The reconstruction of water table depth over the past 3100 years in south-eastern Australia using testate amoebae and potential implications for Pacific climatic variability
Year: 2025
Type: article
Abstract: Due to the temperate and relative dry climate of south-eastern Australia, there are relatively few moisture-sensitive palaeoenvironmental records in the region. The region is of significance as it is influenced by several major ocean-atmospheric modes including El Niño–Southern Oscillation (ENSO) and the Inter-decadal Pacific Oscillation (IPO). In this research we applied a transfer function between (sub)fossil testate amoebae and water table depth to consider local surface wetness, which may reflect effective moisture conditions, at Snowy Flat, a high-altitude Sphagnum -shrub bog in south-eastern Australia over the late Holocene. The reconstruction water table depth, covering the last ∼3100 cal yr B.P., suggested several distinct periods of enhanced surface wetness, perhaps reflecting moisture availability, including from 2400 to 2200, 1350–1100, 920–860 and 670 to 60 cal yr B.P.. After 1800 cal yr B.P., depth to water table (DWT) was more variable and followed well-known trends of the Northern Hemisphere including the Medieval Climatic Anomaly (MCA; increased DWT) and the Little Ice Age (LIA; decreased DWT). We also investigated the instrumental record of rainfall and found a significant negative relationship with the IPO and an IPO-like tripole spatial pattern between rainfall and sea surface temperatures in the Pacific Ocean. This suggests that the late Holocene hydroclimate at the Snowy Flat site, and across south-eastern Australia and more widely, can be related to the IPO and this is especially true after 1800 cal yr B.P. when the relationship apparently strengthened. The reconstruction also indicated that a positive IPO (El Niño-like) mean state prevailed in the MCA and a negative IPO (La Niña-like) mean state dominated the LIA. Surface moisture (DWT) was also related to total solar irradiance (from 10 Be in polar ice): periods of enhanced surface moisture (reduced DWT) (mean negative IPO states) coincided with minima (e.g. 920–860 and 670–60 ca. yr B.P.) and reduced moisture (increased DWT) coincided with maxima (e.g. 850–700 cal yr B.P.). Together these results shed further light on the variability of moisture in south-eastern Australia, and further afield, and the potential mechanisms for these. • Water table depth was reconstructed, over the last ∼3.1 ka, using testate amoeba. • Wetter periods were found 2500–2200, 1350–1100, 920–860 and 670–60 cal yr B.P. • The MCA/LIA were periods of reduced/enhanced moisture availability. • Enhanced moisture availability reflected negative IPO and lower solar irradiance.
Authors: Xianglin Zheng, Geoffrey Hope, Scott D. Mooney
Institutions: UNSW Sydney, Australian National University
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: hybrid
Estimated APC paid: $3,210
OpenAlex ID: W4414008954