Geological record of ice shelf break-up and grounding line retreat, Pine Island Bay, West Antarctica

Abstract

The catastrophic break-ups of the fl oating Larsen A and B ice shelves (Antarctica) in 1995 and 2002 and associated acceleration of glaciers that fl owed into these ice shelves were among the most dramatic glaciological events observed in historical time. This raises a question about the larger West Antarctic ice shelves. Do these shelves, with their much greater glacial discharge, have a history of collapse? Here we describe features from the seafl oor in Pine Island Bay, West Antarctica, which we interpret as having been formed during a massive ice shelf break-up and associated grounding line retreat. This evidence exists in the form of seafl oor landforms that we argue were produced daily as a consequence of tidally infl uenced motion of mega-icebergs maintained upright in an iceberg armada produced from the disintegrating ice shelf and retreating grounding line. The break-up occurred prior to ca. 12 ka and was likely a response to rapid sea-level rise or ocean warming at that time.

New constraints on the timing of West Antarctic Ice Sheet retreat in the eastern Amundsen Sea since the Last Glacial Maximum

“…According to Larter et al (in press) the rates of change currently observed in the ASE are too high to be a simple continuation of deglaciation from the LGM as such high modern retreat rates (i.e., 0.95 ± 0.09 km yr -1 between 1992-2011; Park et al 2013) would have resulted in deglaciation of the entire continental shelf within 500 years, which is in conflict with recent marine geological data (e.g., Smith et al, 2011). There is also a growing body of geomorphological evidence that ice sheet retreat following the LGM was oscillatory with periods of rapid change punctuated by periods of relative stability (Graham et al, 2010;Jakobsson et al 2011). …”

“…6) does raise questions about the deglacial model published in Kirshner et al (2012). Furthermore, if the Jakobsson et al (2011) model for formation of corrugations is also correct, then the ridges imaged on GZW4 must have formed before GZW5, otherwise it would have been impossible to generate icebergs with deep enough keels to form them (see Fig. 4 in Jakobsson et al, 2012).…”

“…Finally, in addition to these sedimentological considerations, recent work has shown that the corrugation ridges described by Jakobsson et al (2011Jakobsson et al ( , 2012, could reflect another bed shaping process. described corrugations and ploughmarks on a ridge beneath the modern PIG ice shelf and suggested their formation by periodic grounding of ice shelf keels during glacier unpinning rather than "catastrophic" ice shelf collapse.…”

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

“…Similar corrugations have been mapped beneath the Pine Island Glacier ice shelf and within iceberg scours located in the main PIT. These corrugations are believed to originate from tidally-modulated, periodic keel grounding beneath a seaward-flowing ice shelf or at the trailing keel of tabular icebergs (Jakobsson et al, 2011). Jakobsson et al (2011) and Larter et al (2012) suggested that icebergs eroding linear, parallel scours may have been embedded within a mélange of sea and brash ice restricting iceberg movement and thus contributed to the linear orientation of the resulting scours as seen here.…”

Ice sheets viewed from the ocean: the contribution of marine science to understanding modern and past ice sheets

“…Does this reflect drainage of meltwater through pore spaces in the till by Darcian throughflow, or does it reflect the fact that existing multi-beam systems are, as yet, unable to resolve these kinds of features over the soft bed? These are unanswered questions, but ones which marine science has the potential to answer through acquisition of well-dated core chronologies and increasing improvements in multi-beam systems [124].…”