21. STABLE ISOTOPE AND CALCIUM CARBONATE RECORDS FROM HYDRAULIC PISTON CORED HOLE 574A: HIGH-RESOLUTION RECORDS FROM THE MIDDLE MIOCENE1

• Main Author: Nicklas G. Pisias
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Antarctic; The Antarctic; Antarc*; Ice Sheet
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.582.7240; http://www.deepseadrilling.org/85/volume/dsdp85_21.pdf

Detailed stable isotopic and calcium carbonate records (with a sampling resolution of 3000 yr.) from the middle Mi-ocene section of hydraulic piston corer (HPC) Hole 574A provide a sequence that records the major shift in the oxygen isotopic composition of the world's oceans that occurred at about 14 Ma. The data suggest that this transition was rapid and spans about 30,000 yr. of sediment deposition. In intervals before and after the shift, the mean δ 1 8 θ values are characterized by a constant mean with a high degree of variability. The degree of variability in both the δ 1 8 θ and δ 1 3C records is comparable to that observed for the Pliocene and earliest Pleistocene and does not show a significant change before or after the major shift in the δ 1 8 θ record. Whereas the oxygen isotopic record is characterized by relatively sta-ble mean values before and after the middle Miocene event, the δ 1 3C record shows a number of significant offsets in the mean value separated by intervals of high-frequency variations. Time and frequency domain analysis of all records from Hole 574A indicate that the frequency components shown to be related to orbital changes in the Pleistocene record are also present in the middle Miocene. The high variability observed in the Site 574 isotopic records places important constraints on models describing the role of formation of the Antarctic ice sheet during the middle Miocene climatic transitions. Thus, HPC Hole 574A provides a valuable sequence for detailed study of climatic variability during an important time in the Earth's history, although we cannot provide a definitive explanation of the major oxygen isotopic event of the middle Miocene.