Kale Sniderman

The timing and duration of the coldest period in the last glacial stage, often referred to as the last glacial maximum (LGM), has been observed to vary spatially and temporally. In Australia, this period is characterised by colder, and in some places more arid, climates than today. We applied Monte-Carlo change point analysis to all available continuous proxy records covering this period, primarily pollen records, from across Australia (n = 37) to assess this change. We find a significant change point occurred (within uncertainty) at 28.6 ± 2.8 ka in 25 records. We interpret this change as a shift to cooler climates, associated with a widespread decline in biological productivity. An additional change point occurred at 17.7 ± 2.2 ka in 24 records. We interpret this change as a shift towards warmer climates, associated with increased biological productivity. We broadly characterise the period between 28.6 (± 2.8) – 17.7 (± 2.2) ka as an extended period of maximum cooling, with low pr...

<p>Under the current rapid global warming, studying how environments responded to past climate change becomes increasingly important to better understand what impact climate variability has on regional flora and fauna. Our new multi-proxy study to the World Heritage Naracoorte Caves in southern Australia provides a unique window into the past climate as they are heavily decorated with speleothems but also contain in-fill deposits rich in Pleistocene vertebrate fossils including the extinct Australian megafauna. Until now, these speleothems have been dated using U-Th series and the fossil-bearing sediments with Optical Stimulated Luminescence and Electro Spin Resonance techniques, but only up to ca. 500 ka. We have U-Pb dated speleothems from the Naracoorte Caves for the first time and extended the record beyond 500 ka. We combined precise chronology with analyses of pollen and charcoal within the speleothems which allows us to better understand how southern Australia’s climate and its vegetation changed during the Quaternary. It also provides a unique insight into the timing and extent of cave opening with important potential for much older vertebrate fossil deposits than previously thought.</p>

<p>Many palaeoclimate and palaeoenvironmental records have low sampling resolution, few age constraints, and are based on climate proxies that may reflect an uncertain mixture of local and regional influences. Objective spatial and temporal comparisons of multiple palaeo records and identification of regional scale trends can therefore be difficult.. Low resolution palaeo records are often excluded from regional syntheses due to low dating or sample density, however such records can contribute meaningful information to regional syntheses if their inherent uncertainties are considered. Explicitly incorporating the age uncertainties allows for a more robust interpretation of synchronous periods of change.</p><p>Here we discuss the use of a method for determining the timing of palaeoclimate events using multiple time-uncertain palaeo records. This method allows for the incorporation of a variety of records, regardless of proxy type or sampling resolution. We demonstrate the power of this method using a case study from the SHeMax project (Southern Hemisphere Last Glacial Maximum project), aiming to understanding the nature and timing of the LGM in Australia. Further expansion of our analyses will allow the incorporation of both continuous and discontinuous climate archives, interrogation of spatial and temporal synchronicity and coherency of climate changes across broad regions.</p><p>An extended LGM period, characterised by multiple distinct stages that varied regionally and in its timing and evolution, has been suggested to have occurred in Australia; however this hypothesis has yet to be tested objectively. Comparisons during this time period have been hampered by the limited number, low resolution, and age-uncertainty of terrestrial archives. In order to gain a greater understanding of the spatial and temporal patterns of climate change during MIS2, we have compiled all available proxy records of climate and envrionmental variability from across Australia for the period 35 – 15 ka (n=40). Analysing age-uncertainty in time series requires an approach that treats all data consistently. For each record, a revised age-depth model was developed using the SH13 calibration curve and Bayesian age-depth modelling techniques. Complex records (e.g. pollen records) were reduced to Principal Curves, in order to provide a one-dimensional summary of patterns of change in each data-set. Monte-Carlo change point analysis was then used to identify the timing of major changes within each record, along with the uncertainty around each change point. We assess the spatial heterogeneity of the timing of the major climatic changes during the 35 – 15 ka period and determine the probability of common timing of change across Australia. We find the onset of an extended period of relative aridity in Australia occurred synchronously (within uncertainty) at ca. 28 ka. Dry and cool conditions persisted at most sites until ca. 15 – 18 ka, with the onset of more humid conditions occurring along a latitudinal gradient. The occurrence of a millennial scale episode of increased moisture balance between ca. 25 – 21 ka is evident only in the most highly resolved records.</p>

