Browsing by Author "Dosseto, A"
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- ItemBuried, but not forgotten — reconciling climate dynamics with catchment evolution in the East Kimberley using 10Be & 26Al(Australian Geosciences Council, 2012-08-05) Swander, ZJ; Dosseto, A; Fink, D; Mifsud, C; Fujioka, TIn the well entrenched bedrock rivers of northwest Australia, fluvial geomorphic processes rely both on intense energy pulses input to the hydrologic system, and the negation of bedrock choke points or “gates”. Established Quaternary paleoclimate records identify warm and wet interglacial conditions associated with catastrophic flood episodes along the inland Ord River during the Upper Pleistocene. Today, the “neo-Ord” cuts a jagged 600km mixed bed course through the semi-arid landscape of the East Kimberley, when seasonally inundated by monsoon. Beneath the Ivanhoe Plain near Kununnura, up to 30m of pre-Holocene aggraded valley fill obscure the river’s paleo-path to the Joseph Bonaparte Gulf, over 100km from present day mouth. By exploring the links between fluvial activity and monsoon variability, this project aims to constrain the chronology of bedrock channel migration in the transition from older to younger bedrock gates, and any associated incision. This was accomplished by quantifying 16 in situ bedrock minimum exposure ages from 5 study sites across varied lithologies. Terrestrial Cosmogenic Radionuclides (TCN), 10Be and 26Al, are the result of incoming cosmic radiation sparking spallation reactions penetrating ∼50cm of the the bedrock surface. Our results will test the hypothesis that multiple early interglacial intensifications of the regional monsoon, dating back to MIS 11, would provide the catalyst for trunk channel migration and a general disruption of the steady-state. Base level readjustment should manifest most clearly by rapid bedrock incision within gorges, and at back-cutting knickpoint retreats along unconstrained rock bars.
- ItemLate quaternary fluvial incision and aggradation in the Lesser Himalaya, India(Elsevier, 2018-10-01) Dosseto, A; May, JH; Choi, JH; Swander, ZJ; Fink, D; Korup, O; Hesse, PP; Singh, T; Mifsud, C; Srivastava, PReconstructing how rivers respond to changes in runoff or sediment supply by incising or aggrading has been pivotal in gauging the role of the Indian Summer Monsoon (ISM) as a geomorphic driver in the Himalayas. Here we present new chronological data for fluvial aggradation and incision from the Donga alluvial fan and the upper Alaknanda River, as well as a compilation of previous work. In addition to conventional OSL-SAR (Single-Aliquot Regenerative-Dose) dating method, we have tested and applied pulsed OSL (POSL) dating for quartz samples that include K-rich feldspar inclusions, which is expected to improve the applicability and validity of OSL ages in the Lesser Himalaya. For previously dated deposits, our OSL ages are shown to be systematically older than previously reported ages. These results suggest periods of aggradation in the Alaknanda and Dehradun Valleys mainly between ∼25 and 35 ka. This most likely reflects decreased stream power during periods of weakened monsoon. In addition, in-situ cosmogenic beryllium-10 was used to infer bedrock surface exposure ages, which are interpreted as episodes of active fluvial erosion. Resulting exposure ages span from 3 to 6 ka, suggesting that strath terraces were exposed relatively recently, and incision was dominant through most of the Holocene. In combination, our results support precipitation-driven fluvial dynamics, which regulates the balance between stream power and sediment supply. On a larger spatial scale, however, fluvial dynamics are probably not spatially homogeneous as aggradation could have been taking place in adjacent catchments while incision dominated in the study area. © 2018 Elsevier Ltd.
- ItemPast changes in sediment dynamics in the Himalayas inferred from uranium-series isotopes(Australian Geosciences Council, 2012-08-05) Dosseto, A; Hesse, PP; Fink, D; Srivastava, PClimate variability has been setting the rhythm of the Earth’s history, but how does the landscape, in particular rivers, adapt to these changes? One possible approach to tackle this question is to investigate how sedimentary deposits have recorded changes in fluvial dynamics. As a proxy for this dynamics, we use the sediment residence time, i.e. the time spent by sediments in a catchment before export (storage in soils + fluvial transport). Recently, it has been proposed that uranium-series isotopes can be used to quantify past variations in sediment residence time. In this study, this approach is applied to alluvial deposits from the upper Ganges River, the Yamuna River and the Dun valley in the foothills of the Himalayas. The age of these deposits has been previously constrained by optically-stimulated luminescence dating and range from 0 to 40 ka. Preliminary work using lithium isotopes has shown a strong link between monsoon activity and weathering intensity. Results from this study will investigate how hillslope erosion and fluvial transport may have responded to past climatic change.
