Rapid retreat of Thwaites Glacier in the pre-satellite era

Abstract

Understanding the recent history of Thwaites Glacier, and the processes controlling its ongoing retreat, is key to projecting Antarctic contributions to future sea-level rise. Of particular concern is how the glacier grounding zone might evolve over coming decades where it is stabilized by sea-floor bathymetric highs. Here we use geophysical data from an autonomous underwater vehicle deployed at the Thwaites Glacier ice front, to document the ocean-floor imprint of past retreat from a sea-bed promontory. We show patterns of back-stepping sedimentary ridges formed daily by a mechanism of tidal lifting and settling at the grounding line at a time when Thwaites Glacier was more advanced than it is today. Over a duration of 5.5 months, Thwaites grounding zone retreated at a rate of >2.1 km per year—twice the rate observed by satellite at the fastest retreating part of the grounding zone between 2011 and 2019. Our results suggest that sustained pulses of rapid retreat have occurred at Thwaites Glacier in the past two centuries. Similar rapid retreat pulses are likely to occur in the near future when the grounding zone migrates back off stabilizing high points on the sea floor.

Comparison and Synthesis of Sea‐Level and Deep‐Sea Temperature Variations Over the Past 40 Million Years

“…With specific focus on processes that are accelerating mass loss in the Greenland ice sheet to centennial and even decadal timescales, Box et al (2022) listed: "tidewater glacier acceleration and destabilization by submarine melting (Khazendar et al, 2019a(Khazendar et al, , 2019bTruffer & Fahnestock, 2007;Wood et al, 2021); loss of floating ice shelves (Mouginot et al, 2015); accelerating interior motion from increased melt and rainfall (Doyle et al, 2015); enhanced basal thawing due to hydraulically released latent heat and viscous warming (Phillips et al, 2010); amplified surface melt run-off due to bio-albedo darkening (Stibal et al, 2017); and impermeable firn layers (MacFerrin et al, 2019) amplified by ice-sheet surface hypsometry (Mikkelsen et al., 2016;." In West Antarctica, sea-floor data indicate sustained pulses of very rapid Thwaites Glacier retreat (>2 km per day) within the past two centuries that are related to tidally modulated grounding-line migration (Graham et al, 2022).…”

Modes of Antarctic tidal grounding line migration revealed by ICESat-2 laser altimetry

“…The signal is an order of magnitude higher than the fastest annual average GL retreat of 1.8 km yr -1 observed at Pine Island Glacier between 1992 and 2011 (Park et al, 2013) and several orders of magnitude higher than average long-term Antarctic GL migration rates (Konrad et al, 2018). For comparison, the highest estimated deglaciation retreat rates from palaeo-records are >2.1 km yr -1 and >10 km yr -1 for Thwaites and Larsen A, respectively (Dowdeswell et al, 2020;Graham et al, 2022). Therefore, to accurately measure long-term GZ change it is necessary to isolate the spatially variable pattern of tidal GL migration.…”

“…The very shallow water column (<100m) immediately seaward of Bungenstockrücken (Johnson and Smith, 1997) suggests that tidal mixing would be strong here, and is likely to be enhanced as water is "pumped" in and out of the cavity as the GL migrates with the tides. Short-term tidal fluctuations in melt rate and tidal mixing have been shown to impact long-term GL retreat in less stable regions (Graham et al, 2022). Given that projections of future ice sheet mass loss are highly sensitive to basal melt at the GL (Arthern and Williams, 2017;Goldberg et al, 2019;Adusumilli et al, 2020), the type of information about tidal GZ behaviour that we can derive from ICESat-2 RTLA will be valuable to improve melt parameterisations in ice sheet models.…”

“…These include impacts on: Ice velocity (Gudmundsson, 2007;Thompson et al, 2014;Robel et al, 2017Robel et al, , 2022Mosbeux et al, 2022); GZ surface profile (e.g. Schoof, 2011); Inland seawater incursion (Warburton et al, 2020;Robel et al, 2022); Variations in subglacial water pressure (Rosier et al, 2015;Begeman et al, 2020); Formation of estuarine features in the GZ (Horgan et al, 2013a); Enhanced basal melt (Makinson et al, 2011;Mueller et al, 2012); Basal shear stress (Anandakrishnan et al, 2003); Till compaction, leading to changes in basal lubrication (Walker et al, 2013;Christianson et al, 2013;Sayag and Worster, 2013); Formation of tidal seabed ridges (Dowdeswell et al, 2020;Graham et al, 2022); Ocean circulation through tidal mixing. The landward and seaward tidal GL positions are labelled as Fmax and Fmin.…”

Comparison and synthesis of sea-level and deep-sea temperature variations over the past 40 million years

“…With specific focus on processes that are accelerating mass loss in the Greenland ice sheet to centennial and even decadal timescales, Box et al (2022) listed: "tidewater glacier acceleration and destabilization by submarine melting (Truffer and Fahnestock, 2007;Khazendar et al, 2019a,b;Wood et al, 2021); loss of floating ice shelves (Mouginot et al, 2015); accelerating interior motion from increased melt and rainfall (Doyle et al, 2015); enhanced basal thawing due to hydraulically released latent heat and viscous warming (Phillips et al, 2010); amplified surface melt run-off due to bio-albedo darkening (Stibal et al, 2017); and impermeable firn layers (MacFerrin et al, 2019) amplified by ice-sheet surface hypsometry (Mikkelsen et al, 2016;van As et al, 2017)." In West Antarctica, sea-floor data indicate sustained pulses of very rapid Thwaites Glacier retreat (>2 km per day) within the past two centuries that are related to tidally modulated grounding-line migration (Graham et al, 2022).…”