NOAA/WDS Paleoclimatology - Pacific Glacial Foraminiferal Radiocarbon and Stable Isotope Data

We investigate the apparent radiocarbon ventilation age in deep equatorial Pacific sediment cores and integrate those results with similar data from around the North Pacific Ocean in a reconstruction for the last glaciation. Here we use the simplest definition of apparent ventilation age: the difference in conventional 14C age between coexisting benthic and planktonic foraminifera, and we consider the glacial interval to have lasted between 15 and 25 14C ka. Most new data from both the Equatorial Pacific and the Emperor Seamounts in the northwestern Pacific come from maxima in abundance of benthic taxa because this strategy reduces the effect of bioturbation. Although there remains considerable scatter in the ventilation age estimates, on average, ventilation ages in the Equatorial Pacific were significantly greater below 3.2 km (~3100 +/-1125 yrs, n=15) than in the depth interval 2.0 to 3.0 km (~1600 +/-310 yrs, n=8). When compared to the average modern seawater D14C profile for the North Pacific, the Equatorial Pacific glacial data suggest an abyssal front located somewhere between 3.0 and 3.2 km modern water depth. Above that depth, the data may indicate slightly better ventilation than today, and below that depth, glacial Equatorial Pacific data are as old as last glacial maximum (LGM) deep water ages reported for the deep southern Atlantic. This suggests that a glacial reservoir of aged waters extended throughout the circumpolar Southern Ocean and into the Equatorial Pacific. Such a large volume of aged (and, by corollary, carbon-rich) water would help to account for the rise in atmospheric pCO2 and the fall in D14C as the glaciation drew to a close and deep ocean ventilation increased.