23 research outputs found
Two-stepping into the icehouse: East Antarctic weathering during progressive ice-sheet expansion at the Eocene-Oligocene transition
In conjunction with increasing benthic foraminiferal ?18O values at the Eocene–Oligocene transition (EOT; ca. 34 Ma), coarse-grained ice-rafted debris (IRD; >425 ?m) appears abruptly alongside fossil fish teeth with continentally derived neodymium (Nd) isotope ratios (?Nd) in Kerguelen Plateau (Southern Ocean) sediments. Increased Antarctic weathering flux, as inferred from two steps to less radiogenic ?Nd values, coincides with two steps in benthic foraminiferal ?18O values. These results indicate that two distinct surges of weathering were generated by East Antarctic ice growth during the EOT. Weathering by ice sheets during a precursor glaciation at 33.9 Ma did not produce significant IRD accumulation during the first ?Nd shift. Glacial weathering was sustained during a terrace interval between the two steps, probably by small high-elevation ice sheets. A large increase in weathering signals the rapid coalescence of small ice sheets into an ice sheet of continental proportions ca. 33.7 Ma. Rapid ice sheet expansion resulted in a suppression of weathering due to less exposed area and colder conditions. Parallel changes in Antarctic weathering flux and deep-sea carbonate accumulation suggest that ice-sheet expansion during the EOT had a direct impact on the global carbon cycle; possible mechanisms include associated changes in silicate weathering on the East Antarctic craton and enhanced fertilization of Southern Ocean waters, both of which warrant further investigation
Transient changes in Southern Ocean Nd isotope composition in response to Antarctic glaciation (abstract of paper presented at: 19th Annual V. M. Goldschmidt Conference, Davos, Switzerland, 21-26 June 2009)
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Late Eocene Record of Hydrology and Temperature From Prydz Bay, East Antarctica
The Eocene-Oligocene transition (EOT) marks the onset of Antarctic glaciation at 33.7 Ma. Although the benthic oxygen isotope record defines the major continental ice sheet expansion, recent sedimentary and geochemical evidence suggests the presence of earlier ephemeral ice sheets. Sediment cores from Ocean Drilling Program Legs 119 and 188 in Prydz Bay provide an archive of conditions in a major drainage system of East Antarctica. We study biomarker and microfossil evidence to discern how the vegetation and climate shifted between 36 and 33 Ma. Pollen was dominated by reworked Permian Glossopterid gymnosperms; however, penecontemporaneous Eocene pollen assemblages indicate that some vegetation survived the glacial advances. At the EOT, brGDGT soil biomarkers indicate abrupt cooling from 13°C to 8°C and soil pH increases from 6.0 to 6.7, suggesting drying which is further supported by plant wax hydrogen and carbon isotopic shifts of 20‰ and 1.1‰, respectively, and evidence for drying from weathering proxies. Although the terrestrial soil biomarker influx mostly precludes the use of TEX86, we find sea surface temperatures of 12°C in the late Eocene cooling to 8°C at the EOT. Marine productivity undergoes a sustained increase after the glacial advance, likely promoted by enhanced ocean circulation. Between the two glacial surge events of the Priabonian Oxygen Maximum at 37.3 Ma and the EOT at 33.7 Ma, we observe warming of 2–5°C at 35.7 and 34.7 Ma, with increase in penecontemporaneous pollen and enhanced marine productivity, capturing the last flickers of Antarctic warmth. © 2021. American Geophysical Union. All Rights Reserved.6 month embargo; first published: 11 April 2021This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]