A significant acceleration of ice volume discharge preceded a major retreat of a West Antarctic paleo-ice stream

摘要

For the period between 14.7 and 11.5 cal. (calibrated) kyr B.P, the sediment flux of Bind-schadler Ice Stream (BIS; West Antarctica) averaged 1.7 x 10(8) m(3) a(-1). This implies that BIS velocity averaged 500 +/- 120 m a(-1). At a finer resolution, the data suggest two stages of ice stream flow. During the first 2400 +/- 400 years of a grounding-zone stillstand, ice stream flow averaged 200 +/- 90 m a(-1). Following ice-shelf breakup at 12.3 +/- 0.2 cal. kyr B.P., flow accelerated to 1350 +/- 580 m a(-1). The estimated ice volume discharge after breakup exceeds the balance velocity by a factor of two and implies ice mass imbalance of -40 Gt a(-1) just before the grounding zone retreated >200 km. We interpret that the paleo-BIS maintained sustainable discharge throughout the grounding-zone stillstand first due to the buttressing effect of its fringing ice shelf and then later (i.e., after ice-shelf breakup) due to the stabilizing effects of grounding-zone wedge aggradation. Major paleo-ice stream retreat, shortly after the ice-shelf breakup that triggered the inferred ice flow acceleration, substantiates the current concerns about rapid, near-future retreat of major glaciers in the Amundsen Sea sector where Pine Island and Thwaites Glaciers are already experiencing ice-shelf instability and groundingzone retreat that have triggered upstream-propagating thinning and ice acceleration.