Gulf of Mexico

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Gulf of Mexico
Undersea topography of the Gulf of Mexico
Location	American Mediterranean Sea
Coordinates	Coordinates: 25°N 90°W
River sources	Mississippi River
Ocean/sea sources	Atlantic Ocean
Basin countries	USA, Mexico, Cuba
Max. width	1,500 km (932.06 mi)
Surface area	1,550,000 km2 (600,000 sq mi)

The Gulf of Mexico (Spanish: Golfo de México) is an ocean basin largely surrounded by the North American continent.^[1] 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. In Texas and Louisiana, the Gulf Coast it is 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.^[2] The Gulf's basin is roughly oval and is approximately 810 nautical miles (1,500 km) 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 Yucatan 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 615,000 mi² (1.6 million km²). Almost half of the basin is shallow continental shelf waters. The basin contains a volume of roughly 660 quadrillion gallons (2.5 × 10⁶ km³).^[3]

Extent

The International Hydrographic Organization defines the southeast limit of the Gulf of Mexico as follows:^[4]

A line joining 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^[2][5][6] who have studied the geology of the Gulf of Mexico, is that prior to 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 Yucatan, 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.^[7][8]

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 thick 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 thickness, 35 kilometers, of normal continental crust. It was at this time that tectonics first created a connection to the Pacific Ocean across central Mexico and later eastward to the Atlantic Ocean. This flooded the subsiding basin created by rifting and crustal thinning to create the Gulf of Mexico. 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. Initially, 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.^{[5][6][9][10]}

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 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.^[5][10][11]

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 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.^[5][10][11]

To the east, the stable Florida platform was not covered by the sea until the latest Jurassic or the beginning of Cretaceous time. The Yucatan 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.^[12]

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.^[13] 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.^{[2][6][10][14]} 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 Yucatan Peninsula.

Today, the Gulf of Mexico has the following 7 main areas:^[12]

• 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 just east of the Mississippi 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 Yucatan 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

Fishing boats in Biloxi

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.

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.^[15] 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.

Geography

Gulf beach near Sabine Pass

The Mississippi River Watershed is the largest drainage basin of the Gulf of Mexico Watershed.^[16]

Map of northern part of Gulf of Mexico

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.^[17] 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.^[18] 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.^[19]

The Gulf is considered aseismic; however, mild tremors have been recorded throughout history (usually 5.0 or less on the Richter scale). Earthquakes may be caused by interactions between sediment loading on the sea floor and adjustment by the crust.^[20]

2006 earthquake

On September 10, 2006, the U.S. Geological Survey National Earthquake Information Center reported that a strong earthquake, ranking 6.0 on the Richter scale, 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 major damages, injuries or casualties.^[21][22] Items were knocked from shelves and seiches were observed in swimming pools in parts of Florida.^[23] The earthquake was described by the USGS as a midplate earthquake, the largest and most widely felt recorded in the past three decades in the region.^[23]
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 of America: Maritime boundary agreement between the United States of America and the Republic of Cuba, of December 16, 1977.

Mexico and United States of America: 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), of June 9, 2000.

On 13 December 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.^[24] 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 13 March 2009, the CLCS accepted Mexico’s arguments for extending its continental shelf up to 350 NM 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.

	Texas	United States  Louisiana •  Mississippi •  Alabama	Florida
	Mexico  Tamaulipas		Atlantic Ocean
		Gulf of Mexico
	Veracruz	Mexico  Tabasco •  Campeche •  Yucatán •  Quintana Roo	Cuba Caribbean Sea

Biota

Various biota include chemosynthetic communities near cold seeps and nonchemosynthetic communities such as bacteria and other microbenthos, 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.^[25] The Gulf of Mexico yields more finfish, shrimp, and shellfish annually than the south and mid-Atlantic, Chesapeake, and New England areas combined.^[3]

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.^[26] 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.^[27]

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^[28] 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.

The Gulf contains a hypoxic dead zone that runs 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.^[29] 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.^[30]

There are 27,000 abandoned oil and gas wells beneath the Gulf. These have generally not been checked for potential environmental problems.^[31]

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

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.^[32] It was in the process of being sealed with cement for temporary abandonment, to avoid environmental problems.^[31] 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.^[33] 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.^[34] 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.^[35] 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. As of May 1, 2010, the oil spill cleanup efforts are underway, but hampered by rough seas and the "tea like" consistency of the oil. As of May 27, 2010, 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)^[36] an increase from earlier estimates. On July 15, 2010, BP announced that the leak stopped for the first time in 88 days.

