The deep water of the Pacific Ocean is a key component of the global climate system on the time scale of late-Pleistocene glaciation and deglaciation. Despite its importance, the deep Pacific during the last glacial maximum has received relatively little attention compared to the deep Atlantic, in part, because the Pacific poorly preserves carbonate sediments on the sea floor. Here, we review the current state of knowledge of the deep hydrography and circulation of the glacial Pacific by examining available nutrient-proxy data, including some new δ13C and δ18O data measured on benthic foraminifera Planulina wuellerstorfi from the vicinity of Japan. Available benthic δ13C and δ18O and radiocarbon data from the Pacific support the presence of a deep hydrographic boundary at around 2000m during the Last Glacial Maximum (Paleoceanography 3 (1988) 343; Paleoceanography 7 (1992) 273; Paleoceanography 13(4) (1998) 323). The deep hydrographic divide in the glacial Pacific is similar to what is inferred in the Atlantic (Quaternary Research 18 (1982) 218; Paleoceanography 3 (1988) 317; Paleoceanography 3 (1988) 343; Annual Reviews of Earth Planetary Sciences 20 (1992) 245; Science 259 (1993) 1148), the Indian (Nature 333 (1988) 651; Paleoceanography 13 (1998) 20), and the Southern Ocean (Paleoceanography 11 (1996) 191), suggesting that this is a global phenomenon during the glacial time. The upper water mass has a distinctly enriched δ13C compared to the deeper water mass, whose possible origins are discussed.
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Discussions with R.F. Anderson, A. Gordon, J.C. Herguera, L. Keigwin, and D. Sigman were very helpful. M. Oda provided samples for KH82-4-14 and BO94-20 PN3PC. Reviews by an anonymous referee and particularly D. Oppo and guidance provided by P. Clark helped improve the manuscript measurably. US National Science Foundation—Monbusho (Japanese Ministry of Education) Young Researcher Summer Exchange Program supported research at Hokkaido University by KM, who appreciates the support of “Hensen” (Geosphere) research group at Hokkaido. All data (new and compiled) will be archived electronically at World Data Center-A for Paleoclimatology, NOAA/NGDC at Boulder. This is LDEO contribution number 6256.
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