The stable isotopes and deuterium excess from the Siple Dome ice core: Implications for the late Quaternary climate and elevation history of the Ross Sea Region, West Antarctica

Predictions of future climate change require detailed knowledge of natural climate variability. Fluctuations in the amount of ice volume stored in high latitude ice sheets are fundamental to the climate system, because of the inverse relationship between ice volume and global sea level. The West Antarctic ice sheet (WAIS) comprises about 5 m of sea level equivalent, and may be particularly sensitive to future climate changes, both because it is grounded below sea level, and because it possesses many active ice streams which are capable of draining a large volume of ice from the ice sheet interior. This thesis presents the isotope and deuterium excess data from the Siple Dome ice core, taken from the West Antarctic ice sheet, and endeavors to constrain the climate and elevation history of the WAIS.; The full, 100,000-year delta18O record from Siple Dome, in combination with the Byrd delta18O record (the only previous deep ice core record from WAIS), represents the first opportunity to separate the climate and elevation effects on the isotopes in ice cores from WAIS. These delta18O records provide new insight into the magnitude of elevation changes of the West Antarctic ice sheet, and its related contributions to global sea level change. The deepest section of the Siple Dome core has extremely depleted delta18O values, suggesting that sometime prior to 100,000 years ago ice from higher on the ice sheet may have overrun this coastal dome. However, Siple Dome delta18O recorded a typical Antarctic climate signal (including millennial scale climate changes), with some important distinctions, and indicates that this dome has been relatively undisturbed for the last 100,000 years. The glacial section of the Siple Dome delta 18O record suggests that portions of West Antarctica have experienced elevation changes which could have contributed a small amount to global sea level change. During the Holocene, West Antarctica appears to have been warming, which is unusual among global climate archives of this period.; The Siple Dome d record is the first d record from WAIS, and is unusual among Antarctic d records because it shares variance with indicators of tropical and Northern Hemisphere climate. This shared variance hints at a link between Southern Pacific Ocean climate and climate of the Northern Hemisphere, an idea which is reinforced by the differences between Siple Dome d and deltaD. However, simple isotope transport modeling precludes unambiguous conclusions on this topic. Sea ice effects on the isotopes could be responsible for the decoupling of Siple Dome d and deltaD, and may provide a mechanism for a teleconnection between the Siple Dome d record and tropical/Northern Hemisphere climate indicators.; The delta18O and d records from ice cores in the Ross Sea region of Antarctica (Siple Dome, Taylor Dome, and Byrd) imply an intriguing link with the El Nino-Southern Oscillation during the Holocene. The similarity between the Siple Dome and Taylor Dome d records suggests a shared Pacific moisture source, and their increase in mean and variance in the mid-Holocene parallels changes observed in ENSO recorders. Simple isotope transport model experiments are again inconclusive as to the full climate implications of the data, but suggest that increasingly El Nino-like conditions in the Pacific since the mid-Holocene could have contributed to the d observations. This explanation requires that d at these ice core sites is more sensitive to El Nino than to La Nina. The model experiments indicate that the delta18O observations are more difficult to explain, but may be partly influenced by differences in precipitation seasonality at the various sites. ENSO cannot be eliminated as a candidate explanation, but the results remain inconclusive until models that more accurately simulate both ENSO and precipitation isotopes can be used.