Gulf of Mexico

• 1. Introduction

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  The Gulf of Mexico is a sea of about 1.6 million square kilometres, and tens of millions of people live along its shores. In 2016 the five American states facing it held 15.8 million residents. The six Mexican states on its southern and western rim held 19.1 million. Three western provinces of Cuba, Havana among them, added another 3,211,000. Yet the gulf is no open ocean. It is a roughly oval marginal sea of the Atlantic, about 810 nautical miles wide and mostly enclosed by North America.

  Its floor hides pools of brine, its warm water feeds some of the most violent storms in the world, and its name has changed many times. How did a patch of dry land become a sea? Who named it, and why is the name still disputed? What lies beneath the surface? And what have drilling and farming done to the water that so many people depend on?

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• 2. Names and Borders

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  To the Aztecs, the gulf was Chalchiuhtlicueyecatl, the House of Chalchiuhtlicue, named for the deity of the seas. They believed that sea and sky merged beyond the horizon. The seas were therefore sky water, unlike finite, landlocked bodies such as lakes. The Maya likely called the gulf nahá, meaning great water.

  Until 1530, European maps drew the gulf but left it unlabeled. Hernán Cortés called it the Sea of the North, or Mar del Norte, in his dispatches. Other Spanish explorers preferred Gulf of Florida or Gulf of Cortés. Abraham Ortelius still labeled it the Sea of the North on his map of 1584. Mapmakers tried many more: Gulf of St. Michael, Gulf of Yucatán, Yucatán Sea, Great Antillean Gulf, Cathayan Sea and Gulf of New Spain. At one stage New Spain encircled the gulf, with the Spanish Main reaching into what later became Mexico and the southeastern United States.

  The name Gulf of Mexico first appeared on a world map in 1550 and in a historical account in 1552. Europeans chose it because Mexico, land of the Mexica, was the destination mariners had to cross the water to reach. It has been the most common name since the mid-17th century, when the gulf was still considered a Spanish sea. French Jesuits used it as early as 1672. In the 18th century, Spanish admiralty charts also called the water Mexican Cove or Mexican Sound. Mexico's own coastline once ran east along the gulf to present-day Louisiana, until the Republic of Texas broke away in 1836.

  No formal protocol governs the naming of international waters. Even so, the International Hydrographic Organization officially recognizes Gulf of Mexico, and all three neighboring countries are among its member states. That body also fixes the gulf's southeast limit as a line joining Cape Catoche Light with the light on Cape San Antonio in Cuba. The line then runs through the island to the meridian of 83 degrees west.

  Water boundaries between the neighbors rest on a series of agreements. In July 1976, Mexico and Cuba exchanged notes setting the limits of Mexico's exclusive economic zone next to Cuban waters. Cuba and the United States signed a maritime boundary agreement in December 1977. Mexico and the United States signed treaties in 1970 and 1978. In June 2000 they also agreed on the continental shelf in the western gulf beyond 200 nautical miles.

  In December 2007, Mexico submitted a claim to the Commission on the Limits of the Continental Shelf. It sought to extend its shelf beyond 200 nautical miles in an area called the Western Polygon. In March 2009 the commission accepted Mexico's arguments, up to 350 nautical miles. That reach runs well into territory claimed by the United States, so the two countries would need a bilateral agreement to delimit their claims.

  In January 2025, an executive order from United States president Donald Trump directed federal agencies to use the name Gulf of America. The order covered the waters bounded by the United States. Some major online map services and several American media outlets voluntarily adopted the change for American users. It also stoked controversy, and Mexican president Claudia Sheinbaum was among those who objected. A February 2025 poll by Marquette University asked 1,018 respondents across the United States about the change. Of them, 71 percent opposed renaming the gulf and 29 percent supported it.

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• 3. Birth of a Basin

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  The gulf took shape through plate tectonics, a process dated to about 300 million years ago. Geologists agree, however, that before the late Triassic the area was dry land. It lay inside the supercontinent Pangaea and included the continental crust that now underlies Yucatán.

  To the north of that land ran a continuous mountain range, from north-central Mexico through the Marathon Uplift in west Texas and the Ouachita Mountains of Oklahoma. In Alabama it joined the Appalachian Mountains. Colliding continental plates had raised the range when Pangaea formed. Geologists Roy Van Arsdale and Randel T. Cox interpret it as breached in the late Cretaceous, when the Mississippi Embayment formed.

