HR: 1340h
AN: PP43C-1536    [Abstracts]
TI: Estimates of Eastern Equatorial Pacific Sea Surface Temperatures During the Pliocene From Carbonate ‘Clumped Isotope' Thermometry
AU: * Thiagarajan, N
EM: nivedita@caltech.edu
AF: California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, United States
AU: Tripati, A
EM: atri02@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, United States
AU: Tripati, A
EM: atri02@gps.caltech.edu
AF: University of Cambridge, Downing Street, Cambridge, Cam CB2 3EQ, United Kingdom
AU: Eiler, J
EM: eiler@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, United States
AB: The early Pliocene (5 to 3 Ma) was an interval in Earth history that was globally warmer than the present; thus, study of the details of Pliocene climate can provide insights into the dynamics of warm climates. There are two competing models of the temperature structure of the tropical Pacific upper-ocean during the early Pliocene: the dynamical ‘ocean thermostat' model [1,2] and the ‘El Padre' (or permanent ‘El Nino') model [3], each of which predict zonal temperature gradients and mean conditions in the Eastern Equatorial Pacific (EEP), and which differ markedly from one another in these predictions. The dynamical ‘ocean thermostat' model predicts an increased temperature contrast between the Western Equatorial Pacific (WEP) and EEP, enhanced thermocline tilt and intensified upwelling under warmer conditions. In contrast, the ‘El Padre' model postulates a collapse of the zonal temperature gradient, reduced thermocline tilt and a reduction in upwelling and/or warmer temperatures of upwelled waters. Existing reconstructions of tropical temperatures produce WEP sea surface temperatures which agree with each other, but yield very different results in the EEP [4,5]. We have reconstructed EEP sea surface temperatures at Ocean Drilling Program (ODP) Site 847 using a few samples spanning key intervals of the last 6 million years using carbonate clumped isotope thermometer [6,7,8]. This technique is based on the temperature dependence of the abundances of ¹³C-¹⁸O bonds in carbonate minerals. Initial measurements of planktonic foraminifera and coccoliths from ODP Site 847 indicate cool EEP sea surface temperatures, supporting models of Pliocene climate that have enhanced zonal temperature gradients, relative to modern. Analyses of Globigerinoides sacculifer (with sac) from sediments indicate calcification temperatures of 20.3°C ± 0.1°C and seawater δ¹⁸O values of –0.8‰ ± 0.1‰ from ~6.1 to 5.1 million years ago. Measurements of a mixed coccolith assemblage from the fine fraction of 5.6 Ma sediments show calcification temperatures of 20.4°C ± 2.3°C and seawater δ¹⁸O values of –1.4‰ ± 0.6‰. G. sacculifer (with sac) and mixed coccoliths from 1.4 Ma sediments yield calcification temperatures of 22.3°C ± 2.5°C and seawater δ¹⁸O values of 1.7‰ ± 0.7‰, and 19.4°C ± 1.8°C and seawater δ¹⁸O values of 0.4‰ ± 0.5‰, respectively. Our preliminary findings are consistent with the ‘dynamical ocean thermostat' model. [1] Clement, A., et al., 1996, An Ocean Dynamical Thermostat, J. of Clim., 9, 2190-2196. [2] Cane, M., et al., 1997, Twentieth-Century Sea Surface Temperature Trends, Science, 957-960. [3] Fedorov, A., et al., 2006, The Pliocene Paradox (Mechanisms for a permanent El Nino), Science, 312, 1437-1443. [4] Rickaby, R. and Halloran, P., 2005, Cool La Nina during the warmth of the Pliocene?, Science, 307, 1948-1953. [5] Wara, M., et al. ,2005, Permanent El Nino-like conditions during the Pliocene Warm Period, Science, 309, 758-761. [6] Ghosh, P., et al., 2006, 13C–18O bonds in carbonate minerals: A new kind of paleothermometer, GCA, 70, 1439–1456. [7] Eiler, J. and Tripati, A., 2007, ‘Clumped isotope' thermometry in benthic foraminifera and ostracods: A novel tool for reconstructing deep-ocean temperatures. Fall AGU. [8] Tripati, A., et al. 2007, ‘Carbonate `clumped isotope' thermometry in planktonic foraminifera and coccoliths. Fall AGU.
DE: 4928 Global climate models (1626, 3337)
DE: 4938 Interhemispheric phasing
DE: 4999 General or miscellaneous
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting