Monthly observations of primary productivity and the related hydrographic and nutrient characteristics have been made at offshore sites near Jamaica and Barbados for more than two years. The annual rate of production was relatively low at Jamaica. Gross primary production varied from
0.08 g C/m2/day to 0.52 g C/m2/day, and averaged 0.18 g C/m2/day, or 66 g C/m2/year. Net primary production did not exceed 0.28 g C/m2/day (range, 0.03-0.28 g C/m2/day). Average daily production was 0.11 g C/m2, or
40 g C/m2/year. At Barbados, gross primary production was considerably higher than at Jamaica, ranging from 0.19 to 0.62 g C/m2/day and averaging 0.38 g C/m2/day, or 139 g C/m2/year. The annual level of production at Barbados is comparable to that
determined for the Sargasso Sea off Bermuda by other investigators. Some evidence of regularly recurring variations of a seasonal nature were seen in the magnitude of productivity at both sites. At Jamaica, short-term peaks in the late spring and fall alternated with periods of relatively
low productivity during the summer and winter. Off Barbados, productivity increased during the spring, was relatively high in the summers of 1962 and 1963, and then dropped during the fall to low values which generally persisted throughout much of the winter. The phytoplankton production
is believed to be controlled primarily by the availability of nutrient salts. Nitrate, nitrite, and phosphate levels generally were low in the euphotic zone throughout most of the year. The temperature and salinity structure of these waters is such that there is little possibility of the relatively
nutrient-rich, deeper waters mixing well with the waters of the upper 100 m.
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