A deep-sea coral record of North Atlantic radiocarbon through the Younger Dryas: Evidence for intermediate water/deepwater reorganization

[ 1] Our record of Younger Dryas intermediate-depth seawater Delta C-14 from North Atlantic deep-sea corals supports a link between abrupt climate change and intermediate ocean variability. Our data show that northern source intermediate water (similar to 1700 m) was partially replaced by C-14-depleted southern source water at the onset of the event, consistent with a reduction in the rate of North Atlantic Deep Water formation. This transition requires the existence of large, mobile gradients of Delta C-14 in the ocean during the Younger Dryas. The Delta C-14 water column profile from Keigwin ( 2004) provides direct evidence for the presence of one such gradient at the beginning of the Younger Dryas (similar to 12.9 ka), with a 100 parts per thousand offset between shallow (< similar to 2400 m) and deep water. Our early Younger Dryas data are consistent with this profile and also show a Delta C-14 inversion, with 35 parts per thousand more enriched water at similar to 2400 m than at similar to 1700 m. This feature is probably the result of mixing between relatively well 14 C ventilated northern source water and more poorly 14 C ventilated southern source intermediate water, which is slightly shallower. Over the rest of the Younger Dryas our intermediate water/deepwater coral Delta C-14 data gradually increase, while the atmosphere Delta C-14 drops. For a very brief interval at similar to 12.0 ka and at the end of the Younger Dryas (11.5 ka), intermediate water Delta C-14 (similar to 1200 m) approached atmospheric Delta C-14. These enriched Delta C-14 results suggest an enhanced initial Delta C-14 content of the water and demonstrate the presence of large lateral Delta C-14 gradients in the intermediate/ deep ocean in addition to the sharp vertical shift at similar to 2500 m. The transient Delta C-14 enrichment at similar to 12.0 ka occurred in the middle of the Younger Dryas and demonstrates that there is at least one time when the intermediate/ deep ocean underwent dramatic change but with much smaller effects in other paleoclimatic records.