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Global Sea Level During the Last Interglacial

Andrea Dutton 1 , Kurt Lambeck 1

1 Research School of Earth Sciences, Australian National University , Canberra , ACT 0200, Australia

The last interglacial (LIG) has received much attention by paleoclimatologists because of its immediate similarity in temperatures and sea level position to the present interglacial. Although there are some important climatic differences between these two time periods, improving our understanding of relation between variables in the climate system such as temperature, sea level, CO 2 levels, and orbital parameters during the LIG can improve our understanding of both the dynamics of the natural climate system and the expected response of the climate system to current anthropogenic forcing.

Previous studies have focused on elucidating the duration of the last interglacial highstand as well as the average temperature and sea level position during the LIG. These studies have reached a general consensus that the LIG was slightly warmer, had slightly higher sea levels than present, and lasted for roughly 11,000 yrs. There has been considerably more debate with respect to the temporal variability in sea level during the last interglacial highstand, due in part to the inherent difficulties in reconstructing small, meter-scale fluctuations in sea level on relatively short timescales. To address this outstanding question, we have combined glacio-hydro-isostatic models and observational data from multiple sites to evaluate the relative position of sea level between the beginning and the end of the last interglacial period.

We have drawn upon existing relative sea level data consisting of precisely dated corals from two tectonically stable regions, Western Australia and the Bahamas. These are the most complete data sets available for relative sea level position during the LIG because they have a population of U-Th ages that span the duration of the highstand. Relative sea level curves generated from these observational data suggest a reasonably constant sea level position during the LIG (Fig. 1). However, model simulations demonstrate that both sites are subject to isostatic adjustments from water loading as the ice sheets melt. This effect can be seen in Figure 1 where the relative sea level (RSL) curves show decreasing sea levels during the LIG where eustatic sea level is assumed to rise by 3 meters during this 11,000-year time span. All the sites have observational data that suggests sea level higher than that predicted by the model during the latter part of the LIG. When these data sets are considered in the context of these glacio-hydro-isostatic changes, we extract a eustatic sea level signal from the observational data that indicates a 5-meter rise in sea level between the beginning and the end of the LIG. Although most of this sea-level rise could have been accommodated by melting from the Greenland ice sheet, it is likely that the Western Antarctic ice sheet also contributed some component of this sea level rise.