Browsing by Author "Stromsoe, N"
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- ItemEcosystem and landscape change in the ‘Top End’ of Australia during the past 35 kyr(Elsevier, 2021-12-01) Samuel, KM; Reynolds, W; May, JH; Forbes, MS; Stromsoe, N; Fletcher, MS; Cohen, T; Moss, PT; Mazumder, D; Gadd, PSThe Indo-Australian Summer Monsoon (IASM) is the dominant climate feature of northern Australia, affecting rainfall/runoff patterns over a large portion of the continent and exerting a major control on the ecosystems of the Australia's Top End, including the viability of wetland ecosystems and the structure of the woody savanna, which characterises Northern Australia. We examined the behaviour the IASM from 35 ka using proxy data preserved in the sediments of Table Top Swamp, a small seasonal swamp in northern Australia. Elemental data, stable C and N isotopes, pollen and sedimentary data were combined to develop a picture of monsoon activity and ecosystem response. Results demonstrated that between 35 and 25 ka conditions were drier and more stable than present, with a more grass dominated savanna and limited wetland development, implying reduced IASM activity. After ~25 ka, there is evidence of increased moisture at the study site, but also increased IASM variability. However, despite evidence of at least periodic increases in moisture, including periods of wetland establishment, the IASM displayed a subdued response to peak precession insolation forcing by comparison to the other global monsoon systems. Instead, the greatest change occurred from ~10 ka when the continental shelf flooded, increasing moisture advection to the study site and resulting in establishment of a quasi-permeant wetland. Whereas the early Holocene was marked by both the onset of pollen preservation and a wetter vegetation mosaic, indicative of a consistently active IASM, the mid-late Holocene was marked by drier vegetation, increased fire, but also increased C3 vegetation and runoff, implying increased IASM variability. Holocene changes in ecosystem dynamics occur coincident with an expansion in human population, which likely also influenced vegetation and landscape response at the study site. © 2021 Elsevier B.V.
- ItemEstimates of late Holocene soil production and erosion in the Snowy Mountains, Australia(Elsevier, 2016-10-01) Stromsoe, N; Marx, SK; Callow, JN; McGowan, C; Heijnis, HSoil production in actively uplifting or high precipitation alpine landscapes is potentially rapid. However, these same landscapes are also susceptible to erosion and can be sensitive to changes in climate and anthropogenic activity which can upset the balance between soil production and erosion. The Snowy Mountains, southeastern Australia, are a tectonically stable, low relief, moderate precipitation mountain environment. The alpine area is extensively blanketed by soil that has been subjected to more intensive episodes of erosion during past periods of anthropogenic disturbance and under cold climate conditions of the late Quaternary. In this study, rates of soil development and hillslope erosion were investigated using radiocarbon dating, fallout radionuclides and sediment cores collected from lakes and reservoirs. Estimated Holocene soil development rates were 20–220 t/km2/y. Erosion rates determined from the radionuclides 137Cs and 210Pb were equivocal, due to the inherent spatial variability of radionuclide inventories relative to apparent erosion rates. Estimated average erosion rates over the past 100 years, determined from 210Pbex inventories, were 60 t/km2/y (95% CI: 10, 90). Inventories of 137Cs observed at the same site implied that more recent erosion rates (over the past 60 years) was below the detection limits of the sampling method applied here (i.e. < 70 t/km2/y). The upper estimate of 90 t/km2/y is comparable to the mean erosion rate estimated using the radionuclide method for uncultivated sites in Australia and is significantly lower than that measured at sites were vegetation cover was disturbed by livestock grazing prior to its exclusion from the alpine area in the 1940s CE. Low erosion and high soil production rates relative to the lowland soils are likely related to extensive vegetation cover, which, in this context, protects soils against erosion and contributes to the formation of organic alpine soils, that rapidly accumulate organic matter by comparison to other soil types.© 2016, Elsevier B.V.
- ItemHigh-resolution palaeodust archive from subantarctic Macquarie Island(Australasian Quaternary Association, 2022-12-06) Johansen, A; Stromsoe, N; Saunders, KM; Marx, SKMineral dust drives climate variability both during atmospheric transport and upon deposition. During transport, dust influences radiative forcing and cloud properties. Upon deposition, nutrients supplied by dust can drive primary productivity and subsequent drawdown of atmospheric carbon. Inputs of Australian dust may be especially critical in the nutrient-limited ecosystems of the South Pacific Southern Ocean and subantarctic islands. This study seeks to understand dust flux to Macquarie Island since the mid-Holocene, and the potential response of plants to changing dust inputs. Peat cores from Macquarie Island were selected to reconstruct the dust flux history as peat plants can effectively capture dust and preserve the dust signal. Peats develop in water-saturated areas where plant decomposition is slowed in the anoxic and reduced conditions. As new growth accumulates over decaying plants, some elemental components of dust are preserved in place in the peat column. We developed high-resolution age-depth models with 210Pb, 239,240Pu, and 14C analysis. We applied 210Pb dating to the top 25 cm of each core, with additional age-control from the peak concentration of anthropogenic 239,240Pu identifying the Southern Hemisphere peak from nuclear weapons testing (about 1964). These data, along with radiocarbon ages to the mid-Holocene, were used to inform the age-depth model, which indicates variability in peat accumulation rates. The quantity and quality of organic matter (OM) were indicated by loss-on-ignition and Fourier-transform infrared (FTIR) spectroscopy. The δ15N values indicated minimal animal inputs. Preliminary inductively coupled plasma mass spectrometry (ICP-MS) data indicates dust inputs by increases in the stable isotopes of Pb in the early and mid-20th century. Dust scavenges Pb during transport, and the Australian production of Pb increased with the opening of the Broken Hill mine in 1885. Work is currently in progress to confirm these findings and extend the dust record prior to the 20th century.
