Back to Fall 1999 AGU abstract list.
Back to the News
|
Sea-Level Since the Last Interglacial From Combined 231Pa and 230Th Dating of Corals Kirsten B. Cutler 1 (1-612-624-9598; bank0026@tc.umn.edu) Fredrick W. Taylor 2 (1-512-471-0453; fred@utig.ig.utexas.edu) R. Lawrence Edwards 1 Hai Cheng 1 Christina D. Gallup 3 George S. Burr 4 1University of Minnesota, Department of Geology and Geophysics, Minneapolis, MN 55455 2University of Texas, Austin, Institute for Geophysics, Austin, TX 78759 3University of Maryland, Department of Geology, College Park, MD 20742 4University of Arizona, Department of Physics, NSF Accelerator Facility for Radioisotope Analysis, Tucson, AZ 85721 We have used high-precision 231Pa dating techniques [1] to test the accuracy of 230Th ages of fossil corals and thereby establish the timing and amplitude of sea-level changes since the last interglacial. We have dated 55 coral samples from Papua New Guinea and Barbados with high precision 230Th and 231Pa dating methods. The results were added to the existing bank of coral-based sea-level data. Data were screened based on 230Th and 231Pa age-concordancy, proximity of the initial d234U value to the modern marine value, and degree to which the local diagenetic processes are constrained. The resulting data were used to obtain a sea-level record. Our data confirm a number of well established aspects of the sea level curve, and also resolve some discrepancies. Furthermore, our data places new constraints on rates of sea-level change for specific portions of the curve. Sea level dropped rapidly between marine oxygen-isotope stages 5e to 5d, 5c to 5b, 5a to 4, and 3 to 2. The most rapid drop took place during the 5a to 4 transition, when sea level dropped at a rate of 10.4 m/ky for nearly 6 ky. Thus, 45\% of glacial maximum ice volume was accommodated in less than 6 ky and during that time the average rate of net ice accumulation on the continents was greater than 18 cm/yr. Finally, our data establishes sea level during stage 5b at 60 m below present, revealing that sea level dropped about 47 m between stages 5c and 5b, and rose about 49 m between stages 5b and 5a. Each of the four periods of rapid sea-level drop correspond in time to intervals of unusually low northern hemisphere summer insolation [2], suggesting a fairly direct relationship between orbital forcing and climate during these intervals. Conventional wisdom suggests that long periods are required to reach maximum glaciation during a glacial cycle. Our data suggest that in fact ice buildup is at times very rapid. Thus, we argue that long intervals of time are required to reach maximum glaciation because the conditions amenable to glacial growth, i.e. very low insolation values, occur for only brief periods of time. References: [1] Pickett D. A. et al. (1994) Analytical Chem., 66, 1044-1049; Edwards et al. (1997) Science, 276, 782-786. [2] Berger A. (1978) Quat. Res., 9, 139-167. |
Meeting: Meeting Section: Special Session: Index Terms: Theme: |
Last Modified: October 8, 1999
Comments: UTIG webmaster