ORIGIN AND COMPOSITION OF WATER MASSES EN TERING THE SOUTHEASTERN CARIBBEAN

The Caribbean Sea receives waters from different origins including con tinental waters transported by marine currents, as well as oceanic wat ers which reach the Caribbean Sea mixed with the former. In spite of t he fact that several studies have been conducted in this area, the mea sured variables have mainly been linked to physical phenomena. It has been established that a 36 parts per thousand salinity allows the diff erentiation of water masses influenced by freshwaters from those which are not. According to this criterion, in the Atlantic Ocean, south of 8-degrees latitude north, between March and June and until November-D ecember north of that latitude, and also in the Caribbean, the influen ce of continental waters is clear. It diminishes however the rest of t he year. In the surface, dissolved oxygen measurement show levels of s aturation ranging from 80 to 90%. This concentration remains in the wh ole water column except for the area comprised between 54-degrees and 56-degrees-W and 6-degrees-N where dramatic reductions are recorded in deep waters; this situation is also observed in front of the Orinoco Delta. The nutrients show important variations along the year and they are generally high: pH ranges between 7.6 and 8.0; phosphates are low between March and July (range 0.006 to 0.48 mugrat 1-1) and higher du ring the rest of the year (> 0.50 mugrat l-1); nitrates show a similar trend with higher values (> 5.0 mugrat l-1) in September. Silicates s how wider ranges (4.0-75.0) mugrat l-1). In conclusion it could be sta ted that water masses entering the Caribbean Sea show a strong compone nt of the Amazon and Orinoco waters. The influence of Amazon waters ex tends from February to June and mainly of the north of 12-degrees-N. W aters of the Orinoco have a higher influence between July and Septembe r to the south of 12-degrees-N.