INVESTIGATION OF DEEP-WATER CIRCULATION MODES IN THE EARLY CENOZOIC USING NEODYMIUM ISOTOPES FROM FOSSIL FISH DEBRIS

The ocean’s deep-water circulation plays a large role in heat transport across the globe. Circulation in the modern begins where cold, dense surface waters of the North Atlantic and Southern oceans sink to form Atlantic Bottom water. However, this mode did not operate in the geologic past. A growing body of Nd isotope data from fossil fish debris is being used to reconstruct the ancient mode of deep-water circulation throughout the early Cenozoic greenhouse interval. Recent data from previous Ocean Drilling Program (ODP) sites suggest that a bipolar mode of meridional overturning circulation may have existed in the Pacific during the early Cenozoic, beginning ~65 million years ago and lasting until ~40 million years ago. Here I present new data from Deep Sea Drilling Project (DSDP) Site 464, Northern Hess Rise, to enhance the reconstruction of deep water mass composition as well as determine if a reductive cleaning step (“clean”) method is necessary during sample preparation. Site 464 εNd(t) values range from -.30 to less radiogenic values of -4.42 from ~56.0 to 32.3 million years ago, showing a shift from a North Pacific deep-water influence to a Southern Ocean influence. The comparison of “clean” versus “unclean” analyses indicates that both record the same seawater composition