| Summary: | Three paleocarbonate ion proxies, size index, planktonic foraminifera shell weight, and calcite crystallinity, have been employed here to a set of core top samples from the western tropical Indian Ocean in the water depth ranges from 1086 to 4730 m. All three proxies complement each other well and reveal that calcite dissolution starts to affect planktonic foraminifera from 2250 m depth onward and intense calcite dissolution begins around 3900 m depth in this sector of the tropical Indian Ocean. Three planktonic foraminifera species, Globigerinoides sacculifer, Pulleniatina obliquiloculata, and Neogloboquadrina dutertrei, show wide variability in shell weights from core top sediments in the depth range of 3300 to 3400 m bathed by similar bottom water CO sub(3) sup (=*) concentrations. This variability is attributed to shell calcification, and shell weights are controlled by CO sub(3) sup(=) concentration in the surface waters. Further, surface water CO sub(3) sup(=) concentrations override milder dissolution effects experienced by samples from shallower water depths bathed by similar bottom water CO sub(3) sup (= *) concentrations
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