Chesapeake Bay

From Wikipedia, the free encyclopedia

 

Coordinates: 36°59′45″N 75°57′34″W

Chesapeake Bay
Estuary
The Chesapeake Bay – Landsat photo
Name origin: Chesepiooc, Algonquian for village "at a big river"
Country	United States
States	Maryland, Virginia
Tributaries
- left	Chester River, Choptank River, Nanticoke River, Pocomoke River
- right	Patapsco River, Patuxent River, Potomac River, Rappahannock River, York River, James River
Source	Susquehanna River
- location	Havre de Grace, MD
- elevation	0 ft (0 m)
- coordinates	39°32′35″N 76°04′32″W
Mouth	Atlantic Ocean
- location	Virginia Beach, VA
- elevation	0 ft (0 m)
- coordinates	36°59′45″N 75°57′34″W
Length	200 mi (322 km)
Width	30 mi (48 km)
Depth	46 ft (14 m)
Basin	64,299 sq mi (166,534 km2)
Area	4,479 sq mi (11,601 km2)
Discharge
- average	78,300 cu ft/s (2,217 m3/s) [1]
- max	389,000 cu ft/s (11,015 m3/s)
- min	9,800 cu ft/s (278 m3/s)
Chesapeake Bay Watershed
Ramsar Wetland
Designated:	June 4, 1987

The Chesapeake Bay (/ˈtʃɛsəpiːk/ CHESS-ə-peek) is an estuary lying inland from the Atlantic Ocean surrounded by the states of Maryland and Virginia, the largest such body in the US.^[2] More than 150 rivers and streams^[2] flow into the bay's 64,299 square miles (166,534 km²) drainage basin, which covers parts of six states (New York, Pennsylvania, Delaware, Maryland, Virginia, and West Virginia) and the District of Columbia.^[3]

The bay is approximately 200 miles (300 km) long from its northern headwaters in the Susquehanna River to its outlet in the Atlantic Ocean. It is 2.8 miles (4.5 km) wide at its narrowest (between Kent County's Plum Point near Newtown and the Harford County shore near Romney Creek) and 30 miles (50 km) at its widest (just south of the mouth of the Potomac River). Total shoreline including tributaries is 11,684 miles (18,804 km), representing a surface area of 4,479 square miles (11,601 km²). Average depth is 46 feet (14 m), reaching a maximum of 208 feet (63 m).

The bay is spanned twice, in Maryland by the Chesapeake Bay Bridge from Sandy Point (near Annapolis) to Kent Island, and in Virginia by the Chesapeake Bay Bridge-Tunnel connecting Virginia Beach to Cape Charles.

Known for both its beauty and bounty, the bay is becoming "emptier", with fewer crabs, oysters, and watermen in recent years.^[4]

Etymology

The word Chesepiooc is an Algonquian word referring to a village "at a big river." It is the seventh oldest surviving English place-name in the U.S., first applied as "Chesepiook" by explorers heading north from the Roanoke Colony into a Chesapeake tributary in 1585 or 1586.^[5] In 2005, Algonquian linguist Blair Rudes "helped to dispel one of the area's most widely held beliefs: that 'Chesapeake' means something like 'Great Shellfish Bay.' It does not, Rudes said. The name might actually mean something like 'Great Water,' or it might have been just a village at the bay's mouth."^[6]

Physical geography

Geology and formation

The Chesapeake Bay is the ria, or drowned valley, of the Susquehanna, meaning that it was where the river flowed when the sea level was lower. It is not a fjord, because the Laurentide Ice Sheet never reached as far south as the northernmost point on the bay. North of Baltimore, the western shore borders the hilly Piedmont region of Maryland; south of the city the Bay lies within the state's low-lying coastal plain, with sedimentary cliffs to the west, and flat islands, winding creeks and marshes to the east. The large rivers entering the bay from the west have broad mouths and are extensions of the main ria for miles up the course of each river.

