Gulf of Mexico

From Wikipedia, the free encyclopedia

 

Gulf of Mexico
Bathymetry of the Gulf of Mexico
Location	American Mediterranean Sea
Coordinates	25°N 90°WCoordinates: 25°N 90°W
River sources	Rio Grande, Mississippi River
Ocean/sea sources	Atlantic Ocean, Caribbean Sea
Basin countries	United States Mexico Cuba
Max. width	1,500 km (932.06 mi)
Surface area	1,550,000 km2 (600,000 sq mi)
Settlements	Houston, New Orleans, Corpus Christi, Tampa, Havana, Campeche, Mobile, Gulfport, Tampico, Key West

Galveston harbor by Verner Moore White

 

The Gulf of Mexico (Spanish: Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. The U.S. states of Texas, Louisiana, Mississippi, Alabama, and Florida border the Gulf on the north, which are often referred to as the "Third Coast", in comparison with the U.S. Atlantic and Pacific coasts. 

The Gulf of Mexico formed approximately 300 million years ago as a result of plate tectonics. The Gulf of Mexico basin is roughly oval and is approximately 810 nautical miles (1,500 km; 930 mi) wide and floored by sedimentary rocks and recent sediments. It is connected to part of the Atlantic Ocean through the Florida Straits between the U.S. and Cuba, and with the Caribbean Sea (with which it forms the American Mediterranean Sea) via the Yucatán Channel between Mexico and Cuba. With the narrow connection to the Atlantic, the Gulf experiences very small tidal ranges. The size of the Gulf basin is approximately 1.6 million km² (615,000 sq mi). Almost half of the basin is shallow continental shelf waters. The basin contains a volume of roughly 2,500 quadrillion liters (550 quadrillion Imperial gallons, 660 quadrillion US gallons, 2.5 million km³ or 600,000 cu mi). The Gulf of Mexico is one of the most important offshore petroleum production regions in the world, comprising one-sixth of the United States' total production.

Extent

The International Hydrographic Organization defines the southeast limit of the Gulf of Mexico as follows:

A line leaving Cape Catoche Light (21°37′N 87°04′W) with the Light on Cape San Antonio in Cuba, through this island to the meridian of 83°W and to the Northward along this meridian to the latitude of the South point of the Dry Tortugas (24°35'N), along this parallel Eastward to Rebecca Shoal (82°35'W) thence through the shoals and Florida Keys to the mainland at eastern end of Florida Bay, all the narrow waters between the Dry Tortugas and the mainland being considered to be within the Gulf.

Geology

Sediment in the Gulf of Mexico

 

The consensus among geologists who have studied the geology of the Gulf of Mexico is that before the Late Triassic, the Gulf of Mexico did not exist. Before the Late Triassic, the area now occupied by the Gulf of Mexico consisted of dry land, which included continental crust that now underlies Yucatán, within the middle of the large supercontinent of Pangea. This land lay south of a continuous mountain range that extended from north-central Mexico, through the Marathon Uplift in West Texas and the Ouachita Mountains of Oklahoma, and to Alabama where it linked directly to the Appalachian Mountains. It was created by the collision of continental plates that formed Pangea. As interpreted by Roy Van Arsdale and Randel T. Cox, this mountain range was breached in Late Cretaceous times by the formation of the Mississippi Embayment.

Geologists and other Earth scientists agree in general that the present Gulf of Mexico basin originated in Late Triassic time as the result of rifting within Pangea. The rifting was associated with zones of weakness within Pangea, including sutures where the Laurentia, South American, and African plates collided to create it. First, there was a Late Triassic-Early Jurassic phase of rifting during which rift valleys formed and filled with continental red beds. Second, as rifting progressed through Early and Middle Jurassic time, continental crust was stretched and thinned. This thinning created a broad zone of transitional crust, which displays modest and uneven thinning with block faulting, and a broad zone of uniformly thinned transitional crust, which is half the typical 40-kilometer (25 mi) thickness of normal continental crust. It was at this time that rifting first created a connection to the Pacific Ocean across central Mexico and later eastward to the Atlantic Ocean. This flooded the opening basin to create the Gulf of Mexico as an enclosed marginal sea. While the Gulf of Mexico was a restricted basin, the subsiding transitional crust was blanketed by the widespread deposition of Louann Salt and associated anhydrite evaporites. During the Late Jurassic, continued rifting widened the Gulf of Mexico and progressed to the point that sea-floor spreading and formation of oceanic crust occurred. At this point, sufficient circulation with the Atlantic Ocean was established that the deposition of Louann Salt ceased. Seafloor spreading stopped at the end of Jurassic time, about 145–150 million years ago. 

During the Late Jurassic through Early Cretaceous, the basin occupied by the Gulf of Mexico experienced a period of cooling and subsidence of the crust underlying it. The subsidence was the result of a combination of crustal stretching, cooling, and loading. Initially, the combination of crustal stretching and cooling caused about 5–7 km (3.1–4.3 mi) of tectonic subsidence of the central thin transitional and oceanic crust. Because subsidence occurred faster than sediment could fill it, the Gulf of Mexico expanded and deepened.

