THE CARIBBEAN AREA 



The Oceanography of the Caribbean 



Topography ; — The Caribbean Sea, together with the Gulf of Mexico, is often called the 

 American Mediterranean Sea. It is shaped like a iride and irregular channel with the mouth 

 facing the North Atlantic. The Caribbean is generally deep. About half of it is 2,000 

 fathans or deeper and about four-fifths deeper than 1,000 fathcnns. It has been proposed 

 by Parr (1936) that the Caribbean Sea area be broken dowi into the Cayman Sea and the 

 Caribbean Sea proper. He regards the former as the region lying between the Yucatan Channel 

 on the northwest and the ridge extending fron Honduras via Jamaica to Haiti. This area is 

 quite complex from a topographic standpoint. Cayman Brae, Grand Cayman, aind Misteriosa Bank 

 emerge from a subjiprine ridge extending westerly fron the southwest point of Cuba (Cape Cruz). 

 Between Misteriosa Bank and Honduras is the tiny Swan Island, Immediately south of the ridge 

 from Cuba is a long, deep, smd nao'row trough known as Bartlett Deep or the Cayman Trough, 

 This trough has recorded depths of more than 3,4-00 fathoms. The Cayman Sea connects with the 

 open Atlantic, by way of Bahaman waters, through the Windward Passage, a channel about /+5 

 miles wide. It is separated from the Caribbean proper by banks and passages on the submarine 

 ridge between Honduras and Jamaica and by a continuation of this ridge, about 105 miles long, 

 between Jamaica auid the southeast point of Haiti, 



The Caribbean proper is of comparatively simple topography except in the Honduras- 

 Jamaica Ridge section. Here there are several deep gvillies and a number of islands and banks. 

 Further eastward there is a slight elevation of the bottom which slopes southwesterly from 

 southern Haiti, Still further eastward, an elevation extends directly south from the eastern 

 bank of Anegada Passage emerging at Aves Island and continuing to the coast of Venezuela. 

 Just west of the Lesser Antilles is another depi-ession, the Grenada Trough, with recorded 

 depths up to about 2,200 fathoms. This terminates at the southern end in about the latitude 

 of Grenada. The Grenada Trough is separated by the Lesser Antilles from the open Atlantic 

 and the depths of the passages are less than those in tiie Trough, Outside of limited areas 

 of relatively shallow waters around the coasts and a few small banks, the Caribbean proper 

 has depths of 2,000 to 2,800 fathoms. Almost half is occupied by the inter-connected 

 Venezuelan Basin and Colombisin Basin each with depths of over 2,000 fathoms. More than half 

 of the remaining area is more than 1,000 fathoms in depth. 



The bottom of the deepest areas is con^osed of globigerina ooze with about 50 percent of 

 calcium carbonate. In the eastern portion, there are areas of red clay. The remainder of 

 the Caribbean bottom is of terrigenous origin. The globigerina oozes are coiaposed chiefly of 

 the calcarious remains of foraminifera which through the ages have sunk from the upper water 

 layers to the bottom. Terrigenous deposits are formed by the disintegration and decomposition 

 of rock. In shallower depths, the bottom is usually more varied. Sand, mud, coral, gravel, 

 and shells may occur in separate bodies or combined depending upon the type of locality. 



Composition of the Water Masses ; — In order to determine the origin and characteristics 

 of the bottom waters of the Caribbean, it is necessary to examine the topography of the area 

 from a slightly different angle than above. Essentially, the Caribbean has depths much 

 greater than the passages leading from the outside into the Caribbean; and, for this reason, 

 there are a ills or thresholds over which water from the outside must pass. 



Thus, the Yucatan Channel has a sill depth of about 1,100 fathoms, the Windward Passage 

 about 900 fathoms, Mona Passage about 300 fathoios, Anegada about 1,100 fathoms, St. Lucia 

 about 600 fathoms, and Martinique Channel about 550 fathoms. Moreover, there are sills be- 

 tween the basins in the Caribbean. The Cayman Ridge is about 1,500 fathoms deep, Rosaline- 

 Pedro Channel about 65O fathcxns, Navassa- Jamaica Channel about 1,000 fathoms, and Aves Swell 

 about 870 fathoms. These barriers to deep circulation might have the effect of rendering 

 the waters below threshold depths in the basins stagnant. Actually, however, this is not 

 the case. Parr (1937) has reported that the bottom waters of the Caribbean and Cayman Seas 

 are virtually identical by temperature and salinity characteristics, but must be entirely 

 distinct bodies having separate external origins and being separated at least below about 

 1,000 fathoms. The bottom waters have proved to be rich in oxygen and not stagnant as once 

 supposed. It is indicated that these bottom waters are of the most recent origin. By 

 means of involved physical and chemical calculations. Parr has determined that there is an 

 actual constant renewal of the bottom waters over the thresholds and that the displaced 

 bottom waters rise and are finally swept away by the friction of the currents in the upper 

 water levels. 