The bay's geology, its present form, and its very location were created by a bolide impact event at the end of the Eocene (about 35.5 million years ago), forming the Chesapeake Bay impact crater and the Susquehanna River valley much later. The bay was formed starting about 10,000 years ago when rising sea levels at the end of the last ice age flooded the Susquehanna River valley.^[3] Parts of the bay, especially the Calvert County, Maryland, coastline, are lined by cliffs composed of deposits from receding waters millions of years ago. These cliffs, generally known as Calvert Cliffs, are famous for their fossils, especially fossilized shark teeth which are commonly found washed up on the beaches next to the cliffs. Scientists' Cliffs is a beach community in Calvert County named for the desire to create a retreat for scientists when the community was founded in 1935.^[7]

Hydrology

View of the Eastern Bay in Maryland at sunset

The Chesapeake Bay Bridge, near Annapolis, Maryland

Much of the bay is shallow. At the point where the Susquehanna River flows into the bay, the average depth is 30 feet (9 m), although this soon diminishes to an average of 10 feet (3 m) from the city of Havre de Grace, Maryland, for about 35 miles (56 km), to just north of Annapolis. On average, the depth of the bay is 21 feet (7 m), including tributaries;^[8] over 24% of the bay is less than 6 ft (2 m) deep.^[9]

Because the bay is an estuary, it has fresh water, salt water and brackish water. Brackish water has three salinity zones: oligohaline, mesohaline, and polyhaline. The freshwater zone runs from the mouth of the Susquehanna River to north Baltimore. The oligohaline zone has very little salt. Salinity varies from 0.5 ppt to 10 ppt, and freshwater species can survive there. The north end of the oligohaline zone is north Baltimore and the south end is the Chesapeake Bay Bridge. The mesohaline zone has a medium amount of salt and runs from the Bay Bridge to the mouth of the Rappahannock River. Salinity there ranges from 10.7 ppt to 18 ppt. The polyhaline zone is the saltiest zone, and some of the water can be as salty as sea water. It runs from the mouth of the Rappahannock River to the mouth of the bay. The salinity ranges from 18.7 ppt to 36 ppt. (36 ppt is as salty as the ocean.)

The climate of the area surrounding the bay is primarily humid subtropical, with hot, very humid summers and cold to mild winters. Only the area around the mouth of the Susquehanna River is continental in nature, and the mouth of the Susquehanna River and the Susquehanna flats often freeze in winter. It is rare for the surface of the bay to freeze in winter, something which happened most recently in the winter of 1976–77.^[10]

The largest rivers flowing directly into the bay, from north to south, are:

• Susquehanna River:
• Patapsco River;
• Chester River;
• Choptank River;
• Patuxent River;
• Nanticoke River;
• Potomac River;
• Pocomoke River;
• Rappahannock River;
• York River;
• James River.

Another river flowing into Chesapeake Bay is the Wicomico River, not to be confused with the tributary of the Potomac River.

Flora and fauna

Food chain diagram for waterbirds of the Chesapeake Bay

The Chesapeake Bay is home to numerous fauna that either migrate to the bay at some point during the year or live there year round. There are over 300 species of fish and numerous shellfish and crab species. Some of these include the Atlantic menhaden, Striped bass, American eel, Eastern oyster, and the Blue crab.

Birds include Osprey, Great Blue Heron, Bald Eagle^[11] and Peregrine Falcon, the last two of which were threatened by DDT; their numbers plummeted but have risen in recent years.^[12] The Piping Plover is a near threatened species which inhabits the wetlands.^[12]

Numerous flora also make the Chesapeake Bay their home both on land and underwater. Common submerged aquatic vegetation includes eelgrass and widgeon grass. A report in 2011 suggested that information on underwater grasses would be released, because "submerged grasses provide food and habitat for a number of species, adding oxygen to the water and improving water clarity."^[13] Other vegetation that makes its home in other parts of the bay are wild rice, various trees like the red maple and bald cypress, and spartina grass and phragmites.^[14]

History

European exploration and settlement

Later (1630) version of the 1612 map by Captain John Smith during his exploration of the Chesapeake. Note that the map is oriented with west at top.

