Late Pleistocene and Holocene climate of SE Australia reconstructed from dust and river loads deposited offshore the River Murray Mouth

Abstract

The terrigenous component of deep-sea sediment core MD03-2611, offshore South Australia, has been examined for mineralogical, geochemical and isotopic tracers to reconstruct the deglacial and Holocene climate on the adjacent southeastern Australian continent. The provenance of the terrigenous component is constrained by using a combination of clay minerals, conservative elements like rare earths (REEs) and Sr- and Nd isotopic ratios. From 17 to 5 ka BP, the sediment signature is dominated by alluvial sediments from the Murray-Darling Basin (MDB). Starting at 8 ka and culminating from 5 ka to the present, enrichment of REEs and kaolinite content, increasing grain size, high 87Sr/86Sr ratios and strongly negative εNd(0) values are attributed to an influx of aeolian dust, probably sourced from older crustal terranes in central and/or western Australia, although the exact provenance of the dust could not be assessed. The input of fluvial material from a common MDB source ceased at 13.5 ka BP, but 2 periods of increased fluvial input, originating mainly in the Murray catchment, are indicated by clay contents, K and Rb concentrations, and Sr and Nd isotope ratios. These fluvial pulses probably reflect periods of increased rainfall in southeastern Australia. The first fluvial pulse from 13.5 to 11.5 ka had not been recorded in the region previously, while the second pulse from 9.5 to 7.5 ka BP corresponds to periods of increased rainfall already documented in records from 2 lakes in the region. The supply of fluvial versus aeolian material in core MD03-2611 mirrors patterns of humidity and aridity inferred from other continental records in SE Australia, although our study provides information for the Late Pleistocene/Holocene transition not recorded elsewhere.