Shadows of the Last Glacial Cycle in Data Interpretation of the Last Interglacial

Abstract:

Sea level indicators from the last interglacial (LIG) suggest that sea level was higher than present day. Thus, present-day sea level is taken as the reference level when interpreting the LIG data. Models of the Earth's and ocean's response to the changing ice sheets are used to understand how the Earth's deformation and ocean redistribution introduces geographic variability into the data. These physical processes are collectively termed glacial isostatic adjustment (GIA).

Neither the Earth nor the ocean are completely recovered from the loading of the last glacial cycle. For this reason, the GIA model results for present day are subtracted from the results at prior times in order to derive the relative sea-level histories that are compared to data. Thus, the unrelaxed GIA signal of the last glacial cycle is effectively propagated back in time in the model predictions. Any difference in this component of the GIA model will contribute to our uncertainty of model prediction during the LIG.

In this contribution, we examine this level of uncertainty that this unrelaxed component will introduce to the analysis of the data. Lack of knowledge of both the ice load history and Earth model will contribute to this uncertainty, and we additionally focus on the contribution of the ice sheet history from the LIG to the last glacial maximum (LGM), which is the least constrained. While the uncertainty contribution is not large, this is a necessary step in developing a more complete uncertainty budget.