Browsing by Author "Clarke, LJ"

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    Growth rate of Antarctic mosses derived from bomb radiocarbon.
    (20th International Radiocarbon Conference, 2009-06-01) Fink, D; Hua, Q; Clarke, LJ; Robinson, SA
    At the previous Radiocarbon Conference in Oxford, 2006, we reported our preliminary results on the use of bomb radiocarbon for the determination of growth rates of two moss species collected from east Antarctica in January 2005. Here, we present an update of this study for four different moss species (Bryoerythrophyllum recurvirostre, Bryum pseudotriquetrum, Schistidium antarctici, and Ceratodon purpureus) from the Vestfold Hills and Windmill Islands in east Antarctica. Samples were collected as a “core” from moss turfs. Approximately 10–20 of the longest shoots were separated from each core and cut into 3-mm sections for AMS 14C analysis. The samples were cleaned with dilute HCl acid, then combusted to CO2 and converted to graphite. AMS radiocarbon measurements have been carried out using the STAR facility at ANSTO. The 14C profile in most cores showed both the rising and falling limbs of bomb radiocarbon, implying that these mosses began growing over 50 years ago. Our results indicated that these Antarctic mosses have grown slowly with average rates ranging from 0.6 to 1.3 mm yr–1. This study is the first to determine the growth rates of Antarctic mosses over a time period spanning decades rather than individual or multiple field seasons. The results also give us an opportunity to investigate whether temporal variations in moss growth rates correlate with climatic change in Antarctica.
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    Monitoring impacts of a changing climate on plant communities of Continental Antarctica
    (British Ecological Society, 2010-09-07) Robinson, SA; Clarke, LJ; King, D; Ayre, DJ; Hua, Q; Fink, D; Lucieer, A
    To determine if climate change is impacting continental Antarctic plant communities we need to measure the growth rates of extremely slow growing organisms and relate this to changing climate. In addition, we need to develop new methodologies for measuring community change at very small scales. We are developing a monitoring system for East Antarctic plant communities using radiocarbon and stable isotope measurements and remote unmanned vehicles to assess physiological and spatial change in remote communities.
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    Radiocarbon bomb spike reveals biological effects of Antarctic climate change
    (Wiley, 2012-01) Clarke, LJ; Robinson, SA; Hua, Q; Ayre, DJ; Fink, D
    The Antarctic has experienced major changes in temperature, wind speed and stratospheric ozone levels during the last 50 years. However, until recently continental Antarctica appeared to be little impacted by climate warming, thus biological changes were predicted to be relatively slow. Detecting the biological effects of Antarctic climate change has been hindered by the paucity of long-term data sets, particularly for organisms that have been exposed to these changes throughout their lives. We show that radiocarbon signals are preserved along shoots of the dominant Antarctic moss flora and use these to determine accurate growth rates over a period of several decades, allowing us to explore the influence of environmental variables on growth and providing a dramatic demonstration of the effects of climate change. We have generated detailed 50-year growth records for Ceratodon purpureus and three other Antarctic moss species using the 1960s radiocarbon bomb spike. Our growth rate and stable carbon isotope (δ13C) data show that C. purpureus’ growth rates are correlated with key climatic variables, and furthermore that the observed effects of climate variation on growth are mediated through changes in water availability. Our results indicate the timing and balance between warming, high-wind speeds and elevated UV fluxes may determine the fate of these mosses and the associated communities that form oases of Antarctic biodiversity. © 2011 Blackwell Publishing Ltd
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    Radiocarbon bomb spike reveals climate change is stunting growth of century old Antarctic moss shoots
    (Ecological Society of America (ESA), 2012-08-09) Robinson, SA; Clarke, LJ; Waterman, MJ; Bramley-Alves, J; Hua, Q; Wanek, W; Fink, D
    The Antarctic has experienced major changes in temperature, wind speed and stratospheric ozone levels over the last 50 years. However until recently continental Antarctica appeared to be little impacted by climate warming, thus biological changes were predicted to be relatively slow. Detecting the biological effects of Antarctic climate change has been hindered by the paucity of long-term data sets, particularly for organisms that have been exposed to these changes throughout their lives. We have shown that radiocarbon signals preserved along shoots of the dominant Antarctic moss flora can be used to determine accurate growth rates over a period of several decades, allowing us to explore the influence of environmental variables on growth and providing a dramatic demonstration of the effects of climate change. Detailed 60-year growth records have been generated for Ceratodon purpureus and three other East Antarctic moss species (Bryum pseudotriquetrum, Schistidium antarctici and Bryoerythrophyllum recurvirostre) using the 1960s radiocarbon bomb spike. Growth rate and stable carbon isotope (d13C) data show that C. purpureus’ growth rates are correlated with key climatic variables, and furthermore that the observed effects of climate variation on growth are mediated through changes in water availability. Many of the sites investigated showed evidence of drying over recent decades and this was associated with reductions in moss growth rate. The most likely cause of this drying is increased wind speeds around the coast of Antarctica linked to depletion of the ozone layer. The finding that stable isotope signals laid down as the mosses grow can be used to determine changes in microhabitat water availability over recent decades means that in future, Antarctic mosses could be used as proxies for past coastal climate. Changes in water availability during the growing season may determine the fate of these mosses and the associated communities that form oases of Antarctic biodiversity. © 2012 Ecological Society of America