Diachronous deposition of ice-rafted debris in sub-Antarctic deep-sea sediments

Abstract

A simple model to explain the distribution of ice-rafted debris in deep-sea sediments of the southern ocean proposes that ice-rafted debris maxima in the high latitudes are associated with interglacial periods and in the lower latitudes with glacial periods. Initial testing of this model is now extended using 9 Eltanin piston cores from the SE Indian Ocean. Frequency variation in the Antarctic radiolarian Antarctissa strelkovi is used as a paleotemperature index, and the ice-rafted debris is measured for the 62- to 250-.mu.m fraction. Departures from the predicted ice-rafted debris-paleotemperature correlations during the Brunhes epoch suggest complexities that could be due to such factors as anomalous ice-shelf development, ice surges, variations of preferred iceberg tracks, periods during which conditions are transitional between extreme glacial and interglacial, or between differential sea-floor dynamic processes. To evaluate such possibilities, the model is now developed to include stages intermediate between extreme glacial and interglacial conditions. Complex ice-rafted debris variations are predicted to result across N-S traverses as climatic fronts sweep between extreme climatic conditions, resulting in difficulty in determining between-core correlations. Attempts have been made to isolate periods of departure from the predicted ice-rafted debris-paleotemperature correlations by computation of down-core-running correlation coefficients between the 2 variables. A lack of fine stratigraphic control at present makes it impossible to test definitively the implications of the more complex model, and thus it stands as a proposed, yet unproven, source of departures from the simple model predictions.