Browsing by Author "Mariani, M"
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- ItemBiogeochemical responses to Holocene catchment-lake dynamics in the Tasmanian World Heritage Area, Australia(American Geophysical Union, 2018-04-30) Mariani, M; Beck, KK; Fletcher, MS; Gell, PA; Saunders, KM; Gadd, PS; Chisari, REnvironmental changes such as climate, land use, and fire activity affect terrestrial and aquatic ecosystems at multiple scales of space and time. Due to the nature of the interactions between terrestrial and aquatic dynamics, an integrated study using multiple proxies is critical for a better understanding of climate- and fire-driven impacts on environmental change. Here we present a synthesis of biological and geochemical data (pollen, spores, diatoms, micro X-ray fluorescence scanning, CN content, and stable isotopes) from Dove Lake, Tasmania, allowing us to disentangle long-term terrestrial-aquatic dynamics through the last 12 kyear. We found that aquatic dynamics at Dove Lake are tightly linked to vegetation shifts dictated by regional hydroclimatic variability in western Tasmania. A major shift in the diatom composition was detected at ca. 6 ka, and it was likely mediated by changes in regional terrestrial vegetation, charcoal, and iron accumulation. High rainforest abundance prior ca. 6 ka is linked to increased terrestrially derived organic matter delivery into the lake, higher dystrophy, anoxic bottom conditions, and lower light penetration depths. The shift to a landscape with a higher proportion of sclerophyll species following the intensification of El Niño-Southern Oscillation since ca. 6 ka corresponds to a decline in terrestrial organic matter input into Dove Lake, lower dystrophy levels, higher oxygen availability, and higher light availability for algae and littoral macrophytes. This record provides new insights on terrestrial-aquatic dynamics that could contribute to the conservation management plans in the Tasmanian World Heritage Area and in temperate high-altitude dystrophic systems elsewhere. ©2018. American Geophysical Union
- ItemCentennial-scale trends in the Southern Annular Mode revealed by hemisphere-wide fire and hydroclimatic trends over the past 2400 years(Geological Society of America, 2018-02-15) Fletcher, MS; Benson, B; Bowman, DMJS; Gadd, PS; Heijnis, H; Mariani, M; Saunders, KM; Wolfe, BB; Zawadzki, AMillennial-scale latitudinal shifts in the southern westerly winds (SWW) drive changes in Southern Ocean upwelling, leading to changes in atmospheric CO2 levels, thereby affecting the global climate and carbon cycle. Our aim here is to understand whether century-scale shifts in the SWW also drive changes in atmospheric CO2 content. We report new multiproxy lake sediment data from southwest Tasmania, Australia, that show centennial-scale changes in vegetation and fire activity over the past 2400 yr. We compare our results with existing data from southern South America and reveal synchronous and in-phase centennial-scale trends in vegetation and fire activity between southwest Tasmania and southern South America over the past 2400 yr. Interannual to centennial-scale rainfall anomalies and fire activity in both these regions are significantly correlated with shifts in the SWW associated with the Southern Annular Mode (SAM; atmospheric variability of the Southern Hemisphere). Thus, we interpret the centennial-scale trends we have identified as reflecting century-scale SAM-like shifts in the SWW over the past 2400 yr. We identify covariance between our inferred century-scale shifts in the SWW and Antarctic ice core CO2 values, demonstrating that the SWW-CO2 relationship operating at a millennial scale also operates at a centennial scale through the past 2400 yr. Our results indicate a possible westerly-driven modulation of recent increases in global atmospheric CO2 content that could potentially exacerbate current greenhouse gas–related warming. © 2021 Geological Society of America
- ItemCoupling of the Intertropical Convergence Zone and Southern Hemisphere mid-latitude climate during the early to mid-Holocene(Geological Society of America, 2017-10-27) Mariani, M; Fletcher, MS; Drysdale, RN; Saunders, KM; Heijnis, H; Jacobsen, GE; Zawadzki, AConceptual models predict a tight coupling between the Intertropical Convergence Zone (ITCZ) and the Southern Westerly Winds (SWW) in response to glacial-interglacial transitions, yet little is known about this relationship under Holocene boundary conditions. Here we present a synthesis of Holocene pollen data from the southwest Pacific mid-latitudes that tracks changes in the SWW. Comparison of our SWW paleoclimate records with data tracking the ITCZ, oceanic circulation, and insolation reveals clearly synchronous and in-phase ITCZ-SWW dynamics between 12 and 5 ka, indicating a tight coupling between the tropics and southern mid-latitudes in response to ocean circulation and insolation. An apparent decoupling of the SWW and ITCZ in the Pacific region after 5 ka is attributable to the overriding influence of the El Niño-Southern Oscillation (ENSO) over the proxy data. © 2017 Geological Society of America
- ItemA high-resolution multi-proxy palaeoecological record of the last two glacial cycles from Lake Selina, Tasmania(Australasian Quaternary Association Inc., 2018-12-10) Fletcher, MS; Lisé-Pronovost, A; Mariani, M; Hopf, F; Gadd, PS; Heijnis, HHere we present the results of a continuous high resolution multi-proxy data set spanning the last two glacial cycles (ca 230,000 years) from Lake Selina, Tasmania. The data set includes pollen, charcoal, geochemistry and magnetic properties. We compare and discuss ecological trends between the Last Interglacial and the Holocene, reflecting on the role of people in radically altering the vegetation landscape. We also present tantalising data suggesting a possible Antarctic Cold Reversal-like shift through the penultimate Glacial Termination (T2).
