24. FINE-FRACTION CARBONATE OXYGEN AND CARBON ISOTOPE RESULTS FROM SITE 704: IMPLICATIONS FOR MOVEMENT OF THE POLAR FRONT DURING THE LATE PLIOCENE1
Ocean Drilling Program Site 704 in the subantarctic South Atlantic was drilled to investigate the response of the Southern Ocean to climatic and Oceanographic developments during the late Neogene. Stable oxygen and carbon isotopes of fine-fraction (<63 µm) carbonate were analyzed to supplement si...
| Main Authors: | , , , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.605.6293 http://www-odp.tamu.edu/publications/114_SR/VOLUME/CHAPTERS/sr114_24.pdf |
| Summary: | Ocean Drilling Program Site 704 in the subantarctic South Atlantic was drilled to investigate the response of the Southern Ocean to climatic and Oceanographic developments during the late Neogene. Stable oxygen and carbon isotopes of fine-fraction (<63 µm) carbonate were analyzed to supplement similar analyses of benthic and planktonic foraminifers. The fine fraction is generally composed primarily of coccoliths, and isotopic analyses of the fine fraction were made to complement the foraminiferal analyses. The isotopic curves thus generated suggest paleoceanographic changes not recognizable by the use of benthic and planktonic foraminifers alone. The global Chron 6 carbon isotope shift, found at 253-244 mbsf (6.39-6.0 Ma) at Site 704 in the planktonic and benthic record, is seen in the fine-fraction δ13C record as a gradual decrease from 255 mbsf (6.44 Ma) to 210 mbsf (4.24 Ma). At 170 mbsf, mean δ 1 8 θ values of Neogloboquadrina pachyderma increase by 0.6°/oo-0.7°/oo (Hodell and Ciesielski, this volume), reflecting decreased temperature and increased continental ice volume. Accumulation rates increase by 3.3 times above this depth (which corresponds to an age of 2.5 Ma), suggesting increased upwelling and biologic productivity. |
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