East Antarctic Ice Sheet and Southern Ocean Response to Orbital Forcing from Late Miocene to Early Pliocene, Wilkes Land, East Antarctica

Abstract

Geological and ice sheet models indicate that marine-based sectors of the East Antarctic Ice Sheet (EAIS) were unstable during periods of moderate climatic warmth in the past. While geological records from the Middle to Late Pliocene indicate a dynamic ice sheet, records of ice sheet variability from the comparatively warmer Late Miocene to Early Pliocene are sparse, and there are few direct records of Antarctic ice sheet variability during this time period. Sediment recovered in Integrated Ocean Drilling Program U1361 drill core from the Wilkes Land margin provides a distal but continuous glacially-influenced record of the behaviour of Antarctic Ice Sheets.

This thesis presents marine sedimentological and x-ray fluorescence geochemical datasets in order to assess changes in the dynamic response of the EAIS and Southern Ocean productivity in the Wilkes Land sector during Late Miocene and Early Pliocene to climatic warming and orbital forcing between 6.2 and 4.4 Ma. Two primary lithofacies are identified which can be directly related to glacial–interglacial cycles; enhanced sedimentation during glacials is represented by low-density turbidity flows that occurred in unison with low marine productivity and reduced iceberg rafted debris. Interglacial sediments contain diatomaceous muds with short-lived, large fluxes of iceberg rafted debris preceding a more prolonged phase of enhanced marine productivity. Interglacial sediments coincide with a more mafic source of terrigenous sediment, interfered to be associated with an inland retreat of the ice margin resulting in erosion of lithologies that are currently located beneath the grounded EAIS. Poleward invigoration of the Antarctic Circumpolar Current during glacial–interglacial transitions is proposed to have intensified upwelling, enhancing nutrient availability for marine productivity, and increasing oceanic heat flux at the ice margin acting to erode marine ice sheet grounding lines and triggering retreat.

Spectral analysis of the datasets indicated orbital frequencies are present in the iceberg rafted debris mass accumulation rates at all three Milankovitch frequencies, with a dominant 100 kyr eccentricity driven ice discharge. Prolonged intervals of marine productivity correlate to 100 kyr cyclicity occurring at peaks in obliquity. The response of both ice sheet and biological systems to 100 kyr cyclicity may indicate eccentricity-modulated sea ice extent controls the influx of warm water onto the continental shelf.