Browsing by Author "Benson, A"

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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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    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.