Dating Wood-Benthic Foram-Planktic Foram Trios from the Panama Basin to Better Constrain Antarctic Intermediate Water Ventilation Age during the Last Deglaciation

Thursday, 18 December 2014
Ning Zhao, Woods Hole Oceanographic Inst., Woods Hole, MA, United States; Massachusetts Institute of Technology, EAPS, Cambridge, MA, United States and Lloyd D Keigwin, WHOI, Woods Hole, MA, United States
Surface reservoir age complicates the age models of marine sediment records. Age model uncertainty may cause different interpretations of the same process. For example, in order to circumvent dealing with surface reservoir age, Marchitto et al. (2007) built their age model on a linkage to Greenland oxygen isotope record. But the proxy they used for the linkage was a minor factor of the sediment diffuse spectral reflectance, and they assumed the sedimentation rate was constant between the tie points which could be several thousand years apart. Based on that age model they showed the Antarctic Intermediate Water (AAIW) was significantly older during deglaciation than LGM and Holocene. However, de Pol-Holz et al. (2010) argued that the change of deglacial AAIW radiocarbon age was not clearly different from the atmospheric change. Their age model was based on planktic foram (PF) 14C dates and an assumption that the surface reservoir age was constantly 400 years for a site near an upwelling region. These records are only as good as their age models. Here, we present a new way to build the age model of marine records, which is to date wood in marine sediments. We found a core in Panama Basin with constantly-present twigs at the same water depth with the core used by Marchitto et al. (705m), and the radiocarbon dates of the wood samples give a very good age-depth relationship without any age reversal. With benthic foram (BF) dated in the same layer where the twigs appear, we will be able to compare the AAIW radiocarbon concentration directly with the atmosphere. In this way, we can get the AAIW ventilation age without worrying about the surface reservoir age and elucidate whether there indeed was old water transported northward by AAIW during the last deglaciation. This would be very important to testify the hypothesis of LGM carbon sequestration in the deep ocean. On the other hand, we can evaluate how the surface reservoir age and/or upwelling strength changed in Eastern Equatorial Pacific (particularly Panama basin) over the last deglaciation by dating PF as well. This presentation will show the first ever wood-based age model of marine records as well as new BF and PF dates.