Sub-Ice Shelf Stratigraphy as Documented From Beneath the Larsen B Ice Shelf, Antarctica

The final disintegration of the Larsen B Ice shelf (March 2002) was a significant event in the history of glaciology. During NBP01-07, the Larsen B Ice shelf area was surveyed as a continuation of a multi-year investigation of the sediment processes and paleohistory of the Larsen B. Six kasten cores (KC1-KC6) were recovered from the Larsen B inlet at depths ranging from 438 m to 676 m. These cores were sampled at 2 cm intervals for grain size analysis and water content. Ice rafted debris (IRD) content was obtained by observing x-rays and counting at 2.5 cm intervals. Magnetic susceptibility was measured every 2.5 cm using the Bartington MS2C 44 mm sensor. 14C-calcite dates were obtained from the top 20 cm in KC2 and KC5. Results from the data allowed for the construction of a general litho-stratigraphy of the Larsen B Ice shelf depositional environments prior to its collapse. KC1-KC6 consist of three main units (from top to bottom): (1) sandy silty clay, (2) stratified sandy mud and muddy sand with granules, and (3) structureless muddy-diamicton. Three different depositional environments are suggested based on the sedimentological features of these units: open-marine, transitional, and glacial. The gravel pavement (0-1 cm) on top of KC5 was deposited as a product of the Larsen B Ice Shelf calving event in 1999. This is significant to our interpretation of the Larsen B­_s sedimentary processes and paleohistory because the stratigraphy of the Larsen A (Pudsey et al. 1998) does not show these angular pebbles and cobbles on top of unit 1, but rather biosiliceous ooze in its silty clay unit . Furthermore, 14C-calcite dates from KC5 (2,300 +/-35 at 2 cm, 2,760+/-35 at 5 cm, and 9,210+/-45 at 20 cm) and KC2 (3,710+/-40 at 2cm, 9,760+/-45 at 15cm, and 10,600+/-55) help confirm that the Larsen B has not experienced a history of recession and reformation since the end of the last Ice Age. Instead the ice shelf seems to have been in place for some time while embayments to the north were experiencing open marine conditions (Domack et al., 2001 & Pudsey et al., 2001). Thus, our investigation illustrates that the disintegration of the Larsen B Ice Shelf was an unprecedented event in which its litho-stratigraphy indicates a sub-ice shelf environment formed during the entire Holocene.