Tim Cohen

Palaeohydrological research provides valuable insights to the understanding of short- and long-term fluvial dynamics in response to climate change and tectonic activity. In landscapes where tectonic activity is minimal fluvial archives record long-term changes in sediment and discharge dynamics related to either intrinsic or extrinsic controls. Isolating the relative controls of these factors is an important frontier in this area of research. Advances in geochronology, the acquisition of high resolution topographic data and geomorphological techniques provide an opportunity to assess the relative importance of intrinsic and extrinsic controls on terrace and floodplain formation. This study presents the results of detailed chrono-stratigraphic research in a partly confined river valley in subtropical southeast Queensland. River systems within this region are characterized by high hydrological variability and have a near-ubiquitous compound channel morphology (macrochannel) where Holo...

Database of published thermoluminescence (TL) ages for aeolian sedimentary records from Sahul. Spatial data includes sample locations (point) and uses the WGS84/Pseudo-Mercator (EPSG: 3857) projected coordinate reference system. Sample metadata is comprehensive and includes bibliographic, contextual, and sample preparation and measurement related information.

Three terrestrial climate proxies are used to investigate the evolution of Holocene palaeoenvironments in southern central Australia, all of which present a coherent record of palaeohydrology. Single-grain optically stimulated luminescence from sediments supplemented by 14C from charcoal and lacustrine shells was obtained to date shoreline deposits (Lake Callabonna) and the adjacent Mt Chambers Creek alluvial fan. Our findings are complemented by a U/Th-based record of speleothem growth in the Mt Chambers Creek catchment, which we interpret to reflect increased precipitation. Together, these archives shed light on the timing of, and possible sources of water for, Holocene pluvial intervals. We identified several phases of elevated lake levels dated at ~5.8–5.2, 4.5, 3.5–2.7 and 1 kyr, most of which correspond to fluvial activity resulting from increased precipitation in the adjacent ranges. The enhanced hydrology during phases of the late Holocene likely increased the reliability of...

Database of published thermoluminescence (TL) ages for fluvial sedimentary records from Sahul. Spatial data includes sample locations (point) and uses the WGS84/Pseudo-Mercator (EPSG: 3857) projected coordinate reference system. Sample metadata is comprehensive and includes bibliographic, contextual, and sample preparation and measurement related information.

Database of published thermoluminescence (TL) ages for lacustrine sedimentary records from Sahul. Spatial data includes sample locations (point) and uses the WGS84/Pseudo-Mercator (EPSG: 3857) projected coordinate reference system. Sample metadata is comprehensive and includes bibliographic, contextual, and sample preparation and measurement related information.

Events some 40,000 to 60,000 years ago marked a critical juncture in the Australian continent’s history. This is when humans first arrived and also the time when many huge beasts, known as megafauna, seem to have disappeared. So what caused their demise: humans, a changing climate, or both? Disciplines Medicine and Health Sciences | Social and Behavioral Sciences Publication Details Cohen, T., Nanson, G., Jansen, J. & Larsen, J. (2015). Drying inland seas probably helped kill Australia’s megafauna. The Conversation, 26 February 1-3. This journal article is available at Research Online: http://ro.uow.edu.au/smhpapers/2846 There's still time to make a tax deductible donation before June 30.

This study was commissioned by the Hawkesbury-Nepean (HNCMA), Sydney Metropolitan (SMCMA) and Southern Rivers (SRCMA) Catchment Management Authorities and undertaken by the University of Wollongong to collate existing data and to provide a preliminary assessment of the potential impacts of coal seam gas (CSG) and coal mining activities on environmental assets within the three CMA regions, where environmental assets were defined under three broad themes; water, land and biodiversity. This study formed part of the Australian Federal Government’s Department of Sustainability, Environment, Water, Population and Communities (SEWPaC) Bioregional Assessment initiative within regions potentially affected by CSG and coal mining activities. The key components of this study included: Creating a database (using on the SEWPaC supplied template) identifying key environmental assets (groundwater, surface water, wetlands, land use, soils, vegetation and threatened species) within each of the three ...

Despite the absence of large-scale glaciation, the Australian continent has experienced substantialenvironmental change throughout the Quaternary period. This is especially pronounced in central Australia,where one seventh of the continent is drained internally to the depocentre, and lowest point in Australia, LakeEyre (Figure 1). Research has shown that at one time, large sandy braided and meandering rivers carried waterthrough dunefields to a large freshwater lake system. Today, the rivers are hostage to the dunefield, andfloodwaters might only reach Lake Eyre once every ten years or so. In order to understand the development ofthis arid desert landscape, and how changing climates have affected it, we need to find out when rivers anddunes were active, and how they are related to each other. Keywords heart, dead, australia, change, climate Disciplines Life Sciences | Physical Sciences and Mathematics | Social and Behavioral Sciences Publication Details Larsen, J, Nanson, GC, Cohen,...

