ended the story: "The Sargassum exists not as a continuous mass, but as scattered patches." What the sea does hold is stranger than what was invented for it. The smallest larvae of the European and American eel are found here and nowhere else, which is why Johannes Schmidt's surveys of the early twentieth century pointed to the Sargasso as the breeding place of a fish that lives in European rivers. A century later that was still an inference. It took satellite tags on twenty-six eels from the rivers of the Azores, reported by Rosalind Wright and colleagues in Scientific Reports in 2022, to put adult eels physically inside the Sargasso Sea for the first time — and even they note that no egg and no spawning adult has ever been sampled there. On 11 March 2014, in Hamilton, the governments of the Azores, Bermuda, Monaco, the United Kingdom and the United States signed a declaration to protect it, expressly "not legally binding", and set up the Sargasso Sea Commission. Later signatories include the British Virgin Islands, the Bahamas, Canada, the Cayman Islands and the Dominican Republic.

There is nothing to visit, and no way to arrive. The Sargasso Sea has no shore, no gate and no marker, and because its edges are currents rather than coastlines they move: the Sargasso Sea Commission's own scientific note states that as the four boundary currents vary, so do the sea's precise boundaries, and that the eastern edge in particular is so diffuse that it is placed, pragmatically, west of the Mid-Atlantic Ridge. There is no line to cross and no sign to photograph. The one place where you can stand on land inside the Sargasso Sea is Bermuda. The Hamilton Declaration puts it plainly in its opening recital: the islands of Bermuda are the only land territory within the Sargasso Sea. Everything else in that 4.16 million km² is high seas, beyond national jurisdiction, except Bermuda's own exclusive economic zone and territorial sea, which the Declaration expressly excludes from its area of collaboration. The weed itself is easiest to meet where it is thrown ashore. Sargassum drifts out of the gyre and washes up on Atlantic and Caribbean beaches, where — as the 2011 science case notes — it feeds shoreline species, helps build dunes and has long been collected as fertiliser for fields inland. On a windward beach after a blow, the golden weed in the strand line is the same holopelagic alga that gives the sea its name. If you are crossing it under sail rather than reading about it, the practical hazard is the opposite of the one in the stories. Nobody is stopped by weed; people are stopped by the absence of wind. The Sargasso sits under the subtropical high, and NOAA's description of these latitudes — calm winds, high pressure, sunny skies and little precipitation — is a warning about passage planning, not atmosphere. Krümmel had already outlined the area of frequent summer calms separately on his 1891 chart, and it is worth reading before choosing a season. Carry fuel and water on the assumption that the wind will fail, which is exactly the lesson the horse latitudes taught the ships that named them. Species you may meet on the surface are worth knowing about: the sargassum fish, a frogfish whose markings and outgrowths imitate the weed so closely that Collins reported it is "practically impossible to distinguish the fish from the floating alga in which it lives", along with the crabs and molluscs that live nowhere else. Loggerhead hatchlings shelter in the same mats. None of it should be collected.