- ItemA landscape-scale approach to examining the fate of atmospherically derived industrial metals in the surficial environment(Elsevier, 2015-02-01) Heijnis, H; Stromsoe, N; Marx, SK; McGowan, HA; Callow, JN; Zawadzki, AIndustrial metals are now ubiquitous within the atmosphere and their deposition represents a potential source of contamination to surficial environments. Few studies, however, have examined the environmental fate of atmospheric industrial metals within different surface environments. In this study, patterns of accumulation of atmospherically transported industrial metals were investigated within the surface environments of the Snowy Mountains, Australia. Metals, including Pb, Sb, Cr and Mo, were enriched in aerosols collected in the Snowy Mountains by 3.5–50 times pre-industrial concentrations. In sedimentary environments (soils, lakes and reservoirs) metals showed varying degrees of enrichment. Differences were attributed to the relative degree of atmospheric input, metal sensitivity to enrichment, catchment area and metal behaviour following deposition. In settings where atmospheric deposition dominated (ombrotrophic peat mires in the upper parts of catchments), metal enrichment patterns most closely resembled those in collected aerosols. However, even in these environments significant dilution (by 5–7 times) occurred. The most sensitive industrial metals (those with the lowest natural concentration; Cd, Ag, Sb and Mo) were enriched throughout the studied environments. However, in alpine tarn-lakes no other metals were enriched, due to the dilution of pollutant-metals by catchment derived sediment. In reservoirs, which were located lower within catchments, industrial metals exhibited more complex patterns. Particle reactive metals (e.g. Pb) displayed little enrichment, implying that they were retained up catchment, whereas more soluble metals (e.g., Cu and Zn) showed evidence of concentration. These same metals (Cu and Zn) were depleted in soils, implying that they are preferentially transported through catchments. Enrichment of other metals (e.g. Cd) varied between reservoirs as a function of contributing catchment area. Overall this study showed that the fate of atmospherically derived metals is complex, and depends upon metal behaviour and geomorphic processes operating at landscape scales. © 2014 Elsevier B.V.
- ItemLate holocene climate variability In the Australian Alps: can sedimentary and geochemical tracers track fine scale paleo-environment change?(Australasian Quaternary Association Inc., 2018-12-10) Stromsoe, N; Vernon, J; Marx, SK; Woodward, C; Saunders, KMThe Australian Alps have experienced some of the most dramatic change in any Australian landscape over the last glacial cycle, i.e. shifting between cold-climate conditions, glacial growth and dominance of periglacial processes and present day (warm) conditions. While these large scale changes are well documented, less is known about how the Alps have responded to more minor palaeo-climate change during the Holocene. Minor temperature changes may result in a measurable landscape response because they would be expected to manifest in changes to the occurrence of cold-climate processes, such as freeze thaw or solifluction, or conversely, increased vegetation cover and landscape stability. Sedimentary records from cirque lakes, therefore offer the potential to examine palaeo-environmental change in the alpine region during the late Holocene. In this study we examine recent (late Holocene) changes in the Alpine region of Kosciuszko National Park using cores extracted from Blue Lake and Club Lake. The two short cores date from 3,500 and 1,900 cal. yr BP, respectively. At Blue Lake, there is relatively little change recorded over most length of the core with the exception of a minor period of changing sedimentation rates and increased charcoal at 2,200-2,800 cal. yr BP, implying possible increased fires and associated landscape instability. Similarly, the Club Lake core also records little variability, although a change in sediment geochemistry implies the addition of less weathered material to the lake during the Little Ice Age, implying a potential increase in physical weathering. The most substantial change in both cores occurred within the last 200 years, with the addition of finer, less organic and significantly more chemically weathered material to the lakes. This coincides with the onset of grazing in the alpine region. This change implies that there has been increase in the contribution of sediment derived from soil to the lakes and, in particular, an increased contribution from subsoil (which in the case of the Australian Alps are more weathered). Finally, there is evidence of recovery in the top few centimetres of the cores implying conditions in the Alps have recovered from the dramatic grazing era perturbation, with conditions now similar to those over most of the late Holocene. © Author(s)
- 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.