- ItemHow old is the Tasmanian cultural landscape? A test of landscape openness using quantitative land-cover reconstructions(John Wiley and Sons, 2017-06-19) Mariani, M; Connor, SE; Fletcher, MS; Theuerkauf, M; Kuneš, P; Jacobsen, GE; Saunders, KM; Zawadzki, AAim To test competing hypotheses about the timing and extent of Holocene landscape opening using pollen-based quantitative land-cover estimates. Location Dove Lake, Tasmanian Wilderness World Heritage Area, Australia. Methods Fossil pollen data were incorporated into pollen dispersal models and corrected for differences in pollen productivity among key plant taxa. Mechanistic models (REVEALS—Regional Estimates of VEgetation Abundance from Large Sites) employing different models for pollen dispersal (Gaussian plume and Lagrangian stochastic models) were evaluated and applied in the Southern Hemisphere for the first time. Results Validation of the REVEALS model with vegetation cover data suggests an overall better performance of the Lagrangian stochastic model. Regional land-cover estimates for forest and non-forest plant taxa show persistent landscape openness throughout the Holocene (average landscape openness ~50%). Gymnoschoenus sphaerocephalus, an indicator of moorland vegetation, shows higher values during the early Holocene (11.7–9 ka) and declines slightly through the mid-Holocene (9–4.5 ka) during a phase of partial landscape afforestation. Rain forest cover reduced (from ~40% to ~20%) during the period between 4.2–3.5 ka. Main conclusions Pollen percentages severely under-represent landscape openness in western Tasmania and this bias has fostered an over-estimation of Holocene forest cover from pollen data. Treeless vegetation dominated Holocene landscapes of the Dove Lake area, allowing us to reject models of landscape evolution that invoke late-Holocene replacement of a rain forest-dominated landscape by moorland. Instead, we confirm a model of Late Pleistocene inheritance of open vegetation. Rapid forest decline occurred after c. 4 ka, likely in response to regional moisture decline. © 2017 John Wiley & Sons Ltd
- ItemHow significant is atmospheric metal contamination from mining activity adjacent to the Tasmanian Wilderness World Heritage Area? A spatial analysis of metal concentrations using air trajectories models(Elsevier, 2019-03-15) Schneider, L; Mariani, M; Saunders, KM; Maher, WA; Harrison, JJ; Fletcher, MS; Zawadzki, A; Heijnis, H; Haberle, SGThis study investigated metal contamination from historical mining in lakes in the Tasmanian Wilderness World Heritage Area (TWWHA) and surrounding region. The largest increase in sedimentation and metal contamination occurred ca. 1930 when open-cut mining commenced and new mining technology was introduced into the region. The geochemical signal of lake sediments changed from reflecting the underlying geology and lithology to that reflecting mining activities. The HYSPLIT air particle trajectory model explains metal distribution in the lakes, with those in the northwest region closest to the mines having the highest metal contamination. Lake metal concentrations since mining activities commenced are in the order: Owen Tarn > Basin Lake > Perched Lake > Lake Dove > Lake Dobson > Lake Cygnus, with Perched Lake and Lakes Dove, Dobson and Cygnus in the TWWHA. Metal contamination affected centres up to 130 km down-wind of mining sites. Enrichment factors (EF) for Pb, Cu, As and Cd are >1 for all lakes, with Owen Tarn and Basin Lake having very high EFs for Cu and Pb (98 and 91, respectively). Pb, Cu, As and Cd concentrations are above the Australia/New Zealand lower sediment guidelines, with Pb, Cu and As above the high guidelines in Owen Tarn and Basin Lake. This study demonstrated the legacy of metal contamination in the TWWHA by mining activities and the consequences of a lack of execution of environmental regulations by past governments in Tasmania.© 2018 Elsevier B.V