Later, loading of the crust within the Gulf of Mexico and adjacent coastal plain by the accumulation of kilometers of sediments during the rest of the Mesozoic and all of the Cenozoic further depressed the underlying crust to its current position about 10–20 km (6.2–12.4 mi) below sea level. Particularly during the Cenozoic, thick clastic wedges built out the continental shelf along the northwestern and northern margins of the Gulf of Mexico.

To the east, the stable Florida platform was not covered by the sea until the latest Jurassic or the beginning of Cretaceous time. The Yucatán platform was emergent until the mid-Cretaceous. After both platforms were submerged, the formation of carbonates and evaporites has characterized the geologic history of these two stable areas. Most of the basin was rimmed during the Early Cretaceous by carbonate platforms, and its western flank was involved during the latest Cretaceous and early Paleogene periods in a compressive deformation episode, the Laramide Orogeny, which created the Sierra Madre Oriental of eastern Mexico.

In 2002 geologist Michael Stanton published a speculative essay suggesting an impact origin for the Gulf of Mexico at the close of the Permian, which could have caused the Permian–Triassic extinction event. However, Gulf Coast geologists do not regard this hypothesis as having any credibility. Instead they overwhelmingly accept plate tectonics, not an asteroid impact, as having created the Gulf of Mexico as illustrated by papers authored by Kevin Mickus and others. This hypothesis is not to be confused with the Chicxulub Crater, a large impact crater on the coast of the Gulf of Mexico on the Yucatán Peninsula. Increasingly, the Gulf of Mexico is regarded as a backarc basin behind the Jurassic Nazas Arc of Mexico.

In 2014 Erik Cordes of Temple University and others discovered a brine pool 3,300 feet (1,005.8 m) below the gulf's surface, with a circumference of 100 feet (30.5 m) and 12 feet (3.7 m) feet deep, which is four to five times saltier than the rest of the water. The first exploration of the site was unmanned, using Hercules, and in 2015, a team of three used the deep submergence vehicle Alvin. The site cannot sustain any kind of life other than bacteria, mussels with a symbiotic relationship, tube worms and certain kinds of shrimp. It has been called the "Jacuzzi of Despair". Because it is warmer than the surrounding water (65 °F (18.3 °C) degrees compared to 39 °F (3.9 °C)), wildlife have been attracted to it and could not survive.

Today, the Gulf of Mexico has the following seven main areas:

• Gulf of Mexico basin, which contains the Sigsbee Deep and can be further divided into the continental rise, the Sigsbee Abyssal Plain, and the Mississippi Cone.
• Northeast Gulf of Mexico, which extends from a point east of the Mississippi River Delta near Biloxi to the eastern side of Apalachee Bay.
• South Florida Continental Shelf and Slope, which extends along the coast from Apalachee Bay to the Straits of Florida and includes the Florida Keys and Dry Tortugas.
• Campeche Bank, which extends from the Yucatán Straits in the east to the Tabasco–Campeche Basin in the west and includes Arrecife Alacran.
• Bay of Campeche, which is an isthmian embayment extending from the western edge of Campeche Bank to the offshore regions just east of the port of Veracruz.
• Western Gulf of Mexico, which is located between Veracruz to the south and the Rio Grande to the north.
• Northwest Gulf of Mexico, which extends from Alabama to the Rio Grande.

History

European exploration

Richard Mount and Thomas Page's 1700 map of the Gulf of Mexico, A Chart of the Bay of Mexico

 

Graph showing the overall water temperature of the Gulf between Hurricanes Katrina and Rita. Although Katrina cooled waters in its path by up to 4 °C, they had rebounded by the time of Rita's appearance.

 

Fishing boats in Biloxi

 

Although Christopher Columbus was credited with the discovery of the Americas by Europeans, the ships in his four voyages never reached the Gulf of Mexico. Instead, Columbus sailed into the Caribbean around Cuba and Hispaniola. The first European exploration of the Gulf of Mexico was by Amerigo Vespucci in 1497. He followed the coastal land mass of Central America before returning to the Atlantic Ocean via the Straits of Florida between Florida and Cuba. In his letters, Vespucci described this trip, and once Juan de la Cosa returned to Spain, a famous world map, depicting Cuba as an island, was produced. 

In 1506, Hernán Cortés took part in the conquest of Hispaniola and Cuba, receiving a large estate of land and Indian slaves for his effort. In 1510, he accompanied Diego Velázquez de Cuéllar, an aide of the governor of Hispaniola, in his expedition to conquer Cuba. In 1518 Velázquez put him in command of an expedition to explore and secure the interior of Mexico for colonization.

In 1517, Francisco Hernández de Córdoba discovered the Yucatán Peninsula. This was the first European encounter with an advanced civilization in the Americas, with solidly built buildings and a complex social organization which they recognized as being comparable to those of the Old World; they also had reason to expect that this new land would have gold. All of this encouraged two further expeditions, the first in 1518 under the command of Juan de Grijalva, and the second in 1519 under the command of Hernán Cortés, which led to the Spanish exploration, military invasion, and ultimately settlement and colonization known as the Conquest of Mexico. Hernández did not live to see the continuation of his work: he died in 1517, the year of his expedition, as the result of the injuries and the extreme thirst suffered during the voyage, and disappointed in the knowledge that Diego Velázquez had given precedence to Grijalva as the captain of the next expedition to Yucatán.

