Rapid climate change during the Holocene from Norwegian Speleothems
by
Lauritzen, Stein-Erik
Department of Earth Sciences, University of Bergen, Allegaten 41, N-5007 Norway

Abstract. Detailed analysis of isotope records from speleothems reveal quite rapid changes between extreme states. Closer inspection on sample size and trends of consecutive data points strongly suggest that these changes reveal correspondingly rapid changes in the surrounding environment. In a north Norwegian stalagmite, which grew up through the Holocene, rates of change from ‘warm’ to ‘cold’ or vice versa, occurred over only a few hundred years. These rapid changes are inherent in the primary data (dated stratigraphy and isotopes). Using a temperature-calibrated function for spelothem d18Oc, these changes convert to around 1°C/ 100 years.

Carbonate speleothems (cave dripstones) as well as many surface travertines are formed by degassing of supersaturated groundwaters, thus depositing calcium carbonate. Since the pumping mechanism, or ‘conveyor belt’ in this process is the meteoric water cycle, travertines and speleothems will pick up climatic proxy signals from the ambient climate and preserve them within the carbonate matrix. Such proxies may be pollen, humic matter, amino acids, fluid inclusions, isotopes, trace elements, etc. (Lauritzen 2003). The fact that speleothems and many travertines can be dated very precisely by means of uranium-series dating techniques, which cover timespans from less than 100 years up to some 700,000 years, makes them extremely valuable as terrstrial climatic archives, Figure 1. This paper present some results from stable isotope analysis of a Holocene speleothem form north Norway, approximately at The Arctic Circle (66° 35’ N), Figure 2.

The sample consists of a 32 cm tall stalagmite of clean, white, translucent calcite, (Figure 3) dated with TIMS U-series (230Th/234U) and analyzed for oxygen (d18Oc) and carbon (d13Cc) isotopes in the calcite (Lauritzen & Lundberg 1999). Using the ‘speleothem delta function’ as a calibrated transfer function, a time-series of annual mean temperature can be constructed for the site through the last 9,000 years. This record has a relatively high temporary resolution, i.e. each subsample taken for stable isotope analysis, corresponds to (and integrates) deposition through 30 years, Figure 4.

Most isotope records of this type display both long-term and short-term variations which may look quite ‘noisy’ at the first glance. At higher resolution, it becomes evident that many of these ‘noisy’ variations actually occur as trends, i.e. several subsequent data points display successive change to either warmer or colder conditions. This observation rules out random effects. Also, the spacing between each data point is far smaller than the size of each individual crystal in this specimen (macrocrystalline calcite), so that it is also unlikely that the observed shifts are due to interface effects between crystals. Also, any process of recrystallization is diffusive, and diffusion would tend to smooth contrasts in the signal rather than create them. and suggest that the changes were indeed real, environmentally controlled isotopic shifts in the groundwater.

In Figure 5, an enlarged section of the speleothem record is shown for a period over 3,500 years. Changes in mean annual temperature occurred several times at rates of up to 1.2 degrees centigrade per 100 years.

References. Lauritzen, S.E. & Lundberg, J. 1999: Calibration of the speleothem delta function: an absolute temperature record for the Holocene in northern Norway. The Holocene 9(6), pp. 659-669.

Lauritzen, S.E. 2003: reconstruction Holocene Climate records from Speleothems. Pp. 242-263 in: Mackay,A., Battarbee,R., Birks, J. & Oldfield, F. (eds) Global Change in the Holocene, Arnold, London. 528 pp. ISBN 0 340 76223 3

Date received: January 27, 2004

Copyright © 2004 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # camu-28.