Andrea Dutton and Kurt Lambeck
Research School of Earth Sciences, The Australian National University, Canberra, ACT, Australia
Paleoshorelines and coral reefs associated with the last interglacial, ~125,000 years ago, have persistently been recorded at 4-6 m higher than present sea level at many localities around the globe. The inference generally made is that this is the result of a smaller continental ice volume than the present configuration; however, elevated shorelines in some cases can be the result of tectonic uplift or residual isostatic response, or some combination of these three variables. Our modeling of the last interglacial focuses on (1) assessing the eustatic sea level signal, which is essentially a reflection of the continental ice volume at that time, and (2) determining whether evidence for sea level instability during the last interglacial is representative of fluctuations in eustatic sea level or whether these observations are attributes of the spatial variability of the isostatic response. We have approached this problem with a combination of glacio-hydro-isostatic modeling and field work that is focusing on improving the quality and resolution of sedimentologic and geochronologic data in far-field localities that play a key role in the process of modeling the eustatic sea level function.
At all locations the response of last interglacial sea level to changes in surface ice loading is a function of: (1) the ice model consisting of the ice margins and thickness of the ice – both before and after the last interglacial, (2) the rheological model of the mantle which determines the rate, magnitude, and wavelength of the response to the ice sheets, and (3) the eustatic sea level function, or volume of continental ice volume and ice grounded on the shelves. In principle, it is possible to separate out these three contributions given an observational dataset that has good geographic and temporal distribution in an analogous way to analyses of post-last glacial maximum sea levels.This presentation will focus on the advances we have made in our understanding of last interglacial eustatic sea level through both modeling and recent field results. Modeling results for characteristic sites in far-field and intermediate field sites will be discussed as well as the implications for interpreting data from these sites in the context of eustatic sea level changes during the last interglacial.