Submarine glacial landform distribution across the West Antarctic margin, from grounding line to slope: the Pine Island-Thwaites ice stream system

About 30% of ice draining the West Antarctic Ice Sheet discharges through several glacier systems into the Amundsen Sea Embayment (ASE) (Fig. 1a). Two major ice-stream outlets, Pine Island and Thwaites glaciers, have undergone significant twentieth century changes (e.g. Rignot et al. 2008) and much effort has focused upon understanding their late Quaternary glacial history (Larter et al. 2014). At the Last Glacial Maximum (LGM), the ice sheet in the ASE expanded to reach the outer shelf and is postulated to have reached the shelf edge (Graham et al. 2010). The Pine Island and Thwaites glaciers combined regularly through Quaternary glaciations to carve out a >500 km long trough that extends from the shelf break back to the modern-day grounding line and beyond. Geophysical data exist for the breadth of this transect, including sub-ice-shelf bathymetry (Jenkins et al. 2010), making it one of the most complete palaeo-ice-stream landsystems known offshore of Antarctica. Deglaciation of the trough was underway by c. 20 cal. ka BP and was episodic, reaching a mid-shelf position by c. 13.5–12 cal. ka BP and retreating rapidly to the inner ASE by c. 11–9 cal. ka BP (Kirshner et al. 2012; Hillenbrand et al. 2013; Smith et al. 2014). Repeated pauses and several phases of ice-shelf break-up have been interpreted to have taken place during deglaciation based upon a well-preserved landform and sediment record (Lowe & Anderson 2002; Graham et al. 2010; Jakobsson et al. 2011).