Hundreds of automatic drip counters reveal infiltration water discharge characteristics in Australian caves

Abstract:

Quantifying the timing and character of cave drip water discharge is crucial for our understanding of speleothem climate proxies. Since 2010, we have established a long-term, national monitoring program of drip water infiltration onto cave stalagmites using automated Stalagmate© loggers. Five karst regions, from semi-arid to sub-tropical climates, have been instrumented. Over 200 loggers (between 10 and 40 per cave) have collected data on the timing and amount of drip water infiltration, from sites of contrasting limestone geology. Here, we present results demonstrating the timing and characteristics of drip water discharge from 2010 to present. At the semi-arid Cathedral Cave, with a range of depths from 0-40 m, there is a decreasing frequency of recharge events with depth below ground surface. High-intensity, long-duration rainfall events are confirmed to be the primary driver of infiltration events at semi-arid sites, whereas annual rainfall amount is the primary driver at a Mediterranean climate site with high primary porosity. Inter-annual variability in the frequency and relative amount of drip water infiltration is compared to climate forcing variables such as the ENSO and surface temperature. Our cave observatory system helps improve our understanding of the drip water recharge process, drip-water related speleothem proxy records, and provides a baseline monitoring network for diffuse groundwater recharge during a period of climate change.