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Reconstructed Holocene lake-level curves from two saline, hydrologically closed maar crater lakes in southwestern Victoria, Australia, show near synchronous lake-level changes throughout the Holocene. We show that lake levels, reconstructed from sediment particle size and ostracod valve chemistry (δ18O and Sr/Ca) have undergone rapid (<100 yr), large (>10 m) fluctuations throughout the Holocene. Finer sampling resolution shows a more sensitive response to Holocene climate than was previously presented for Lake Keilambete. Both maar crater lakes show a short-lived maximum in Holocene lake levels around 7.2 ka. The period of lake filling leading to peak lake levels matches the phase of most effective precipitation (7.4–7.0 ka) reconstructed from a high-resolution speleothem record from northern Tasmania. Water levels declined in both lakes during the mid Holocene, with a more substantive decline after ~5 ka which coincides with the end of the Southern Hemisphere hypsithermal. Water levels continued to oscillate with a periodicity of around 300–700 years, before reaching a late-Holocene nadir around 1.8 ka (Keilambete) and 1.3 ka (Gnotuk). The trend and periodicity of oscillations in the maar water levels show commonalities to δD in the Dome C ice core, and suggest that temperature may be a significant component in influencing the Precipitation/Evaporation (P/E) ratio in southeastern Australia during the Holocene. [ABSTRACT FROM AUTHOR]

Abstract: Reconstructions of primary productivity at low latitudes have been the focus of several studies to better understand how the export of nutrient-rich, intermediate Southern Ocean (SO) waters influences productivity at these latitudes. This was triggered by the general observation of minima in the planktonic foraminiferal δ13C values during deglaciations, which was interpreted as an isotopic signal of intermediate SO waters, together with a concomitant increase in diatom productivity at some equatorial sites. However, the impact of these SO waters on productivity at higher latitudes is not well constrained. Here, we compare a high-resolution planktonic foraminiferal δ13C record with total organic carbon and biomarker records for Proboscia diatoms and haptophytes in marine sediments from offshore Southeastern Australia. The planktonic foraminiferal δ13C record shows distinct minima during deglaciations and the Marine Isotope Stage 4/3 transition, tentatively suggesting that 13C-depleted SO waters reached the coast of Southeastern Australia. However, it did not result in increased productivity during these periods. Instead, the highest primary productivity period, as indicated by total organic carbon and alkenone accumulation rates, occurred during the Last Glacial Maximum while Proboscia diatoms mainly proliferated during interglacials and Marine Isotope Stage 3 matching periods of increased diatom productivity in some sites of the Eastern Equatorial Pacific. Our study suggests that increased primary productivity offshore Southeastern Australia was mainly due to stronger westerly winds during glacial periods while Proboscia diatom productivity was probably controlled by the transport of silicic acid to this area. [Copyright &y& Elsevier]

Several well-dated and high-resolution, multi-proxy Holocene palaeoclimatic records have recently emerged that permit a cross-continent comparison of climatic changes in Australia. This synthesis seeks to compare these records with recently published records from southern Australia and investigate the role of far-field teleconnections that have played in the mid to late Holocene climatic history of the region. The modern climate of southeastern Australia (SEA) is influenced by the Indian Ocean sector of the Southern Annular Mode (IOS-SAM), the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) and contrasts with southwestern Australia (SWA), which is predominantly influenced by variations in the IOS-SAM. Both regions have undergone a period of increasing aridity through the second half of the Holocene in response to the southerly migration of the mean position of the Inter-Tropical Convergence Zone (ITCZ) and the southerly migration of the IOS-SAM. Comparison of the palaeorecords stemming from both SEA and SWA suggests that the SWA record differs from the climate recorded from SEA from approximately 5.6ka. This difference is ascribed to an increased influence of large-scale climate drivers including the IOD and ENSO variability in SEA, which have negligible impact on the climate of SWA. Throughout the Holocene, the southerly migration of the ITCZ results in a weaker Asian summer monsoon. However, the rate of Asian summer monsoon weakening slowed during the middle Holocene and this coincides with a larger sea-surface temperature gradient across the equatorial Indian Ocean that resulted in a prolonged mode of positive IOD and a period of significantly increased evaporation in SEA. Those phenomena engendered a general decline in the lake levels in SEA, which is not seen in SWA as this region was not significantly affected by the IOD throughout the Holocene. This positive IOD period lasted until ~4.3ka, before a return to the strengthening (weakening) of the Australian (Asian) summer monsoon conditions that resulted in a southward shift of the ITCZ during the austral winter. The southerly shift in the ITCZ was associated with a more southerly mean position of the IOS-SAM and drier conditions for SEA and SWA. The climate affecting SEA after 4.3ka coincides with an increasing incidence and strengthening of the El Niño (non-El Niño or La Niña) mode coupled with positive (negative) modes of the IOD that resulted in a net deficit (excess) of water. The driest phase in SEA occurs at ca. 1.8ka, when far-field palaeoclimate records indicate a peak in El Niño intensity, although the impact of the IOD cannot be discounted. Conversely, both the IOD and ENSO phenomena do not affect the climate of SWA, thus leading to significant differences in the climate across the southern margin of the Australian continent. [ABSTRACT FROM AUTHOR]