In 1523, Ángel de Villafañe sailed toward Mexico City, but was shipwrecked en route along the coast of Padre Island, Texas, in 1554. When word of the disaster reached Mexico City, the viceroy requested a rescue fleet and immediately sent Villafañe marching overland to find the treasure-laden vessels. Villafañe traveled to Pánuco and hired a ship to transport him to the site, which had already been visited from that community. He arrived in time to greet García de Escalante Alvarado (a nephew of Pedro de Alvarado), commander of the salvage operation, when Alvarado arrived by sea on July 22, 1554. The team labored until September 12 to salvage the Padre Island treasure. This loss, in combination with other ship disasters around the Gulf of Mexico, gave rise to a plan for establishing a settlement on the northern Gulf Coast to protect shipping and more quickly rescue castaways. As a result, the expedition of Tristán de Luna y Arellano was sent and landed at Pensacola Bay on August 15, 1559. 

On December 11, 1526, Charles V granted Pánfilo de Narváez a license to claim what is now the Gulf Coast of the United States, known as the Narváez expedition. The contract gave him one year to gather an army, leave Spain, be large enough to found at least two towns of 100 people each, and garrison two more fortresses anywhere along the coast. On April 7, 1528, they spotted land north of what is now Tampa Bay. They turned south and traveled for two days looking for a great harbor the master pilot Miruelo knew of. Sometime during these two days, one of the five remaining ships was lost on the rugged coast, but nothing else is known of it.

In 1697, Pierre Le Moyne d'Iberville sailed for France and was chosen by the Minister of Marine to lead an expedition to rediscover the mouth of the Mississippi River and to colonize Louisiana which the English coveted. Iberville's fleet sailed from Brest on October 24, 1698. On January 25, 1699, Iberville reached Santa Rosa Island in front of Pensacola founded by the Spanish; he sailed from there to Mobile Bay and explored Massacre Island, later renamed Dauphin Island. He cast anchor between Cat Island and Ship Island; and on February 13, 1699, he went to the mainland, Biloxi, with his brother Jean-Baptiste Le Moyne de Bienville. On May 1, 1699, he completed a fort on the north-east side of the Bay of Biloxi, a little to the rear of what is now Ocean Springs, Mississippi. This fort was known as Fort Maurepas or Old Biloxi. A few days later, on May 4, Pierre Le Moyne sailed for France leaving his teenage brother, Jean-Baptiste Le Moyne, as second in command to the French commandant.

Shipwrecks

The Mardi Gras shipwreck around the early-19th century about 35 miles (56 km) off the coast of Louisiana in 4,000 feet (1,200 m) of water. She is believed to have been a privateer or trader. The shipwreck, whose real identity remains a mystery, lay forgotten at the bottom of the sea until it was discovered in 2002 by an oilfield inspection crew working for the Okeanos Gas Gathering Company (OGGC). In May 2007, an expedition, led by Texas A&M University and funded by OGGC under an agreement with the Minerals Management Service (now BOEM), was launched to undertake the deepest scientific archaeological excavation ever attempted at that time to study the site on the seafloor and recover artifacts for eventual public display in the Louisiana State Museum. As part of the project educational outreach Nautilus Productions in partnership with BOEM, Texas A&M University, the Florida Public Archaeology Network and Veolia Environmental produced a one-hour HD documentary about the project, short videos for public viewing and provided video updates during the expedition. Video footage from the ROV was an integral part of this outreach and used extensively in the Mystery Mardi Gras Shipwreck documentary.

On July 30, 1942 Robert E. Lee, captained by William C. Heath, was torpedoed by the German submarine U-166. She was sailing southeast of the entrance to the Mississippi River when the explosion destroyed the #3 hold, vented through the B and C decks and damaged the engines, the radio compartment and the steering gear. After the attack she was under escort by USS PC-566, captained by Lieutenant Commander Herbert G. Claudius, en route to New Orleans. PC-566 began dropping depth charges on a sonar contact, sinking U-166. The badly damaged Robert E. Lee first listed to port then to starboard and finally sank within about 15 minutes of the attack. One officer, nine crewmen and 15 passengers were lost. The passengers aboard Robert E. Lee were primarily survivors of previous torpedo attacks by German U-boats. The wreck's precise location was discovered during the C & C Marine survey that located the U-166. 

The German submarine U-166 was a Type IXC U-boat of Nazi Germany's Kriegsmarine during World War II. The submarine was laid down on December 6, 1940 at the Seebeckwerft (part of Deutsche Schiff- und Maschinenbau AG, Deschimag) at Wesermünde (modern Bremerhaven) as yard number 705, launched on November 1, 1941 and commissioned on March 23, 1942 under the command of Oberleutnant zur See Hans-Günther Kuhlmann. After training with the 4th U-boat Flotilla, U-166 was transferred to the 10th U-boat Flotilla for front-line service on June 1, 1942. The U-boat sailed on only two war patrols and sank four ships totalling 7,593 gross register tons (GRT). She was sunk on July 30, 1942 in Gulf of Mexico.

