GPS Rates of Vertical Bedrock Motion Suggest Late Holocene Ice‐Sheet Readvance in a Critical Sector of East Antarctica

Abstract

Models of Antarctic glacial isostatic adjustment (GIA) show substantial differences, partly because of lack of data to constrain them Whitehouse et al., 2019). These differences represent uncertainty that affects estimates of ice-sheet mass change from satellite gravimetry and, to a lesser extent, satellite altimetry-both in terms of the ice-sheet wide contribution to sea-level change, as well the contribution over regional or basin-level scales (e.g., King et al., 2012).Over the recent decade, Global Positioning System (GPS)-estimates of bedrock velocities have become increasingly important for testing the different GIA model predictions of bedrock displacement or as data to inform empirical estimates (e.g.,

Stability of the Antarctic Ice Sheet during the pre-industrial Holocene

“…In East Antarctica, 70 m of thinning and episodes of increased glacier melting are recorded from 4,000 years ago in eastern Dronning Maud Land 27,37 , ice unloading accelerated from 2,700 years ago at Larsemann Hills 48 and glacial discharge increased from 4,500 years ago in Prydz Bay and from 1,700 years ago in Adélie Land-George V Land 134,135 . Modern observations of bedrock uplift also indicate ice mass loss occurred during the Late Holocene in the vicinity of Totten Glacier, Wilkes Land 130 . Furthermore, ice sheet models simulate continued ice loss into the Late Holocene in East Antarctica, mostly located in Dronning Maud Land, Princess Elizabeth Land and Wilkes Land -although not all models agree and limited empirical data are available to confirm this apparent ice loss (Fig.…”

Reversible ice sheet thinning in the Amundsen Sea Embayment during the Late Holocene

“…However, boundary conditions during a late Holocene retreat-readvance cycle were not identical to present conditions. Thus, whether our results, or other evidence for Holocene retreat-readvance and/or RSL fall elsewhere in Antarctica (Bradley et al, 2015;Kingslake et al, 2018;Venturelli et al, 2020;King et al, 2022), can be used to understand the importance of glacioisostatic rebound feedback in stabilizing present grounding line retreat in the Amundsen Sea region depends on (i) the difference between isostatic responses to large-scale LGM-to-Holocene thinning that took place over thousands of years and thinning of lesser magnitude observed in recent decades; (ii) the relative importance to grounding line position of relative sea level change, ice shelf buttressing, and sub-ice-shelf melting driven by oceanographic conditions, which cannot be deduced from any data presented here; and (iii) past and present bed topography in the region of grounding lines. In addition, the past thinning-thickening cycle that we have detected spanned a duration of at least 3000 years, which is geologically rapid but slow by comparison to the timescale of projected sea-level rise impacts of present ice sheet thinning.…”

“…Thus, existing observations require either (i) zero change in ice thickness in the last several thousand years, or (ii) continued thinning below the present ice surface, followed by thickening to the present configuration. Stable ice thickness for millennia appears unlikely given dynamic late Holocene boundary conditions, including relative sea level (RSL) change forced by eustatic and glacioisostatic effects, climate and oceanographic changes (Walker and Holland, 2007;Hillenbrand et al, 2017), and changes in grounding line position elsewhere in Antarctica (Venturelli et al, 2020;King et al, 2022). In addition, apparent 14 C exposure ages of 4-7 ka on samples below the 1966 ice surface (Fig.…”

Constraints on the Timing and Extent of Deglacial Grounding Line Retreat in West Antarctica

“…These methods enable us to reconstruct when ice retreated from a location; however, they likely do not provide a full picture of more complicated ice histories (e.g., Greenwood et al, 2018). Emerging evidence from model simulations (Kingslake et al, 2018), paleoglaciological reconstructions (Venturelli et al, 2020), gaps in the above-ice glacial-geologic record (Johnson et al, 2022), and modern observations (King et al, 2022) indicates that grounding lines around Antarctica likely retreated inland of present during deglaciation from the LGM and have recently readvanced to the configuration we observe today. Such a retreat scenario implies that we do not yet know the southernmost extent of deglacial grounding line retreat; therefore, we cannot fully assess the sensitivity of AIS to past drivers of this most recent deglaciation or quantify the internal and external mechanisms that enabled readvance.…”