The sensitivity of tectonic uplift corrections to the penultimate deglacial ice volume and configuration

Abstract

Reconstructions of peak global mean sea-level (GMSL) change during the interglacials and interstadials between Quaternary glacial cycles provide insight into the past behavior of the cryosphere and climate system and may inform projections of future change. Erosional and constructional terraces and other relative indicators of past sea-level high stands are a key component of GMSL reconstructions as these indicators provide a geographically widespread dataset that is readily comparable to geophysical model predictions. However, along tectonically active margins, the present-day elevation of a relative sea level (RSL) indicator reflects vertical motion due to active tectonics (and other processes) such that any inference of GMSL involves a correction for the latter (and vice versa). The most robust method to estimate tectonic uplift for field localities with a Last Interglacial (Marine Isotope Stage (MIS) 5e) RSL indicator is to compute the difference between the observed elevation of the MIS 5e indicator and a site-specific peak LIG relative sea level computed from a glacial isostatic adjustment model. Dividing the difference between the observed indicator elevation and computed sea level value by the age of the MIS 5e high stand provides an uplift rate. If the resulting tectonic uplift rate is presumed to be constant throughout the recent glacial–interglacial cycle, then this rate can be applied to other RSL indicators at the same site, such as those formed during the MIS 5a and 5c interstadials, to compute the uplift-corrected local RSL elevation. Here we explore the sensitivity of the tectonic uplift-correction applied to MIS 5a RSL indicator elevations to the volume and configuration of continental ice sheets during the MIS 6 penultimate glacial maximum and deglaciation (Termination II), as this ice history impacts the local modeled MIS 5e high stand elevation input into the tectonic uplift correction calculation. We explored 5 models of ice volume and configuration that vary the total ice volume and the relative ratio of continental ice in North America and Eurasia. We find that these ice models produce ∼5–10 m shifts in the elevation of uplift-corrected MIS 5a relative sea level indicators (or, equivalently, ∼6–12 cm/kyr variation in tectonic uplift rates) for sites along the Pacific coasts of the U.S. and Mexico, U.S. Atlantic coast, and Caribbean. Future assessments of GMSL during MIS 5a, MIS 5c, or other interglacials/interstadials that rely upon relative sea level indicators subject to a tectonic uplift correction should account for the sensitivity of the local modeled MIS 5e elevation to the MIS 6 glacial maximum ice volume and configuration.