In 1524, Italian explorer Giovanni da Verrazzano, (1485-1528), in service of the French crown, (famous for sailing through and thereafter naming the entrance to New York Bay as the "Verrazzano Narrows", including now in the 20th Century, a suspension bridge also named for him) sailed past the Chesapeake, but did not enter the bay.^[15] Spanish explorer Lucas Vásquez de Ayllón sent an expedition out from Hispaniola in 1525 which reached the mouths of the Chesapeake and Delaware Bays. It may have been the first European expedition to explore parts of the Chesapeake Bay, which the Spaniards called "Bahía de Santa María" ("Bay of St. Mary")or "Bahía de Madre de Dios."("Bay of the Mother of God")^[16] De Ayllón established a short-lived Spanish mission settlement, San Miguel de Gualdape, in 1526 along the Atlantic coast. Many scholars doubt the assertion that it was as far north as the Chesapeake; most place it in present-day Georgia's Sapelo Island.^[17] In 1573, governor of Spanish Florida, Pedro Menéndez de Márquez conducted further exploration of the Chesapeake.^[15]

With the arrival of English colonists under Sir Walter Raleigh and Humphrey Gilbert in the late 16th Century to found a colony, later settled at Roanoke Island (off the present-day coast of North Carolina) for the Virginia Company, marked the first time that Europeans approached the gates to the Chesapeake Bay between the capes of Cape Charles and Cape Henry. Three decades later, in 1607, Europeans again entered the Bay. Captain John Smith of England explored and mapped the bay between 1607 and 1609, resulting in the publication in 1612 back in the British Isles of "A Map of Virginia".^[18] Smith wrote in his journal: "Heaven and earth have never agreed better to frame a place for man's habitation."^[19] The new laying out of the "Captain John Smith Chesapeake National Historic Trail", the United States' first designated "all-water" National Historic Trail, was created in July 2006, by the National Park Service of the U.S. Department of the Interior following the route of Smith's historic 17th Century voyage.^[20]

Because of economic hardships and civil strife in the "Mother Land", there was a mass migration of southern English Cavaliers and their servants to the Chesapeake Bay region between 1640 and 1675, to both of the new colonies of the Province of Virginia and the Province of Maryland.

American Revolution to the present

The Chesapeake Bay was the site of the Battle of the Chesapeake (also known as the "Battle of the Capes" - Cape Charles and Cape Henry) in 1781, during which the French fleet defeated the Royal Navy in the decisive naval battle of the American Revolutionary War and enabling General George Washington along with his French allied armies under Comte de Rochambeau, marching down from New York to bottle up the rampaging southern British Army of Lord Cornwallis from the North and South Carolinas at the siege of Battle of Yorktown in Yorktown, Virginia. Their marching route from Newport, Rhode Island through Connecticut, New York State, Pennsylvania, New Jersey and Delaware to the "Head of Elk" by the Susquehanna River along the shores and also partially sailing down the Bay to Virginia (it is also the subject of another designated National Historic Trail under the National Park Service as the Washington-Rochambeau Revolutionary Route). It would again see conflict during War of 1812; During the year of 1813, from their base on Tangier Island, British naval forces under the command of Admiral George Cockburn raided and plundered several towns on the shores of the Chesapeake, treating the Bay as if it were a "British Lake". In September 1814, British warships attacked Fort McHenry in Baltimore with Admirals Cockburn and Alexander Cochrane and sent ashore Gen. Robert Ross who was later killed by snipers before engaging in the Battle of North Point with fierce Maryland state militia resistance. In response, the Chesapeake Bay Flotilla, a fleet of shallow-draft armed barges under the command of U.S. Navy Commodore Joshua Barney, was assembled to stall British shore raids and attacks, but were later driven up the Patuxent River and scuttled. In a separate attack earlier, British ships loaded with troops sailed up the Chesapeake, landed on the west side of the Patuxent at Benedict, Maryland near Washington D.C., and trekked overland to burn the capital in August 1814. A few days later in a "pincer attack", they also sailed up the Potomac River to attack Fort Washington below the National Capital and demand a ransom from the nearby port town of Alexandria, Virginia.

There were so-called "Oyster Wars" in the late Nineteenth and early Twentieth Centuries. During the Great Depression in the 1930s, catching and eating oysters continued to be popular.^[21]

Today, the Calvert Cliffs Nuclear Power Plant on the historic "Calvert Cliffs" in Calvert County on the Western Shore of Maryland since the 1960s uses water from the Bay to cool its reactor.

