Oligocene to early Miocene glacimarine sedimentation of the central Ross Sea, and implications for the evolution of the West Antarctic Ice Sheet
Today the West Antarctic Ice Sheet (WAIS) is grounded mostly below sea level on a landward-sloping continental shelf, making it sensitive to oceanic temperature and circulation changes. However, recent reconstructions of the Cenozoic bedrock topographic evolution of West Antarctica have suggested th...
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| Format: | Thesis |
| Language: | unknown |
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2016
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| Online Access: | https://doi.org/10.26686/wgtn.20388075 https://figshare.com/articles/thesis/Oligocene_to_early_Miocene_glacimarine_sedimentation_of_the_central_Ross_Sea_and_implications_for_the_evolution_of_the_West_Antarctic_Ice_Sheet/20388075 |
| Summary: | Today the West Antarctic Ice Sheet (WAIS) is grounded mostly below sea level on a landward-sloping continental shelf, making it sensitive to oceanic temperature and circulation changes. However, recent reconstructions of the Cenozoic bedrock topographic evolution of West Antarctica have suggested that the WAIS may have first formed as a terrestrial ice sheet at the Eocene-Oligocene boundary (34 Ma), when there was up to 20% more land area in West Antarctica. At some point during the Oligocene to mid-Miocene (34-14.5 Ma) vast areas of West Antarctica became an over-deepened marine continental shelf, as is observed today. Atmospheric CO₂ also fluctuated between 600 and 200 parts per million (ppm) during this time period. Constraining the development of a marine-based WAIS during these climates with significant CO₂ fluctuations is critical in the context of understanding the sensitivity of ice sheet systems to environmental change. In order to better constrain the development of the WAIS this study re-examined the Oligocene to early Miocene aged sediment cores recovered from the central Ross Sea, a principal drainage area of the WAIS, at Deep Sea Drilling Project Site 270 (77° 26.48’ S, 178° 30.19’ W). Using high-resolution visual core descriptions, as well as grainsize analysis to identify changes in ice-rafted debris and characterise the background sedimentation, six lithofacies were recognised. By incorporating new geochemical and magnetic susceptibility data, as well as existing information of the palynology and foraminifera, with the facies, six lithostratigraphic units were recognised. Together with the existing Ross Sea seismic framework the lithostratigraphic units were used to reconstruct the glacial history of the central Ross Sea during the Oligocene to early Miocene. The late Oligocene was examined in detail, because the decreasing or invariant atmospheric CO₂ values appear to contradict the contemporaneous δ¹⁸O records which imply a climatic warming and/or ice volume loss. This study shows that marine ... |
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