- ItemThe impacts of intensive mining on terrestrial and aquatic ecosystems: A case of sediment pollution and calcium decline in cool temperate Tasmania, Australia(Elsevier, 2020-10-01) Beck, KK; Mariani, M; Fletcher, MS; Schneider, L; Aquino-López, MA; Gadd, PS; Heijnis, H; Saunders, KM; Zawadzki, AMining causes extensive damage to aquatic ecosystems via acidification, heavy metal pollution, sediment loading, and Ca decline. Yet little is known about the effects of mining on freshwater systems in the Southern Hemisphere. A case in point is the region of western Tasmania, Australia, an area extensively mined in the 19th century, resulting in severe environmental contamination. In order to assess the impacts of mining on aquatic ecosystems in this region, we present a multiproxy investigation of the lacustrine sediments from Owen Tarn, Tasmania. This study includes a combination of radiometric dating (14C and 210Pb), sediment geochemistry (XRF and ICP-MS), pollen, charcoal and diatoms. Generalised additive mixed models were used to test if changes in the aquatic ecosystem can be explained by other covariates. Results from this record found four key impact phases: (1) Pre-mining, (2) Early mining, (3) Intense mining, and (4) Post-mining. Before mining, low heavy metal concentrations, slow sedimentation, low fire activity, and high biomass indicate pre-impact conditions. The aquatic environment at this time was oligotrophic and dystrophic with sufficient light availability, typical of western Tasmanian lakes during the Holocene. Prosperous mining resulted in increased burning, a decrease in landscape biomass and an increase in sedimentation resulting in decreased light availability of the aquatic environment. Extensive mining at Mount Lyell in the 1930s resulted in peak heavy metal pollutants (Pb, Cu and Co) and a further increase in inorganic inputs resulted in a disturbed low light lake environment (dominated by Hantzschia amphioxys and Pinnularia divergentissima). Following the closure of the Mount Lyell Co. in 1994 CE, Ca declined to below pre-mining levels resulting in a new diatom assemblage and deformed diatom valves. Therefore, the Owen Tarn record demonstrates severe sediment pollution and continued impacts of mining long after mining has stopped at Mt. Lyell Mining Co. ©2020 Elsevier Ltd
- ItemThe impacts of intensive mining on terrestrial and aquatic ecosystems: a case study from cool temperate Tasmania, Australia(International Union for Quaternary Research (INQUA), 2019-07-30) Beck, KK; Mariani, M; Fletcher, MS; Gadd, PS; Heijnis, H; Saunders, KM; Zawadzki, AMining has caused extensive damage to aquatic systems worldwide with acidification, heavy metal pollution, increased sediment loading and Ca decline of freshwaters. While some aquatic ecosystems are thought to be recovering from past mining, a long-term context is needed to determine if pre-impact conditions have been restored. Here we explore the palaeoenvironmental history of Owen Tarn, western Tasmania, to assess the impacts of mining from Mt. Lyell on aquatic ecosystems. Analysis of a new sediment core using radiometric dating, sediment geochemistry, pollen, and diatoms are used to examine the full extent of mining and heavy metal pollution on aquatic and terrestrial ecosystems pre- and post-mining in this region. Our analysis indicates four key phases of environmental change: (1) A pre-mining phase (550-1160 CE); (2) an early impact phase (British invasion) shows land clearance and vegetation removal by burning during mineral exploration; (3) an intense mining period (1950 CE) had severe negative impact on the diatom community in which sediment pollution from a lack of vegetation and heavy erosion, rather than acidification, was the main driver of change; and (4) a post-mining phase (2006 CE) in which vegetation on the landscape began to recover and aquatic productivity increased. Despite this apparent recovery of the system, the aquatic community continues to experience impacts from mining. The diatom community has not returned to its pre-impact state, but rather there is evidence of a secondary impact from declining Ca in the system. The relevance of these findings demonstrates the importance of well dated palaeoecological records to inform management and mitigate human impacts on the environment.
