Holocene on the High Country: A multiproxy interrogation of paleoenvironmental sensitivity along an elevational transect of high-altitude Australia

Abstract

High-altitude landscapes are among the most sensitive environments to climate and land use change. However, paleoscientific determinations of high-altitude sensitivity are disproportionately informed by paleoecological reconstructions from mountains sensu stricto. These biases limit constraints on broader ‘systemic’ (i.e., biotic and abiotic) sensitivity across entire high-altitude complexes (i.e., mountains and highlands). This thesis applies multiproxy analyses to thirteen sedimentary sequences along an elevational transect of the High Country, a vulnerable mountain-highland complex in southeastern Australia, to reconstruct paleoenvironmental changes since ~13,900 cal yr BP. By comparing these data with independent records of climate and land use change, the systemic sensitivity of the High Country is resolved at the site, zonal and regional scale. This study demonstrates that regional systemic variability was primarily dictated by hydroclimate over most of the Holocene until ~2600 cal yr BP, when there was a synchronous cross-altitudinal increase in moisture availability despite declining precipitation and warming. This signal is argued to reflect a threshold shift in sensitivity towards an intensified El Niño Southern Oscillation, albeit through regionally bifurcated mechanisms. Regardless of specific climatic forcings, mountain catchments appear to have been consistently more sensitive to climate change than highland catchments over the Holocene.

A similar mountain-highland dichotomy is exhibited in the context of European-era land use change, suggesting mountains are also more sensitive to such. European-era instability for both domains is unprecedented since at least ~3200 cal yr BP, confirming the High Country has been more perturbed by European land use change than any climatic perturbation over this interval. Reconstructions suggest that future disequilibrium will be exacerbated by ongoing climate and land use change.