Sediment Characteristics of Subglacially Drained Sediments from Pine Island Bay, West Antarctica
Alexandra E. Kirshner1, John B. Anderson1, Carolyn M. Branecky1, and Witold Szczuciński2
1Rice University, Houston TX, USA 77005
2Adam Mickiewicz University, Poznan Poland
Modern Pine Island and Thwaites Glaciers, which both drain into Pine Island Bay, are some of the fastest changing portions of the cryosphere and are among the least stable ice streams in Antarctica. Here we show that the uppermost sediments in Pine Island Bay were deposited from a meltwater plume, a plumite, which occurred since the late stages of ice sheet retreat ~7-8.6 k cal yr BP. It is a hydraulically sorted, glacially sourced, draping deposit that overlies proximal glacimarine sediments and thickens towards the modern grounding line.
Geophysical mapping in the inner part of Pine Island Bay reveals several basins that are linked by channels with a storage capacity on the order of 70 km3 of water and sediment. The plumite is a product of non-steady-state processes in which low background sedimentation alternates with sediment sequestration in the large bedrock- carved basins and episodic purging. This is caused by changes in hydraulic potential and glacial reorganization. Grain shape analyses are used to better understand the mode of transport. Radiocarbon ages and 210Pb profiles are used to calculate the rate of deposition for the meltwater silt unit and to estimate sediment flux. The most recent release of sediment coincides with rapid retreat of the grounding line in historical time and has an order of magnitude greater flux relative to the entire unit.
The occurrence of a meltwater-derived deposit has profound implications for understanding glacial instability and numerical modeling studies of ice sheet dynamics for more improved prediction of future sea level. This study demonstrates that punctuated meltwater-intensive glacial retreat occurred at least three times in the Holocene in this region. We further suggest that the modern Thwaites Glacier is poised for an analogous meltwater-intensive similar retreat.
AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013