- ItemThe influence of fine-scale topography on the impacts of Holocene fire in a Tasmanian montane landscape(John Wiley & Sons, Inc, 2019-07-23) Cadd, HR; Fletcher, MS; Mariani, M; Heijnis, H; Gadd, PSTasmania's montane temperate rainforests contain some of Australia's most ancient and endemic flora. Recent landscape-scale fires have impacted a significant portion of these rainforest ecosystems. The complex and rugged topography of Tasmania results in a highly variable influence of fire across the landscape, rendering predictions of ecosystem response to fire difficult. We assess the role of topographic variation in buffering the influence of fire in these endemic rainforest communities. We developed a new 14 000-year (14-ka) palaeoecological dataset from Lake Perry, southern Tasmania, and compared it to neighbouring Lake Osborne (<250 m distant) to examine how topographic variations influence fire and vegetation dynamics through time. Repeated fire events during the Holocene cause a decline in montane rainforest taxa at both sites; however, in the absence of fire, rainforest taxa are able to recover. Montane temperate rainforest taxa persisted at Lake Perry until European settlement, whilst these taxa were driven locally extinct and replaced by Eucalyptus species at Lake Osborne after 2.5 ka. Contiguous topographic fire refugia within the Lake Perry catchment probably provided areas of favourable microclimates that discouraged fire spread and supported the recovery of these montane temperate rainforests. Copyright © 2019 John Wiley & Sons, Ltd.
- ItemA northward shift of the southern westerlies during the Antarctic cold reversal: evidence from Tasmania(Australasian Quaternary Association, 2018-12-10) Alexander, J; Fletcher, MS; Pedro, JB; Mariani, M; Beck, KK; Blaauw, M; Hodgson, D; Heijnis, H; Gadd, PS; Lisé-Pronovost, AThe Last Glacial Termination (LGT) was interrupted in the Southern Hemisphere by the Antarctic Cold Reversal (ACR; 14.7 to 13 ka), a millennial-scale cooling event that coincided with the Bølling– Allerød warm phase in the North Atlantic (14.7 to 12.7 ka). This inter-hemispheric asynchrony of climate change through the LGT, the bipolar seesaw, has been theoretically linked to latitudinal shifts in the southern westerly wind belt (SWW) and their proposed influence over the global carbon cycle via wind-driven upwelling of CO2 rich deep waters in the Southern Ocean (SO). However, while climate models and theory predict a northward shift of the SWW during the ACR in response to ocean-atmosphere heat dynamics, proxy-based reconstructions disagree on the behaviour of the SWW through this interval, and the role of the SWW during the LGT remains contested. Here we present terrestrial proxy palaeoclimate data (pollen, μXRF geochemistry, charcoal) from multiple lakes across Tasmania (40-44⁰S), an island located at the northern edge of the SWW. Our data reveal a clear SWW increase over Tasmania during the ACR, synchronous with reduced SWW-driven upwelling in the SO at the southern edge of the SWW. When combined with evidence from Antarctic ice cores and terrestrial records from New Zealand and Patagonia our results suggest a hemisphere-wide migration of the SWW during the LGT, lending support to the hypothesis that changes in wind-driven ventilation of CO2 from the Southern Ocean were a key driver of the global carbon cycle during the LGT. © The Authors.
- ItemPatterns of aeolian deposition in subtropical Australia through the last glacial and deglacial periods(Cambridge University Press, 2021-02-08) Lewis, RJ; Tibby, J; Arnold, LJ; Gadd, PS; Jacobsen, GE; Barr, C; Negus, PM; Mariani, M; Penny, D; Chittleborough, D; Moss, EDebate about the nature of climate and the magnitude of ecological change across Australia during the last glacial maximum (LGM; 26.5–19 ka) persists despite considerable research into the late Pleistocene. This is partly due to a lack of detailed paleoenvironmental records and reliable chronological frameworks. Geochemical and geochronological analyses of a 60 ka sedimentary record from Brown Lake, subtropical Queensland, are presented and considered in the context of climate-controlled environmental change. Optically stimulated luminescence dating of dune crests adjacent to prominent wetlands across North Stradbroke Island (Minjerribah) returned a mean age of 119.9 ± 10.6 ka; indicating relative dune stability soon after formation in Marine Isotope Stage 5. Synthesis of wetland sediment geochemistry across the island was used to identify dust accumulation and applied as an aridification proxy over the last glacial-interglacial cycle. A positive trend of dust deposition from ca. 50 ka was found with highest influx occurring leading into the LGM. Complexities of comparing sedimentary records and the need for robust age models are highlighted with local variation influencing the accumulation of exogenic material. An inter-site comparison suggests enhanced moisture stress regionally during the last glaciation and throughout the LGM, returning to a more positive moisture balance ca. 8 ka. © 2021 University of Washington