In 2001 the wreck of U-166 was found in 5,000 feet (1,500 m) of water, less than two miles (3.2 km) from where it had attacked Robert E. Lee. An archaeological survey of the seafloor before construction of a natural gas pipeline led to the discoveries by C & C Marine archaeologists Robert A. Church and Daniel J. Warren. The sonar contacts consisted of two large sections lying approximately 500 feet (150 m) apart at either end of a debris field that indicated the presence of a U-boat.

Geography

Gulf beach near Sabine Pass

 

The Mississippi River Watershed is the largest drainage basin of the Gulf of Mexico Watershed.

 

Map of northern part of Gulf of Mexico

 

The shaded relief map of the Gulf of Mexico and Caribbean area.

 

The Gulf of Mexico's eastern, northern, and northwestern shores lie along the US states of Florida, Alabama, Mississippi, Louisiana, and Texas. The US portion of the Gulf coastline spans 1,680 miles (2,700 km), receiving water from 33 major rivers that drain 31 states. The Gulf's southwestern and southern shores lie along the Mexican states of Tamaulipas, Veracruz, Tabasco, Campeche, Yucatán, and the northernmost tip of Quintana Roo. The Mexican portion of the Gulf coastline spans 1,743 miles (2,805 km). On its southeast quadrant the Gulf is bordered by Cuba. It supports major American, Mexican and Cuban fishing industries. The outer margins of the wide continental shelves of Yucatán and Florida receive cooler, nutrient-enriched waters from the deep by a process known as upwelling, which stimulates plankton growth in the euphotic zone. This attracts fish, shrimp, and squid. River drainage and atmospheric fallout from industrial coastal cities also provide nutrients to the coastal zone.

The Gulf Stream, a warm Atlantic Ocean current and one of the strongest ocean currents known, originates in the gulf, as a continuation of the Caribbean Current-Yucatán Current-Loop Current system. Other circulation features include the anticyclonic gyres which are shed by the Loop Current and travel westward where they eventually dissipate, and a permanent cyclonic gyre in the Bay of Campeche. The Bay of Campeche in Mexico constitutes a major arm of the Gulf of Mexico. Additionally, the gulf's shoreline is fringed by numerous bays and smaller inlets. A number of rivers empty into the gulf, most notably the Mississippi River and Rio Grande in the northern gulf, and the Grijalva and Usumacinta rivers in the southern gulf. The land that forms the gulf's coast, including many long, narrow barrier islands, is almost uniformly low-lying and is characterized by marshes and swamps as well as stretches of sandy beach.

The Gulf of Mexico is an excellent example of a passive margin. The continental shelf is quite wide at most points along the coast, most notably at the Florida and Yucatán Peninsulas. The shelf is exploited for its oil by means of offshore drilling rigs, most of which are situated in the western gulf and in the Bay of Campeche. Another important commercial activity is fishing; major catches include red snapper, amberjack, tilefish, swordfish, and various grouper, as well as shrimp and crabs. Oysters are also harvested on a large scale from many of the bays and sounds. Other important industries along the coast include shipping, petrochemical processing and storage, military use, paper manufacture, and tourism. 

The gulf's warm water temperature can feed powerful Atlantic hurricanes causing extensive human death and other destruction as happened with Hurricane Katrina in 2005. In the Atlantic, a hurricane will draw up cool water from the depths and making it less likely that further hurricanes will follow in its wake (warm water being one of the preconditions necessary for their formation). However, the Gulf is shallower; when a hurricane passes over the water temperature may drop but it soon rebounds and becomes capable of supporting another tropical storm.

The Gulf is considered aseismic; however, mild tremors have been recorded throughout history (usually 5.0 or less on the Richter magnitude scale). Earthquakes may be caused by interactions between sediment loading on the sea floor and adjustment by the crust.

2006 earthquake

On September 10, 2006, the U.S. Geological Survey National Earthquake Information Center reported that a magnitude 6.0 earthquake occurred about 250 miles (400 km) west-southwest of Anna Maria, Florida, around 10:56 AM EDT. The quake was reportedly felt from Louisiana to Florida in the Southeastern United States. There were no reports of damage or injuries. Items were knocked from shelves and seiches were observed in swimming pools in parts of Florida. The earthquake was described by the USGS as an intraplate earthquake, the largest and most widely felt recorded in the past three decades in the region. According to the September 11, 2006 issue of The Tampa Tribune, earthquake tremors were last felt in Florida in 1952, recorded in Quincy, 20 miles (32 km) northwest of Tallahassee

Maritime boundary delimitation agreements

Cuba and Mexico: Exchange of notes constituting an agreement on the delimitation of the exclusive economic zone of Mexico in the sector adjacent to Cuban maritime areas (with map), of July 26, 1976. 

Cuba and United States: Maritime boundary agreement between the United States of America and the Republic of Cuba, of December 16, 1977.

