SEASONAL CHANGES IN ENVIRONMENTAL CONDITIONS AT THREE NORTHWESTERN AUSTRALIA CAVES

Tropical speleothems have proven to be important paleomonsoon proxies because they can be precisely dated using U-Th methods and their oxygen isotopic ratios reflect the intensity of monsoon rains. Reconstructions of monsoon activity across northwestern Australia have previously been developed using stalagmites from (or near) three cave sites: KNI-51 (eastern Kimberley), Ball Gown cave (western Kimberley), and Star Chamber cave (Cape Range). Each of these sites is undergoing a multi-year monitoring program in which rainfall, air temperature, barometric pressure, and humidity are tracked above the cave above and within each cave. Of particular interest are seasonal changes in temperature, humidity and air pressure and also the relationship between rainfall and infiltration. We report the results of the first two years of this study.

Measurements at KNI-51 were made 500 m from the single cave entrance, in the room from which stalagmites used for paleomonsoon reconstruction had been collected. Here, air temperature varied little, with mean values of 28.8±0.7˚C. Humidity was also constant at ~100%, and barometric pressure varied little (±1 kPa). Ball Gown cave has an entrance at either end of the cave system and thus air flow is higher than at KNI-51. Humidity remained at 100% at all loggers during the monsoon season but slowly dropped to as low as 60% during the winter. Temperature similarly cycled seasonally across a range of ~3˚C. No stalagmites from Star Chamber have yet been studied but it is near to other Cape Range caves that have yielded samples. Air temperatures varied little with mean values of 25.9±0.3˚C. Humidity and barometric pressure data were lost due to equipment malfunction. At each site, rain was monitored using Driptych Pluvimates while drip rates were measured with Driptych Stalagmate acoustic drip counters. All three caves responded quickly to the beginning and ending of rainfall events except Ball Gown cave for which no drips were recorded.