THE CARIBBEAN AREA 



The Caribbean receives its water masses mainly at the eastern end through the various 

 passages between the Antilles from the Virgin Islands to Trinidad. ScMie further cc«tri- 

 butions may also be received through the Mona Passage and through the Windward Passage. 

 The origin of these water masses has been determined by studies of salinity and ten^erature 

 relationsliips . In general, there are relatively low salinities at the surface (36,0°/oo to 

 36.2''/oo) which increase sharply to a high maximum (36.5V00 to 36.7V00) around 150 to 200 

 meters. They drop again to a minimum (about 34.78°/oo to 3^.92*/oo) around 800 meters depth 

 and finally rise slightly to about 3^.96''/oo to 35.00Voo in the bottom waters. The vertical 

 distribution curves of salinity in the Caribbean are quite similar to those of the North 

 Equatorial region, and the characteristics of the upper water masses are similar to those of 

 adjacent North Atlantic waters. There is a relatively shallow homogeneous top layer and be- 

 low this a nearly discontinuous decrease in tanperature indicating a more or less perpetual 

 thermocline. 1/ In most localities, a maximum salinity is found within the discontinuity 

 layer. Water masses entering through the Lesser Antilles passages show a streaky distri- 

 bution of salinity with narrow bands of highly saline water alternating with bands of low 

 salinity water. These differences are rapidly smoothed out by intense surface mixing, and 

 on arrival at the Yucatan Channel the waters are of almost uniform character. 



The upper surface waters flowing into the Caribbean are mainly of North Atlantic origin 

 but they contain considerable admixtures of water of the South Atlantic type. The proportion- 

 al composition has been determined by comparison of temperature-salinity relations from the 

 South Atlantic, the Sargasso Sea, and the Yucatan Channel. At the higher ten^eratures, the 

 current passing through the Yucatan Channel carries about 1 part of South Atlantic water to 

 about 3 1/2 parts of North Atlantic. The total transport is about 26 million cubic meters 

 per second with about 6 million cubic meters per second representing South Atlantic contri- 

 butions. 



Below the upper layers, there is a considerable amount of Antarctic Intermediate water. 

 The water at the intermediate salinity minimum (about 3^.78 °/oo to 3^.92'/oo at 800 meters) 

 is thus mainly of South Atlantic origin (Nicken, 1925) (Parr, 1937). The intermediate 

 salinity minimums decrease in intensity with the How direction so that in the Eastern 

 Caribbesui (about longitude 68 degrees W. ), the average mini mum salinity is about 34.73 Voo 

 whereas in the Yucatan Channel it is 3'i+.88''/oo. This shift is due mainly to vertical mix- 

 ins within the moving water mass. (Seiwell, 1938). 



Tempe ratures ; — Surface temperatures in the Caribbean are, in general, high, with an 

 overall annual average of about 27 degrees C. The average minimum is reached in February 

 when the sea surface over the entire area is about 25.5 degrees C. From February to 

 September, the trend is upward, so that in the latter month, sea-surface temperatures aver- 

 age about 28.2 degrees C. There is a slight rise of teniae ratures from north to south. At 

 the extreme northwest comer, including the Yucatan Channel and southwest Cuba, the average 

 is about 26.3 degrees C. while in the offshore Gulf of Darien area, it is about 1 degree C. 

 higher. There is very little fluctuation in the average annual sea-surface ten^Jeratures frcm 

 east to west, although the central area between eastern Cuba and the Gulf of Darien appears 

 to be slightly warmer than the areas to each side of it. The greatest monthly variations in 

 temperature of the sea surface are found in the -'estem part of the Caribbean. Off southwest 

 Cuba the variation is from 23.7° to 28.8" C. — a difference of S.l'C. In the Yucatan Channel 

 area, the difference is between 2U.L,° and 28.4." C. or 4°. The monthly temperature variation 

 to the eastward becomes less and jvist inside the Lesser Antilles it is only 1.6°C. 



The greatest differences between areas are found in January and these become less until 

 September, ^en they again rise. It is not possible to give a definite explanation for these 

 teiqjerature variations since more data would be required to do so. They may be caused by the 

 heating of the sun, by cooling effects of winds, by vertical upwelling or mixing, by inflows 

 of cool water from other areas, or by other factors. Ihere is some possibility that upwell- 

 ing might occur in the Yucatan Channel — Southwest Cuba area. If so, this is probably seasonal 

 and would influence the productivity of the area to a great extent. 



1/ Itie thermocline is a discontinuity layer foiind in series taken vertically in serial 

 water tengjeratures. It is usually regarded as the area where there is the greatest change 

 in temperature Tdthin the narrowest limits. 



