Three thousand years of effective infiltration in eastern Australia: A multi proxy stalagmite record from Wombeyan Caves, New South Wales, Australia

Understanding how climate drivers have influenced Eastern Australia (EA) hydroclimate variability over recent millennia is hampered by the short duration of instrumental climate records (<120 years). Proxy data measured from a stalagmite collected from Wombeyan Caves (NSW, Australia) extends the EA hydroclimate record to a 3000-year period, from 1045 BCE to 2006 CE. High-resolution time series of past water infiltration are derived from microstratigraphy, trace element concentrations, stable carbon and oxygen isotope ratios, and dated using radiocarbon. Principal Component Analysis (PCA) of hydroclimate-sensitive trace elements identified a dominant mode of variability (PC1) that strongly aligns with cool-season water balance. This mode demonstrates coherence with known climate drivers, highlighting a persistent influence of the El Niño–Southern Oscillation (ENSO), the Interdecadal Pacific Oscillation (IPO) and the Southern Annular Mode (SAM) on EA hydroclimate over the past three millennia. Solar variability, volcanic aerosol forcing and temperature variability also modulate effective infiltration, which closely follows reconstructed Common-Era temperature trends, suggesting that atmospheric precipitation-temperature scaling can increase total precipitation and/or precipitation intensity in EA with increasing temperatures. Decades-to-centuries-long wetter conditions (from ca. 200–1080 CE and in the 15th and 16th centuries) alternated with dry conditions of similar duration (for example from 1490 to 1590 CE, in the early and later parts of the 1800s and in the early 1900s), supporting the idea that pluvial and drought periods can be even longer than those observed in the instrumental record. The Wombeyan stalagmite provides a baseline for advancing our current understanding of how interactions between different drivers of hydroclimate in EA result in long drought spells/pluvial events.