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Sea Level Record for the Last 200,000 Years from Concordant U-Th and U-Pa Dates of Fossil Corals: Implications for Deep-Sea Temperature Changes and for Early Sea Level Rise During Termination II Christina D Gallup 1 (301-405-4088; gallup@geol.umd.edu) Kirsten B Cutler 2 Hai Cheng 2 R. Lawrence Edwards 2 Robert Speed 3 Frederick W Taylor 4 Jess Adkins 5 George S Burr 6 1Dept. of Geology, University of Maryland, College Park, MD 20742, United States 2Dept. of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, United States 3Dept. of Geological Sciences, Northwestern University, Evanston, IL 60208, United States 4Institute for Geophysics, University of Texas at Austin, Austin, TX 78759, United States 5Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10954, United States 6NSF Accelerator Facility for Radioisotope Analysis, Dept. of Physic University of Arizona, Tuscon, AZ 85721, United States We have constructed a sea level record for the last 200,000 years from New Guinea and Barbados fossil corals that have concordant U-Th and U-Pa ages and have an initial $^{234}$U/$^{238}$U ratio within 8 per mil of the modern marine ratio. The decision to limit samples to those that pass both the test for an initial $^{234}$U/$^{238}$U ratio near the modern value and U-Th/U-Pa concordance was made because many samples that pass the initial $^{234}$U/$^{238}$U ratio test do not have concordant U-Th and U-Pa ages, and thus may have been altered. Our sea level curve includes the times of relatively high sea level, corresponding to oxygen isotope sub-stages 7.1, 6.5, the 6/5e transition (Termination II), 5e, 5c, 5a, and 1. All times (with the exception of the timing of Termination II) correspond to times of high northern-hemisphere summer insolation, indicating that insolation is an important factor influencing sea level. In this presentation, we will concentrate on two aspects of this sea level record: 1) the timing and amplitude of sea level during Termination II and oxygen-isotope event 6.5 and 2) the implications for deep sea temperature change when the sea level record is compared with benthic oxygen-isotope records. New data from Barbados fossil corals indicate that Termination II precedes most of the rise in northern-hemisphere summer insolation, consistent with earlier studies (Winograd et al., 1992; Esat et al., 1999). Possible triggers for Termination II include (1) indirect forcing, ultimately resulting from northern-hemisphere summer insolation change, (2) insolation forcing that is not simply northern-hemisphere summer, such as southern-hemisphere insolation change (Henderson et al., 1999), (3) other factors related to some kind of inherent instability of the climate system. By correlating our sea level curve with benthic deep-sea oxygen isotope records, we have separated the ice volume and temperature contributions to marine oxygen isotope variations at a Pacific and an Atlantic site. Both sites record significant deep sea warming during Termination I (about 2 degrees in the Pacific and 4 degrees in the Atlantic, consistent with earlier work) and significant cooling subsequent to 5e. These data are consistent with southern ocean warming of about 2 degrees during Termination I, and a Termination I switch from southern source waters to North Atlantic Deep Water at the Atlantic site. We also observe that cooling subsequent to 5e was smaller than Termination I warming at both sites. This temperature residual is linearly correlated with sea level between stages 5c and 2. |
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