Antarctic glacial history and sea-level change – Leg 178 samples Antarctic Peninsula margin sediments
The Antarctic Ice Sheet is a key feature of the
global climate engine today, and has been so
for most of its 35 Myr or longer history. It influences
global circulation (mainly through bottom
water production), eustatic sea-level change, biological
production and albedo. And yet the details
of that history are poorly known, despite two decades
of measurement and interpretation of lowlatitude
ice-volume proxies. The most effective of
those proxy measurements, oxygen isotopes and
sea-level change, are ambiguous, and disagree.
Recently, a way out of this impasse has
emerged, that is technically difficult but much
more direct. It involves sampling and dating sediments
transported beneath the grounded ice sheet
and deposited seaward of the grounding line
around the Antarctic margin. We now appreciate
that the ice sheet “drains” mainly by rapid flow in
ice streams that slide on a shearing bed of diamict.
Over the life of the ice sheet, those glacially-transported
sediments have formed progradational
wedges on the outer continental shelf. They, and
their derived sediments redeposited in drifts on the
upper continental rise, should therefore contain a
record of ice sheet advance to the continental shelf
edge. The prograded wedge is essentially unsorted
making it difficult to recover, and the topsets are
prone to subsequent erosion. The drifts have
formed by more continuous deposition of sorted
silty clays that are easier to recover but less direct,
needing clues from the wedge to aid interpretation.
The two depositional environments are complementary.
Additional useful features of the Antarctic
margin are the deep basins eroded on the inner
continental shelf during glacial maxima, which preserve
an expanded Holocene record of climate
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