31. ICE RAFTING, GLACIAL-MARINE SEDIMENTS, AND SILICEOUS OOZES: SOUTH

In the modern Southern Ocean, very little debris is delivered to the sea by icebergs. Whatever debris may be present beneath the ice sheets is lost near the grounding line. Whatever till is present beneath ice streams is also lost near the grounding line, but it may significantly contribute to fine-sized suspensoids. The bulk of the ice-rafted debris encountered at Ocean Drilling Program Leg 114 drill sites was delivered in the geologic past, when antarctic glaciers had greater erosive power (Warnke, 1970). Whatever ice-rafted detritus is present is essentially only an admixture to rapidly accumulating siliceous oozes. These oozes present a paradox because, in general, primary production in the open Southern Ocean is quite low. However, because the preservation of antarctic diatoms is far better than their preservation in low latitudes, high sedimentation rates result. These relationships are explained either in terms of high flux rates during the growth season, or as the result of a "stressed ecosystem, " given to significant fluctuations, or as a combination of both mechanisms. These relationships lead to uncertainties in the computation of apparent mass-accumulation rates (AMARs) of ice-rafted detritus (details presented by Allen and Warnke, this volume). Nevertheless, a clear picture of the changes in antarctic glaciation emerges, particularly when viewed in the light of investigative results by Froelich et al. (this volume) and Hodell et al. (this volume). The most significant results of our investigations of ice-rafted detritus are the recognition of (1) the antiquit