Dive Atlas Of The World: An Illustrated Reference To The Best Sites - Jack Jackson (2016)

THE CARIBBEAN SEA

by Jack Jackson

COMPARED WITH THE OCEANS, THE CARIBBEAN SEA, a suboceanic basin of the western Atlantic, is minute. It has a surface area of only 2,754,000 sq km (1,063,000 sq miles) and lies between 9°N and 22° N and between 89°W and 60° W. To the north it is bounded by the Greater Antilles islands of Cuba, Hispaniola (Haiti and the Dominican Republic), Jamaica, and Puerto Rico and to the south by the coasts of Panama, Colombia and Venezuela. To the west it is bounded by the Yucatán Peninsula of Mexico, Guatemala, Belize, Honduras, Nicaragua and Costa Rica and to the east by the Lesser Antilles chain, consisting of the island arc that extends from the Virgin Islands in the northeast to Trinidad and Tobago off the Venezuelan coast in the southeast.

The preferred oceanographic term for the Caribbean is the Antillean-Caribbean Sea which, together with the Gulf of Mexico, forms the Central American Sea. It is presumed to have been connected with the Mediterranean during Palaeozoic times and to have separated from it as the Atlantic Ocean was formed. Connections with the Pacific Ocean were lost when South America welded to Central America, closing the isthmus of Panama. This greatly altered the currents of the Caribbean Sea and the North Atlantic and limited the number of species found in the Caribbean.

Most of the islands are fringed by coral reefs and have gentle currents. The islands and connecting ridges of the eastern Caribbean prevent the interchange of deep water from the Atlantic, so the tides are smaller and visibility good. The region also has sophisticated infrastructures, a mild tropical climate, ideal conditions for novices and leisurely diving, a potpourri of diverse cultures and a laid-back attitude to life.

The islands vary from mountainous and lush to almost flat and arid, but the diving does not vary much. The islands bordering the Atlantic have more of the larger pelagic species on their Atlantic coasts. Stronger currents give exciting drift-dives off such places as Cozumel and Tobago; and trade winds produce rough seas on the windward sides of Aruba, Bonaire and Curaçao.

While themed dives (diving with stingrays, sharks or dolphins) are popular, reefs are the main attraction and many of the islands have initiated artificial reef programmes by sinking ships and aeroplanes that had been cleaned to be environmentally sound. Some ‘treasure ships’ have been located, dating from the Spanish colonial period, when the world’s richest maritime trade was prey to pirates, naval engagements and storms. Several more modern wrecks are regularly dived.

The Caribbean climate is tropical, but there are many local variations depending on the altitude of mountains, local currents and the trade winds. Rainfall varies from about 254mm (10 in) per year on the island of Bonaire to 8,890mm (350 in) per year in regions of Dominica. The Northeast Trade Winds dominate the area with an average velocity of 15-30km (9½-20 miles) per hour.

Storms of hurricane strength occur seasonally in the northern Caribbean and in the Gulf of Mexico, but are rare in the far south. Although the exact path of a hurricane is unpredictable, most form near the Cape Verde Islands in the eastern Atlantic and follow the path of the trade winds into the Caribbean and the Gulf of Mexico. The hurricane season is June to November, but they are most frequent in September. The Caribbean has fewer hurricanes than the Gulf of Mexico or the western Pacific, where they are called typhoons.

THE WEST INDIES

The West Indies stretch more than 3200km (2000 miles) from Cuba almost to the north coast of South America. Principally divided into the Greater and Lesser Antilles, this island chain separates the Caribbean Sea from the Atlantic Ocean. Other islands of the region are isolated groups on the continental perimeter of the Antilles, including the Bahamas, Trinidad and Tobago, and the Netherlands (Dutch) Antilles.

The shape and alignment of the Greater Antilles, Cuba, Jamaica, Hispaniola (Haiti and the Dominican Republic), and Puerto Rico, are determined by an ancient chain of mountains that extended from Central America through the Caribbean. Remnants of this chain are found in the Blue Mountains of Jamaica, the Sierra de los Órganos and the Sierra Maestra in Cuba and Duarte Peak, 3170m (10,400ft), in the Dominican Republic, the highest point in the Caribbean.

Mixed tides (both diurnal and semidiurnal) occur in the Caribbean and the Gulf of Mexico and are much smaller than those in the main Atlantic Ocean, usually less than 1m (40 in). Storm surges caused by hurricanes can cause local sea levels to rise by 1m (40 in).

TOPOGRAPHY

The Caribbean’s greatest known depth is the Cayman Trench, also known as the Bartlett Deep or Bartlett Trough. It runs east-northeast to west-southwest between Cuba and Jamaica reaching 7,686m (25,216ft) below sea level.

Although the interior of the Caribbean is tectonically inactive, its margins are not. Volcanic activity and earthquakes produced by the interactions between crustal plates are common as the elongated plate of the Caribbean Sea is bordered to the west and east by subduction zones where other plates slide beneath the Caribbean Plate. The northeast edge of the Cocos Plate runs parallel to the Pacific coast 95-200km (60-125 miles) offshore. This plate abuts on the southwest edge of the Caribbean Plate, whose northern edge is marked by fault zones extending across southern Guatemala to include the active Cayman trough. To the north and northwest, the American Plate is relatively stable and has allowed the accumulation of limestones on the Yucatán Peninsula. The eastern edge of the Cocos Plate is in contact with the Panama block of the Nazca Plate. The Cocos Plate is moving northeast relative to the Caribbean Plate at a rate of 10m (33ft) per century which, by geologic standards, is very fast.

