The Role of Dynamic Topography on Glacial Inception in North America

Glacial inception in the northern hemisphere marks an abrupt transition in climate dynamics around 2.7 Ma when the Laurentide Ice Sheet began to grow from snow cover persisting year-round in high elevation regions of Baffin Island. Although it has been the focus of many studies, the exact driver of this glacial inception remains elusive. We examine the role of long timescale, solid earth process in generating favorable conditions for ice growth. Daradich et al. (2017), after Donn and Shaw (1977), argued that true polar wander (TPW), the motion of the Earth's rotation axis relative to the surface, and continental drift have moved the North American continent to increasingly high latitudes over the last 40 Myr. This change in latitude had the effect of cooling local climate and therefore decreasing glacial ablation in Baffin Island. We propose a third process acting in tandem with TPW and continental drift, namely the effect of dynamic topography, triggered glacial inception by increasing regional crustal elevation.

To predict dynamic topography changes in the past, we run the mantle convection model ASPECT backwards in time from present day conditions to 5 Ma and track the evolution of normal stresses at the surface. Dynamic topography is calculated as the compensation height that balances these stresses. Our predictions for dynamic topography based on both global and regional tomography models show uplift across the Baffin Island region on the order of 75-150 m over 5 million years. These modelled results of uplift are in line with high present-day residual topography data in Baffin Bay (Hoggard et al., 2017), as well as geological constraints across the passive margin in west Greenland (Japsen et al., 2006). Uplifting topography during the Plio-Pleistocene would reduce local surface temperatures and alter precipitation patterns. Using both our predictions for dynamic topography and previous estimates for paleolatitudes from TPW and continental drift, we reconstruct paleotopography across Baffin Island and use this to estimate changes in glacial mass balance. The imbalance between snow accumulation and ablation increases for increasing elevation and latitude (through time) allowing us to define a threshold after which glacial inception was possible.