Abstract The widespread formation of organic rich sediments in south-east Australia during the Holocene (Marine Isotope Stage [MIS] 1) reflects the return of wetter and warmer climates following the Last Glacial Maximum (LGM). Yet, little is known about whether a similar event occurred in the region during the previous interglacial (MIS 5e). A 6.8 m sediment core (#LC2) from the now ephemeral Lake Couridjah, Greater Blue Mountains World Heritage Area, Australia, provides insight into this question. Organic rich sediments associated with both MIS 1 and 5e are identified using 14C and optically stimulated luminescence (OSL) dating techniques. Also apparent are less organic sedimentary units representing MIS 6, 5d and 2 and a large depositional hiatus. Sediment δ13C values (−34 to −26‰) suggests that C3 vegetation dominates the organic matter source through the entire sequence. The pollen record highlights the prevalence of sclerophyll trees and shrubs, with local hydrological changes driving variations in the abundance of aquatic and lake-margin species. The upper Holocene sediment (0–1.7 m) is rich in organic matter, including high concentrations of total organic carbon (TOC; 20–40%), fine charcoal and macrophyte remains. These sediments are also characterised by a large proportion of epiphytic diatoms and a substantial biogenic component (chironomids and midges). These attributes, combined with low δ13C and δ15N values, and C:N ratios of approximately 20, indicate a stable peat system in a swamp like setting, under the modern/Holocene climate. In comparison, the lower organic rich unit (MIS 5e-d) has less TOC (5–10%), is relatively higher in δ13C and δ15N, and is devoid of macrophyte remains and biogenic material. Characterisation of the organic matter pool using 13C-NMR spectroscopy identified a strong decomposition signal in the MIS 5e organic sediments relative to MIS 1. Thus the observed shifts in δ13C, δ15N and C:N data between the two periods reflects changes in the organic matter pool, driven by decompositional processes, rather than environmental conditions. Despite this, high proportions of aquatic pollen taxa and planktonic diatoms in the MIS 5e–d deposits, and their absence in the Holocene indicates that last interglacial Lake Couridjah was deeper and, or, had more permanent water, than the current one.

This study describes a multivariate statistical model (derived using partial least squares regression, PLS-R) that derives charring intensity (reaction temperature and duration) from the attenuated total reflectance (ATR) Fourier Transform Infrared (FTIR) spectra of charcoal. Data for the model was obtained from a library of charcoal samples produced under laboratory conditions at charring intensities (CI) relevant to wildfires and a series of feedstocks representing common tree species collected from Australia. The PLS-R model developed reveals the potential of FTIR to determine the charring intensity of charcoal. Though limited by the differences between laboratory-produced charcoal and the more heterogeneous and less-structured charcoal produced in a wildfire, the method was tested against fossil charcoal from a well-dated sediment core collected from Thirlmere Lakes National Park, Australia and showed a distinct change in CI that can be related to other climatic and environmental proxies. We suggest that the method has the potential to offer insights into the conditions under which natural charcoal is formed including the modelling of charring intensities of fossil charcoal samples isolated from sediments, archaeological applications or characterisation of contemporary fire events from charcoal in soils.

The peopling of Sahul (the combined continent of Australia and New Guinea) represents the earliest continental migration and settlement event of solely anatomically modern humans, but its patterns and ecological drivers remain largely conceptual in the current literature. We present an advanced stochastic-ecological model to test the relative support for scenarios describing where and when the first humans entered Sahul, and their most probable routes of early settlement. The model supports a dominant entry via the northwest Sahul Shelf first, potentially followed by a second entry through New Guinea, with initial entry most consistent with 50,000 or 75,000 years ago based on comparison with bias-corrected archaeological map layers. The model’s emergent properties predict that peopling of the entire continent occurred rapidly across all ecological environments within 156–208 human generations (4368–5599 years) and at a plausible rate of 0.71–0.92 km year−1. More broadly, our methods...

