NOAA/WDS Paleoclimatology - Uamh an Tartair, Scotland 1000Yr Stalagmite SU967 Stable Isotope Data

High-resolution (annual to decadal) stable isotope records of oxygen and carbon are analysed from an annually laminated stalagmite from NW Scotland. The sample, which was deposited for ~1000 yrs until 1996 AD, has previously provided annual resolution climate reconstructions of local rainfall and regional winter North Atlantic Oscillation (wNAO) from variations in annual growth rate. For our stalagmite, for which modern cave monitoring demonstrates that equilibrium deposition is highly likely for d18O but not for d13C, stalagmite d13C originally derives from soil CO2 produced predominantly by microbial respiration, modified by degassing-related kinetic fractionation, and d18O from the composition of infiltrating water during periods of infiltrating water. Both the presence of fluorescent laminae and modern drip-water monitoring demonstrate a drip hydrology that comprises both event and storage components. Over the instrumental period, no correlations between stalagmite or rainfall d18O and precipitation amount or temperature are observed, but correlations are observed between rainfall d18O and 500 mb height at regional IAEA monitoring stations. However, no correlations are observed between stalagmite d18O and instrumental and reconstructed atmospheric circulation, preventing a simple palaeoclimate interpretation of the stalagmite d18O proxy. Stalagmite d13C has a stronger temporal autocorrelation than d18O, indicative of soil mixing of respired CO2 and significant variability between drips and at different times; correlations with instrumental climate data are therefore not possible. The relative timing of changes in growth rate, d18O and d13C are discussed, and interpretations compared with other regional climate records. We conclude that, over the last millennium at this mid-latitude cave site, neither d18O nor d13C cannot be interpreted as a simple paleoclimate proxy.