  Zones of weakness in Pangaea guided the rifting that opened the basin. These included sutures where the Laurentia, South American and African plates had collided. First came a phase in the late Triassic and early Jurassic, when rift valleys formed and filled with continental red beds. Through the early and middle Jurassic, the crust stretched and thinned, in places to half its typical 40 kilometre thickness.

  Rifting first opened a connection to the Pacific across central Mexico. Later it opened one eastward to the Atlantic. Seawater flooded the basin and created an enclosed marginal sea. The sinking crust was blanketed with Louann Salt and related evaporites, which are minerals left behind as seawater dries. In the late Jurassic the basin widened until seafloor spreading created new oceanic crust. Circulation with the Atlantic then grew strong enough to end the salt deposits. Spreading stopped at the close of the Jurassic, about 145-150 million years ago.

  Afterward the basin cooled and sank. Stretching and cooling dropped the central crust by roughly 5-7 kilometres. The basin deepened because the floor sank faster than sediment could fill it. Kilometres of later sediment pressed the crust down further, to about 10-20 kilometres below sea level. To the east, the Florida Platform stayed dry until the latest Jurassic or the start of the Cretaceous. The Yucatán Platform stayed dry until the mid-Cretaceous. In the west, the Laramide Orogeny of the latest Cretaceous and early Paleogene raised the Sierra Madre Oriental of eastern Mexico.

  Today the gulf floor is 41 percent continental slope, 32 percent continental shelf and 24 percent abyssal plain. Its greatest depth, 12,467 feet, lies in the Sigsbee Deep.

  The gulf is considered aseismic, yet mild tremors of 5.0 or less have been recorded through history. On the 10th of September 2006, the U.S. Geological Survey reported a magnitude 6.0 earthquake about 400 kilometres west-southwest of Anna Maria, Florida. People felt it from Louisiana to Florida. Nothing was reported damaged and no one was hurt, though items fell from shelves and water sloshed in swimming pools. The agency called it an intraplate earthquake, the largest and most widely felt in the region in three decades. The Tampa Tribune reported that tremors had last been felt in Florida in 1952, at Quincy, 32 kilometres northwest of Tallahassee.

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• 4. Salt and Brine

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  The Louann Salt still stretches beneath most of the continental shelf around the northern gulf, from west of Florida to Texas. Under the weight of overlying sediment, the salt deforms and slowly migrates, a process called salt tectonics. Masses of it can rise through the sediment as salt domes. Others squeeze out along the Sigsbee Escarpment, where the slope of the shelf exposes deeper layers.

  Wherever gulf water meets this salt along faults or in loose sediments, it turns to brine. The brine collects in pools that range from 1 metre across to 20 kilometres long. It usually exceeds 200 parts per thousand of salt, against an average of 35 for seawater. That makes it at least 25 percent denser. The difference keeps the brine from mixing, so it flows downslope and gathers in hollows.

  Hydrocarbons and gas hydrates rising from salt diapirs, which are columns of rising salt, can dome the seafloor. Gas sometimes erupts hard enough to leave a rimmed depression, and brine may pool inside it.

  The East Flower Garden Bank pool sits in a crater formed when the cap of a salt dome collapsed. It covers 500 square metres, reaches 25 centimetres at its deepest and lies 70 metres below the surface. It is anoxic, meaning it has no oxygen, and it holds hydrogen sulfide and methane.

  Two other pools, GB425 and GC233, lie at similar depths of 600 and 650 metres. A mud volcano feeds GB425, whose surface runs on average 20 degrees Celsius warmer than normal bottom temperatures. GC233 sits in a depression on top of a mound and covers about 190 square metres. It receives less brine and runs about 15 degrees cooler than GB425. Even so, both have a salinity near 130 parts per thousand, few sulfides, almost no sulfates and high levels of hydrocarbons.

  The Orca Basin lies 2100 metres down and covers about 400 square kilometres, with a maximum depth of 350 metres. Several merged salt domes explain its size. Salinity climbs gradually over 75 metres and reaches 300 parts per thousand at depth, where no oxygen is dissolved.

  A pool found in 2014 at a depth of 3300 feet has a circumference of 100 feet and a depth of 12 feet. It is four to five times saltier than the water around it. Only bacteria, mussels with symbiotic partners, tube worms and certain shrimp can live there. Nicknamed the Jacuzzi of Despair, it sits at 65 degrees Fahrenheit while the surrounding water is 39.

