Glacial–interglacial deep-water changes in the NW Pacific inferred from single foraminiferal δ18O and δ13C

Oxygen and carbon isotope values of single benthic foraminiferal tests in a core from the Shatsky Rise, NW Pacific Ocean, show greater intra-horizon variance during the Holocene than during the Last Glacial Maximum (LGM). This greater variance is caused by the introduction of glacial specimens some 20 cm upward from their original deposition layer due to bioturbation. In contrast, foraminiferal populations belonging to glacial layers do not include Holocene specimens. The difference in direction of bioturbation greatly modifies climate information in horizons formed during and after deglacial events. After omitting glacial specimens from Holocene sediments, the glacial–interglacial difference in δ18O suggests that Pacific deep-water temperature changed by 2.4–3.8°C at the most. The δ13C values suggest that nutrient concentration was higher during the LGM than the Holocene. The glacial deep North Pacific Ocean apparently was influenced by cold deep waters of southern origin.