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Faunal provinces of planktonic Foraminiferida are delineated by oceanic water masses and available food supply. Species diversity decreases generally from tropical to polar waters, as well as from fertile to infertile areas. Productivity is probably higher and more continuous in tropical current systems than in subpolar regions. Test size and porosity decrease from low to high latitudes. These factors combine to yield higher accumulation rates of foraminiferal carbonate in tropical-subtropical than in subpolar-polar ocean basins (at depths above the CaCO3 compensation depth).
The bipolar nature of the species distributions is evident from the reciprocal faunal zones in the northern and southern hemispheres. The Indo-Pacific fauna is richer than the Atlantic fauna. Most species (23) live in the warm-water region between approximately 40°N and 40°S lat. Tropical species, such as Globigerinoides sacculifer and Globorotalia menardii, inhabit the relatively eutrophic equatorial current systems and are transported to mid-latitudes by western boundary currents. Some subtropical species (Globorotalia hirsuta, G. truncatulinoides, etc.) live in the central oligotrophic areas of the oceans. Other species (Globigerinoides ruber, Globoquadrina dutertrei, etc.) are abundant in both tropical and subtropical latitudes, especially off continental margins. Salini y influences the distribution patterns of the 2 most successful species, G. ruber and G. sacculifer.
The northern and southern cold-water regions are inhabited by a total of only 8 species. The subpolar fauna is characterized by Globigerina bulloides, and left-coiling G. pachyderma is the sole representative of the polar provinces. Mixed assemblages of subpolar and subtropical species appear in convergence regions and areas of upwelling along eastern boundary currents.
Apparent species compositions and distribution patterns can be modified artificially by the mesh sizes of plankton net samplers.
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