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• 5. Currents and Storms

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  Only two passages join the gulf to the wider ocean: the Yucatán Channel between Mexico and Cuba, and the Straits of Florida between the United States and Cuba. That narrow link keeps the gulf's tidal ranges very small.

  Water enters through the Yucatán Channel as the Yucatán Current. It leaves through the Florida Straits as the Florida Current, which becomes the Gulf Stream. Both passages are shallow, with maximum depths of 1800 metres and 900 metres, so the flow stays in the upper layers. The Yucatán Current fills most of its channel to a depth of up to 800 metres, with a maximum flow of 120 centimetres per second. The Florida Current reaches 800 metres and peaks at 110. Between 1999 and 2013 the flow through the Yucatán Channel varied from 15.8 to 28.1 Sverdrups, a unit of ocean flow. Through the Florida Straits it stayed between 27.2 and 27.9.

  A clockwise bend called the Loop Current links the two. It can reach 300 kilometres in diameter and is as strong as the Gulf Stream. It may push into the northeastern gulf and onto the shelf off the west coast of Florida. At irregular intervals it sheds large warm-core rings, or eddies, also up to 300 kilometres wide, which drift into the western gulf. The outer currents of a ring flow at up to 4 knots, while the ring as a whole moves west at about 0.20 knots. Clockwise and anticlockwise eddies form pairs that often dominate the western gulf.

  About 40 percent of the inflowing water comes from the South Atlantic and is warmer and fresher than the rest. Deeper in the current runs Antarctic Intermediate Water. The remainder comes from various North Atlantic masses.

  In summer the gulf's surface averages around 28 degrees Celsius, warm enough to feed hurricanes such as Hurricane Katrina. In the open Atlantic, a hurricane draws up cool water from the depths, which makes further storms less likely. The shallower gulf cools when a hurricane passes but soon rebounds enough to support another tropical cyclone. From 1970 to 2020 the surface warmed by about 1 degree Celsius, or 0.19 degrees per decade, roughly twice the rate of the global ocean surface.

  Moisture from the gulf also reaches Tornado Alley in the United States, one of the most tornado-prone areas in the world. Dry air from the Rocky Mountains converges with it there, producing storms and supercells that spawn some of the most violent tornadoes anywhere. A study in the Journal of Climate by Dongmin Kim, Sang-Ki Lee and Hosmay Lopez found that the Madden-Julian oscillation strengthens the North American low-level jet. That jet carries more gulf moisture and atmospheric instability into the central United States, furthering tornado formation.

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• 6. Peoples and Explorers

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  The earliest people to reach the gulf coast found an arid landscape. They hunted mostly rabbits, hare and rodents, and supplemented them with a wide range of foraged plants. Around 5,000 BC, climatic change brought more stable waterways, lakes, shoals and lagoons, which made fishing, agriculture and permanent settlement possible. By about 1,000 BC barrier islands had begun to form, and the sea rose about a metre to near modern levels.

  In Florida, human remains date back to 10,000 BC. By 3,000 BC the climate had shifted from dry prairie to wetlands. From the Florida Keys to the mangrove islets, the Glades culture built a complex society on fishing, shellfish and plants. The Deptford culture, stretching from Cedar Key north along the panhandle, developed a distinct fired pottery. Along the northern shore, villages developed through the first millennium AD, and oyster harvests were probably timed to the tides. Texas and northern Mexico were home mainly to hunter-gatherers who relied heavily on shellfish. Maize spread along the coast, probably as a trade good.

  From roughly 1200 to 400 BC, the Olmec flourished on the southern coast. They built complex cities such as San Lorenzo Tenochtitlán along the rivers that flow into the Bay of Campeche. The Maya used the gulf as a major trade route, paddling long dugout canoes carved from single hardwood trunks such as mahogany. They stayed near the coast and steered by landmarks and lookout towers. Isla Cerritos, north of the Yucatán, and Isla Mujeres were major ports. Maya traders swapped coastal goods such as seafood, salt, cotton, cacao, spices, feathers and jaguar pelts for highland obsidian, basalt and jade. Archaeologists have found dugout canoes dating back to 0 AD.

  Northwestern Cuba is the only significant gulf coast not connected to mainland North America, so people settled it millennia later. Its earliest known site, Levisa, dates to 3100 BC. After 2000 BC, sites spread more widely. The Guanahatabey and Cayo Redondo cultures of western Cuba used largely stone and shell tools.

