The anatomy of interglacial sea levels: The relationship between sea levels and ice volumes during the Last Interglacial

The elevations and chronology of interglacial shorelines and other sea-level indicators provide information on ice volumes for these earlier periods compared with today. But, as for the Holocene, the relationship between sea levels and ice volumes for earlier interglacials is not simple because of the planet's deformational, gravitational and rotational response to changes in ice-water loads (glacio-hydro isostasy). In particular, the pattern of global sea level for a particular interglacial will be a function of the earth and ocean response to ice loads applied before, during and after the interglacial in question. This paper examines the role of glacio-hydro isostasy during these glacial cycles to make three key points. The first is to demonstrate why interglacial sea levels cannot be interpreted directly in terms of ice volume. The second is to illustrate the spatial variability that can be expected in interglacial sea levels because of the Earth's isostatic response to changing ice and water loads and to demonstrate why observations from different localities should not be combined into a single sea-level function without first correcting for differential isostatic effects. The third addresses the question whether, in the absence of perfect knowledge of the ice sheets and earth rheology, inferences can be made about ice volumes during an interglacial. We conclude that if these isostatic factors are ignored, interpretations of interglacial sea levels can lead to serious errors in the inferences about ice volumes during the interglacials.