Seasonal meteoric and calcite precipitation recorded in two active stalagmites and cave monitoring data from Katerloch, Austria

In the course of a multi-annual and partially automated
cave monitoring program we study active sites of carbonate
deposition in Katerloch Cave (Austria, SE-rim of the Alps).
This includes the collection of two active stalagmites (K8,
K10), short stalagmite top drill cores, fresh precipitates on
glass substrates (8 yrs growth), data logging of drip rates and
air temperatures, as well as the chemical- and isotopic
compositions of drip waters. Multiple 238U-234U-230Th ages of
stalagmite K10 (71 cm long) revealed several growth
intervals starting from 129.1 ±1.2 kyr BP up to now. These
are separated by distinct growth interruptions, e.g. around
termination of the African Humid Period. The active
stalagmite K8 (40 cm) archived a relatively short time
interval of the last ca. 1500 yrs. Stable isotope transects
micromilled at 0.25 mm resolution from the uppermost 20 cm
of K10 (mid- and late Holocene) show δ13C values from -9.3
to -4.6 ‰ and δ18O from -8.0 to -5.1 ‰ (VPDB) and K8
(0.1/1 mm res.) revealed values from -11.0 to -3.8 ‰ and -7.4
to -4.5 ‰ for δ13C and δ18O, respectively. These values are
significantly different compared to isotopic compositions of
Katerloch stalagmites from older time intervals. The modern
stalagmites, however, show a seasonal lamination typical of
all investigated Katerloch stalagmites (translucent/dense vs.
white/porous), although more regular patterns (K8) are
distinguished from samples showing more pronounced interannual
variability (K10). Calcite δ18O and δ13C are variably
related to these patterns. Monitored drip rates also allow of
some distinction between two different groups depending on
modern meteoric precipitation vs. drip response, base flow
and snowmelt effect (e.g. drips of K8 vs. K10). Drip water
δ2H/δ18O values support a major influence of Mediterranean
moisture sources to regional precipitation next to dominant
Atlantic advection. Moreover, a significant decrease in δ18O
was recorded both in the collected drip waters and associated
modern calcite precipitates on artificial substrates during our
multi-annual cave monitoring.