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 nine Eltanin piston cores from the southeast 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-µm fraction. The merit in using ice-rafted debris–temperature relationships (rather than magnitudes of debris) is demonstrated by the presence of high concentrations of ice-rafted debris in cores of low sedimentation rate, showing that the debris can be a residual coarse fraction rather than an index of higher deposition rates from icebergs.
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 north to south 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 two 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 un-proven, source of departures from the simple model predictions.