Flowstone speleothem growth beneath Mount Arthur, New Zealand shows a clear relationship to vegetation density and soil development on the surface above. Flowstone does not currently form beneath sub-alpine Nothofagus forest above ca. 1000–1100 m altitude but U-Th dating shows it has formed there during past intervals of warmer-than-present conditions including an early–mid Holocene optimum and the last interglacial from ca. 131–119 ka. Some flowstones growing beneath ca. 600 m surface altitude, currently mantled with dense broadleaf-podocarp forest, grew during full glacial conditions, indicating that local tree line was never below this altitude. This implies that Last Glacial Maximum annual temperature was no more than ca. 4 °C cooler than today. Flowstone growth appears to be a robust indicator of dense surface vegetation and well-developed soil cover in this setting, and indicates that past interglacial climates of MIS 7e, 5e, the early–mid Holocene and possibly MIS 5a were mor...

Fossil pollen from two stalagmites is examined to reconstruct a c. 2400-year history of vegetation change on the Nullarbor Plain. Environmental changes are reflected by variation in chenopod species abundance, and by a peak in woody taxa between 1000 and 800 years ago which is interpreted as evidence of increased moisture conditions associated with a positive phase of the Southern Annular Mode. While no strong palynological signal is observed at the time of European colonization of Australia, a significant change occurs in the past 40 years, which is interpreted as a vegetation response to a recorded fire event. As speleothems (secondary cave carbonates including stalagmites, stalactites and flowstones) rarely contain enough fossil pollen for analysis, the taphonomic biases of speleothem archives remain poorly understood. This study, as well as being a high-resolution record of environmental change, presents an opportunity to examine these taphonomic filters. The record is shown to ...

Critics point out that a weakness of Lourandos' 'intensification' paradigm for southwestern Victoria is a lack of dates for iconic fish traps of the Lake Condah region. McNiven et al. (2012) detailed excavations at Muldoons Trap Complex at Lake Condah in Gunditjmara Country, where charcoal recovered from channel infill sediments indicated initial construction at least 6600 cal. BP, making the site one of the world's oldest known fish traps. Channel excavations also revealed the addition of basalt block walls dating to ca 600-800 cal. BP. Subsequent excavations at a second location at Muldoons demonstrate that a barrier/dam feature associated with artificial ponding of flood waters and containment of eels was added to the site complex ca 300-500 cal. BP and possibly elaborated in the nineteenth century. These results show that Muldoons Trap Complex underwent phased redevelopment and major elaboration over the past 800 years. This redevelopment followed little or no activity during the preceding 4000 years, which we argue reflected drier climatic conditions and the inability of flood waters to reach the site. Use of the site complex 5400-6600 and <800 years ago took advantage of regional increases in effective precipitation and lake water levels. Redevelopment of Muldoons Trap Complex within the past 800 years coincided with increased use of occupation sites across the broader region. Importantly, our research presents a methodological way forward to document the history of construction and use of stone-walled fish traps in the Lake Condah region.

Southern Australia today experiences a winter-dominated rainfall regime, governed by the seasonal migration of the Southern Hemisphere subtropical anticyclone. The history of this rainfall seasonality regime is poorly understood, because well dated, late Neogene climate records are scarce, both in Australia and in the Southern Hemisphere more generally. However, it has been assumed that the initiation of this rainfall regime

Early Pleistocene vegetation in upland southeastern Australia included diverse rainforests and sclerophyll forests, which alternated on precessional timescales. The nature and timing of transitions between these biomes, and the role of fire in maintaining or driving transitions between them, are uncertain. Here we present a high-resolution pollen record from Stony Creek Basin, a small Early Pleistocene palaeolake in southeastern Australia. The pollen record documents a pattern of vegetation change, over ca. 10 ka at ca. 1590–1600 ...

ABSTRACT First application of the U/Pb speleothem chronometer to studies of biotic change.•First radiometric framework for correlating Australasian Miocene vertebrates.•Allows reliable correlation of changes in Miocene vertebrates with global climates.