Mexico and United States: Treaty to resolve pending boundary differences and maintain the Rio Grande and Colorado River as the international boundary, of November 23, 1970; Treaty on maritime boundaries between the United States of America and the United Mexican States (Caribbean Sea and Pacific Ocean), of May 4, 1978, and Treaty between the Government of the United States of America and the Government of the United Mexican States on the delimitation of the continental shelf in the Western Gulf of Mexico beyond 200 nautical miles (370 km; 230 mi), of June 9, 2000.

On December 13, 2007, Mexico submitted information to the Commission on the Limits of the Continental Shelf (CLCS) regarding the extension of Mexico's continental shelf beyond 200 nautical miles. Mexico sought an extension of its continental shelf in the Western Polygon based on international law, UNCLOS, and bilateral treaties with the United States, in accordance with Mexico's domestic legislation. On March 13, 2009, the CLCS accepted Mexico's arguments for extending its continental shelf up to 350 nautical miles (650 km; 400 mi) into the Western Polygon. Since this would extend Mexico's continental shelf well into territory claimed by the United States, however, Mexico and the U.S. would need to enter a bilateral agreement based on international law that delimits their respective claims.

Biota

Various biota include chemosynthetic communities near cold seeps and nonchemosynthetic communities such as bacteria and other micro – benthos, meiofauna, macrofauna, and megafauna (larger organisms such as crabs, sea pens, crinoids, and demersal fish and cetaceans including endangered ones) are living in the Gulf of Mexico. Recently, resident Bryde's whales within the gulf were classified as an endemic, unique subspecies and making them as one of the most endangered whales in the world. The Gulf of Mexico yields more finfish, shrimp, and shellfish annually than the south and mid-Atlantic, Chesapeake, and New England areas combined.

The Smithsonian Institution Gulf of Mexico holdings are expected to provide an important baseline of understanding for future scientific studies on the impact of the Deepwater Horizon oil spill. In Congressional testimony, Dr. Jonathan Coddington, Associate Director of Research and Collections at the Smithsonian's National Museum of Natural History, provides a detailed overview of the Gulf collections and their sources which Museum staff have made available on an online map. The samples were collected for years by the former Minerals Management Service (renamed the Bureau of Ocean Energy Management, Regulation and Enforcement) to help predict the potential impacts of future oil/gas explorations. Since 1979, the specimens have been deposited in the national collections of the National Museum of Natural History.

Pollution

Dead zone in the Gulf of Mexico

 

The major environmental threats to the Gulf are agricultural runoff and oil drilling. 

There are frequent "red tide" algae blooms that kill fish and marine mammals and cause respiratory problems in humans and some domestic animals when the blooms reach close to shore. This has especially been plaguing the southwest and southern Florida coast, from the Florida Keys to north of Pasco County, Florida.

In 1973 the United States Environmental Protection Agency prohibited the dumping of undiluted chemical waste by manufacturing interests into the Gulf and the military confessed to similar behavior in waters off Horn Island.

The Gulf contains a hypoxic dead zone that runs by east-west along the Texas-Louisiana coastline. In July 2008, researchers reported that between 1985 and 2008, the area roughly doubled in size and now stretches from near Galveston, Texas, to near Venice, Louisiana. It is now about 8,000 square miles (21,000 km²), nearly the record. Poor agricultural practices in the northern portion of the Gulf of Mexico have led to a tremendous increase of nitrogen and phosphorus in neighboring marine ecosystems, which has resulted in algae blooms and a lack of available oxygen. Occurrences of masculinization and estrogen suppression were observed as a result. An October 2007 study of the Atlantic croaker found a disproportioned sex ratio of 61% males to 39% females in hypoxic Gulf sites. This was compared with a 52% to 48% male-female ratio found in reference sites, showing an impairment of reproductive output for fish populations inhabiting hypoxic coastal zones.

Microplastics within semi-enclosed seas like the Gulf have been reported in high concentrations and the Gulf's first such study estimated concentrations that rival the highest globally reported.

There are 27,000 abandoned oil and gas wells beneath the Gulf. These have generally not been checked for potential environmental problems.

Ixtoc I explosion and oil spill

In June 1979, the Ixtoc I oil platform in the Bay of Campeche suffered a blowout leading to a catastrophic explosion, which resulted in a massive oil spill that continued for nine months before the well was finally capped. This was ranked as the largest oil spill in the Gulf of Mexico until the Deepwater Horizon oil spill in 2010.

