Fundamental controls on triple oxygen-isotope ratios in Antarctic precipitation and ice cores

• Main Author: Schoenemann, Spruce W.
• Other Authors: Steig, Eric J
• Format: Thesis
• Language: English
• Published: 2015
• Subjects: 17O-excess; Antarctica; general circulation model; ice core; oxygen isotopes; sea ice; Paleoclimate science; Geochemistry; Climate change; earth and space sciences; Antarctic; The Antarctic; Antarc*; Sea ice
• Online Access: http://hdl.handle.net/1773/33054

Thesis (Ph.D.)--University of Washington, 2015 Stable isotope ratios of water (δD and δ18O) in polar precipitation and ice cores have long been used to study past climate variations and the hydrological cycle. Recently-developed methods permit the precise measurement of δ17O and the 17O-excess, relative to the δ17O vs. δ18O meteoric water line. The novel isotope parameter "17Oexcess" provides an additional tool for investigating the global hydrological cycle. Early experimental and modeling studies showed that 17Oexcess in atmospheric water vapor is sensitive to relative humidity during evaporation from the ocean surface, and suggested that there was little fractionation during condensation. It was therefore expected that 17Oexcess in polar snow could be used as an indicator for humidity in the ocean source regions where polar moisture originates. Later work shows that the magnitude of 17Oexcess change between the last glacial period and the Holocene warm period, measured in Antarctic ice cores, increases from the Antarctic coast towards the interior, suggested significant fractionation during transport. Full interpretation of these conflicting results has been challenging, hindered in part by the labor-intensive nature of making 17Oexcess measurements and by the lack of an accepted standard for reporting 17Oexcess values. This thesis provides a new, comprehensive assessment of the 17Oexcess of Antarctic precipitation and ice core data. The contributions from this work also include improvements to 17Oexcess measurement techniques, using both isotope-ratio mass spectrometry and collaborative developments in laser spectroscopy, and a formal calibration of international water standards for 17Oexcess. It further addresses both the spatial and temporal variations observed in Antarctic 17Oexcess values, providing a coherent explanation for both. New Antarctic 17Oexcess measurements from this work show that there is a strong negative spatial gradient of 17Oexcess in snowfall towards the interior of Antarctica, a ...