Mg records of two stalagmites from B7-Cave (northwest Germany) indicating long-term precipitation changes during Early to Mid-Holocene

Abstract

Two stalagmites from B7-Cave in northwest Germany, which is part of the same cave system as the intensively studied Bunker Cave, were re-dated by multi collector inductively coupled plasma mass spectrometry (MC-ICPMS) 230Th/U-dating. Furthermore, the concentration of Mg, Sr, Ba, P, Y, Zn, and Al were determined at high-resolution by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Stalagmite B7-1 grew from 10.8 to 5.8 ka BP. Stalagmite B7-7 grew during three growth phases from 11.0 to 6.2, 3.13 to 2.86 (late Bronze Age), and 1.27 to 1.15 ka BP (early Medieval Period). Aluminium is a proxy for detrital material and corresponds very well with the visible detrital layers in stalagmite B7-1 and the oldest growth phase of stalagmite B7-7. The two younger growth phases of stalagmite B7-7 are very clean and show very low Al concentrations. Phosphorus, Y, and Zn show positive correlations in both stalagmites and all growth phases, but do not show a relationship to temperature or precipitation. This may be related to the elevated detrital content in both stalagmites. Barium and Sr also show a positive correlation in both stalagmites and all growth phases, which is related to their dependency on growth rate. Magnesium is most probably influenced by prior calcite precipitation and therefore a proxy for past precipitation/infiltration. The Mg records of stalagmite B7-1 and of the oldest growth phase of stalagmite B7-7 show decreasing Mg concentration with time reflecting decreasing prior calcite precipitation and therefore increasing precipitation during the Early to Mid-Holocene. This is consistent with other climate reconstructions from Central Europe.