Browsing by Author "Fletcher, MS"

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    Biogeochemical 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, R
    Environmental 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
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    Centennial-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, A
    Millennial-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
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    Changes in biomass burning mark the onset of an ENSO-influenced climate regime at 42°S in southwest Tasmania, Australia
    (Elsevier, 2015-06-15) Fletcher, MS; Benson, A; Heijnis, H; Gadd, PS; Cwynar, L; Rees, ABH
    We use macroscopic charcoal and sediment geochemistry analysis of two proximal upper montane lakes located at 42°S in southwest Tasmania, Australia, to test the role of the southern hemisphere westerly winds (SWW) and the El Niño-Southern Oscillation (ENSO) in governing the climate of this sector of the southern mid-to high-latitudes. Inter-annual climate anomalies in the study area are driven by changes in both ENSO and the Southern Annular Mode (SAM - an index that describes seasonal to decadal shifts in the SWW), making it an ideal location to test assumptions about the varying influence of the SWW and ENSO, two important components of the global climate system, through time. We find multi-millennial scale trends in fire activity that are remarkably consistent with trends in hydroclimate reconstructed at the same latitude in southern South America, providing empirical support for the notion of zonally symmetric changes in the SWW governing the climate at this latitude in the Southern Hemisphere between 12 and 5 cal ka BP. A transition from multi-millennial scale to sub-millennial scale trends in fire activity occurs after ca 5 cal ka BP in concert with the onset of high frequency and amplitude ENSO variability in the tropical Pacific Ocean region. We conclude that the onset of sub-millennial scale trends in ENSO drove changes in fire activity in our study region over the last ca 5 cal ka. Geochemical data reveals divergent local impacts at the two study sites in response to these major climate transitions that are related to local topography and geography. © 2015 Elsevier Ltd.
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    Chronostratigraphy of a 270-ka sediment record from Lake Selina, Tasmania: combining radiometric, geomagnetic and climatic dating
    (Elsevier, 2021-03-01) Lisé-Pronovost, A; Fletcher, MS; Simon, Q; Jacobs, Z; Gadd, PS; Heslop, D; Herries, AIR; Yokayama, Y
    Lake sediment archives covering several glacial cycles are scarce in the Southern Hemisphere and they are challenging to date. Here we present the chronostratigraphy of the oldest continuous lake sediment archive in Tasmania, Australia; a 5.5 m and 270 ka (Marine Isotope Stage 8) sediment core from Lake Selina. We employ radiometric dating (radiocarbon and optically stimulated luminescence) and relative dating (geomagnetic and climate comparisons). Bayesian modeling of the radiometric ages reaches back to 80 ka (1.7 m) and relative dating using a dynamic programing algorithm allows dating of the full sequence. Elemental data, magnetic properties and beryllium isotopes from Lake Selina reveal a close fit to Antarctic ice core climate proxies. Weaker correlation during the Last Glacial Period (MIS 2–4) is attributed to additional local factors impacting Lake Selina proxies at a time of climate changes and human arrival into Tasmania. Over that period, full vector paleomagnetic records and authigenic 10Be/9Be ratios are combined to identify the Laschamp geomagnetic excursion for the first time in Australia and constrain the chronology. The multi-method approach provides two preferred age models, indiscernible within their uncertainties, which allows the use of a geomagnetic dipole-independent (full archive) or a climate-independent (111 ka to present) age model. © 2021 Elsevier B.V.
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    Chronostratigraphy of sediment cores from Lake Selina, southeastern Australia: radiocarbon, optically stimulated luminescence, paleomagnetism, authigenic beryllium isotopes and elemental data
    (Elsevier B. V., 2022-06) Lisé-Pronovost, A; Fletcher, MS; Simon, Q; Jacobs, Z; Gadd, PS; Herriers, AIR; Yokoyama, Y
    This Data in Brief paper comprises dataset obtained for sediment cores collected from Lake Selina, located in the West Coast Range of Tasmania, Australia. Datasets include radiocarbon and optically stimulated luminescence age estimates, elemental composition, beryllium isotopes, magnetic properties and the paleomagnetic record measured on the cores assigned as TAS1402 (Location: Tasmania, Year: 2014, Site number: 02). The multi-proxy dataset was used to develop a chronostratigraphy for the 5.5 m and 270,000 year old record. See Lisé-Pronovost et al. (2021) (10.1016/j.quageo.2021.101152) for interpretation and discussion. The data presented in this study serve as an archive for future studies focusing on Earth system dynamics and the timeline and linkages of environmental changes across Tasmania, the Southern Hemisphere and at a global scale. 2022 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND licence.
