A New Antarctic glacial history approaching spatial and temporal resolution required for contemporary geodesy

Assessment of crustal motions and gravity change driven by glacial isostatic adjustment (GIA) in Antarctica is critically dependent on the reconstruction of the Late Pleistocene and Holocene differential mass load. Over the past two decades, reconstructions were dominated by weak constraints inferred from far-field sea level modeling, and/or from poorly dated Pleistocene grounding line positions located offshore. A number of the past models involve a large total loss of ice mass to the world's oceans since LGM, with equivalent mean sea level rise (ESLR): Δ ξ ≈ 20 ↔ 37m. However, the collection and analysis of new field data for improving the reconstruction has occurred at an accelerated pace during the past decade. At the same time, space-based imaging and altimetry, combined with on-ice velocity measurements using Global Positioning System (GPS) geodesy, has provided better assessments of the present-day mass balance of the Antarctic ice sheet. Present-day mass change appears to be dominated by deglaciation and is, most likely, a continuation of late-Holocene evolution. A new ice load model is constructed (`IJ05'), based on a synthesis of the current constraints on past ice history and present-day mass imbalance. The new model has about one-third to one-half of the total post-LGM mass loss (i.e., Δ ξ ≈ 10 m) compared to many previous models. It is tuned to recent ice core stratigraphy, glacier moraine and rock surface exposure dates, and to the offshore grounding line retreat chronology. In summary, the new forward model offers improvement in 4 aspects: (i) the timing of volume losses in the region ranging from the Ross Sea sector to the Antarctic Peninsula; (ii) the maximum differential ice heights in parts of the Ellsworth and Transantarctic Mountains; (iii) the maximum grounding line position in Pine Island Bay, Bellingshausen Sea, the Antarctic Peninsula, and in the Ross Sea, and retreat from those positions; (iv) incorporation of present-day net mass balance estimates. The predicted present-day GIA uplift rates peak at 14 - 18 mm/yr and geoid rates peak at 4 - 5 mm/yr for two contrasting viscosity models. If the asthenosphere underlying West Antarctica has a low viscosity then the predictions could change substantially due to the extreme sensitivity to recent (past two millennia) ice mass variability. Future observations of crustal motion and gravity change will substantially improve the understanding of sub-Antarctic lithospheric and mantle rheology.