Navigation

Lighthouses and lightships such as Chesapeake have helped guide ships into the bay

The Chesapeake Bay forms a link in the Intracoastal Waterway, of the bays, sounds and inlets between the off-shore barrier islands and the coastal mainland along the Atlantic coast connecting the Chesapeake and Delaware Canal (linking the Bay to the north and the Delaware River) with the Albemarle and Chesapeake Canal (linking the Bay, to the south, via the Elizabeth River, by the cities of Norfolk and Portsmouth to the Albemarle Sound and Pamlico Sound in North Carolina and further to the Sea Islands of Georgia). A busy shipping channel (dredged by the U.S. Army Corps of Engineers since the 1850s) runs the length of the Bay, is an important transit route for large container vessels entering or leaving the Port of Baltimore, and further north through the Chesapeake and Delaware Canal to the ports of Wilmington and Philadelphia on the Delaware River.

During the later half of the 19th Century and first half of the 20th Century, the Bay was plied by passenger steamships and packet boat lines connecting the various cities on it, notably the Baltimore Steam Packet Company ("Old Bay Line").

In the later Twentieth Century, a series of road crossings were built. One, The Chesapeake Bay Bridge (also known as the Governor William Preston Lane Bridge) between the state capital of Annapolis, Maryland and Matapeake on the Eastern Shore, crossing Kent Island, constructed 1949-1952. The Chesapeake Bay Bridge-Tunnel, connecting Virginia's Eastern Shore with its mainland (at the metropolitan areas of Virginia Beach, Norfolk, Portsmouth, and Chesapeake), is approximately 20 miles (32 km) long; it has trestle bridges as well as two stretches of two-mile (3 km)-long tunnels which allow unimpeded shipping; the bridge is supported by four 5.25-acre (21,200 m²) man-made islands.^[22]

Tides

Tides in the Chesapeake Bay exhibit an interesting and very unique behavior due to the nature of the topography (both horizontal and vertical shape), wind driven circulation, and how the Bay interacts with oceanic tides. Studies into the peculiar behavior of tides both at the northern and southern extents of the Bay have been made as far back as the late 1970s. Wang and Elliot [1979] noted sea level fluctuations at periods of 5 days, driven by sea level changes at the Bay’s mouth on the Atlantic coast and local lateral winds, and 2.5 days, caused by resonant oscillations driven by local longitudinal winds.^[23] Wang [1979] later found that the geometry of the Bay permits for a resonant period of 1.46 days using quarter wavelength theory.^[24]

Figure 2 from Zhong et al. [2008]: (a) energy spectra of water level fluctuations at three tidal gauge stations at 95% confidence intervals and (b) a zoom-in view of the tidal band.

More recently, Zhong, Li, and Foreman [2008] investigated the sea level variability and resonance of the Chesapeake Bay.^[25] They found that the disparity in sea level variability exhibited at sites in the northern versus southern Bay are due to strong frictional dissipation from shallowing water depth in the northern Bay. This can be seen in the energy spectra from various sites in the Bay (at left). Part B shows that the Baltimore metropolitan area and the Chesapeake Bay Bridge-Tunnel (CBBT) exhibit strong power at the 0.5 day period, with CBBT showing a larger response to this period, corresponding to normal semi-diurnal tides. In contrast, at a period larger than 1 day, Baltimore and CBBT both exhibit an oscillatory period of ~1.3 days, but the location feeling the larger influence is Baltimore.

A good example of how the different Chesapeake Bay sites experience different tides can be seen in the tidal predictions put out by the National Oceanographic and Atmospheric Administration (NOAA), (see figure at right).

Example Chesapeake Bay tides from Baltimore and CBBT for quarter and full moons during June 2013.

Examples will be shown for Baltimore and CBBT sites for June 16–17, 2013 (first quarter moon) and for June 23–24, 2013 (full moon); these sun-earth-moon geometries hold through the lunar month as well as year.

