A Joint Inversion Estimate of Antarctic Ice Sheet Mass Balance Using Multi-Geodetic Data Sets

Many recent mass balance estimates using the Gravity Recovery and Climate Experiment (GRACE) and satellite altimetry (including two kinds of sensors of radar and laser) show that the ice mass of the Antarctic ice sheet (AIS) is in overall decline. However, there are still large differences among previously published estimates of the total mass change, even in the same observed periods. The considerable error sources mainly arise from the forward models (e.g., glacial isostatic adjustment [GIA] and firn compaction) that may be uncertain but indispensable to simulate some processes not directly measured or obtained by these observations. To minimize the use of these forward models, we estimate the mass change of ice sheet and present-day GIA using multi-geodetic observations, including GRACE and Ice, Cloud and land Elevation Satellite (ICESat), as well as Global Positioning System (GPS), by an improved method of joint inversion estimate (JIE), which enables us to solve simultaneously for the Antarctic GIA and ice mass trends. The GIA uplift rates generated from our JIE method show a good agreement with the elastic-corrected GPS uplift rates, and the total GIA-induced mass change estimate for the AIS is 54 ± 27 Gt/yr, which is in line with many recent GPS calibrated GIA estimates. Our GIA result displays the presence of significant uplift rates in the Amundsen Sea Embayment of West Antarctica, where strong uplift has been observed by GPS. Over the period February 2003 to October 2009, the entire AIS changed in mass by −84 ± 31 Gt/yr (West Antarctica: −69 ± 24, East Antarctica: 12 ± 16 and the Antarctic Peninsula: −27 ± 8), greater than the GRACE-only estimates obtained from three Mascon solutions (CSR: −50 ± 30, JPL: −71 ± 30, and GSFC: −51 ± 33 Gt/yr) for the same period. This may imply that single GRACE data tend to underestimate ice mass loss due to the signal leakage and attenuation errors of ice discharge are often worse than that of surface mass balance over the AIS

An investigation into recent outlet glacier dynamics within Vincennes Bay, Wilkes Land, East Antarctica.

The Antarctic Ice Sheet has been in a state of negative mass balance over recent decades, with mass loss largely occurring from the West Antarctic Ice Sheet. However, recent studies indicate that Wilkes Land, East Antarctica, has lost mass at accelerating rates over the past two decades, exhibiting a dynamic response to oceanic forcing. Overlying the marine-based Aurora Subglacial Basin (ASB), Wilkes Land has been referred to as the potential ‘weak underbelly’ of the East Antarctic Ice Sheet and is drained by several major outlet glaciers. Despite their potential importance, few of these glaciers have been studied in detail. This includes the six outlet glaciers draining into Vincennes Bay, a region recently reported to have the warmest intrusions of modified Circumpolar Deep Water (mCDW) ever recorded in East Antarctica. This thesis seeks to improve our understanding of the understudied Vincennes Bay outlet glaciers, providing a first overview of recent ice dynamics observed between 1963 and 2022. Optical satellite imagery, differential satellite synthetic aperture radar interferometry (DInSAR) techniques and a range of secondary datasets were employed in order to assess change across four fundamental glacier parameters: terminus position, ice surface velocity, ice surface elevation, and grounding line position. Decadal fluctuations between terminus advance and terminus retreat recorded across the Vincennes Bay outlet glaciers correspond closely with wider patterns reported across Wilkes Land, potentially correlated to variations in sea ice production. Ice surface velocities were generally stable between 2000 and 2021, with some fluctuations measured across the grounding line of Bond East Glacier. Observed changes in ice surface elevation were spatially variable, with a consistent, albeit relatively modest, thinning trend seen across Vanderford Glacier between 2003 and 2017. Enhanced rates of ice thinning were measured across each of the Vanderford, Adams, Anzac, and Underwood Glaciers between 2017 and 2020, potentially linked to the widespread decline in Antarctic sea ice extent reported during the austral spring of 2016. Most importantly, extensive grounding line retreat was observed at Vanderford Glacier, measured at 18.6 km between 1996 and 2020. Such rapid grounding line retreat (0.8 km yr-1) is consistent with the notion that warm mCDW is able to access deep cavities formed below the Vanderford Ice Shelf, driving high rates of basal melting. With an inland retrograde bed slope observed along the Vanderford Trench, such oceanic forcing may have significant implications for the future stability of Vanderford Glacier. This study shows that the dynamic response of Vanderford Glacier has been more muted than expected given the high magnitude of grounding line retreat observed. Enhanced thinning and the onset of ice flow acceleration may therefore be predicted over the coming decades