Increased ventilation age of the deep northeast Pacific Ocean during the last deglaciation

The rise in atmospheric carbon dioxide during the last deglaciation may have been driven by the release of carbon from the abyssal ocean(1,2). This mechanism would require a poorly ventilated deep Pacific Ocean during the Last Glacial Maximum and enhanced exchange with the atmosphere during deglaciation. Here we use radiocarbon measurements of planktonic and benthic foraminiferal shells from a core collected at 2.7 km water depth in the northeast Pacific to estimate the ventilation age of deep waters using the projection age method. In contrast to the above scenario, we show that ventilation ages during the Last Glacial Maximum were similar to today. This suggests that this part of the Pacific was not an important reservoir of carbon during glacial times. During deglaciation, ventilation ages increased by similar to 1,000 years, indicating a decrease in the ventilation rate, an increase in the surface water reservoir age in the Southern Ocean, or an influx of old carbon from another source. Despite the increased ventilation age during deglaciation, the deep northeast Pacific still had a higher C-14/C ratio than intermediate waters near Baja California(3). We therefore conclude that the deep northeast Pacific was apparently not old enough to be the source of deglacial radiocarbon anomalies found shallower in the water column.