The paradox of a long grounding during West Antarctic Ice Sheet retreat in Ross Sea

Abstract

Marine geological data show that the West Antarctic Ice Sheet (WAIS) advanced to the eastern Ross Sea shelf edge during the Last Glacial Maximum (LGM) and eventually retreated ~1000 km to the current grounding-line position on the inner shelf. During the early deglacial, the WAIS deposited a voluminous stack of overlapping grounding zone wedges (GZWs) on the outer shelf of the Whales Deep Basin. The large sediment volume of the GZW cluster suggests that the grounding-line position of the paleo-Bindschadler Ice Stream was relatively stationary for a significant time interval. We used an upper bound estimate of paleo-sediment flux to investigate the lower bound duration over which the ice stream would have deposited sediment to account for the GZW volume. Our calculations show that the cluster represents more than three millennia of ice-stream sedimentation. This long duration grounding was probably facilitated by rapid GZW growth. The subsequent punctuated large-distance (~200 km) grounding-line retreat may have been a highly non-linear ice sheet response to relatively continuous external forcing such as gradual climate warming or sea-level rise. These findings indicate that reliable predictions of future WAIS retreat may require incorporation of realistic calculations of sediment erosion, transport and deposition.

Post‐LGM Grounding‐Line Positions of the Bindschadler Paleo Ice Stream in the Ross Sea Embayment, Antarctica

“…The second band of smaller‐scale ridges is located further to the south and was originally described by Bart et al () from Figure b. Within 20 km of the RIS calving front, the seafloor is elevated above grade by ~5 m and exhibits a series of low‐relief ridges with a few hundred meters spacing.…”

“…Moreover, none of the individual GZWs were mapped separately because the individual topsets and bottomset surfaces are not regional seismic reflections. Regional correlations of the amalgamated upper and lower bounding surfaces of this CGZW demonstrate that all seven individual GZWs on the outer and middle continental shelf are confined to the basin (Bart et al, ).…”

“…Other large volume backstepped deposits in Ross Sea (Joides and Drygalski Basins, see Shipp et al, ) and other Antarctic margins (Batchelor & Dowdeswell, ) might also be CGZWs. Deposition probably compensated for the longer‐term deflation of the WAIS and/or any post‐LGM sea level rise (Anandakrishnan et al, ; Bart et al, ). In other words, the stratal stacking pattern strongly suggests that GZW deposition influenced the location of subsequent stillstands by contemporaneously reducing the water depth at the grounding line.…”

“…Fewer studies have focused on eastern Ross Sea troughs (e.g., Whales Deep and Little America Basins). To our knowledge, Mosola and Anderson () and Bart et al () are the only two studies that explicitly focused on WAIS retreat from the Whales Deep Basin.…”

“…Bart et al () used seismic transects from expedition NBP1502B and four other surveys (~7,400 line km) (Figure b) to determine the sediment thickness distribution of the backstepped GZWs in the Whales Deep Basin. The deposits they mapped are equivalent to GZW5b and GZW5c from Mosola and Anderson ().…”