Search

Abstract: In this paper we synthesise existing palaeoenvironmental data from the arid and semi-arid interior of the Australian continent for the period 40–0 ka. Moisture is the predominant variable controlling environmental change in the arid zone. Landscapes in this region respond more noticeably to changes in precipitation than to temperature. Depending on their location, arid zone records broadly respond to tropical monsoon-influenced climate regimes, the temperate latitude westerly systems, or a combination of both. The timing and extent of relatively arid and humid phases vary across the continent, in particular between the westerly wind-controlled temperate latitudes, and the interior and north which are influenced by tropically sourced precipitation. Relatively humid phases in the Murray-Darling Basin on the semi-arid margins, which were characterised by large rivers most likely fed by snow melt, prevailed from 40 ka to the Last Glacial Maximum (LGM), and from the deglacial to the mid Holocene. By contrast, the Lake Eyre basin in central Australia remained relatively dry throughout the last 40 ka, with lake high stands at Lake Frome around 35–30 ka, and parts of the deglacial period and the mid-Holocene. The LGM was characterised by widespread relative aridity and colder conditions, as evidenced by extensive desert dune activity and dust transport, lake level fall, and reduced but episodic fluvial activity. The climate of the deglacial period was spatially divergent. The southern part of the continent experienced a brief humid phase around ∼17–15 ka, followed by increased dune activity around ∼14–10 ka. This contrasts with the post-LGM persistence of arid conditions in the north, associated with a lapsed monsoon and reflected in lake level lows and reduced fluvial activity, followed by intensification of the monsoon and increasingly effective precipitation from ∼14 ka. Palaeoenvironmental change during the Holocene was also spatially variable. The early to mid-Holocene was, however, generally characterised by moderately humid conditions, demonstrated by lake level rise, source-bordering dune activity, and speleothem growth, persisting at different times across the continent. Increasingly arid conditions developed into the late Holocene, particularly in the central arid zone. [Copyright &y& Elsevier]

The Australian region spans some 60° of latitude and 50° of longitude and displays considerable regional climate variability both today and during the Late Quaternary. A synthesis of marine and terrestrial climate records, combining findings from the Southern Ocean, temperate, tropical and arid zones, identifies a complex response of climate proxies to a background of changing boundary conditions over the last 35,000 years. Climate drivers include the seasonal timing of insolation, greenhouse gas content of the atmosphere, sea level rise and ocean and atmospheric circulation changes. Our compilation finds few climatic events that could be used to construct a climate event stratigraphy for the entire region, limiting the usefulness of this approach. Instead we have taken a spatial approach, looking to discern the patterns of change across the continent. The data identify the clearest and most synchronous climatic response at the time of the Last Glacial Maximum (LGM) (21 ± 3 ka), with unambiguous cooling recorded in the ocean, and evidence of glaciation in the highlands of tropical New Guinea, southeast Australia and Tasmania. Many terrestrial records suggest drier conditions, but with the timing of inferred snowmelt, and changes to the rainfall/runoff relationships, driving higher river discharge at the LGM. In contrast, the deglaciation is a time of considerable south-east to north-west variation across the region. Warming was underway in all regions by 17 ka. Post-glacial sea level rise and its associated regional impacts have played an important role in determining the magnitude and timing of climate response in the north-west of the continent in contrast to the southern latitudes. No evidence for cooling during the Younger Dryas chronozone is evident in the region, but the Antarctic cold reversal clearly occurs south of Australia. The Holocene period is a time of considerable climate variability associated with an intense monsoon in the tropics early in the Holocene, giving way to a weakened monsoon and an increasingly El Niño-dominated ENSO to the present. The influence of ENSO is evident throughout the southeast of Australia, but not the southwest. This climate history provides a template from which to assess the regionality of climate events across Australia and make comparisons beyond our region. [ABSTRACT FROM AUTHOR]

Vegetation structure in vast semi-arid to temperate continental land masses, such as Australia, plays a considerable role in global terrestrial carbon sequestration. However, whether soil carbon from these regions is a net atmospheric carbon source or sink remains contentious, introducing large uncertainties on long-term storage of vegetation-sequestered carbon dioxide. We investigate the interplay between catchment erosion quantified using uranium isotopes, vegetation (pollen), catchment carbon cycling, wetland response (diatoms), and lake carbon accumulation on glacial-interglacial timescales in south-eastern Australia. The analyses are applied to sediments from Lake Couridjah, in the Sydney Basin during the last (133.5 ka to 107.6 ka) and current (17.8 cal ka BP to present day) glacial-interglacial transitions. Robust phase-relationships between catchment erosion, vegetation composition and carbon cycling during both glacial-interglacial periods were revealed by statistical analyses. Vegetation structure had a direct control on catchment erosion, and, thus, on soil organic carbon (SOC) erosion in the catchment. Overall wetter and warmer peak interglacial conditions promoted the expansion of a canopy and mid-storey vegetation cover reducing catchment erosion, while simultaneously increasing SOC storage, catchment and lake primary productivity, and lake carbon storage. The results suggest increased terrestrial carbon sequestration in temperate Australian landscapes in warmer and wetter climates. • Novel trace metal isotope method quantifies "palaeo-sediment residence times" as proxy for catchment erosion • First continuous catchment erosion record for the last and current glacial-interglacial cycle in SE Australia • Link between catchment vegetation cover and erosion highlights the role of Australia as global carbon sink [ABSTRACT FROM AUTHOR]