At the eastern end of the Caribbean Sea, the volcanic islands forming the island arc of the Lesser Antilles mark the edge where the North Atlantic Ocean floor is sliding under the Caribbean Plate.

The Caribbean Sea is divided into five submarine basins separated from one another by submerged ridges and rises - the Yucatán, Cayman, Colombian, Venezuelan, and Grenada basins. The Yucatán Basin is separated from the Gulf of Mexico by the Yucatán Channel between Cuba and the Yucatán Peninsula. It has a sill depth (the depth of the submarine ridge between basins) of about 1,600m (5,250ft). To the south the Cayman Basin is partially separated from the Yucatán Basin by the Cayman Ridge, a narrow ridge that extends from Guatemala towards the southern part of Cuba. This ridge rises above sea level as the Cayman Islands. Further south, the Nicaraguan Rise is a wide triangular ridge with a sill depth of about 1,220m (4,000ft), which runs from Honduras and Nicaragua to Hispaniola. It separates the Cayman Basin from the Colombian Basin and rises above the surface as the island of Jamaica. The Colombian Basin is partly separated from the Venezuelan Basin in its northern half by the Beata Ridge, but these two basins are connected by the submerged Aruba Gap at depths greater than 3960m (13,000ft). To the east, the Aves Ridge, which is broken at its southern end, separates the Venezuelan Basin from the small Grenada Trough, whose eastern limit is the islands of the Antillean arc.

CURRENTS

High in oxygen content, North Atlantic Deep Water enters the Caribbean beneath the Windward Passage, which runs between east Cuba and northwest Haiti on Hispaniola. It then divides to fill the Yucatán, Cayman, and Colombian basins at depths of around 1,980m (6,500ft). This Caribbean Bottom Water also enters the Venezuelan Basin, introducing oxygen-rich water at depths of 1,800-2990m (5,900-9,800ft). Subantarctic Intermediate Water enters the Caribbean below the Anegada Passage at depths of 490-1,000m (1,600-3,300ft). At the Antillean arc, the shallow sill depths block the Antarctic Bottom Water, with the result that the bottom temperature of the Caribbean Sea is around 4°C (39°F), as opposed to the Atlantic bottom temperature of less than 2°C (36°F).

Surface currents enter the Caribbean mainly through the channels and passages of the southern Antilles. The Guiana Current and part of the North Equatorial Current flow past Saint Lucia almost unimpeded. The trade winds push these waters through the Yucatán Channel into the Gulf of Mexico. In the western Caribbean and the Gulf of Mexico, the trade winds force the surface waters northwards, away from the mainland, causing nutrient-rich upwellings.

The wind-driven surface water builds up in the Yucatán Basin and the Gulf of Mexico, resulting in a higher average sea level than in the Atlantic Ocean. This forms a hydrostatic head, thought to be the main driving force behind the Gulf Stream.

The Gulf Stream is fed by the westward-flowing North Equatorial Current moving from North Africa to the West Indies. This current splits into two off the northeast coast of South America, forming the Caribbean Current, which passes into the Caribbean Sea and through the Yucatán Channel into the Gulf of Mexico, and the Antilles Current, which flows to the north and east of the West Indies. The Caribbean Current flows back into the Atlantic through the Straits of Florida between the Florida Keys and Cuba as the Florida Current. Diverted northeast by the submerged Great Bahama Bank southeast of the Florida Peninsula, this swift current combines with the Antilles Current and then flows roughly parallel to the eastern coast of North America to Cape Hatteras. There part of the Gulf Stream forms a countercurrent that flows south and then west to rejoin the Gulf Stream on its seaward side along the coast of Florida and the Carolinas.

Fire corals (Millepora spp.) have many stinging nematocysts that produce a painful sting if they touch sensitive bare skin. Washing the stung area with vinegar immobilizes any unspent nematocysts.

An adult Spotted Drum (Equetus punctatus). These fish inhabit secluded areas of the reef, under ledges and large debris or near small caves and only come out in the open to feed at night.

With its climate and recreational resources, the Caribbean has become one of the world’s main winter vacation resorts and cruise ship destinations. Lack of capital and limited natural resources have discouraged most islands from large industrial development, though oil storage or production occurs on some. Atlantic-Pacific shipping via the Panama Canal passes through the Caribbean, which means that oil spills from normal tanker operations and occasional large-scale tanker or other shipping catastrophes are a problem.

The Caribbean Sea suffers from the same problems of pollution, sedimentation and over-fishing as any of the oceans, but on a smaller scale. Many islands make an effort to conserve their marine habitat.

Xcaret Lagoon in the Yucatán is at the terminus of an underground river which flows through this ancient limestone region to the sea, where a resort has now been established.

Isla Mujeres has superb sandy beaches and is only a short boat ride north of Cancún. The shallow reefs have some of the largest fish populations in the Caribbean.