Reconstruction of Early Paleogene North Pacific Deep-Water Circulation using the Neodymium Isotopic Composition of Fossil Fish Debris
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To better understand the operating mode of the deep oceans during fundamentally warm climate intervals, we present new Nd isotope data from Deep Sea Drilling Project and Ocean Drilling Program sites in the North Pacific to expand the reconstruction of water mass composition and structure during the early Cenozoic. Fossil fish debris from Sites 192, 464, 465, 883, 884 and 1208 (paleowater depths spanning 900 to 4000 m) were used to reconstruct the water mass composition from ~85 to 30 Ma. The fish debris is shown to not be overprinted as there was no systematic offset between the detrital silicate and the fish debris composition. Cleaned and uncleaned fish debris were both included in the reconstruction of water mass composition as they were found to record the same Nd isotope composition. North Pacific deep water convection occurred from ~67 to 45 Ma, the peak in production is recorded by broadly coincident trends at Sites 192, 464 and 883. Further support for North Pacific deep-water convection during the early Paleogene are the geographic trends in detrital silicate versus fish debris composition, greater separation at the more northerly Emperor Seamount sites, and the location of the most radiogenic detrital values at the Emperor Seamount sites. The Emperor Seamount chain likely played a major role in the flow of the North Pacific deep-water mass as it acted as a physical barrier to flow at deep-water sites compared to shallow depths (albeit still deep-water). εNd values indicate the timing of the cessation of major, deep convection in the North Pacific occurred much earlier, ~52 Ma than the timing obtained from shallower Shatsky Rise sites, ~45 Ma. Convection in the North Pacific likely produced a dense water mass that influenced the deeper sites in this study more than the shallower sites until ~52 Ma when convection was not as intense or the waters were not sufficiently dense to impact the deeper sites. Deep water convection was most intense during the relatively “cool” portion of the Late Cretaceous and Early Paleocene.
Hague, Ashley Melissa (2011). Reconstruction of Early Paleogene North Pacific Deep-Water Circulation using the Neodymium Isotopic Composition of Fossil Fish Debris. Master's thesis, Texas A&M University. Available electronically from