Terrestrial data spanning the Last Glacial Maximum (LGM) and deglaciation from the southern Australian region are sparse, and limited to discontinuous sedimentological and geomorphological records with relatively large chronological uncertainties. This dearth of records has prevented a critical assessment of the role of the Southern Hemisphere mid-latitude westerly winds on the region’s climate during this time period. In this study, two precisely-dated speleothem records for Mairs Cave, Flinders Ranges, are presented, providing a detailed terrestrial hydroclimatic record for the southern Australian drylands during 23–15 ka for the first time. Enhanced recharge to Mairs Cave is interpreted from the speleothem record by the activation of growth, physical flood layering and δ<sup>18</sup>O and δ<sup>13</sup>C minima. Periods of lowered recharge are indicated by isotopic enrichment, primarily affecting…

The partly confined valleys of south-eastern Australia provide suitable conditions for the formation of vertically accreted floodplains with laterally stable channels. Three reaches in the Bellinger catchment in the New England Fold Belt on the mid-north coast of New South Wales (NSW) provide sites to assess the attributes of confined floodplains and the impact of European settlement on otherwise highly stable systems. The nature of Late Quaternary floodplain processes in a bedrock-dominated landscape are investigated, providing the evolutionary context for contemporary channel processes.The Bellinger catchment is characterised by an assemblage of stepped Late Quaternary alluvial units. Late Pleistocene terraces represent large more competent rivers that reworked almost entire valley floors, however, a progressive decline in discharge since the Last Glacial Maximum has resulted in the abandonment of these deposits as elevated terraces or residual alluvium onlapped by contemporary fl...

Key Points • the reintroduction of wood through the construction of Engineered Log Jams (ELJs), can successfully increase geomorphic diversity and stability in an incised, partly confined sand-bed stream • ELJs can provide a stable pool habitat that would otherwise have not existed without intervention. • ELJ design and frequency can significantly affect patterns of pool and bar development • The increased habitat provided by constructed ELJs is further enhanced by natural wood recruitment and the colonisation of in-channel vegetation within sand-bed streams Abstract In April 2002, 26 Engineered Log Jams (ELJs) were built within a 2 km treatment reach of what was a degraded ephemeral sand-bed stream at Stockyard Creek, Wollombi, NSW. Coupled with ~ 20 years of ongoing native revegetation this project aimed to increase the geomorphic diversity and ecological characteristics of the ephemeral stream. The experiment was set up as a standard Before-After Control-Impact (BACI) design, wit...

The terminal lake systems of central Australia are key sites for the reconstruction of late Quaternary paleoenvironments. Paleoshoreline deposits around these lakes reflect repeated lake filling episodes and such landforms have enabled the establishment of a luminescence-based chronology for filling events in previous studies. Here we present a detailed documentation of the morphology and chemistry of soils developed in four well-preserved beach ridges of late Pleistocene and mid-to-late Holocene age at Lake Callabonna to assess changes in dominant pedogenic processes. All soil profiles contain evidence for the incorporation of eolian-derived material, likely via the formation of desert pavements and vesicular horizons, and limited illuviation due to generally shallow wetting fronts. Even though soil properties in the four studied profiles also provide examples of parent material influence or site-specific processes related to the geomorphic setting, there is an overall trend of inc...

The potential environmental impacts and hazards of coal seam gas mining in Australia are highly contentious and poorly understood. Concerns have been raised by communities, and the Australian government has incorporated management tools and strategies to address these concerns. The primary environmental issue associated with coal seam gas mining would be on the aquifers above the target coal seam. If the upper aquifers are affected in terms of quantity and quality, then there are cumulative impacts to the surface environment such as groundwater dependent ecosystems and surface waters. This paper will examine the Australian situation with regard to coal seam gas mining and present a methodology for rapid assessment of the potential impacts and hazards of coal seam gas extraction on aquifers and surface environments. A GIS analysis method for developing broad scale potential impact and hazard criterion for aquifers above the target coal zone are discussed. Current investigations and f...

