Abstract
Displaced Antarctic diatoms were identified and counted in a suite of 23 giant gravity cores from the east flank of the Vema Channel, providing a semi-quantitative index of Late Pleistocene/Holocene fluctuations in Antarctic Bottom Water (AABW) flow. Twelve species of Antarctic diatoms were counted, and three of these ( Nitzschia kerguelensis, Eucampia antarctica and Coscinodiscus lentiginosus) occur in sufficient quantity for statistically meaningful interpretations. The number of diatom specimens per gram of carbonate-free sediment was determined for core top, last glacial maximum, last interglacial, and penultimate glacial maximum intervals. Antarctic diatoms are abundant in cores from depths in excess of 4100 m and disappear abruptly in core tops between approximately 4125 and 3975 m water depth. No specimens of Antarctic diatoms are present in cores shallower than 3744 m. The top of this transition zone corresponds with the isotherms ϑ = 1.9°C and the isopycnal σ 4 = 45.93 that Hogg et al. (1982) selected as a suitable reference level between northward and southward flow in the Vema Channel axis. The sediments from the Vema Channel indicate no significant shallowing or deepening of this level during the glacial or interglacial intervals examined. Displaced Antarctic diatoms are generally less abundant during glacial maxima than during interglacials. Downcore counts of displaced Antarctic diatoms reveal two peaks of dramatically increased abundances at the isotopic stage 6 7 and 3 2 boundaries. In other cores within the Vema Channel from below 3965 m, late Pleistocene hiatuses are common.
Published Version
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