17. CENOZOIC PALEOTEMPERATURES AT SITE 398, EASTERN NORTH ATLANTIC: DIAGENETIC EFFECTS ON CARBON AND OXYGEN ISOTOPIC SIGNAL
The oxygen and carbon isotopic history at Site 398, based on analyses of planktonic and benthic foraminifers, is greatly affected by diagenesis and selective dissolution. Nevertheless, a global de-crease in surface temperatures of 4 ° to 5°C, and in bottom temp-eratures of 10°C through the Tertiary...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.620.2184 http://www.deepseadrilling.org/47_2/volume/dsdp47pt2_17.pdf |
| Summary: | The oxygen and carbon isotopic history at Site 398, based on analyses of planktonic and benthic foraminifers, is greatly affected by diagenesis and selective dissolution. Nevertheless, a global de-crease in surface temperatures of 4 ° to 5°C, and in bottom temp-eratures of 10°C through the Tertiary can be related to the esta-blishment of deep-water circulation from polar origin. At 48 m.y. B.P., a North Atlantic deep-water supply is responsible for increas-ing primary production and lowering of l^C/l^C ratios. Eocene surface temperatures were about 17°C. Near the Eocene/Oligocene boundary, an important shift in the oxygen isotope composition of the total calcitic microfaunas is related to the establishment of the psychrosphere, at-38 m.y.B.P. Oligocene bottom tempera-tures were approximately 5°C and the surface-to-bottom temp-erature gradient was near 3CC. The onset of major Antarctic glaciations, with Antarctic bottom water and Antarctic Circumpolar Current (ACC) formation, the timing of which is not yet well established, does not provide any striking isotopic change. A first cooling event in the early Miocene (-23 m.y.B.P.) is tentatively referred to the ACC. Northern latitude Quaternary glaciations are responsible for an-other important shift in oxygen isotope values. During the Quater-nary, bottom water temperatures averaged 4 C. |
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