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Five species of Holocene planktonic Foraminiferida (Globigerinella siphonifera, Globigerinoides sacculifer, Globorotalia menardii, Globorotalia tumida, and Neogloboquadrina dutertrei) from cores in the Indian Ocean were selected for study of intraspecific latitudinal variations in test porosity and pore density. Each species exhibits a change in test porosity with latitude, with greater test porosities characteristic of the location nearer the equator. Pore density results are inconclusive. It was assumed originally that test porosity might be dependent on pore density, but indications are that porosity is controlled by pore diameter and is essentially independent of pore density. We suggest that test porosity may be a buoyancy adaptation of planktonic Foraminiferida, wit greater test porosities characteristic of less dense surface water. The density of the surface water in turn is related directly to surface water temperature; test porosity, therefore, might prove to be a useful tool in paleotemperature determinations, a tool which would not require knowledge of the distribution of extant species.
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