OCEAN CIRCULATION IN THE NORTHWESTERN PACIFIC (ODP SITE 884) FROM THE MIDDLE EOCENE TO THE EARLY OLIGOCENE (45-33 MA)

New high-resolution benthic foraminiferal δ¹⁸O and δ¹³C data from ODP Site 884 (northwestern Pacific) adds significant structure to a low-resolution record (Pak and Miller 1995), providing new insights into paleoceanographic changes from the middle to the late Eocene in the Pacific. Site 884 δ¹⁸O data, compared with published ODP records from the Atlantic (Sites 1260 and 1053) and Southern (Site 689) Oceans, indicate that the northwestern Pacific was one of the warmest deepwater locations from the middle middle to the late Eocene (~46-34 Ma). A comparison among Site 884 and other published ODP Pacific δ¹³C records (Sites 883, 865, and 1218) suggests that the water mass bathing the northwest Pacific (Site 883 and 884) during the middle middle Eocene was not the same water mass flowing in the western and eastern equatorial Pacific (Sites 865 and 1218). Together, we interpret the δ¹⁸O and δ¹³C comparisons as indicative of a localized deepwater influence in the northwestern Pacific. The relatively low δ¹³C values recorded at the northwestern Pacific sites in the middle middle Eocene, together with the published neodymium isotopic results and tectonic reconstructions for this region, do not support a deepwater source in the higher latitudes of the North Pacific. However, in the late Eocene, the Site 884 record shifts towards higher δ¹³C values, implying a change in deepwater circulation. This late Eocene change recorded in the northwestern Pacific may have been related to tectonic movements that opened key Southern Ocean gateways; the formation of a proto- Antarctic Circumpolar Current as a consequence of opening of the Drake Passage and the Tasman Rise has been shown to affect deepwater circulation in the Northern Hemisphere.