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Late Quaternary Paleoclimatic Applications of Mean Size Variations in Globigerina bulloides d'Orbigny in the Southern Indian Ocean

Björn A. Malmgren and James P. Kennett
Journal of Paleontology
Vol. 52, No. 6 (Nov., 1978), pp. 1195-1207
Stable URL: http://www.jstor.org/stable/1303930
Page Count: 13
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Late Quaternary Paleoclimatic Applications of Mean Size Variations in Globigerina bulloides d'Orbigny in the Southern Indian Ocean
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Abstract

In modern surface sediments of the southern Indian Ocean, the mean test size of the cold water planktonic foraminifer Globigerina bulloides d'Orbigny grades from large (maxima of about 350 μm) in the Subantarctic, the area of optimum environmental conditions, to small (minima of about 200 μm) in temperate regions. The paleoclimatic applicability of this modern trend has now been tested by analysis of three Late Quaternary deep-sea core sequences from the Antarctic Convergence (E45-74), the central Subantarctic (E49-19) and the Subtropical Convergence (E48-22). In the Subantarctic and Subtropical Convergence cores, oscillations in the mean size of G. bulloides closely match paleoclimatic curves based on principal component analysis of abundance data, coiling ratios of Neogloboquadrina pachyderma and 18O/16O ratios. Mean sizes are greater during cooler epochs and less during warm epochs as suggested by the surface sediment distributions. Mean size variations in the Antarctic Convergence core do not show obvious relations to climate. In the Subantarctic, the area of inferred optimum conditions for G. bulloides, down-core size variations seem to be synchronous with paleoclimatic oscillations, but at the Subtropical Convergence (E48-22) the mean size variations are offset from the paleoclimatic changes by about 5,000-22,000 years, perhaps indicating a delayed ecological response in this region. Absolute paleotemperatures, estimated by regression analysis from the relationship between annual average surface-water temperatures and mean sizes in the surface sediments, ranged from about 9°C ± 1°C to 16°C ± 1°C at the Subtropical Convergence and from about 3°C ± 1°C to 10°C ± 1°C in the central Subantarctic. Coiling ratio changes in G. bulloides in the Late Quaternary sequences show no relation with paleoclimatic history despite the fact that coiling ratios are related to seawater temperatures in surface sediments of the southern Indian Ocean.

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