@article{MarkowskaFohlmeisterTrebleetal.2019,
  author    = {Markowska, Monika and Fohlmeister, Jens Bernd and Treble, Pauline C. and Baker, Andy and Andersen, Martin S. and Hua, Quan},
  title     = {Modelling the C-14 bomb-pulse in young speleothems using a soil carbon continuum model},
  series = {Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society},
  volume    = {261},
  journal   = {Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0016-7037},
  doi       = {10.1016/j.gca.2019.04.029},
  pages     = {342 -- 367},
  year      = {2019},
  abstract  = {The 'bomb-pulse' method is a chronological approach to further constrain the age of speleothems that grew between 1950 CE - present. Establishing dependable chronological constraints is crucial for modern calibration studies of speleothems to instrumental climate records, which provides the basis for paleoclimate interpretations. However, a large unknown is how 14C is transferred from the atmosphere to any individual speleothem owing to the site-specific residence times of organic matter above cave systems. Here, we employ the bomb-pulse method to build chronologies from 14C measurements in combination with a new unsaturated zone C model which considers C decomposition as a continuum, to better understand unsaturated zone 14C dynamics. The bomb-pulse curves of eight speleothems from southern Australia in three contrasting climatic regions; the semi-arid Wellington Caves site, the mediterranean Golgotha Cave site and the montane Yarrangobilly Caves site, are investigated. Overall, the modelled 14C bomb-pulse curves produce excellent fits with measured 14C speleothem data (r2 = 0.82-0.99). The C modelling reveals that unsaturated zone C is predominately young at the semi-arid site, with a weighted-mean residence time of 32 years and that tree root respiration is likely an important source of vadose CO2. At the montane site, ∼39\% of C is young (<1 years), but the weighted-mean C ages are older (145-220 years). The mediterranean site has very little contribution from young C (<12\%: 0-1 years), with weighted-mean ages between 157 and 245 years, likely due to greater adsorption of organic matter in the upper vadose zone during matrix flow, and remobilisation of C from young syngenetic karst. New end members for low speleothem Dead Carbon Proportion (DCP) are identified (2.19\% and 1.65\%, respectively) for Australian montane and semi-arid zone speleothems, where oversupply of modern CO2 in the vadose zone leads to lower DCP. It is also demonstrated that DCP can be quite variable over small time scales, that processes may be difficult to untangle and a constant DCP assumption is likely invalid. DCP variability over time is mainly controlled by the changes vadose zone CO2, where vegetation regeneration, wild-fires and karst hydrology play an important role.},
  language  = {en}
}
@article{HuaCookFohlmeisteretal.2017,
  author    = {Hua, Quan and Cook, Duncan and Fohlmeister, Jens Bernd and Penny, Dan and Bishop, Paul and Buckman, Solomon},
  title     = {Radiocarbon Dating of a Speleothem Record of Paleoclimate for Angkor, Cambodia},
  series = {Radiocarbon : an international journal of cosmogenic isotope research},
  volume    = {59},
  journal   = {Radiocarbon : an international journal of cosmogenic isotope research},
  number    = {Special Issue 6 / 2},
  publisher = {The University of Arizona, Department of Geosciences},
  address   = {Tucson, Ariz.},
  issn      = {0033-8222},
  doi       = {10.1017/RDC.2017.115},
  pages     = {1873 -- 1890},
  year      = {2017},
  abstract  = {We report the chronological construction for the top portion of a speleothem, PC1, from southern Cambodia with the aim of reconstructing a continuous high-resolution climate record covering the fluorescence and decline of the medieval Khmer kingdom and its capital at Angkor (similar to 9th-15th centuries AD). Earlier attempts to date PC1 by the standard U-Th method proved unsuccessful. We have therefore dated this speleothem using radiocarbon. Fifty carbonate samples along the growth axis of PC1 were collected for accelerator mass spectrometry (AMS) analysis. Chronological reconstruction for PC1 was achieved using two different approaches described by Hua et al. (2012a) and Lechleitner et al. (2016a). Excellent concordance between the two age-depth models indicates that the top similar to 47 mm of PC1 grew during the last millennium with a growth hiatus during similar to 1250-1650 AD, resulting from a large change in measured C-14 values at 34.4-35.2 mm depth. The timing of the growth hiatus covers the period of decades-long droughts during the 14th-16th centuries AD indicated in regional climate records.},
  language  = {en}
}