- ItemRapid carbon accumulation in soil rapidly forming in the Southern Alps of New Zealand(Australian Nuclear Science and Technology Organisation, 2021-11-17) Raines, E; Hua, Q; Dosseto, A; Lukens, CE; Deslippe, JR; Norton, KPBiota contribute 3-7 orders of magnitude more potential energy to landscapes than climate or tectonics alone. This potential energy is quantified as the system’s net primary productivity (NPP), i.e., the net gain of photosynthetically sourced carbon. The effects of biological energy on landscape evolution is likely highly non-negligible, yet, has proven difficult to properly quantify in the past. Current methods for quantifying NPP vary in accuracy and can involve careful and costly study over the course of many years. The associated costs are often prohibitive for geomorphic studies. Therefore, NPP is not a commonly included measurement made in such studies. While relating biological to geomorphic processes in rapidly forming soils could help increase the predictive ability of current geomorphic models, a more suitable method for quantifying NPP is required to make this possible. Here, we present a novel method combining uranium and carbon isotopes that can be used for quantifying soil NPP. The study was carried out on a rapidly forming, New Zealand soil. The uranium isotope composition of the soil was used to derive a soil age of 178 years. Given the soil’s age, the soil production rate is 1.7 mm yr-1 which is one of the most rapid every quantified. Geomorphic models fail to predict such rapid soil production by a factor of ~2. Carbon-14 (14C) was also isolated from the same soil and quantified by AMS. The 14C measurements allow for the soil organic carbon (SOC) mean residence time (MRT) to be calculated. Utilizing a commonly employed biogeochemical model, the MRT allows for the calculation of the concentration of SOC as a function of time. In the rapidly forming soil, we measured a SOC content of 536 g-C m-1. Employing MRT and SOC to calculate the expected age of soil yielded a predicted soil age of 408 years. The discrepancy in MRT predicted age and the observed soil age indicates that the biogeochemical model fails to predict the rate of carbon accretion in the rapidly forming soil by a factor of ~2. The work presented here is the first biogeochemical characterization of a soil forming more rapidly than current geomorphic models can accurately determine. Both the observed soil NPP and the soil formation rate exceed current model predictions. It is possible that a causal relationship exists, however, further cocharacterization of biological energy input rates and soil formation rates is needed to test this hypothesis. © The Authors
- ItemReconstructing atmospheric particulate loads over the north-western Pacific Ocean during the mid to late Holocene: volcanism, dust and human perturbation of regional aerosol loads/composition(Australasian Quaternary Association Inc., 2022-12-06) Marx, SK; Hooper, J; Irino, T; Seki, O; Stromsoe, N; Saunders, KM; Zawadzki, A; Dosseto, A; Jacobson, GEAtmospheric particulate transport over the North Pacific Ocean is known to be significant for regional biogeochemical processes and climate. For example, dust aerosol is known to fertilize phytoplankton, increasing the effectiveness of the biological C pump. Despite its importance, there has been little work tracing the changing sources and relative loads of particulate aerosols in this key region over the Holocene. The deserts of northern East Asia are the 2nd largest global dust source, while the eastern extent of East Asia forms part of the Pacific ring of fire, indicating tephra forms a significant, albeit episodic component of atmospheric particulate loads. Critically, East Asia has also undergone a significant transformation over recent decades, with widespread agricultural intensification and a massive increase in industrial activity, especially following China’s Great Leap Forward from late 1950s. This has likely perturbed regional atmospheric aerosol characteristics. In this study, we use peat mires from the Daisetsuzan Mountains in central Hokkaido, Japan, to reconstruct the history of atmospheric particulate deposition over the mid to late Holocene. Results show that over the past 4 kyr mineral flux was relatively low and dominated by dust input from mainland China, as evidenced by the rare earth element (REE) and eNd composition of sediments deposited in the mire. Within the last millennium, particulate fluxes changed more significantly, with the deposition of at least two major tephras. Further dramatic changes are recorded in the very top sections of the peat mire, where Chinese dust input becomes more geochemically significant. At the same time, the onset of nascent particulate matter is recorded by increasing concentrations of ‘industrial’ metals such as Pb and Cu. Collectively, this demonstrates the vast scale of human perturbation of atmospheric particulate, even within a region where the atmosphere is loaded with ‘natural’ particulate aerosol.