Deepwater Horizon explosion and oil spill

Deepwater Horizon in flames after the explosion

 

On April 20, 2010, the Deepwater Horizon oil platform, located in the Mississippi Canyon about 40 miles (64 km) off the Louisiana coast, suffered a catastrophic explosion; it sank a day-and-a-half later. It was in the process of being sealed with cement for temporary abandonment, to avoid environmental problems. Although initial reports indicated that relatively little oil had leaked, by April 24, it was claimed by BP that approximately 1,000 barrels (160 m³) of oil per day were issuing from the wellhead, about 1-mile (1.6 km) below the surface on the ocean floor. On April 29, the U.S. government revealed that approximately 5,000 barrels (790 m³) per day, five times the original estimate, were pouring into the Gulf from the wellhead. The resulting oil slick quickly expanded to cover hundreds of square miles of ocean surface, posing a serious threat to marine life and adjacent coastal wetlands, and to the livelihoods of Gulf Coast shrimpers and fishermen. Coast Guard Rear Adm. Sally Brice O'Hare stated that the U.S. government will be "employing booms, skimmers, chemical dispersants and controlled burns" to combat the oil spill. By May 1, 2010, the oil spill cleanup efforts were underway, but hampered by rough seas and the "tea like" consistency of the oil. Cleanup operations were resumed after conditions became favorable. On May 27, 2010, The USGS had revised the estimate of the leak from 5,000 barrels per day (790 m³/d) to 12,000–19,000 barrels per day (3,000 m³/d) an increase from earlier estimates. On July 15, 2010, BP announced that the leak stopped for the first time in 88 days.

In July 2015 BP reached an $18.7bn settlement with the US government, the states of Alabama, Florida, Louisiana, Mississippi and Texas, as well as 400 local authorities. To date BP's cost for the clean-up, environmental and economic damages and penalties has reached $54bn.

Minor oil spills

According to the National Response Center, the oil industry has thousands of minor accidents in the Gulf of Mexico every year.

Brutus oil spill

On May 12, 2016, a release of oil from subsea infrastructure on Shell's Brutus oil rig released 2,100 barrels of oil. This leak created a visible 2 by 13 miles (3.2 by 20.9 km) oil slick in the sea about 97 miles (156 km) south of Port Fourchon, Louisiana, according to the U.S. Bureau of Safety and Environmental Enforcement.

Petroleum seep

From Wikipedia, the free encyclopedia

Naturally occurring oil seep near McKittrick, California, United States.

 

Petroleum seep near the Korňa in northern Slovakia.

 

Tar "volcano" in the Carpinteria, California asphalt mine. Oil exudes from joint cracks in the petroliferous shale forming the floor of mine. 1906 photo, U.S. Geological Survey Bulletin 321

 

Tar bubble at La Brea Tar Pits, California

 

A petroleum seep is a place where natural liquid or gaseous hydrocarbons escape to the earth's atmosphere and surface, normally under low pressure or flow. Seeps generally occur above either terrestrial or offshore petroleum accumulation structures. The hydrocarbons may escape along geological layers, or across them through fractures and fissures in the rock, or directly from an outcrop of oil-bearing rock. 

Petroleum seeps are quite common in many areas of the world, and have been exploited by mankind since paleolithic times. Natural products associated with these seeps include bitumen, pitch, asphalt and tar. In locations where seeps of natural gas are sufficiently large, natural "eternal flames" often persist. The occurrence of surface petroleum was often included in location names that developed; these locations are also associated with early oil and gas exploitation as well as scientific and technological developments, which have grown into the petroleum industry.

History of petroleum seep exploitation

Prehistory

The exploitation of bituminous rocks and natural seep deposits dates back to paleolithic times. The earliest known use of bitumen (natural asphalt) was by Neanderthals some 70,000 years ago, with bitumen adhered to ancient tools found at Neanderthal sites in Syria.

Ancient civilizations

After the arrival of Homo sapiens, humans used bitumen for construction of buildings and waterproofing of reed boats, among other uses. The use of bitumen for waterproofing and as an adhesive dates at least to the fifth millennium BCE in the early Indus community of Mehrgarh where it was used to line the baskets in which they gathered crops. The material was also used as early as the third millennium BCE in statuary, mortaring brick walls, waterproofing baths and drains, in stair treads, and for shipbuilding. According to Herodotus, more than four thousand years ago natural asphalt was employed in the construction of the walls and towers of Babylon, great quantities of it were found on the banks of the river Issus, one of the tributaries of the Euphrates, and this fact confirmed by Diodorus Siculus. Herodotus mentioned pitch spring on Zacynthus (Ionian islands, Greece). Also, Herodotus described a well for bitumen and oil near Ardericca in Cessia.

In ancient times, bitumen was primarily a Mesopotamian commodity used by the Sumerians and Babylonians, although it was also found in the Levant and Persia. Along the Tigris and Euphrates rivers, the area was littered with hundreds of pure bitumen seepages. The Mesopotamians used the bitumen for waterproofing boats and buildings. Ancient Persian tablets indicate the medicinal and lighting uses of petroleum in the upper levels of their society. In ancient Egypt, the use of bitumen was important in creating Egyptian mummies — in fact, the word mummy is derived from the Arab word mūmiyyah, which means bitumen. Oil from seeps was exploited in the Roman province of Dacia, now in Romania, where it was called picula. 

In East Asia these locations were known in China, where the earliest known drilled oil wells date to 347 CE or earlier. The ancient records of China and Japan are said to contain many allusions to the use of natural gas for lighting and heating. Petroleum was known as burning water in Japan in the 7th century. In his book Dream Pool Essays written in 1088, the polymathic scientist and statesman Shen Kuo of the Song Dynasty coined the word 石油 (Shíyóu, literally "rock oil") for petroleum, which remains the term used in contemporary Chinese. 