• For the CBBT site, at the southernmost point of the Bay where it meets the Atlantic Ocean near Norfolk, Virginia and the capes of Charles and Henry, there is a distinct semi-diurnal tide throughout the lunar month, with small amplitude modulations during spring (new/full moon) vs. neap (one/three quarter moon) tidal periods. The main forcing of the CBBT tides are typical, semi-diurnal ocean tides that the East Coast of the United States experiences.
• In contrast, Baltimore, in the northern portion of the Bay, experiences a noticeable modulation to form its mixed tidal nature during spring vs. neap tides. Spring tides, when the sun-earth-moon system forms a line, cause the largest tidal amplitudes during lunar monthly tidal variations. In contrast, neap tides, when the sun-earth-moon system forms a right angle, are muted, and in a semi-diurnal tidal system (such as that seen at the Ches. Bay Bridge site) this can be seen as a lowest intertidal range.

Two interesting points of comparison that arises from using these two sites at opposite ends of the bay is in their tidal characteristics: semi-diurnal tide for CBBT and mixed tide for Baltimore (due to resonance in the Bay) and the differences in amplitude (due to dissipation in the Bay), points which have been expounded upon earlier.

Left: Contours of locations in the Bay which experience the same range (corange) between high and low tide.Right: Contours of locations in the Bay showing (in solar hours) how the tide progresses up the Bay and what locations experience at the same time (cotidal) the high/low tide.

To understand the Chesapeake Bay tides structure further than just the CBBT and Baltimore sites, two additional plots show the cotidal ranges and time of occurrence are included (at left; adapted from Fisher [1986]). They qualitatively show locations in the bay that experience similar magnitude tidal ranges as well as how the tidal signal progresses through the Bay. For example, using the mouth of the Bay (near CBBT) as a reference, the plot on the left shows that Upper Bay sites (Baltimore for example) should experience a lag in their tidal signals close to 12 hours. This is confirmed in the tidal gauge plots above, with the evening high tide at CBBT on June 23 occurring 12 hours prior to the morning high tide at Baltimore on June 24.

It is important to note that due to its estuarine nature, the Chesapeake Bay experiences not only barotropic flows driven by tidal induction but also experiences baroclinic flows driven by density differences, both of which have tidal characteristics [Li et al., 1998].^[26] In the north part of the Bay, where the Bay is both shallow and quasi-vertically homogeneous with respect to density, the main component of the Bay's tides are the barotropic component (the Lunar and Solar components). However, as you travel south in the bay, density in the vertical begins to vary and stratification occurs due to the relatively fresher water flowing out of the Bay with relatively more saline water flowing into the Bay at depth.^[27] The most significant density gradients in the vertical are near the center channel of the Bay, where it is deepest, and at the mouth, where the inflow of oceanic waters are most saline. Due to this vertical stratification, baroclinic waves can set up along the density interface and can have a non-negligible impact on the tidal flow, and both the barotropic and baroclinic parts of the ultimate tidal flow are also dependent on the depth of the water [Li et al., 1998].^[26]

Economy

Fishing industry

A skipjack, part of the oystering fleet in Maryland

The bay is mostly known for its seafood production, especially blue crabs,^[28] clams and oysters. In the middle of the twentieth century, the bay supported 9,000 full-time watermen, according to one account.^[28] Today, the body of water is less productive than it used to be because of runoff from urban areas (mostly on the Western Shore) and farms (especially on the Eastern Shore and in the Susquehanna River watershed), over-harvesting, and invasion of foreign species.

The plentiful oyster harvests led to the development of the skipjack, the state boat of Maryland, which is the only remaining working boat type in the United States still under sail power. Other characteristic bay-area workboats include sail-powered boats such as the log canoe, the pungy, the bugeye, and the motorized Chesapeake Bay deadrise, the state boat of Virginia.^[29]

In contrast to harvesting wild oysters, oyster farming is a growing industry for the bay to help maintain the estuary's productivity as well as a natural effort for filtering impurities such as excess nutrients from the water in an effort to reduce the effects of man-made pollution. The Chesapeake Bay Program is using oysters to reduce the amount of nitrogen compounds entering the Chesapeake Bay.^[30]

Oysters are hermaphroditic and will change gender at least once during their lifetime, often starting as male and ending as female; there are numerous ways to cook and eat them, as well as recipes and sauces to accompany oyster dishes.^[21] One account:

The Chesapeake oyster – sometimes called Chesapeake white gold – has a flavor and texture that begs connoisseurs to come back and shuck just a few more.

