Antarctic glacial history and sea-level change – Leg 178 samples Antarctic Peninsula margin sediments

first_imgThe Antarctic Ice Sheet is a key feature of theglobal climate engine today, and has been sofor most of its 35 Myr or longer history. It influencesglobal circulation (mainly through bottomwater production), eustatic sea-level change, biologicalproduction and albedo. And yet the detailsof that history are poorly known, despite two decadesof measurement and interpretation of lowlatitudeice-volume proxies. The most effective ofthose proxy measurements, oxygen isotopes andsea-level change, are ambiguous, and disagree.Recently, a way out of this impasse hasemerged, that is technically difficult but muchmore direct. It involves sampling and dating sedimentstransported beneath the grounded ice sheetand deposited seaward of the grounding linearound the Antarctic margin. We now appreciatethat the ice sheet “drains” mainly by rapid flow inice streams that slide on a shearing bed of diamict.Over the life of the ice sheet, those glacially-transportedsediments have formed progradationalwedges on the outer continental shelf. They, andtheir derived sediments redeposited in drifts on theupper continental rise, should therefore contain arecord of ice sheet advance to the continental shelfedge. The prograded wedge is essentially unsortedmaking it difficult to recover, and the topsets areprone to subsequent erosion. The drifts haveformed by more continuous deposition of sortedsilty 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 Antarcticmargin are the deep basins eroded on the innercontinental shelf during glacial maxima, which preservean expanded Holocene record of climatechange.last_img

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