Rapid climate oscillations in the northeast Pacific during the last deglaciation reflect northern and southern hemisphere sources

Planktic foraminiferal species abundances, benthic and planktic foraminiferal stable isotopes, radiocarbon, and organic carbon contents of deep-sea cores off Oregon and Northern California reveal abrupt millennial-scale climate oscillations during the past 20,000 years. Changes in the near-surface ocean are essentially coincident with the Bølling-Allerød and Younger-Dryas climate oscillations observed in Greenland ice cores and North Atlantic sediments. This finding supports the concept of atmospheric transmission of climate signals between oceans within the Northern Hemisphere. Abrupt cooling of North Pacific surface waters occurred in mid-Holocene time, indicating that the warm events of the early Holocene and deglaciation are anomalous relative to modern climate. Higher export productivity is associated with warm events in the North Pacific. These biotic changes may have contributed to variations in the shallow (˜400 m depth) oxygen minimum zone off California, and may in part explain the apparent coincidence of local anoxia with warming in Greenland. Benthic foraminiferal δ¹³C and¹⁴C data from lower intermediate waters (980 m depth) suggests that higher ventilation (either faster formation or greater gas exchange) occurred during the Bølling-Allerød and early Holocene warm events. Synchronicity with surface ocean changes points to North Pacific source waters, and ventilation during warming leads to a hypothesis that salinity rather than temperature controls intermediate water formation at these times. In the deep North Pacific (2700 m depth) benthic foraminiferal δ¹⁸O changes imply early warming roughly synchronous with warming of the Southern Ocean. Both δ¹³C and¹⁴C suggest an abyssal ventilation event (either faster formation or greater gas exchange) during deglaciation at the same time as short-term cooling in Antarctica, pointing to a Southern Ocean source of variability in the deep Pacific. Thus, climate changes that characterize both northern and southern sources appear to propagate through the Pacific Ocean.