- ItemScientific drilling of sediments at Darwin Crater, Tasmania(Copernicus Publications, 2019-06-12) Lisé-Pronovost, A; Fletcher, MS; Mallett, T; Mariani, M; Lewis, RJ; Gadd, PS; Herries, AIR; Blaauw, M; Heijnis, H; Hodgson, DA; Pedro, JBA 70 m long continental sediment record was recovered at Darwin Crater in western Tasmania, Australia. The sediment succession includes a pre-lake silty sand deposit overlain by lacustrine silts that have accumulated in the ∼816 ka meteorite impact crater. A total of 160 m of overlapping sediment cores were drilled from three closely spaced holes. Here we report on the drilling operations at Darwin Crater and present the first results from petrophysical whole core logging, lithological core description, and multi-proxy pilot analysis of core end samples. The multi-proxy dataset includes spectrophotometry, grain size, natural gamma rays, paleo- and rock magnetism, loss on ignition, and pollen analyses. The results provide clear signatures of alternating, distinctly different lithologies likely representing glacial and interglacial sediment facies. Initial paleomagnetic analysis indicate normal magnetic polarity in the deepest core at Hole B. If acquired at the time of deposition, this result indicates that the sediment 1 m below commencement of lacustrine deposition post-date the Matuyama–Brunhes geomagnetic reversal ∼773 ka. © Author(s) 2019.
- ItemUnderstanding human-environment interactions in space and time: 3 case studies from the Holocene in Australia(Australasian Quaternary Association Inc, 2018-12-10) Fletcher, MS; Romano, A; Mariani, M; Zawadzki, AUnderstanding human-environment interactions has emerged as a prominent research agenda within both archaeology and palaeoecology. Palaeoenvironmental research has demonstrated the important role that climate has in determining the development and distribution of ecosystems, however the impact of humans on ecosystems and of environmental change on humans remains contentious, particularly when studies of environmental change are conducted in isolation from archaeology. Here we present three separate analyses of human-environment interactions through time in Australia that are focussed at range of spatial scales: local, regional and continental. We highlight a tight coupling between palaeoenvironmental change and human population dynamics at all of these scales in the case studies and attempt to disentangle the reciprocal relationships between environmental change and human activity. The governing question underpinning this presentation is: how does the information provided by palaeoecology and archaeology about human-environment interactions through time vary with the spatial and temporal scale of the primary data? © The Authors
- ItemWhat happened at the end of the mid-Pleistocene transition in the Southern Hemisphere? Insights from western Tasmania, Australia(International Union for Quaternary Research (INQUA), 2019-07-30) Fletcher, MS; Lisé-Pronovost, A; Mallett, T; Mariani, M; Cooley, S; May, JH; Gadd, PS; Herries, A; Blaauw, M; Heijnis, H; Hodgson, DA; Pedro, JBThe current southward shift in the southern westerlies that is stripping southern Australia of rainfall is unprecedented over the past 12 kyrs years at least, and is due to the effects of both the anthropogenic hole in the ozone layer and greenhouse gas-driven global warming. Predictions of future climate suggest the Earth is moving in to a “super-interglacial” (peak warming) because of anthropogenic greenhouse gas release. “Super-interglacials”, which are warmer than today, are uncommon in the geological record. A recent increase in the frequency of these peak warming events since ca. 450 ka (the end of the mid-Pleistocene transition; MPT) is associated with a 7° latitude southward shift of the southern westerlies and an increase in atmospheric CO2 that warmed the atmosphere - a stark similarity to current trends. Here, we present multi-proxy analyses of two closely spaced (<50 km) sediment cores that comprise a complete sequence from the mid-Pleistocene to the present from western Tasmania, Australia - in the mid-latitudes of the Southern Hemisphere. Lake Selina is a modern-day lake with a continuous ca. 230 kyr sediment sequence, while Darwin Crater is a palaeo-lake within a meteorite impact crater that formed at ca. 816 ka and which completely in-filled during MIS5 (ca. 120 ka). We report on petrophysical whole core logging, lithological core description, spectrophotometry, grain size, natural gamma ray, paleo- and rock-magnetism, loss-on-ignition, pollen analyses and micro-XRF geochemisrty. The composite record is unique in the Australian sector of the Southern Hemisphere and we discuss the data in the context of the global and regional changes that occurred at the end of MPT, paying particular attention to impact of the shift toward warmer super-interglacials, the large-scale southward shift of the southern westerlies and higher atmospheric CO2 content that occurred at ca. 450 ka (MIS11 to present).