- ItemReconstructing atmospheric particulate loads over the north-western Pacific Ocean during the mid to late Holocene: volcanism, dust and human perturbation of regional aerosol loads/composition.(Australasian Quaternary Association, 2022-12-06) Marx, SK; Hooper, J; Irino, T; Seki, O; Stromsoe, N; Saunders, KM; Zawadzki, A; Dosseto, A; Jacobson, GEAtmospheric particulate transport over the North Pacific Ocean is known to be significant for regional biogeochemical processes and climate. For example, dust aerosol is known to fertilize phytoplankton, increasing the effectiveness of the biological C pump. Despite its importance, there has been little work tracing the changing sources and relative loads of particulate aerosols in this key region over the Holocene. The deserts of northern East Asia are the 2nd largest global dust source, while the eastern extent of East Asia forms part of the Pacific ring of fire, indicating tephra forms a significant, albeit episodic component of atmospheric particulate loads. Critically, East Asia has also undergone a significant transformation over recent decades, with widespread agricultural intensification and a massive increase in industrial activity, especially following China’s Great Leap Forward from late 1950s. This has likely perturbed regional atmospheric aerosol characteristics. In this study, we use peat mires from the Daisetsuzan Mountains in central Hokkaido, Japan, to reconstruct the history of atmospheric particulate deposition over the mid to late Holocene. Results show that over the past 4 kyr mineral flux was relatively low and dominated by dust input from mainland China, as evidenced by the rare earth element (REE) and eNd composition of sediments deposited in the mire. Within the last millennium, particulate fluxes changed more significantly, with the deposition of at least two major tephras. Further dramatic changes are recorded in the very top sections of the peat mire, where Chinese dust input becomes more geochemically significant. At the same time, the onset of nascent particulate matter is recorded by increasing concentrations of ‘industrial’ metals such as Pb and Cu. Collectively, this demonstrates the vast scale of human perturbation of atmospheric particulate, even within a region where the atmosphere is loaded with ‘natural’ particulate aerosol.
- ItemUsing 10Be cosmogenic isotopes to estimate erosion rates and landscape changes during the Plio-Pleistocene in the Cradle of Humankind, South Africa(Elsevier, 2016-07) Dirks, PJHM; Placzek, CJ; Fink, D; Dosseto, A; Roberts, EConcentrations of cosmogenic 10Be, measured in quartz from chert and river sediment around the Cradle of Humankind (CoH), are used to determine basin-averaged erosion rates and estimate incision rates for local river valleys. This study focusses on the catchment area that hosts Malapa cave with Australopithecus sediba, in order to compare regional versus localized erosion rates, and better constrain the timing of cave formation and fossil entrapment. Basin-averaged erosion rates for six sub-catchments draining the CoH show a narrow range (3.00 ± 0.28 to 4.15 ± 0.37 m/Mega-annum [Ma]; ±1σ) regardless of catchment size or underlying geology; e.g. the sub-catchment with Malapa Cave (3 km2) underlain by dolomite erodes at the same rate (3.30 ± 0.30 m/Ma) as the upper Skeerpoort River catchment (87 km2) underlain by shale, chert and conglomerate (3.23 ± 0.30 m/Ma). Likewise, the Skeerpoort River catchment (147 km2) draining the northern CoH erodes at a rate (3.00 ± 0.28 m/Ma) similar to the Bloubank-Crocodile River catchment (627 km2) that drains the southern CoH (at 3.62 ± 0.33 to 4.15 ± 0.37 m/Ma). Dolomite- and siliciclastic-dominated catchments erode at similar rates, consistent with physical weathering as the rate controlling process, and a relatively dry climate in more recent times. Erosion resistant chert dykes along the Grootvleispruit River below Malapa yield an incision rate of ∼8 m/Ma at steady-state erosion rates for chert of 0.86 ± 0.54 m/Ma. Results provide better palaeo-depth estimates for Malapa Cave of 7–16 m at the time of deposition of A. sediba. Low basin-averaged erosion rates and concave river profiles indicate that the landscape across the CoH is old, and eroding slowly; i.e. the physical character of the landscape changed little in the last 3–4 Ma, and dolomite was exposed on surface probably well into the Miocene. The apparent absence of early Pliocene- or Miocene-aged cave deposits and fossils in the CoH suggests that caves only started forming from 4 Ma onwards. Therefore, whilst the landscape in the CoH is old, cavities are a relatively young phenomenon, thus controlling the maximum age of fossils that can potentially be preserved in caves in the CoH. © 2016 Elsevier Ltd.