Hydroclimate complexity across the last glacial cycle in tropical Australia: reassessing the uniqueness of the Holocene

Where and when water is available is a pivotal control on environments. Changes in water availability are frequently invoked to explain past changes in human, flora, fauna, and fire behaviour, especially regarding the transition from the Late Pleistocene to the ostensibly more complex Holocene. Previous syntheses have characterised the Holocene as a period of uniquely elevated hydroclimate complexity—a hypothesis that has significant implications for interpreting past human and ecological responses to climate change. Reconstructions from further back in time tend to be poorer quality, which must be considered when synthesising records. This study analyses 69 natural palaeoenvironmental archives from tropical Australia spanning the last 130,000 years. Archives are highly concentrated near the coast. Temporal sample resolution of archives tends to decrease with age, with no published hydrological records of sub-decadal resolution before 1900 years ago. We analyse a random subset of archives from the well-represented Holocene epoch, equal to the number of archives available in past stages, finding no support for the hypothesis that the Holocene is uniquely hydrologically heterogeneous. We also show records for the well-dated, densely sampled Girraween Lagoon archive do not become more temporally variable in the Holocene. These analyses suggest the trend of reduced resolution in the past could be mistaken as a trend towards greater complexity. To understand how any region fits into the greater climate system, Quaternary science must be explicit about what can and cannot be determined from the data available.