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    Critical thresholds in aquatic ecosystems: a case study of Tasmanian diatom community response to regional and local environmental change
    (Australian Society for Limnology, 2016-09-29) Beck, KK; Fletcher, MS; Saunders, KM; Benson, A; Gadd, PS; Heijnis, H; Wolfe, B; Zawadzki, A
    Aquatic ecosystems are often hyper-sensitive and rapid responders to local and regional environmental change, in large part, due to fast reproduction and short lifespans of organisms relative to, for example, terrestrial vegetation. Here, we explore the response of a local diatom community to rapid shifts in rainforest vegetation driven by climate and fire over the last 2,400 years. We use a suite of palaeolimnological data to determine changes in vegetation, nutrient cycling, sediment delivery and diatom community structure to test the response of the local aquatic ecosystems to climate-driven terrestrial environment changes. We find that the diatom community in our study lake, Lake Vera in southwest Tasmania, Australia, remains complacent through phases of substantial changes in the terrestrial environment, hinting at a degree of resilience to both regional climatic and local terrestrial ecosystem change. We also identify a major compositional changes in diatom community – a shift from a planktonic dominance (i.e. Discostella stelligera) to a benthic dominance (i.e. Fragilaria spp. and Achnanthes didyma) – at ca. 930 cal yr BP, prior to a climate-driven terrestrial ecosystem change at ca. 800 cal yr BP. This aquatic ecosystem state-shift reflects the crossing of a critical threshold/tipping point in response to regional drivers and/or local dynamics that, thus, provides critical insights in to the long-term drivers and responses of aquatic ecosystem dynamics.
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    An early onset of ENSO influence in the extra-tropics of the southwest Pacific inferred from a 14, 600 year high resolution multi-proxy record from Paddy's Lake, northwest Tasmania
    (Elsevier B.V., 2017-02-01) Beck, KK; Fletcher, MS; Gadd, PS; Heijnis, H; Jacobsen, GE
    Tropical El Niño Southern Oscillation (ENSO) is an important influence on natural systems and cultural change across the Pacific Ocean basin. El Niño events result in negative moisture anomalies in the southwest Pacific and are implicated in droughts and catastrophic wildfires across eastern Australia. An amplification of tropical El Niño activity is reported in the east Pacific after ca. 6.7 ka; however, proxy data for ENSO-driven environmental change in Australia suggest an initial influence only after ca. 5 ka. Here, we reconstruct changes in vegetation, fire activity and catchment dynamics (e.g. erosion) over the last 14.6 ka from part of the southwest Pacific in which ENSO is the main control of interannual hydroclimatic variability: Paddy's Lake, in northwest Tasmania (1065 masl), Australia. Our multi-proxy approach includes analyses of charcoal, pollen, geochemistry and radioactive isotopes. Our results reveal a high sensitivity of the local and regional vegetation to climatic change, with an increase of non-arboreal pollen between ca. 14.6–13.3 ka synchronous with the Antarctic Cold Reversal, and a sensitivity of the local vegetation and fire activity to ENSO variability recorded in the tropical east Pacific through the Holocene. We detect local-scale shifts in vegetation, fire and sediment geochemistry at ca. 6.3, 4.8 and 3.4 ka, simultaneous with increases in El Niño activity in the tropical Pacific. Finally, we observe a fire-driven shift in vegetation from a pyrophobic association dominated by rainforest elements to a pyrogenic association dominated by sclerophyllous taxa following a prolonged (>1 ka) phase of tropical ENSO-amplification and a major local fire event at ca. 3.4 ka. Our results reveal the following key insights: (1) that ENSO has been a persistent modulator of southwest Pacific climate and fire activity through the Holocene; (2) that the climate of northwest Tasmania is sensitive to long-term shifts in tropical ENSO variability; and (3) that there has been possible stationarity in the spatial influence of ENSO over this region through the Holocene. © 2016 Elsevier Ltd.
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    Ecosystem 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, PS
    The 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.
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    A 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, H
    Here 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).
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    How 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, A
    Aim 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
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    How 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, SG
    This 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
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    The 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, A
    Mining 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
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    The 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, A
    Mining 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.
