Pleistocene paleoenvironmental record of the planktonic foraminifera of the north-central Gulf of Mexico
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Pleistocene-age samples from Green Canyon Wells 39 and 254 on the continental slope off the shore of Louisiana were studied to examine how planktonic foraminifera respond to glacial/interglacial cycles in the low-latitude, semi- restricted Gulf of Mexico. This study concentrated on seven major species that comprise about 77% of the total fauna. Some species have much larger abundance variations in the late Pleistocene than the early Pleistocene. For example, species abundance patterns of G. ruber, G. sacculifer and right-coiling form of G. truncatulinoides present a two-type variability: low-amplitude variability dominates the lower Pleistocene; high-amplitude variability characterizes the upper Pleistocene. Factor analysis of quantitative species abundance data delineates the two different patterns of variation: the amplitudes of variation in the first three factors are low below the boundary of oxygen isotope stages 15 and 16, but are higher above that boundary. This indicates that paleoclimate in the north-central Gulf changed its character around that boundary. Detailed comparisons of the planktonic oxygen isotope record and species abundance records reveal that the relative abundances of warm- and cold-water species do not have a consistent relationship to the oxygen isotope curve. This means glacial/interglacial temperature changes were not large enough to be a prime factor controlling species abundance in the north-central Gulf of Mexico. In addition, relative abundances of species were not the same in every peak glacial condition, which indicates that full glacial conditions were not always identical through the Pleistocene in the Gulf of Mexico.