The dating of stalagmites and their palaeoclimatological significance

Abstract

Speleothems are primarily studied in order to collect details about climatic and environmental changes during the
Pleistocene and Holocene. In this paper geochemical results obtained from Hungarian stalagmite samples are presented,
as well as their potential role and usage as a terrestrial alternative in palaeoclimate research.
Radiometric dating of the layers of stalagmites or their growth sections are needed to provide time constraints on the
selection of optimal periods in deposition. In particular, these time ranges coincide with wet and warm climate periods
based on the stable isotope data (δ13C, δ18O and δD).
The precise chronologies of speleothem samples from Hungary (ca. 180 U–Th data) have led to significant advances in
identifying favoured growth periods with unevenly distributed age data. They are overlapped in time by known climate
optima, whereas younger samples deposited during cold/dry periods are rare. Therefore, precise timing of the climate
optima and the subsequent environmental changes can be studied by the complex geochemical study of stalagmites, with
even decadal resolution.
Here the first U-series dated, high-resolution stable stable isotope records are presented for two stalagmites from
Hungary; these records cover the Last Interglacial (MIS 5.5) and the last glacial – Holocene periods. The first selected
stalagmite — from the Baradla Cave (NE Hungary) — grew from 127.5 to 110 ka. Accelerated growth rates have been
detected by U/Th age data in the 127 to 126 ka and 119 to 117 ka parts. The extent of temperature and precipitation variations
is also reflected by the stable isotope compositions. Oxygen isotope composition shows a continuous increase from 127.5
ka until about 118 ka (this is most probably related to temperature rise), whereas C isotope values are shifted in a negative
direction, suggesting increasing humidity and vegetation activity in the soil zone. The presumably warmest period at ca.
118 ka is associated with a rather arid climate, as indicated by peak δ18O values coinciding with the highest δD values of the
fluid inclusion water. This is followed by a pronounced negative shift in both O and H isotope values, most probably related
to cooling.
Warm spells (59.5–56.9 and 34.7–32.7 ka) during the warmer periods of the last glacial period (MIS 3.) and the
Holocene growth section are distinguished and represented within another sample from the Baradla Cave (BAR VIII
stalagmite). The measured stable isotope values obtained provided evidence for the different environmental conditions.