Investigating the influence of mid- to late-Holocene loading on horizontal ANET GPS motions in the Ross Sea Region, Antarctica

Abstract:

Horizontal motions predicted by Antarctic GIA models utilizing a 1D earth profile are radially outward from modelled centers of ice mass loss, yet observed motions from ANET (Antarctic Network) GPS measurements in Antarctica do not follow this pattern in the Ross Sea region. Specifically, in the Transantarctic Mountains, GPS-derived crustal motions are towards the Ross Embayment and the modelled center of post-LGM ice mass loss, while motions in the Marie Byrd Land region are radially outward from this region. This apparently anomalous observed pattern of deformation motivates the investigation of alternative ice model and earth model scenarios. We have previously explored Wilkes Subglacial Basin ice loading scenarios using 1-D GIA models, and also 3-D GIA models invoking a boundary in earth properties beneath the Transantarctic Mountains. Results show that these scenarios can partially simulate observed horizontal crustal motions, but they do not fully replicate them. Here we investigate the influence of ice sheet changes and associated loading along the Siple Coast induced by 1) centennial-scale thickening and thinning of the Kamb, Whillans, and MacAyeal ice streams, and 2) millennial-scale grounding-line retreat and readvance along the whole of the Siple Coast. We find predicted motions from these model scenarios do not replicate both reversed motions towards the Siple Coast in the southern Transantarctic Mountains and motions radially away from the Siple region of ice mass change in Marie Byrd Land. However, the spatial extent of deformation induced by Siple Coast loading is significant, and triggers ongoing motion that can be detected at the majority of ANET GPS sites in the Ross Sea region. Maximum modelled rates yield magnitudes of predicted motion that are one-third to one-half the magnitude of GPS-derived motions for sites within the zone of deformation. These results suggest that examination of alternate spatial and temporal ice load histories, such as presented here, are essential to effectively utilizing GPS observations to constrain GIA models.