<p>The eastern seaboard of Australia is characterized by a passive margin and a continental divide that separates the inland-draining rivers from those that drain to the Coral and Tasman seas. Seaward of this divide lies the Great Escarpment (GE) of Australia that separates a moderate relief coastal plain from a low relief, high elevation plateau. Quantifying the spatial variation of erosion rates from temperate New England (NE), NSW and tropical Bellenden Ker (BK), Queensland, two regions with distinctly different climates and escarpment embayment, could help constrain erosional controls that contribute to escarpment form. In this study, we compared forty detrital 10Be samples collected from sediments in the main trunk and tributaries of five major rivers: the Macleay, Bellinger, and Clarence in NE and the Russel-Mulgrave and North Johnstone in BK. We then traced the escarpment position in ARCGIS and calculated a sinuosity ratio to better compare the degree of embayment in each region. Across both datasets we found that for NE, which has deep gorges cutting into the plateau, the degree of embayment was twice that of BK, where the escarpment position is significantly less embayed and erosion rates significantly more variable (ratio of .18 vs .38). Erosion rates in low slope areas, such as on the plateau, were universally low with no other significant controlling factors. There was no correlation between erosion rates and catchment area, and that our data echo previous studies that find that once mean rainfall passes an approximate threshold (around 2000mm/yr) basin characteristics that are known to control erosion rates, such as slope and lithology, are subdued.</p> <p> In temperate NE, where rainfall ranges from approximately 800-1200mm/yr, there was a moderate linear correlation with mean catchment rainfall and erosion rates (R<sup>2</sup> .50), which is likely due to a strong orographic effect due to the escarpment. Erosion rates from tributaries below the plateau were highly variable and ranged from 5m/Ma up to 60m/Ma and correlated strongly with mean catchment slope (R<sup>2</sup> .86). In addition, there were moderate inverse linear correlations between erosion rate and the catchment total percent granite and sedimentary rock (R<sup>2</sup> .53 and .63 respectively) and a moderate correlation between erosion rate and catchment total percent metamorphic rock (R<sup>2</sup> .57). Similar to previous studies, these data suggest that in temperate climates with moderate amounts of annual rainfall, individual basin characteristics play a significant role in controlling basin wide erosion rates.</p> <p>In contrast, data from tropical BK, where mean rainfall amounts are in excess of 2000mm/yr, erosion rates from tributaries below the plateau were significantly less variable than NE. Rates had a mean of 37m/Ma ± 9 (standard deviation 5m/Ma, N=10) and were not significantly correlated with mean catchment slope nor catchment lithology. The mean erosion rate of BK is similar to that of other studies in the region, though with slightly less variability, and possibly reinforces the hypothesis from other researchers that in tropical climates with significant mean rainfall, soil depth effectively armors hillslopes and prevents bedrock erosion from occurring.</p>

Optically stimulated and thermoluminescence ages from relict shorelines, along with accelerator mass spectrometer 14C ages from freshwater molluscs reveal a record of variable moisture sources supplied by northern and southern river systems to Lake Mega-Frome in southern central Australia during the late Quaternary. Additional lacustrine, palynological and terrestrial proxies are used to reconstruct a record that extends back to 105ka, confirming that Lakes Mega-Frome and Mega-Eyre were joined to create the ...

ABSTRACT Hydrospatial analyses of catchment topographic indices for 112 unregulated (unimpaired) gauging stations show that mean catchment elevation is the primary control on annual precipitation, runoff depth, runoff coefficients and evapotranspiration in the Snowy Mountains. Catchments with mean elevations greater than 1850 m show a steep increase in yield over the trend for lower elevation catchments and have runoff coefficients greater than one. Precipitation undercatch because of high winds and winter snowfall is the cause for this unusual situation, with deep accumulations of blown and drifted snow contributing significantly to runoff from small, high elevation catchments. Climate change effects on precipitation, runoff, runoff coefficients and the timing of peak snowmelt discharges vary across an elevational gradient. Annual precipitation shows strongly significant declines of up to 11.0 mm yr−1 from 1944 to 2009, with the magnitude of precipitation declines increasing with increasing elevation. Lower elevation catchments show greater sensitivity to drought than higher elevation catchments, exhibiting sharp declines in annual runoff coefficients due to smaller average differences between evapotranspiration and precipitation, and switching from energy (demand) to supply (precipitation) limited water balances. Climate change effects on the timing of peak winter–spring (June to November) snowmelt discharges for the highest elevation gauged catchments in Australia are pronounced with average shifts toward earlier peak discharges of 6.2 and 4.0 days per decade for the Snowy and Geehi Rivers, respectively. A lapse rate model using elevation as a substitute for temperature change highlights the sensitivity of mean annual runoff coefficients in the Snowy Mountains to changes in mean annual temperature, declining by 15% and increasing by 17% per degree centigrade rise and fall, respectively. Runoff coefficient sensitivity is driven by elevation (temperature) driven controls on the proportion of precipitation falling as snow vs. rain, combined with decreasing evapotranspiration with increasing elevation. Temperature (elevation) driven decreases in evapotranspiration resulting from changes in rain–snow precipitation balances, widespread snowpack accumulation and largely treeless catchments dominated by alpine vegetation during cool phases of the last glacial cycle offer a simple but comprehensive explanation for the greater runoff volumes in the Murray-Darling basin from the SE Australian highlands preserved by palaeochannels considerably larger than present river systems.