| 13 Nov 2026
Common Era Hydroclimate in south-eastern Australia: a decadal-scale diatom-inferred salinity record from Lake Bullen Merri, Victoria
Abstract. Understanding past hydroclimate variability at decadal scales over multiple centuries is critical for assessing the potential recurrence of prolonged droughts and floods and for informing sustainable environmental and economic planning. This study presents a sub‑decadal to decadal hydroclimate reconstruction spanning the last ~2500 years from Lake Bullen Merri, a ~58 m deep maar lake in south‑eastern Australia. Lake water salinity, recorded as electrical conductivity (EC), is inferred from sedimentary diatom assemblages. A chronology is established using nine AMS radiocarbon (14C) dates on pollen concentrates, 210Pb dating, plutonium concentrations, and the first appearance of exotic Pinus pollen. EC, which is inversely related to lake water volume, reveals a prolonged high lake-level phase between ~1380 and 1750 CE, which overlaps with the Little Ice Age (LIA). Prior to this, lake water EC was higher, characterised by three prominent centennial-scale periods of high EC and lower lake levels leading up to the last quarter of the first millennium of the common era (CE). Using a new calibration model for diatom-inferred EC reconstructions, we compare our record to diatom records from nearby Tower Hill Main Lake, Lake Elingamite and Lake Surprise which show broadly similar patterns, indicating a coherent hydroclimate signal in the western Victorian maar lakes. Overall, these records confirm that the LIA was a comparatively wet interval in south-eastern Australia, followed by drying in the late eighteenth and nineteenth centuries. This contrast is not clearly expressed in existing tree-ring and ice-core-derived reconstructions, most of which began during the wet phase. Together, these records show that south-eastern Australian hydroclimate shifted between wetter and drier states on multi-decadal to multi-centennial timescales. This much broader range of hydroclimatic variability compared to those represented by shorter reconstructions provides the needed baseline for long-term water-resource planning.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Climate of the Past.
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