| Summary: | Typescript (photocopy) Thesis (PhD) -- University of Melbourne, Faculty of Science, 2004 Includes bibliographical references (leaves 259-280) Stable water isotope records may be used to reconstruct tropical climate variability on seasonal to glacial time scales. Isotopic ratios in precipitation are archived in tropical ice cores, and may be interpreted as records of precipitation, temperature and atmospheric circulation variability in the tropics. Isotopic ratios in the carbonate skeletons of coral and foraminifera record local and mean ocean isotopic ratios as well as sea surface temperature. Reconstruction of past climate from isotopic records requires assumptions about the isotope-climate relationship on the relevant time scale. In order to test these assumptions, an isotopic tracer scheme in the Melbourne University General Circulation Model is- used to simulate the isotope-climate relationship for present day and Last Glacial Maximum climate. A scheme to calculate surface ocean and river runoff isotopic ratios is developed and used to test the sensitivity of the surface ocean isotopic distribution to changes in climate forcing. Present day climate from 1950-1999 is simulated using observed sea surface temperatures and sea ice coverage, and the interannual variability of the modelled isotopic ratios in precipitation and the surface ocean are compared with observational records. On interannual time scales, the modelled isotopic ratios in tropical precipitation are predominantly controlled by precipitation amount. The isotopic signal also reflects strong modes of tropical climate variability, including El Nino-Southern Oscillation and monsoon variability. The modelled surface ocean isotopic ratios respond to interannual precipitation and evaporation variability, with a strong El Nino-Southern Oscillation signal in the tropical Pacific. The isotopic variability archived in coral and foraminiferal carbonates reflects both sea surface temperature and local precipitation and evaporation changes, and a ...
|
|---|