Interior hydrography and circulation of the glacial Pacific Ocean

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 δ 13C and δ 18O data measured on benthic foraminifera Planulina wuellerstorfi from the vicinity of Japan. Available benthic δ 13C and δ 18O and radiocarbon data from the Pacific support the presence of a deep hydrographic boundary at around 2000 m 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 δ 13C compared to the deeper water mass, whose possible origins are discussed.