The bay is famous for its rockfish, a regional name for striped bass. Once on the verge of extinction, rockfish have made a significant comeback because of legislative action that put a moratorium on rockfishing, which allowed the species to re-populate. Rockfish are now able to be fished in strictly controlled and limited quantities.

Tourism and recreation

The Thomas Point Shoal Light in Maryland

The Chesapeake Bay is a main feature for tourists who visit Maryland and Virginia each year. Fishing, crabbing, swimming, boating, kayaking,^[11] and sailing are extremely popular activities enjoyed on the waters of the Chesapeake Bay. As a result, tourism has a notable impact on Maryland's economy^[31] One report suggested that Annapolis was an appealing spot for families, water sports and boating.^[32] Commentator Terry Smith spoke about the bay's beauty:

The water is glassy, smooth and gorgeous, his wake white against the deep blue. That's the problem with the Chesapeake. It's so damned beautiful.^[19]

One account suggested how the Chesapeake attracts people:

You see them everywhere on Maryland's Eastern Shore, the weekend sailors. They are unmistakable with their deep tans, their baggy shorts, their frayed polo shirts, their Top-Siders worn without socks. Some may not even own their own boats, much less win regattas, but they are inexorably drawn to the Chesapeake Bay ... I planned to spend my days boating, eating as many Chesapeake Bay blue crabs as possible and making a little study of Eastern Shore locals. For city folk like me, they're interesting, even exotic –the weather-beaten crabbers and oystermen called "watermen," gentlemen-farmers and sharecroppers, boat builders, antiques dealers – all of whom sound like Southerners with mouthfuls of marbles when they talk. — Susan Spano, LA Times, 2008^[33]

Environmental problems

Pollution and runoff

Tidal wetlands of the Chesapeake Bay

Environmental Protection Agency photo of dead menhaden floating in the bay in June 1973

Reeds along the bay

In the 1970s, the Chesapeake Bay was discovered to contain one of the planet's first identified marine dead zones, where hypoxic waters were so depleted of oxygen that they were unable to support life, resulting in massive fish kills. Today the bay's dead zones are estimated to kill 75,000 tons of bottom-dwelling clams and worms each year, weakening the base of the estuary's food chain and robbing the blue crab in particular of a primary food source. Crabs are sometimes observed to amass on shore to escape pockets of oxygen-poor water, a behavior known as a "crab jubilee". Hypoxia results in part from large algal blooms, which are nourished by the runoff of residential, farm and industrial waste throughout the watershed. One report in 2010 criticized Amish farmers for having cows which "generate heaps of manure that easily washes into streams and flows onward into the Chesapeake Bay."^[34]

U.S. Navy sailors looking for trash during "Clean The Bay Day" in 2008

The runoff and pollution have many components that help contribute to the algal blooms which is mainly fed by phosphorus and nitrogen.^[35] This algae prevents sunlight from reaching the bottom of the bay while alive and deoxygenates the bay's water when it dies and rots. The erosion and runoff of sediment into the bay, exacerbated by devegetation, construction and the prevalence of pavement in urban and suburban areas, also blocks vital sunlight. The resulting loss of aquatic vegetation has depleted the habitat for much of the bay's animal life. Beds of eelgrass, the dominant variety in the southern bay, have shrunk by more than half there since the early 1970s. Overharvesting, pollution, sedimentation and disease has turned much of the bay's bottom into a muddy wasteland.^[36]

One particularly harmful source of toxicity is Pfiesteria piscicida, which can affect both fish and humans. Pfiesteria caused a small regional panic in the late 1990s when a series of large blooms started killing large numbers of fish while giving swimmers mysterious rashes, and nutrient runoff from chicken farms was blamed for the growth.^[37]

The bay improved slightly in terms of the overall health of its ecosystem, earning a rating of 31 out of 100 in 2010, up from 28 in 2008.^[2] An estimate in 2006 from a "blue ribbon panel" said cleanup costs would be $15 billion.^[19] Compounding the problem is the fact that 100,000 new residents move to the area each year.^[19] A report in 2008 in the Washington Post suggested that government administrators had overstated progress on cleanup efforts as a way to "preserve the flow of federal and state money to the project."^[38] In 2011 in January, there were reports that millions of fish had died, but officials suggested it was probably the result of extremely cold weather.^[39]

Depletion of oysters

Oyster boats at war off the Maryland shore (1886 wood engraving). Regulation of the oyster beds in Virginia and Maryland has existed since the 19th century.

