Increased ventilation age of NE Pac' Ocean during the last deglaciation
http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1272.html
NATURE GEOSCIENCE | LETTER
Increased ventilation age of the deep northeast Pacific Ocean during the last deglaciation
David C. Lund, Alan C. Mix & John Southon
Nature Geoscience (2011) doi:10.1038/ngeo1272
Received 08 November 2010 Accepted 25 August 2011 Published online 02 October 2011
The rise in atmospheric carbon dioxide during the last deglaciation may have been driven by the release of carbon from the abyssal ocean1, 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 ~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 14C/C ratio than intermediate waters near Baja California3. 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.
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