Sea surface temperature changes in the Okhotsk Sea and adjacent North Pacific during the last glacial maximum and deglaciation Naomi Harada a,n , Miyako Sato a , Osamu Seki b , Axel Timmermann c , Heiko Moossen d , James Bendle d , Yuriko Nakamura a , Katsunori Kimoto a , Yusuke Okazaki a , Kana Nagashima a , Sergey A. Gorbarenko e , Akira Ijiri f , Takeshi Nakatsuka g , Laurie Menviel h , Megumi O. Chikamoto a , Ayako Abe-Ouchi a,i , Stefan Schouten j a Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan b Institute of Low Temperature Science, Hokkaido University, Kita-19, Nishi-8, Kita-ku, Sapporo 060-0819, Japan c International Pacific Research Center (IPRC), School of Ocean and Earth Science and Technology, University of Hawai’i, 2525 Correa Road, Honolulu, HI 96822, USA d Glasgow Molecular Organic Geochemistry Laboratory (G-MOL), Department of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lilybank Gardens, University of Glasgow, Glasgow G12 8QQ, United Kingdom e V.I. II’ichev Pacific Oceanological Institute, Far East Branch of Russian Academy of Science, Vladivostok, Russia f Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 200 Monobe Otsu, Nankoku 783-8502, Japan g Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan h Climate and Environmental Physics, Oeschger Centre for Climate Change Research, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland i Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa 277-8568, Japan j Department of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, Texel, The Netherlands article info Available online 10 January 2012 Keywords: Alkenone Tetraethers TEX 86 Sea surface temperature Deglaciation Last glacial maximum North Pacific Okhotsk Sea abstract We estimated sea surface temperatures (SSTs) in the western Okhotsk Sea during the last glacial maximum (LGM) and the last glacial termination from measurements of the alkenone unsaturation index (U K 0 37 ), the Tetra Ether inde X of tetraethers consisting of 86 carbon atoms (TEX 86 ), and TEX 86 L in piston core sediments, which reveal the climate response of this region to different types of forcings. TEX 86 L is a modification of TEX 86 proposed for high-latitude ocean regions. The TEX 86 L -derived temperatures were not different from the alkenone-derived temperatures from the same and nearby sediment samples. During the LGM, alkenone-derived temperatures in the Okhotsk Sea were relatively warm. These and similarly warm alkenone-derived temperatures found at many other sites in the western North Pacific may reflect a shift in the season of biomarker production from early summer and autumn to mid-summer during the LGM as a result of the expansion of the season of sea-ice cover. Empirical orthogonal function (EOF) analysis of alkenone-derived temperatures at 14 sites from the North Pacific suggested substantial cooling between 20 and 14 cal kyr BP during the deglaciation at 11 of the sites (including 4 sites in the Okhotsk Sea). This dominant EOF mode suggests either an overall seasonal bias in alkenone-derived temperatures or potential shifts in the Haptophyseae production season. The second EOF mode of variability indicated a deglacial warming trend punctuated by millennial-scale cold events, associated with reorganizations of the Atlantic Meridional Overturning Circulation. The SST pattern corresponding to this EOF mode is indicative of millennial-scale meridional shifts of the axis of the westerly jet, which may have affected heat transport across the Kuroshio. Reconstructed temperature changes, in particular in the Okhotsk Sea, provide insight into the conditions that modulated the ventilation history of intermediate waters in the North Pacific. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction The mid- to high-latitude region of the western–central North Pacific – including the Kuroshio–Oyashio transition area and marginal seas (the Okhotsk, Japan, and Bering Seas) – is a key area for understanding present-day climate variability of the eastern Asian continent (Yasuda, 2003). An important climate variability pattern in this region is the Pacific Decadal Oscillation (PDO), which relates the intensity of the Aleutian Low to changes in marine ecosystems (Mantua et al., 1997). The PDO is estimated as the leading empirical orthogonal function (EOF) mode of the monthly mean Pacific sea surface temperature (SST) anomaly in the region from 201N poleward and has a 20–30 year periodicity. A positive (negative) PDO is associated with a strengthened Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/dsr2 Deep-Sea Research II 0967-0645/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr2.2011.12.007 n Corresponding author. Tel.: þ81 46 867 9504; fax: þ81 46 867 9455. E-mail address: haradan@jamstec.go.jp (N. Harada). Deep-Sea Research II 61-64 (2012) 93–105