A physical record of the circumpolar circulation of the Southern Ocean - late Miocene to Pleistocene

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

This work will increase our understanding of how deep-ocean circulation has changed with respect to important climate changes of the late Cenozoic. Today, deep waters of the three oceans blend in the Antarctic Circumpolar Current (ACC) as they are continually transported from one ocean basin to the next one east. This flow, now about 100 to 150 million cubic meters per second, is responsible for most of the heat and nutrient transport among the deep Atlantic, Indian and Pacific Oceans. The ACC also isolates Antarctica from the warmer world to the north and its surface waters provide moisture to the continent. As such, a carefully constructed history of this flow would significantly increase our understanding of late Cenozoic global change. We propose to develop a detailed physical record of the Antarctic Circumpolar Current that spans the last 9 Myr. To achieve this we will apply the methods developed in studying deep-sea drift deposits elsewhere to the drift sediments recovered by ODP Leg 178 on the Pacific margin of the Antarctic Peninsula. Data generated by the scientific party of Leg 178, along with our preliminary information, suggest that these deposits are a faithful monitor of ocean-wide events. The primary tool of our analysis will be the anisotropy of magnetic susceptibility (AMS) which is a quantitative measure of the fabric--or degree of alignment--in a sediment. We and others have shown that stronger currents result in more pronounced fabrics. Other data to be generated will include: the grain-size distribution of the terrigenous sediment component, which allows discrimination between drift-related sediments and distal turbidites; the weight percent of terrigenous sediment in each sample, and by difference in this two-component deposit, the amount of opal; the mass accumulation rate of these components; and by orienting the fabric information to the magnetic field vector recorded in the same sample, the direction of the flow. The educational impact of this work centers on the graduate student for whom this research will provide a Ph.D. thesis project, but also involves undergraduates in hands-on research.