Now showing 1 - 2 of 2
  • Publication
    The coupled δ13C-radiocarbon systematics of three late Glacial/early Holocene speleothems; insights into soil and cave processes at climatic transitions
    The coupled δ13C-radiocarbon systematics of three European stalagmites deposited during the Late Glacial and early Holocene were investigated to understand better how the carbon isotope systematics of speleothems respond to climate transitions. The emphasis is on understanding how speleothems may record climate-driven changes in the proportions of biogenic (soil carbon) and limestone bedrock derived carbon. At two of the three sites, the combined δ13C and 14C data argue against greater inputs of limestone carbon as the sole cause of the observed shift to higher d13C during the cold Younger Dryas. In these stalagmites (GAR-01 from La Garma cave, N. Spain and So-1 from Sofular cave, Turkey), the combined changes in δ13C and initial 14C activities suggest enhanced decomposition of old stored, more recalcitrant, soil carbon at the onset of the warmer early Holocene. Alternative explanations involving gradual temporal changes between open- and closed-system behaviour during the Late Glacial are difficult to reconcile with observed changes in speleothem δ13C and the growth rates. In contrast, a stalagmite from Pindal cave (N. Spain) indicates an abrupt change in carbon inputs linked to local hydrological and disequilibrium isotope fractionation effects, rather than climate change. For the first time, it is shown that while the initial 14C activities of all three stalagmites broadly follow the contemporaneous atmospheric 14C trends (the Younger Dryas atmospheric 14C anomaly can be clearly discerned), subtle changes in speleothem initial 14C activities are linked to climate-driven changes in soil carbon turnover at a climate transition.
      1398Scopus© Citations 67
  • Publication
    A late-Holocene climate record in stalagmites from Modrič Cave (Croatia)
    Few terrestrial Holocene climate records exist from Southeastern Europe despite its important geographic position as a transitional climatic zone between the Mediterranean and mainland continental Europe. In this study we present new petrographic and stable isotope data for two Holocene speleothems from Modrič Cave, Croatia (44o15’N, 15o32’E), a coastal Adriatic site (120 metres inland). Modern meteorological and cave conditions have been monitored for two years to understand the links between the climate variability and the stable isotope time-series records in speleothems. Typical of a Mediterranean-type climate, a negative water balance exists between April and September, so that recharge of the aquifer is restricted to the winter months. The weighted mean δ18O of the rainfall is -5.96‰ (2σ =2.83), and the weighted mean D/H rainfall value is -36.83‰ (2σ = 19.95), slightly above the Global Meteoric Water Line (GMWL), but well below the Mediterranean Meteoric Water Line (MMWL). Modern calcite from the tops of each stalagmite exhibits δ18O values that are close to isotopic equilibrium with their respective drip water values. Unfortunately, the relatively young ages and low uranium contents (c. 50 ppb) of both stalagmites hamper the use of U-series dating. Radiocarbon dates have been used instead to constrain their chronology using a dead carbon correction. Aside from some Isotope Stage 3 material (c. 55 ka), both stalagmites were deposited during the late Holocene. Climatic conditions during the late Holocene are inferred to have been sufficiently wet to maintain stalagmite growth and any hiatuses appear to be relatively short lived. Inferred changes in the stalagmite diameters during deposition are linked to δ13C and δ18O variations, indicating alternating periods of drier and wetter conditions. Drier conditions are inferred for the late Roman Ages warm period and the mid-Medieval Warm Period (MWP). Wetter conditions are associated with the Little Ice Age period.
      1144Scopus© Citations 32