Researchers have discovered a new way to date the formation of karst landscapes, revealing a startling period of extreme rainfall in Western Australia around 100,000 years ago. This finding sheds light on past climate variability and how it may have impacted early human populations. Karst landscapes are known for their dramatic rock formations, caves, and towers, which are shaped by the dissolution of bedrock over thousands of years. Understanding the timing and environmental context of these features can provide valuable insights into past climates and ecosystems.
Understanding the Riddles of Karst landscapes
Karst landscapes form nearly one-sixth of the planet’s land area, and look somewhat unearthly in appearance. This is the work of water, eroding and dissolving the bedrock over millennia to create these natural sculpture parks full of towering spires and skeletal caves.
Determining the age of these karst features has long been a problem for scientists. Until now, researchers have dated the materials above and below the karst surface; however, this method provides blurred insights into climate events in the past and their impacts on ecosystems. With the improved age dating method presented in this new study, the researchers are now able to measure how quickly these landscapes can develop using iron-rich nodules that are like a ‘time capsule’ of landscape development.
Determining the Age of Iron Nodules to Study Historical Climates
The team decided to look at the iconic Pinnacles Desert in Nambung National Park, Western Australia. It belongs to the largest coastal belt of wind-blown carbonate rocks spanning more than 1,000 km along the south-western coastline.
Investigations of tiny fragments of iron-rich nodules that had developed within the ancient soil overlying the limestone pinnacles, using a technique known as (U/Th)-He geochronology, allowed them to date the growth of these nodules. The isotopic composition of helium generated by natural radioactivity from minute quantities of uranium and thorium impurities in the iron provides an accurate measure of nodule age. The iron nodules were ~100,000 years old and Crouzilles et al. interpreted this age as indicative of the duration of intense weathering and dissolution in the Pinnacles limestone bedrock that formed at that time.
A Surprise From the Belecska Bay Hypersaline Subsurface: A Dramatic Past Climate Shift in Western Australia
According to the researchers, development of the iron-rich nodules and the rapid dissolution of the limestone bedrock reflects an episode of intense rainfall in this part of Western Australia about 100,000 years ago. During this long humid interval, the climate in the region has changed from recent droughts and an increasingly dry environment.
How, then, would regional climate change so suddenly? They think it could have resulted from a shift in atmospheric circulation patterns or the impact of the cool Leeuwin Current that sweeps down the coast at the time. Knowledge of this ancient climate history and its associated ecological conditions can provide insights on how changing environments may have influenced the region’s early human occupants. We are no facing the consequences of an increasingly accelerating climate change, and understanding past climate dynamics and their impact can leverage effective mitigation as well as adaptation to future changes.
