North Pacific Modulation of the Global Carbon Cycle Through MIS-2: Insights from IODP Expedition 341

IODP Expedition 341 Site U1419, at 680 m water depth on the upper continental slope of the Gulf of Alaska, experienced 90 m of sediment accumulation over the past 50,000 years. Paired benthic-planktic radiocarbon dates from U1419, as well as site survey piston core EW0408-85JC, potentially record millennial-scale variability in North Pacific Ocean ventilation from recent stadial MIS-2 through the Holocene. The modern site is bathed in North Pacific Intermediate Water (NPIW), with a modern (pre-bomb) surface ocean reservoir age of 880 ± 80 years and bottom waters aged an additional 510 ± 130 years. Over the past 11,000 years B-P differences vary smoothly, averaging 745 ± 120 years (n = 21). Throughout the MIS-2 portion of the record average B-P differences are a similar 765 ± 260 (n=63), but display significantly different structure with three abrupt increases to >1000 years centered at 25,500, 17,500 and 12,500 cal ybp. All three of these events correspond with periods of increasing atmospheric CO2, with the latter two and largest (B-P differences approaching 1,500 years) events corresponding to the episodes of rapid atmospheric CO2 rise during Termination 1. This may reflect the transient presence of an older intermediate water mass extending to the high-latitude Northeast Pacific associated with reorganization of circulation in the Southern Ocean.