Ocean access to a cavity beneath Totten Glacier in East Antarctica

Abstract

Totten Glacier, the primary outlet of the Aurora Subglacial Basin, has the largest thinning rate in East Antarctica 1,2 . Thinning may be driven by enhanced basal melting due to ocean processes 3 , modulated by polynya activity 4,5 . Warm modified Circumpolar Deep Water, which has been linked to glacier retreat in West Antarctica 6 , has been observed in summer and winter on the nearby continental shelf beneath 400 to 500 m of cool Antarctic Surface Water 7,8 . Here we derive the bathymetry of the sea floor in the region from gravity 9 and magnetics 10 data as well as ice-thickness measurements 11 . We identify entrances to the ice-shelf cavity below depths of 400 to 500 m that could allow intrusions of warm water if the vertical structure of inflow is similar to nearby observations. Radar sounding reveals a previously unknown inland trough that connects the main ice-shelf cavity to the ocean. If thinning trends continue, a larger water body over the trough could potentially allow more warm water into the cavity, which may, eventually, lead to destabilization of the low-lying region between Totten Glacier and the similarly deep glacier flowing into the Reynolds Trough. We estimate that at least 3.5 m of eustatic sea level potential drains through Totten Glacier, so coastal processes in this area could have global consequences.The Totten Glacier drains into the Sabrina Coast in an area where we find coastal ice grounded below sea level and the potential for local marine ice sheet instability 12 upstream of the grounding line ( Fig. 1b). We infer the bathymetry seaward of the grounding line using inversions of gravity data 9 informed by magnetics data 10 and ice-thickness measurements 11 . The inversion reveals the southwest area of the Totten Glacier Ice Shelf (TGIS) cavity is the deepest, reaching 2.7 ± 0.19 km below sea level ( Fig. 2), comparable to the grounding line depths of Amery Ice Shelf 13 and the segment of the Moscow University Ice Shelf (MUIS) overlying the Reynolds Trough 11 . The shallowest area of the cavity (∼300 mbsl) is found beneath the calving front of the ice shelf where a large coastparallel ridge connects Law Dome with a peninsula of grounded ice protruding from the east side of the cavity (Fig. 2). The ridge extends 40 km seaward of the calving front and would have been a source of backstress on the Totten Glacier as recently as 1996 when ice rises were last detected 14 . The inversion reveals depressions located near the centre of the ridge (650 ± 190 mbsl) and to the east of the grounded ice peninsula (860 ± 190 mbsl) (Fig. 2, Profile A-A ). Looking along the long axis of the full Totten cavity we see it is an average of 500 m deeper along the western (Law Dome) side. We infer two basins on the long axis reaching depths of 2.7 ± 0.19 km and 2.0 ± 0.19 km (SW and NE, respectively; Fig. 2) separated by a narrow ridge causing an ice rise near the middle of the ice shelf (the left-hand panel in Fig. 2) 14 .Published grounding lines 14,15 indicate an area of grounded ice bounded by the MUIS t...

Oligocene TEX<sub>86</sub>-derived seawater temperatures from offshore Wilkes Land (East Antarctica)

“…Observations show that glaciers on East Antarctica are also vulnerable to basal melt 50 through warming of the ocean waters when they are grounded below sea level (Greenbaum et al, 2015;Miles et al, 2016), making the East Antarctic ice sheet (EAIS) not as stable as previously thought (Mcmillan et al, 2014).…”

Simultaneous disintegration of outlet glaciers in Porpoise Bay (Wilkes Land), East Antarctica, driven by sea ice break-up

“…Following recent work that highlighted the potential vulnerability of the East Antarctic Ice Sheet in Wilkes Land to ocean-climate forcing and marine ice-sheet instability (Greenbaum et al, 2015;Aitken et al, 2016;Miles et al, 2013Miles et al, , 2016, we analyse the recent calving activity of six outlet glaciers in the Porpoise Bay region using monthly satellite imagery between November 2002 and March 2012. In addition, we also observe the start of a large calving event in 2016.…”

Ocean forced variability of Totten Glacier mass loss

“…1c for the location) has the largest outflow (70 ± 4 km 3 a −1 ) of any glacier in East Antarctica, and has the third highest ice flux of all Antarctic glaciers, behind only the Pine Island and Thwaites glaciers (Rignot & Thomas 2002), both in the Amundsen Sea (AS) region of West Antarctica. The Aurora Subglacial Basin is an extensive region of grounded ice that drains primarily through the main trunk of the TG (Roberts et al 2011;Young et al 2011;Wright et al 2012) and contains enough marine-based ice to raise the global sea level by 3.5 m (Greenbaum et al 2015). The TG has an extensive embayed floating ice shelf adjoining a weakly grounded 'ice plain' containing topographical features that have previously been interpreted as 'ice rumples', with the ice surface slightly above the flotation limit (Greenbaum et al 2015).…”

“…The Aurora Subglacial Basin is an extensive region of grounded ice that drains primarily through the main trunk of the TG (Roberts et al 2011;Young et al 2011;Wright et al 2012) and contains enough marine-based ice to raise the global sea level by 3.5 m (Greenbaum et al 2015). The TG has an extensive embayed floating ice shelf adjoining a weakly grounded 'ice plain' containing topographical features that have previously been interpreted as 'ice rumples', with the ice surface slightly above the flotation limit (Greenbaum et al 2015). It is thought that, by analogy with observed changes in the AS region of West Antarctica (Shepherd & Wingham 2007;Pritchard et al 2009Pritchard et al , 2012, these features make the TG susceptible to rapid grounding zone retreat via the marine ice-sheet instability mechanism (Schoof 2007) and potentially sensitive to changing ocean conditions (Li et al 2016).…”