In southwest Asia the first streets of 8th century Baghdad were paved with tar, derived from natural seep fields in the region. In the 9th century, oil fields were exploited in the area around modern Baku, Azerbaijan. These fields were described by the Arab geographer Abu al-Hasan 'Alī al-Mas'ūdī in the 10th century, and by Marco Polo in the 13th century, who described the output of those wells as hundreds of shiploads. Distillation of petroleum was described by the Persian alchemist, Muhammad ibn Zakarīya Rāzi (Rhazes). There was production of chemicals such as kerosene in the alembic (al-ambiq), which was mainly used for kerosene lamps. Arab and Persian chemists also distilled crude oil in order to produce flammable products for military purposes. Through Islamic Spain, distillation became available in Western Europe by the 12th century. It has also been present in Romania since the 13th century, being recorded as păcură.

Eighteenth century Europe

In Europe, petroleum seeps were extensively mined near the Alsace city of Pechelbronn, where the vapor separation process was in use in 1742. In Switzerland c. 1710, the Russian-born Swiss physician and Greek teacher Eyrini d'Eyrinis discovered asphaltum at Val-de-Travers, (Neuchâtel). He established a bitumen mine de la Presta there in 1719 that operated until 1986. Oil sands here were mined from 1745 under the direction of Louis Pierre Ancillon de la Sablonnière, by special appointment of Louis XV. The Pechelbronn oil field was active until 1970, and was the birthplace of companies like Antar and Schlumberger. In 1745 under the Empress Elisabeth of Russia the first oil well and refinery were built in Ukhta by Fiodor Priadunov. Through the process of distillation of the "rock oil" (petroleum) he received a kerosene-like substance, which was used in oil lamps by Russian churches and monasteries (though households still relied on candles).

Colonial Americas

The earliest mention of petroleum seeps in the Americas occurs in Sir Walter Raleigh's account of the Pitch Lake on Trinidad in 1595. Thirty-seven years later, the account of a visit of a Franciscan, Joseph de la Roche d'Allion, to the oil springs of New York was published in Sagard's Histoire du Canada. In North America, the early European fur traders found Canadian First Nations using bitumen from the vast Athabasca oil sands to waterproof their birch bark canoes. A Swedish scientist, Peter Kalm, in his 1753 work Travels into North America, showed on a map the oil springs of Pennsylvania.

In 1769 the Portolà expedition, a group of Spanish explorers led by Gaspar de Portolà, made the first written record of the tar pits in California. Father Juan Crespí wrote, "While crossing the basin the scouts reported having seen some geysers of tar issuing from the ground like springs; it boils up molten, and the water runs to one side and the tar to the other. The scouts reported that they had come across many of these springs and had seen large swamps of them, enough, they said, to caulk many vessels. We were not so lucky ourselves as to see these tar geysers, much though we wished it; as it was some distance out of the way we were to take, the Governor [Portola] did not want us to go past them. We christened them Los Volcanes de Brea [the Tar Volcanoes]."

Modern extraction and industry

During the nineteenth and the beginning of the twentieth century, oil seepages in Europe were exploited everywhere with the digging, and later drilling, of wells near to their occurrences and the discovery of numerous small oil fields such as in Italy.

The modern history of petroleum exploitation, in relation to extraction from seeps, began in the 19th century with the refining of kerosene from crude oil as early as 1823, and the process of refining kerosene from coal by Nova Scotian Abraham Pineo Gesner in 1846. It was only after Ignacy Łukasiewicz had improved Gesner's method to develop a means of refining kerosene from the more readily available "rock oil" ("petr-oleum") seeps in 1852 that the first rock oil mine was built near Krosno in central European Galicia (Poland/Ukraine) in 1853. In 1854, Benjamin Silliman, a science professor at Yale University, was the first American to fractionate petroleum by distillation. These discoveries rapidly spread around the world. 

The world's first commercial oil well was drilled in Poland in 1853, and the second in nearby Romania in 1857. At around the same time the world's first, but small, oil refineries were opened at Jasło in Poland, with a larger one being opened at Ploiești in Romania shortly after. Romania is the first country in the world to have its crude oil output officially recorded in international statistics, namely 275 tonnes. By the end of the 19th century the Russian Empire, particularly in Azerbaijan, had taken the lead in production.

The first oil "well" in North America was in Oil Springs, Ontario, Canada in 1858, dug by James Miller Williams. The US petroleum industry began with Edwin Drake's drilling of a 69-foot (21 m) oil well in 1859 on Oil Creek near Titusville, Pennsylvania, both named for their petroleum seeps. 

Other sources of oil initially associated with petroleum seeps were discovered in Peru's Zorritos District in 1863, in the Dutch East Indies on Sumatra in 1885, in Persia at Masjed Soleiman in 1908, as well as in Venezuela, Mexico, and the province of Alberta, Canada.

By 1910, these too were being developed at an industrial level. Initially these petroleum sources and products were for use in fueling lamps, but with the development of the internal combustion engine, their supply could not meet the increased demand; many of these early traditional sources and "local finds" were soon outpaced by technology and demand.

