Stable isotope variations in stalagmites from northwestern Sweden document changes in temperature and vegetation during the early Holocene: a comment on Sundqvist et al. 2007a

We offer an alternative palaeoenvironmental interpretation of oxygen-isotope data obtained on two early-Holocene stalagmite records from caves in the Scandes Mountains of northern Sweden (Korallgrottan and Labrintgrottan), and the well-known Soylegrotta (Norway) SG93 record with which they are compared, that differs in several respects from that proposed by the authors. Contrary to viewing these as inverted palaeotemperature records, we suggest that they primarily reflect changes in the delta O-18 of local annual precipitation, modified by secondary temperature-dependent variation in water-calcite oxygen-isotope fractionation, at each of the three sites. This is supported by the striking similarity over the entire Holocene between the SG93 calcite delta O-18 record and the lacustrine carbonate delta O-18 record from Lake Tibetanus (northern Sweden), which implies straightforward transfer of annual precipitation delta O-18 signals into cave drip waters. Recent studies of drip waters in Korallgrottan also support this model. This further enhances the value of cave deposits as palaeoclimate archives in this region and provides additional evidence of the sensitivity of the precipitation 'isotope thermometer' to changes in atmospheric circulation patterns.