Trace element variations in fossil corals from Tahiti collected by IODP Expedition 310: Reconstruction of marine environments during the last deglaciation (15 to 9 ka) Mayuri Inoue a, ⁎, Yusuke Yokoyama a,b,c , Mariko Harada a,b , Atsushi Suzuki d , Hodaka Kawahata a,e , Hiroyuki Matsuzaki f , Yasufumi Iryu g a Ocean Research Institute, The University of Tokyo, Japan b Department of Earth and Planetary Sciences, The University of Tokyo, Japan c Institute of Biogeosciences, Earth and Life History Research Program, Japan Agency for Marine-Earth Science and Technology, Japan d Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Japan e Graduate School of Frontier Sciences, The University of Tokyo, Japan f Department of Nuclear Engineering and Management, The University of Tokyo, Japan g Department of Earth & Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Japan abstract article info Article history: Received 4 July 2009 Received in revised form 7 February 2010 Accepted 17 February 2010 Available online 25 February 2010 Communicated by: Dr. G.J. de Lange Keywords: fossil coral deglaciation upwelling Tahiti IODP Climate responses and changes in marine environments during the last deglaciation have been controversial and few paleoceanographic data are available from the tropical South Pacific, though this region is crucial in the investigations of ocean–atmosphere interactions. Integrated Ocean Drilling Program Expedition 310 was conducted to establish the time course of the postglacial sea-level rise at Tahiti in the South Pacific. A principal objective of this expedition was to examine the variation of marine environments during the last deglaciation. As fossil Porites coral is ideal for assessing past marine environments, we selected only Porites specimens from the many coral specimens retrieved, examined them by XRD, and dated them by the 14 C method. In all, we obtained 17 pristine Porites specimens composed of only aragonite with ages from 15 to 9 ka. Then, we measured Mg/Ca, Ba/Ca, and U/Ca ratios and Cd contents as proxies for upwelling and sea surface temperature. Higher Ba/Ca ratios and Cd content together with lower reconstructed SSTs using U/Ca ratios in the coral specimens between 12.6 and 9.8 cal ka compared to around 15 cal ka suggest that upwelling and/or entrainment of subsurface water into mixed layer was enhanced around Tahiti during this period. This finding is consistent with previous reports and supports the idea that the South Pacific was characterized by La Niña-like conditions at least from 12.6 to 9.8 cal ka. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The transition from the last glacial maximum (LGM) to the Holocene is punctuated by various climate oscillations, including the Younger Dryas (YD; ca. 13.0–11.5 ka) cold period and the Antarctic Cold Reversal (ACR; ca. 14.1–12.4 ka) when global ice volumes reduced in a non linear fashion from the end of the LGM (19,000 years ago: Yokoyama et al., 2000, 2007a). These climate changes may not have been global in extent, and their geographic distribution is still a matter of considerable debate (Broecker and Hemming, 2001; Clark et al., 2002). While it appears that climate changes observed in Greenland ice cores are synchronous with changes recorded at most Northern Hemisphere latitudes (eg., Wang et al., 2008; Yokoyama et al., 2006), evidence from the Southern Hemisphere is sparse. To investigate global climate conditions, including El Niño — Southern Oscillation (ENSO) activity, during the deglaciation, paleo- ceanic data from tropical South Pacific are essential. Several studies from the eastern equatorial Pacific (EEP) indicated that the glacial to deglacial Pacific was La Niña-like condition (eg., Martinez et al., 2003, 2006) include debris flow deposits from the coasts of southern Peru and northern Chile for the period between 12.9 and 8.4 ka (Vargas et al., 2006). Reconstructions of sea surface temperature (SST) in higher resolution both spatially and temporary are desired, yet a compilation of SST records obtained from deep sea sediment cores for the last deglaciation from the Pacific Ocean (Kiefer and Kienast, 2005) contains neither coral based reconstruction nor marine sediment based data from the central to southeastern tropical Pacific. Trace elements in corals have been utilized as indices of paleo climate. Both Sr/Ca and U/Ca ratios have been employed as SST proxy (eg., Beck et al., 1997; Min et al., 1995) whereas Ba/Ca ratios and Cd contents in corals have been successfully applied to reconstruct upwelling (Montaggioni et al., 2006; Matthews et al., 2008). Although the latter have potentially important to understand physical ocean- ographic conditions in the past, few studies on the fossil corals have been conducted (Montaggioni et al., 2006). In this study, we analyzed Ba/Ca ratios and Cd contents in fossil corals (Porites sp.) obtained from Tahiti by Integrated Ocean Drilling Marine Geology 271 (2010) 303–306 ⁎ Corresponding author. E-mail address: mayuri-inoue@ori.u-tokyo.ac.jp (M. Inoue). 0025-3227/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.margeo.2010.02.016 Contents lists available at ScienceDirect Marine Geology journal homepage: www.elsevier.com/locate/margeo