  Christopher Columbus reached Cuba but is not recorded entering the gulf. The map of Juan de la Cosa, who sailed with Columbus and later with Amerigo Vespucci, shows a speculative body of water beyond Cuba. In 1517, Francisco Hernández de Córdoba discovered the Yucatán Peninsula. It was the first European encounter with an advanced civilization in the Americas, with solid buildings and complex societies the Spanish found comparable to the Old World. They also expected gold. Hernández died in 1517 from injuries and extreme thirst, disappointed that Diego Velázquez de Cuéllar had given precedence to Juan de Grijalva as captain of the next expedition. Grijalva sailed in 1518.

  Hernán Cortés had joined the conquest of Hispaniola and Cuba in 1506 and received a large estate. In 1510 he accompanied Velázquez to conquer Cuba. Velázquez put him in command of an expedition in 1518, and the one that sailed in 1519 led to the Conquest of Mexico.

  A treasure ship wrecked at Padre Island, Texas. The viceroy requested a rescue fleet and sent Ángel de Villafañe overland from Mexico City. García de Escalante Alvarado, a nephew of Pedro de Alvarado, commanded the salvage and arrived by sea on the 22nd of July 1554. His team labored until the 12th of September. This loss and other ship disasters led to a plan for a settlement on the northern coast. Tristán de Luna y Arellano landed at Pensacola Bay on the 15th of August 1559.

  On the 11th of December 1526, Charles V of the Holy Roman Empire granted Pánfilo de Narváez a license to found settlements along the present-day Gulf Coast of the United States. He had one year to gather an army and leave Spain. He had to found at least two towns of 100 people each and garrison two fortresses. On the 7th of April 1528, his ships spotted land north of Tampa Bay. They turned south in search of a great harbor that the master pilot Miruelo knew. One of the five remaining ships was lost on the rugged coast.

  In 1697, the French sailor Pierre Le Moyne d'Iberville was chosen to rediscover the mouth of the Mississippi River and settle Louisiana. René-Robert Cavelier, Sieur de La Salle had named the region in 1682 for King Louis XIV. D'Iberville's fleet sailed from Brest on the 24th of October 1698 and reached Santa Rosa Island near Pensacola. He went on to Mobile Bay and Massacre Island and anchored between Cat Island and Ship Island. On the 13th of February 1699 he went ashore at what is now Biloxi with his teenage brother, Jean-Baptiste Le Moyne de Bienville. Fort Maurepas, on the northeast side of the Bay of Biloxi, was completed on the 1st of May. Three days later d'Iberville sailed for France, leaving his brother as second in command.

  Fort Maurepas, now Ocean Springs, Mississippi, was the first permanent settlement. By then the French had also built a small fort at the mouth of the Mississippi, at a settlement called La Balize, which means seamark in French.

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• 7. Oil and Wrecks

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  By 1975, about 400 offshore drilling rigs in the gulf housed more than 10,000 workers on any given day. They rotated on staggered weekly schedules, and later automation shrank the offshore workforce. The gulf is one of the largest offshore petroleum regions in the world, supplying 14 percent of United States crude oil production. Most rigs sit on the shelf in the western gulf and the Bay of Campeche.

  In 2002, an oilfield inspection crew working for the Okeanos Gas Gathering Company came across a forgotten ship. It lay 56 kilometres off Louisiana, in 1200 metres of water. Now called the Mardi Gras, the vessel sank around the early 19th century, and its real identity remains a mystery. It is believed to have been a privateer or trader. In 2007, an expedition led by Texas A&M University set out to study the site. The company funded it under an agreement with the Minerals Management Service, now BOEM. It became the deepest scientific archaeological excavation to that date, and artifacts were recovered for display in the Louisiana State Museum. Nautilus Productions made a documentary, Mystery Mardi Gras Shipwreck, using footage from the underwater robot.

  On the 30th of July 1942, the steamship Robert E. Lee, captained by William C. Heath, was torpedoed by U-166. She was bound for New Orleans, southeast of the Mississippi River entrance. Her escort was USS PC-566, captained by Lieutenant Commander Herbert G. Claudius. The explosion destroyed the No. 3 hold and tore through the B and C decks. It also damaged the engines, radio compartment and steering gear. PC-566 dropped depth charges on a sonar contact and sank U-166. The liner listed to port, then to starboard, and sank within about 15 minutes. One officer, nine crew members and 15 passengers were lost. Most of the passengers were survivors of earlier U-boat attacks. In 2001, the C & C Marine survey found both wrecks. U-166 lay in 5000 feet of water, about 3 kilometres from where it had attacked the liner.