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    The indirect response of an aquatic ecosystem to long-term climate-driven terrestrial vegetation in a subalpine temperate lake
    (John Wiley & Sons, Inc, 2017-12-15) Beck, KK; Fletcher, MS; Kattel, G; Barry, LA; Gadd, PS; Heijnis, H; Jacobsen, GE; Saunders, KM
    Aim To assess whether climate directly influences aquatic ecosystem dynamics in the temperate landscape of Tasmania or whether the effects of long-term climatic change are mediated through the terrestrial environment (indirect climate influence). Location Paddy's Lake is located at 1065 m a.s.l. in temperate north-west Tasmania, a continental island south-east of mainland Australia (41°15–43°25′ S; 145°00–148°15′ E). Methods We developed a new 13,400 year (13.4 kyr) palaeoecological dataset of lake sediment subfossil cladocerans (aquatic grazers), bulk organic sediment carbon (C%) and nitrogen (N%) and δ13C and δ15N stable isotopes. Comparison of this new data was made with a recently published pollen, geochemistry and charcoal records from Paddy's Lake. Results Low cladoceran diversity at Paddy's Lake is consistent with other temperate Southern Hemisphere lakes. The bulk sediment δ15N values demonstrate a significant lagged negative response to pollen accumulation rate (pollen AR). Compositional shifts of dominant cladoceran taxa (Bosmina meridionalis and Alona guttata) occur following changes in both pollen AR and pollen (vegetation) composition throughout the 13.4 kyr record at Paddy's Lake. The δ15N values demonstrate a significant positive lagged relationship to the oligotrophic:eutrophic cladoceran ratio. Main conclusions Long-term changes in cladoceran composition lag changes in both pollen AR and terrestrial vegetation composition. We interpret pollen AR as reflecting climate-driven changes in terrestrial vegetation productivity and conclude that climate-driven shifts in vegetation are the principal driver of the cladoceran community during the last ca. 13.4 kyr. The significant negative lagged relationship between pollen AR and δ15N reflects the primary control of vegetation productivity over within-lake nutrient status. Thus, we conclude that the effects of long-term climate change on aquatic ecosystem dynamics at our site are indirect and mediated by the terrestrial environment. Vegetation productivity controls organic soil development and has a direct influence over lake trophic status via changes in the delivery of terrestrial organic matter into the lake. © 2017 John Wiley & Sons Ltd
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    The influence of fine-scale topography on the impacts of Holocene fire in a Tasmanian montane landscape
    (John Wiley & Sons, Inc, 2019-07-23) Cadd, H; Fletcher, MS; Mariani, M; Heijnis, H; Gadd, PS
    Tasmania'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.
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    A Late Holocene record of environmental change from the east coast of New South Wales, Australia
    (International Union for Quaternary Research (INQUA), 2019-07-30) Mackenzie, LL; Fletcher, MS; Gadd, PS
    A multi-proxy palaeoenvironmental record from a lake (36° 5'37.33"S; 150° 7'26.02"E) on the east coast of Australia provides a record of coastal development and vegetation succession over the last 3,800 cal. yr BP. Lead-210 and 14C dating built a robust age-depth chronology for the 61cm long core. Pollen, charcoal and x-ray fluorescence analysis provide records of vegetation change, fire regimes and catchment dynamics during the late Holocene. This study finds that an open coastal environment dominated by Amaranthaceae and Eucalyptus was present between 3,800 and 3,000 cal. yr BP when sea level on the east coast of Australia was ~1.7-1.5m higher than present. Rainforest indicators including Cyathea, Pomaderris and Nothofagus suggest a mixed wet Sclerophyll community was present either regionally or locally. Low pollen concentration and relatively high counts of Fe, S and Ca suggest iron sulfides and shell hash accumulated in a shallow or periodically exposed basin. Microscopic charcoal counts varied between 4,000 and 3,500 cal. yr BP and may indicate an increase in regional fire events. From 3,000 cal. yr BP Casuarinaceae and Poaceae increased and aquatic types Typha and Cyperaceae first appeared in the record suggesting the falling sea level allowed a barrier dune to form and a brackish to freshwater wetland to develop. Between 3,000 and 2,000 cal. yr BP Sr and Ti counts varied significantly, suggesting terrestrial and marine sediments may have periodically washed over the barrier dune and accumulated in the wetland during a period when sea level was ~1.1m higher than present. Sclerophyll open forest dominated by Casuarinaceae expanded until 2,000 cal. yr BP and then remained constant until present. Local and regional fire indicators increased briefly at 2,000 cal. yr BP. The presence of European settlers in the region is clearly identified by the occurrence of Pinus and the significant increase in regional and local fire regimes from 1900 AD and 1920 AD respectively. This multi-proxy record from a coastal lake in eastern New South Wales identifies the impact of sea level change and coastal progradation on vegetation and fire regimes and investigates natural and anthropogenic driven environmental change during the late-Holocene.
