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The Antarctic Paleoenvironment: A Perspective on Global Change: Part One, p. 349-376

DOI: 10.1029/ar056p0349

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Late Quaternary climatic cycles as recorded in sediments from the Antarctic continental margin

Journal article published in 1992 by Hannes Grobe ORCID, Andreas Mackensen ORCID
This paper is available in a repository.
This paper is available in a repository.

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Abstract

To reveal the late Quaternary paleoenvironmental changes at the Antarctic continental margin, we test a lithostratigraphy adjusted to a stable isotope record from the eastern Weddell Sea. The stratigraphy is used to produce a stacked sedimentological data Set of 11 sediment cores. We derive a general model of glaciomarine sedimentation and paleoenvironmental changes at the East Antarctic continental margin during the last two climatic cycles (300 kyr). The sedimentary processes considered include biological productivity, ice rafting, current transport, and gravitational downslope transport. These processes are controlled by a complex interaction of sea level changes and paleoceanographic and paleoglacial conditions in response to changes of global climate and local insolation. Sedimenta-tion rates are mainly controlled by ice rafting which reflects mass balance and behavior of the Antarctic ice sheet. The sedimentation rates decrease with distance from the continent and from interglacial to glacial. Highest rates occur at the very beginning of interglacials, i.e., of oxygen isotope events 7.5, 5.5, and 1.1, these being up to 5 times higher than those during glacials. The sediments can be classified into five distinct facies and correlated to different paleoenvironments: at glacial. terminations (isotope events 8.0, 6.0, and 2.0), the Antarctic cryosphere adjusts to new climatic conditions. The sedimentary processes are controlled by the rise of sea level, the destruction of ice shelves, the retreat of sea ice, and the recommenced feeding of warm North Atlantic Deep Water (NADW) to the Circumpolar Deep Water (CDW). During peak warm interglacial periods (at isotope events 7.5,7.3, 5.5, and 1.1), the CDW promotes warmer surface waters and thus the retreat of sea ice which in turn controls the availability of light in surface waters. At distinct climatic thresholds, local Insolation might also influence sea ice distribution. Primary productivity and bioturbation increase, the calcite compensation depth rises, and carbonate dissolution occurs in slope sediments also in shallow depth. Ice shelves and coastal polynyas favor the formation of very cold and sahne Ice Shelf Water which contributes to bottom water formation. During the transition from an interval of peak warmth to a glacial episode (isotope stages 7.2-7.0 and 5.4-5.0), the superimposition of both intense ice rafting and reduced bottom currents produces a typical facies which occurs with a distinct lag in the time of response of specific sedimentary processes to climatic change. With the onset of a glacial episode (at isotope events 7.0 and 5.0) the Antarctic ice sheet expands owing to the lowering of sea level with the extensive glaciations in the northern hemisphere. Gravitational sediment transport becomes the most active process, and sediment transfer to the deep sea is provided by turbidity currents through canyon Systems. During Antarctic glacial maxima (isotope stages 6.0 and 4.0-2.0) the strongly reduced input of NADW into the Southern Ocean favors further advances of the ice shelves far beyond the shelf break and the continuous formation of sea ice. Below ice shelves andlor closed sea ice coverage contourites are deposited On the slope.