Stable isotope stratigraphy of Holocene speleothems: examples from a cave system in Rana, northern Norway

High-precision TIMS U-series dates and continuous stable oxygen and carbon isotope profiles of a 4000 year stalagmite record from Rana, northern Norwa y, are presented and compared with data from two other speleothems from the same cave. The dating results yield ages from 3875 +/- 34 to 296 +/- 3 yea rs before AD2000, with 2sigma errors from 0.5 to 1%. The overall growth rat e is 35 mm/ka, corresponding to a temporal resolution of 29 years/mm. The s talagmite is tested for isotopic equilibrium conditions, where all 'Hendy' tests, except one, indicate isotopic equilibrium or quasi equilibrium depos ition. Both the stable oxygen and carbon isotope records reveal a strong an d abrupt enrichment in the near-top measurements. This corresponds in time to the opening of a second cave entrance in the late 1960s, which caused ch anges in the cave air circulation. The stable oxygen isotope signal is enri ched compared to the modern value over the last 300 years, indicating a neg ative response to temperature changes. Likewise, the stable carbon isotope record is enriched in this period. However, both of the stable isotope reco rds are shown to be significantly enriched compared to the isotope ranges d isplayed by other stalagmites in the same cave, and this questions the reli ability of the proxy records derived from the presented stalagmite. Still, a general good correspondence of large scale fluctuations is found between the three stable oxygen isotope records from this cave. The stable carbon i sotope records show large variations within the cave and are believed to be governed by soil-zone conditions, percolation pathways and possibly dripra tes. (C) 2001 Elsevier Science B.V. All rights reserved.