While the bay's salinity is ideal for oysters and the oyster fishery was at one time the bay's most commercially viable,^[40] the population has in the last fifty years been devastated. Maryland once had roughly 200,000 acres (810 km²) of oyster reefs. Today it has about 36,000.^[40] It has been estimated that in pre-colonial times, oysters could filter the entirety of the bay in about 3.3 days; by 1988 this time had increased to 325 days.^[41] The harvest's gross value decreased 88% from 1982 to 2007.^[42] One report suggested the bay had fewer oysters in 2008 than 25 years earlier.^[4]

A cluster of oysters grown in a sanctuary

The primary problem is overharvesting. Lax government regulations allow anyone with a license to remove oysters from state-owned beds, and although limits are set, they are not strongly enforced.^[40] The overharvesting of oysters has made it difficult for them to reproduce, which requires close proximity to one another. A second cause for the oyster depletion is that the drastic increase in human population caused a sharp increase in pollution flowing into the bay.^[40] The bay's oyster industry has also suffered from two diseases: MSX and Dermo.^[43]

The depletion of oysters has had a particularly harmful effect on the quality of the bay. Oysters serve as natural water filters, and their decline has further reduced the water quality of the bay. Water that was once clear for meters is now so turbid that a wader may lose sight of their feet before their knees are wet.

Efforts of federal, state and local governments, working in partnership through the Chesapeake Bay Program, and the Chesapeake Bay Foundation and other nonprofit environmental groups, to restore or at least maintain the current water quality have had mixed results. One particular obstacle to cleaning up the bay is that much of the polluting substances arise far upstream in tributaries lying within states far removed from the bay. Despite the state of Maryland spending over $100 million to restore the bay, conditions have continued to grow worse. Twenty years ago, the bay supported over six thousand oystermen. There are now fewer than 500.^[44]

Efforts to repopulate the bay via hatcheries have been carried out by a group called the Oyster Recovery Partnership, with some success. They recently placed 6 million oysters on 8 acres (32,000 m²) of the Trent Hall sanctuary.^[45] Scientists from the Virginia Institute of Marine Science at the College of William & Mary claim that experimental reefs created in 2004 now house 180 million native oysters, Crassostrea virginica, which is far fewer than the billions that once existed.^[46]

Publications

There are several magazines and publications that cover topics directly related to the Chesapeake Bay and life and tourism within the bay region.

The Capital, a newspaper based in Annapolis, reports about news pertaining to the Western Shore of Maryland and the Annapolis area.^[47] Chesapeake Bay Magazine and PropTalk focus on powerboating while SpinSheet focuses on sailing.^[48][49][50]

Cultural depictions

In literature

• Beautiful Swimmers: Watermen, Crabs and the Chesapeake Bay (1976) is a Pulitzer Prize winning non-fiction book by William W. Warner about the Chesapeake Bay, blue crabs and watermen.
• Chesapeake, a 1978 novel by author James A. Michener
• John Barth's 1982 Sabbatical: A Romance, a novel centered on a yacht race through the Chesapeake Bay
• John Barth's 1987 The Tidewater Tales, a novel in which a married couple tell stories to each other as they cruise the bay.
• Jacob Have I Loved by Katherine Paterson, winner of the 1981 Newbery Medal. This is a novel about the relationship between two sisters in a waterman family who grow up on an island in the Bay.

In film

• The Bay (film), a 2012 found footage style eco-horror movie about a pandemic due to deadly pollution from chicken factory farm run-off and mutant isopods and aquatic parasites able to infect humans.

Other media

Tom Wisner has recorded several albums, often about the Chesapeake Bay, and he tried to "capture the voice of the water and the sky, of the rocks and the trees, of the fish and the birds, of the gods of nature he believed still watched over it all."^[51] He was known as the Bard of the Chesapeake Bay.^[51] The 1976 hit Moonlight Feels Right by Starbuck refers to Chesapeake Bay: "I'll take you on a trip beside the ocean / And drop the top at Chesapeake Bay."