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    The legacy of mid-Holocene fire on a Tasmanian montane landscape
    (Wiley Blackwell, 2014-03-01) Fletcher, MS; Wolfe, BB; Whitlock, C; Pompeani, DP; Heijnis, H; Haberle, SG; Gadd, PS; Bowman, DMJS
    AimTo assess the long-term impacts of landscape fire on a mosaic of pyrophobic and pyrogenic woody montane vegetation. LocationSouth-west Tasmania, Australia. MethodsWe undertook a high-resolution multiproxy palaeoecological analysis of sediments deposited in Lake Osborne (Hartz Mountains National Park, southern Tasmania), employing analyses of pollen, macroscopic and microscopic charcoal, organic and inorganic geochemistry and magnetic susceptibility. ResultsSequential fires within the study catchment over the past 6500years have resulted in the reduction of pyrophobic rain forest taxa and the establishment of pyrogenic Eucalyptus-dominated vegetation. The vegetation change was accompanied by soil erosion and nutrient losses. The rate of post-fire recovery of widespread rain forest taxa (Nothofagus cunninghamii and Eucryphia spp.) conforms to ecological models, as does the local extinction of fire-sensitive rain forest taxa (Nothofagus gunnii and Cupressaceae) following successive fires. Main conclusionsThe sedimentary analyses indicate that recurrent fires over several centuries caused a catchment-wide transition from pyrophobic rain forest to pyrophytic eucalypt-dominated vegetation. The fires within the lake catchment during the 6500-year long record appear to coincide with high-frequency El Nino events in the equatorial Pacific Ocean, signalling a potential threat to these highly endemic rain forests if El Nino intensity amplifies as predicted under future climate scenarios. © 2014, Wiley-Blackwell.
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    The long-term impacts of climate and fire on catchment processes and aquatic ecosystem response in Tasmania, Australia
    (Elsevier, 2019-10-01) Beck, KK; Fletcher, MS; Gadd, PS; Heijnis, H; Saunders, KM; Zawadzki, A
    The impacts of fire and climate on freshwater ecosystems are not well understood, masking the potential impacts of anthropogenic climate change on these systems. A 9200 year Holocene record of sedimentary Carbon/Nitrogen, x-ray fluorescence, charcoal, pollen, and diatoms preserved within a freshwater lake in Tasmania was used to understand the influences of climate variability and fire on aquatic ecosystem response. Western Tasmania is a cool temperate environment where fire occurrence is driven by hydroclimate. High rainfall during the early to mid-Holocene drove an increase in rainforest and peat in the absence of fire, resulting in an oligotrophic and turbid aquatic environment. This also resulted in leaching of humic acid from the catchment, increasing acidity and dystrophy. The onset of a drier, more variable hydroclimate from the mid-to late Holocene drove lower lake levels and a shift to the dominant planktonic diatom species, Discostella stelligera, the result of the unusual bathymetry of Lake Vera where planktonic diatoms increase with lower lake levels. Further drying caused burning of the rainforest (at ca. 2.3 ka) and increased terrigenous deposition into the lake, leading to a productive, alkaline and disturbed diatom community. Repeated fire disturbance resulted in increased inorganic material deposition, the removal of nutrient rich peat, and an invasion of ferns and sclerophyll vegetation. These fire-driven catchment changes caused a shift in the diatom community to low productivity, oligotrophic and acidic assemblages, likely due to restricted light availability and nutrient uptake by increased deposition of terrigenous material. Therefore, the aquatic ecosystem is responding to climate-mediated changes in the terrestrial environment consistent with regional trends in nearby terrestrial-aquatic Holocene records. ©2019 Elsevier Ltd
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    A 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, A
    The 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.
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    Re-assessment of the mid to late Quaternary glacial and environmental history of the Boco Plain, western Tasmania
    (Elsevier, 2017-03-15) Augustinus, PC; Fink, D; Fletcher, MS; Thomas, I
    The glacial geomorphology and drill core-based stratigraphy of the Boco Plain, western Tasmania, reveal a complex sequence of Quaternary glacial and non-glacial episodes. The upper part of the southern Boco Plain stratigraphy was previously dated by 14C and U-series on interbedded organics of MIS 1 to MIS 5 affinity. U-series dating of ferricretes associated with glacial diamictons from Boco Plain cores suggested that there were glacial advances broadly correlative with MIS 6, 8 and ≥10. However, terrestrial cosmogenic nuclide (10Be and 26Al) exposure ages for the moraine sequence preserved on the wider Boco Plain area indicate that moraines previously attributed to MIS 6 and 8 advances were deposited during MIS 10 or earlier cold stages. There is no evidence for MIS 2, 4 or 6 affinity glacial advances onto the Boco Plain with ice of this age restricted to the West Coast Range. New palynological records from the Boco Plain core 6690 confirmed the late Quaternary ages of the upper part of the sequence, whilst extinct palynomorphs indicate a pre-Quaternary age for the glacial diamictons at the base of core Boco 4 and 10. Consequently, the mid-Pleistocene glacial sequence preserved in the Boco Plain is significantly older than previously envisaged, with the post MIS 10 to 12 geomorphology of the plain dominated by fluvial deltaic, swamp peat and lacustrine environments. © 2017 Elsevier Ltd.