Mid-Holocene climate conditions and moisture source variations based on stable H, C and O isotope compositions of speleothems in Hungary

This paper presents stable C and O isotope data, as well as water contents and stable hydrogen isotope compositions of inclusion-hosted water of 230Th-dated stalagmites collected from the Leány and Pál-völgyi Caves of Central Hungary, within and about 50 km NW from Budapest, respectively. A good replication of contemporaneous stalagmite oxygen isotope records and their agreement with the COMNISPA record from the Eastern Alps suggest that the stalagmite oxygen isotope variation reflects past climate change. H2O contents in the Leány stalagmite indicate a relationship with the oxygen isotope compositions and hence with climate conditions, raising the possibility of its use as a climate proxy in future studies. The stalagmites show strong negative δ18O excursions for two cold periods at about 5.4–6 and 8–9 ka, whereas the oxygen isotope data are relatively high in the period of 6–7 ka, indicating warmer conditions. The stalagmite hydrogen and d-excess series positively correlate with the COMNISPA record, interpreted as a sign of moisture source variations. High d-excess values in the periods of low δ18O data for the Leány Cave at about 5.4–6 and 8–9 ka suggest a shift to Mediterranean moisture source domination when the COMNISPA record indicate weaker North Atlantic Oscillation (NAO) activity. Lower d-excess values in the period of 6–7 ka are associated with low δ18O values in the COMNISPA record, corresponding to NAO+ phase. The inferred moisture source changes are in accordance with published instrumental data covering the last hundred years and atmospheric circulation model results, and demonstrate that NAO activity influenced the climate conditions of the Carpathian Basin during most of the Holocene.