  The National Response Center says the oil industry has thousands of minor accidents in the gulf each year. In June 1979, the Ixtoc I platform in the Bay of Campeche suffered a blowout and a catastrophic explosion. The well was not capped until April 1980.

  On the 20th of April 2010, the Deepwater Horizon platform exploded and later sank. It stood in the Mississippi Canyon about 64 kilometres off Louisiana and was operated by the British company BP. Oil flowed from a wellhead 1.5 kilometres below the surface. The slick covered hundreds of square kilometres and threatened marine life, coastal wetlands and the livelihoods of shrimpers and fishermen.

  Estimates of the flow jumped several times. On the 24th of April, BP's estimate was 160 cubic metres. On the 28th of April, a NOAA scientist raised it to 5000 barrels. On the 27th of May, the USGS put the rate at 12000-19000 barrels a day. Final estimates reached 62000 barrels a day, a scale that independent observers and federal scientists had suggested early on. A report by the government commission investigating the response said the White House Office of Management and Budget had suppressed official attempts to release modeling data.

  On the 15th of July, BP announced that the leak had stopped. BP agreed to pay $18.7 billion to the United States government, the states of Alabama, Florida, Louisiana, Mississippi and Texas, and 400 local authorities. It had also spent $54 billion on cleanup, penalties and repairs to environmental and economic damage.

  On the 12th of May 2016, subsea infrastructure on Shell's Brutus oil rig released 2,100 barrels of oil. According to the U.S. Bureau of Safety and Environmental Enforcement, the slick lay about 156 kilometres south of Port Fourchon, Louisiana.

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• 8. Life and Pollution

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  Cold seeps on the seafloor support chemosynthetic communities, organisms that draw energy from chemicals rather than sunlight. The gulf's other residents range from bacteria and tiny bottom-dwellers to crabs, sea pens, crinoids, bottom-dwelling fish and cetaceans. The Caribbean monk seal is extinct. Resident Bryde's whales were recently classified as an endemic subspecies, making them one of the most endangered whales in the world.

  Along the wide shelves of Yucatán and Florida, upwelling lifts cooler, nutrient-rich water from the deep. It stimulates plankton growth, which attracts fish, shrimp and squid. River drainage and atmospheric fallout from industrial coastal cities add more nutrients. The American coastline spans 2700 kilometres and receives water from 33 major rivers that drain 31 states and two Canadian provinces. The Mexican coastline spans 2200 kilometres. Each year the gulf yields more fish, shrimp and shellfish than the south and mid-Atlantic, the Chesapeake and New England combined. Major catches include red snapper, amberjack, tilefish, swordfish, grouper, shrimp and crabs, and oysters are harvested on a large scale.

  Since 1979, specimens collected for years by the former Minerals Management Service have been deposited in the Smithsonian's National Museum of Natural History. In Congressional testimony, Jonathan Coddington, an associate director at the museum, described these collections. They are expected to give a baseline for studying the impact of the Deepwater Horizon spill.

  Agricultural runoff and oil drilling are the major environmental threats. Some 27,000 abandoned oil and gas wells lie beneath the gulf, and they have generally not been checked for environmental problems. In 1973, the United States Environmental Protection Agency prohibited the dumping of undiluted chemical waste into the gulf. The military confessed to similar behavior in waters off Horn Island. A first study of microplastics, begun in 2015, estimated concentrations that rival the highest reported anywhere.

  Frequent red tide algae blooms kill fish and marine mammals and cause respiratory problems in people and some domestic animals. They have especially plagued the southwest and southern Florida coast, from the Florida Keys to north of Pasco County.

  A low-oxygen dead zone runs east-west along the Texas-Louisiana coastline. In July 2008, researchers reported that it had roughly doubled in size between 1985 and 2008. In 2017 it covered 22730 square kilometres, the largest ever recorded. Poor agricultural practices in the northern gulf have added large amounts of nitrogen and phosphorus to the water, fueling algae blooms that drain the oxygen. A 2007 study of the Atlantic croaker found 61 percent males and 39 percent females at low-oxygen sites. Reference sites showed 52 percent males and 48 percent females, a sign of impaired reproduction.

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