Petroleum seep formation

Tar seep at Rozel Point, on the mud (salt) flats of the Great Salt Lake.

 

Re-worked tar on beach at Rozel Point, Utah. The black rocks are basalt: the tar is brown and looks like cow manure.

 

A petroleum seep occurs as a result of the seal above the reservoir being breached, causing tertiary migration of hydrocarbons towards the surface under the influence of the associated buoyancy force. The seal is breached due to the effects of overpressure adding to the buoyancy force, overcoming the capillary resistance that initially kept the hydrocarbons sealed.

Causes of overpressure

The most common cause of overpressure is the rapid loading of fine-grained sediments preventing water from escaping fast enough to equalise the pressure of the overburden. If burial stops or slows, then excess pressure can equalize at a rate that is dependent on the permeability of the overlying and adjacent rocks. A secondary cause of overpressure is fluid expansion, due to changes in the volume of solid and/or fluid phases. Some examples include: aquathermal pressuring (thermal expansion), clay dehydration reactions (such as anhydrite) and mineral transformation (such as kerogen to oil/gas and excess kerogen).

Types of seeps

There are two types of seep that can occur, depending on the degree of overpressure. Capillary failure can occur in moderate overpressure conditions, resulting in widespread but low intensity seepage until the overpressure equalizes and resealing occurs. In some cases, the moderate overpressure cannot be equalized because the pores in the rock are small so the displacement pressure, the pressure required to break the seal, is very high. If the overpressure continues to increase to the point that it overcomes the rock's minimum stress and its tensile strength before overcoming the displacement pressure, then the rock will fracture, causing local and high intensity seepage until the pressure equalizes and the fractures close.

California seeps

Diatomite outcrop containing oil that seeps out in hot weather, near McKittrick, in Kern County California.

 

Oil stained outcrop near Kern River oilfield, in Kern County California.

 

Oil Seep in the Simi Valley area of Ventura County, CA

 

California has several hundred naturally occurring seeps, found in 28 counties across the state. Much of the petroleum discovered in California during the 19th century was from observations of seeps. The world's largest natural oil seepage is Coal Oil Point in the Santa Barbara Channel, California. Three of the better known tar seep locations in California are McKittrick Tar Pits, Carpinteria Tar Pits and the La Brea Tar Pits.

At Kern River Oil Field, there are no currently active seeps. However, oil-stained formations in the outcrops remain from previously active seeps. Petroleum seeps may be a significant source of pollution.

Seeps known as the McKittrick Tar Pits occur in the McKittrick Oil Field in western Kern County. Some of the seeps occur in watersheds that drain toward the San Joaquin Valley floor. These seeps were originally mined for asphalt by Native Americans, and in the 1870s larger scale mining was undertaken by means of both open pits and shafts. In 1893, Southern Pacific Railroad constructed a line to Asphalto, two miles from present day McKittrick. Fuel oil for the railroad was highly desired, especially since there are very few coal-bearing formations in California. The field is produced now by conventional oil wells, as well as by steam fracturing. 

The oil seeps at McKittrick are located in diatomite formation that has been thrust faulted over the younger sandstone formations. Similarly, in the Upper Ojai Valley in Ventura County, tar seeps are aligned with east-west faulting. In the same area, Sulphur Mountain is named for the hydrogen sulfide-laden springs. The oil fields in the Sulphur Mountain area date from the 1870s. Production was from tunnels dug into the face of a cliff, and produced by gravity drainage.

The petroleum fly (Helaeomyia petrolei) is a species of fly that was first described from the La Brea Tar Pits and is found at other California seeps as well. It is highly unusual among insects for its tolerance of crude oil; larvae of this fly live within petroleum seeps where they feed on insects and other arthropods that die after becoming trapped in the oil.

Offshore seeps

In the Gulf of Mexico, there are more than 600 natural oil seeps that leak between one and five million barrels of oil per year, equivalent to roughly 80,000 to 200,000 tonnes. When a petroleum seep forms underwater it may form a peculiar type of volcano known as an asphalt volcano.

The California Division of Oil, Gas and Geothermal Resources published a map of offshore oil seeps from Point Aguello (north of Santa Barbara) to Mexico. In addition, they published a report describing the seeps. The report also discusses the underground blowout at Platform A which caused the 1969 Santa Barbara oil spill. It also describes accounts from divers, who describe seepage changes after the 1971 San Fernando earthquake.

In Utah, there are natural oil seeps at Rozel Point on the Great Salt Lake. The oil seeps at Rozel Point can be seen when the lake level drops below an elevation of approximately 4,198 feet (1,280 m); if the lake level is higher, the seeps are underwater. The seeps can be found by going to the Golden Spike historical site, and from there, following signs for the Spiral Jetty. Both fresh tar seeps and re-worked tar (tar caught by the waves and thrown up on the rocks) are visible at the site. 

The petroleum seeping at Rozel Point is high in sulfur, but has no hydrogen sulfide. This may be related to deposition in a hypersaline lacustrine environment.