Late Pleistocene to Holocene Strata from Soft-Sediment Coring at the AND-1B Site, ANDRILL McMurdo Ice Shelf Project, Antarctica

Prior to rotary coring, a range of soft-sediment coring tools were deployed to recover the sediment-water interface and the upper few metres of strata, whose integrity was threatened by embedment of the sea riser for drilling of the ANDRILL (AND)-1A/1B holes. These coring options included (1) a sediment gravity corer deployed through the ice-shelf hole, and (2) a push corer deployed through the sea riser suspended a few metres above the seabed. Within the AND-1A hole (during an attempt at sea-riser embedment) an extended-nose corer was advanced in front of the sea riser with limited success. The hydraulic piston corer was not deployed as a consequence of the fi rmness of the Last Glacial Maximum (LGM) diamicton and the occurrence of outsized clasts that could damage the drill string and compromise the deeper coring options. Successive attempts at gravity and push coring recovered 12 cores up to a maximum of 1.56 metres below sea-fl oor (mbsf). The longest core was dedicated to sampling for microbial life and pore-water geochemical studies which were expected to show the greatest gradients in the upper few metres of the sediment column. All cores sampled Holocene sub-iceshelf sediments above the LGM diamicton, and displayed a similar stratigraphy to a previously obtained site survey core, 250 m to the southeast (McKay et al., in press), with an unconsolidated diamicton passing upwards into muddy sub-ice-shelf facies. The sediment cores record the retreat of the grounding line through the region about 10 000 years ago and a transition from grounding line proximal, through sub-ice-shelf to calving-line proximal environments.