PP31A-2202
Hydrological Influence on the Dead Carbon Fraction in a Tropical Speleothem During the Younger Dryas and the Last Millennium

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Michael L Griffiths1, Quan Hua2, Russell Drysdale3, Petra Bajo3, Daniella Jenkins4, John Charles Hellstrom4, Kathleen R Johnson5, Michael K Gagan6 and Jian-Xin Zhao7, (1)William Paterson University of New Jersey, South River, NJ, United States, (2)Australian Nuclear Science and Technology Organization, Kirrawee, Australia, (3)University of Melbourne, Parkville, VIC, Australia, (4)University of Melbourne, Parkville, Australia, (5)University of California Irvine, Irvine, CA, United States, (6)Australian National University, Canberra, ACT, Australia, (7)University of Queensland, St Lucia, Australia
Abstract:
The number of paleoclimate records derived from speleothems has increased significantly in recent years. In addition, speleothems have been used for calibration of the radiocarbon timescale beyond the range of the tree-ring record. One critical issue for reliable speleothem-based radiocarbon calibration and 14C dating of speleothems is constraining the temporal variations in the radioactively dead carbon (i.e. dead carbon fraction (DCF)) that is incorporated into this archive and to determine the potential mechanisms driving such changes. While some studies have shown insignificant variations in DCF through time and highlighted the potential utility of speleothems to extend/improve the radiocarbon calibration curve, others have reported significant temporal variability in speleothem DCF associated with changes in cave recharge.

To further assess the potential hydrological control on speleothem radiocarbon variability, we constructed a new high-resolution DCF record from a speleothem from Flores, Indonesia for two different time periods, the Younger Dryas (YD) chronozone and the Last Millennium. A total of thirty-four 14C analyses (twenty for the YD and fourteen for the Last Millennium) were conducted on pieces of calcite extracted from stalagmite LR06-B1, which was well-dated by ~90 U-Th ages. To better characterize the paleoclimate and environmental changes, high-resolution stable-isotope (δ18O, δ13C) and trace-element (Mg/Ca, Sr/Ca) measurements were also conducted along the same sections of stalagmite.

Broad comparison of the DCF record with the hydrologically-controlled proxy data suggests that increases in rainfall were matched by DCF increases. In line with a previous interpretation of DCF variability for the same specimen, but during the time interval 2.4-2.8 cal kyr BP and the post-bomb period, we interpret the DCF during the YD and the Last Millennium to have been primarily controlled by limestone dissolution associated with changes in open- versus closed-system conditions, rather than other potential factors such as kinetic fractionation and/or variations in the age-spectrum of soil organic matter above the cave.

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