Living planktonic foraminifera during the late summer monsoon period in the Arabian Sea
Abstract
During the late summer monsoon living planktonic foraminifera were collected in the southeastern Arabian Sea between 3~'N and 15~'N by using six vertical plankton tows. Sixteen species of planktonic foraminifera were identified. Among them, @iGlobigerinoides ruber@@ and @iG. sacculifer@@ are the most abundant species, while the ecologically most important species @iGlobigerina bulloides@@ is very rare. The low abundance of @iG. bulloides@@ can be explained by the warming of the surface water in combination with deepening of the mixed layer, since this species preferentially dwells in nutrient-rich upwelling waters. The population density of planktonic foraminifera ranges between 31 and 185 specimens per 10@u-3@@m@u3@@. The low absolute numbers of planktonic foraminifera are similar to the numbers which were reported before from the non-upwelling areas in the Arabian Sea. The low absolute numbers and the collected foraminiferal assemblages are therefore highly indicative of the Arabian Sea non-upwelling areas. Particularly significant are the low absolute and relative numbers of the non-spinose species @iGloborotalia menardii@@ and @iNeogloboquadrina dutertrei@@. The absence of these species indicate the relatively low nutrient levels in this area at the tail end of the summer monsoon period
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