Holocene sea level history, modern-day vertical uplift and forebulge evolution: further constraints on the GIA process over the North American continent

Abstract:

The intense cycles of glaciation and deglaciation that have characterized Earth's climate over the past 900,000 years have had a profound impact on the Earth system. The significant imprints that the related variations in surface mass load have had on sea level history and the Earth’s shape can be employed to constrain models of the glacial isostatic adjustment (GIA) process. These models rely on two fundamental inputs, namely a history of ice-sheet loading and a representation of the variation of viscosity in the lithosphere and in the mantle. Especially important GIA related observables include Global Positioning System (GPS) observations of the movement of the solid Earth's surface and inferences of past relative sea level evolution. Depending on the region from which they originate, these data provide information on different model characteristics. In particular, while the relative sea level constrained relaxation occurring near former centers of glaciation can be relatively easily parametrized to facilitate an inversion for mantle viscosity, the same process in the regions of forebulge collapse is much more complex but nevertheless provides essential further constraints upon mantle viscosity.

In this paper, we examine how recently available high-quality datasets of relative sea level evolution from the U.S. East coast (Engelhart et al., Geology, 2011) and the North American Pacific coast (Engelhart et al., QSR, 2015) can be employed, together with an extensive dataset of space-geodetic observations of present-day vertical uplift of the crust over North America (Peltier et al., JGR – Solid Earth, 2015), to further improve the latest state-of-the-art ICE-6G_C (VM5a) model (Peltier et al., JGR – Solid Earth, 2015). It will be demonstrated that the high quality of the data does not only provide further constraints on radial variations of viscosity in the mantle, but also on the history of the deglaciation that occurred over North America after the Last Glacial Maximum. Finally, these improvements, which only arise from a careful, simultaneous study of all relevant geophysical observables (especially those over the regions of forebulge collapse in North America), will also be considered in light of their impact upon our understanding of the evolution of the shape of the forebulge during the late Holocene.