Palaeo-ice stream pathways and retreat style in the easternmost Amundsen Sea Embayment, West Antarctica, revealed by combined multibeam bathymetric and seismic data

Abstract

Multibeam swath bathymetry data sets collected over the past two decades have been compiled to identify palaeo-ice stream pathways in the easternmost Amundsen Sea Embayment. We mapped~3000 glacial landforms to reconstruct ice flow in the~250-km-long cross-shelf Abbot Trough. This bathymetric feature was occupied by a large ice stream, which was fed by two tributaries (Cosgrove and Abbot) and reached the continental shelf edge during the last maximum ice sheet advance. Geomorphological mapping has enabled a clear differentiation between subglacial landforms indicating warm-(e.g., megascale glacial lineations) and cold-based (e.g., hill-hole pairs) ice conditions on the continental shelf during the last glaciation. Grounding-zone wedges and recessional moraines, mapped within the palaeo-ice stream troughs and on adjacent sea-floor highs (referred to as inter-ice stream ridges) indicate grounding line stillstands or re-advances of the West Antarctic Ice Sheet during the last deglaciation of the shelf. We observe that the locations of grounding-zone wedges coincide with trough constrictions as well as local topographic highs of harder substrate. This combination of trough 'bottlenecks' and local pinning points on an otherwise retrograde slope is likely to have modified the pace of grounding-line retreat, causing the grounding zone to pause and deposit grounding-zone wedges. The episodic retreat recorded within Abbot Trough corresponds to post-glacial episodic retreat interpreted for the neighbouring Pine Island-Thwaites palaeo-ice stream trough, thus suggesting a uniform pattern of retreat across the eastern Amundsen Sea Embayment. Locally, indications are strong that a change in basal thermal regime of the ice from warm-to cold-based conditions occurred prior to final retreat, as hill-hole pairs overprint megascale glacial lineations. Further, the correlation of grounding-zone wedges with geological boundaries emphasises the influence of subglacial geology on ice stream flow. Our new geomorphological map of the easternmost Amundsen Sea Embayment resolves the pathways of palaeo-ice streams that were probably all active during the last maximum extent of the ice sheet, and the extent of adjacent inter-ice stream ridges. It reveals information about the style of, and the basal thermal regime during, the subsequent grounding line retreat. Such information provides an important empirical framework by which the accuracy of ice sheet models can be gauged.

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

“…However, a flattening in trough profile beyond the mid-shelf and the existence of multiple outer-shelf troughs, including new landform evidence of streaming ice within Abbot Trough ( Fig. 1b; Klages et al 2015), raises the possibility that outer parts of the ice sheet were configured in widespread distributed fast ice flow or even as divergent fast-flowing trunks during glacial maxima ). Although we cannot constrain the precise glaciological regime, it is evident from recent mapping that the geomorphological character of the outer shelf is as complex as the inner-shelf counterpart, and not a relatively simple imprint of full-glacial conditions (cf.…”

“…GZW1 is c. 15 m thick, while GZW 2 may be .40 m high. Equivalent and probably corresponding wedges are also mapped to the east in Abbot Trough (not shown; Klages et al 2015).…”

Atmosphere‐ocean‐ice interactions in the Amundsen Sea Embayment, West Antarctica

“…Multibeam‐swath bathymetry data revealed that several bathymetric troughs extend from the modern ASE coast across the continental shelf to near the shelf break [e.g., Nitsche et al ., ; Jacobs et al ., ; Livingstone et al ., ; Larter et al ., ] (see Figure ). A variety of subglacial bedforms mapped within these troughs give evidence that the troughs mark the pathways of fast‐flowing paleo‐ice streams, which had advanced across the ASE shelf during past glacial periods [ Lowe and Anderson , ; Evans et al ., ; Graham et al ., , ; Larter et al ., ; Jakobsson et al ., , ; Nitsche et al ., ; Klages et al ., , ]. In contrast, a distinct bed form assemblage observed on an intervening shallow ridge suggests that paleo‐ice flow there was slower than in the neighboring troughs [ Klages et al ., ].…”

Past ice-sheet behaviour: retreat scenarios and changing controls in the Ross Sea, Antarctica

“…Small repeating corrugation ridges have been observed within fields of iceberg furrows or within individual iceberg furrows (Fig. 2h, k;Anderson, 1999;Jakobsson et al, 2011;Klages et al, 2015). Although the exact mechanism for their formation remains somewhat controversial, corrugation ridges are thought to form as icebergs move vertically with tides, causing iceberg keels to intermittently contact the bed (Jakobsson et al, 2011;Graham et al, 2013).…”