Browsing by Author "Butz, C"

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    Assessing feral animal impacts on World Heritage sub-Antarctic Macquarie Island
    (International Union for Quaternary Research (INQUA), 2019-07-30) Saunders, KM; Roberts, SJ; Butz, C; Grosjean, M; Hodgson, DA
    Animals introduced by human activities to remote islands can be ecologically devastating as they often have a large proportion of endemic species with limited resilience to non-indigenous ones. Sub-Antarctic islands are remote, small islands in the vast Southern Ocean. Most have experienced some form of impact from non-indigenous fauna (e.g. rabbits, rats, mice, cats) that became feral pests soon after their deliberate and unintended introductions. Conservation and management efforts are increasingly focused on their control and/or eradication. World Heritage UNESCO Biosphere listed Macquarie Island (54°S) is one of the most impacted sub-Antarctic islands, in particular due to the introduction of rabbits in 1879, to the extent that its World Heritage values were considered threatened in the early 2000s. The values relate to Macquarie Island’s geological, geomorphic and physiographic features, and exceptional natural beauty and aesthetic importance. The latter includes the presence of a large number of lakes, tarns and ponds, and extensive peat beds. The largest rabbit and rodent eradication program for any sub-Antarctic island was undertaken from 2010-2014. Monitoring to assess recovery focused on geomorphological (including erosion) processes, vegetation and some fauna (i.e. invertebrates, burrowing petrels and albatross species) using previous studies as baselines. All of these studies were undertaken after rabbits were introduced, and no pre-introduction data exist beyond some limited historical documents after its discovery in 1810. No monitoring to assess recovery of the lakes, tarns, ponds or peat beds was undertaken. In the absence of long term data, palaeoecology may be used to determine the nature, magnitude and spatial extent of impacts in the context of long term natural variability. To provide a long-term context for assessing the island’s pre-invasion state, invasion impacts, and to provide baseline information for the waterbodies, we undertook a palaeoecological study using high-resolution x-ray fluorescence scanning and hyperspectral imaging together with biological (diatoms), geochemical (total organic carbon and nitrogen) and sedimentological (grain size) analyses of lake sediment cores in two different areas of Macquarie Island. Results showed that Macquarie Island lakes have undergone unprecedented and statistically significant environmental changes since the introduction of rabbits in 1879. Sediment accumulation rates increased by more than 10 times at one site, 100 times at another, due to enhanced catchment inputs and within- lake production. Total organic carbon and total nitrogen contents of the sediments increased by a factor of four. The diatom flora became dominated by two previously rare species in both lakes. This study provides an example of how palaeoecology may be used to determine baseline conditions prior to the introduction of non-indigenous species, quantify the timing and extent of changes, and help identify a basis for monitoring the recovery of waterbodies following successful non-indigenous species eradication programs ©The Authors
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    Holocene dynamics of the Southern Hemisphere westerly winds and possible links to CO2 outgassing
    (Springer Nature, 2018-07-23) Saunders, KM; Roberts, SJ; Perren, B; Butz, C; Sime, L; Davies, S; van Nieuwenhuyze, W; Grosjean, M; Hodgson, DA
    The Southern Hemisphere westerly winds (SHW) play an important role in regulating the capacity of the Southern Ocean carbon sink. They modulate upwelling of carbon-rich deep water and, with sea ice, determine the ocean surface area available for air–sea gas exchange. Some models indicate that the current strengthening and poleward shift of these winds will weaken the carbon sink. If correct, centennial- to millennial-scale reconstructions of the SHW intensity should be linked with past changes in atmospheric CO2, temperature and sea ice. Here we present a 12,300-year reconstruction of wind strength based on three independent proxies that track inputs of sea-salt aerosols and minerogenic particles accumulating in lake sediments on sub-Antarctic Macquarie Island. Between about 12.1 thousand years ago (ka) and 11.2 ka, and since about 7 ka, the wind intensities were above their long-term mean and corresponded with increasing atmospheric CO2. Conversely, from about 11.2 to 7.2 ka, the wind intensities were below their long-term mean and corresponded with decreasing atmospheric CO2. These observations are consistent with model inferences of enhanced SHW contributing to the long-term outgassing of CO2 from the Southern Ocean. © 2021 Springer Nature Limited
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    Westerly wind variability at sub-Antarctic Macquarie Island: links to the Southern Annular Mode and Southern Hemisphere rainfall and temperature
    (International Union for Quaternary Research (INQUA), 2019-07-30) Saunders, KM; Roberts, SJ; Griffiths, AD; Meredith, KT; Dätwyler, C; Hernandez-Almedia, I; Butz, C; Sime, L; Neukom, R; Grosjean, M; Hodgson, DA
    The position and strength of the Southern Hemisphere westerly winds is important for temperature and rainfall variability from the mid- to high-latitudes of the Southern Hemisphere. They also influence Southern Ocean circulation and sea ice extent around Antarctica and are closely linked to changes in the Southern Annular Mode (SAM). While observations available since the 1950s show the winds have strengthened and shifted southwards, this period is too short to understand their natural variability, especially as stratospheric ozone depletion and rising greenhouse gases from anthropogenic activities are considered to be driving these changes. Sub-Antarctic islands, such as Macquarie Island (54°S, 158°E), are ideally situated to reconstruct changes in the westerly winds as they lie within the latitudes where the winds are strongest. Here, we reconstruct changes in westerly wind strength of the last ca. 1800 years using lake sediment records from Macquarie Island. The reconstruction involves the application of a diatom-sea spray inference model (transfer function) supported by geochemical, minerogenic and sedimentological analyses. The inference model was used to assess changes in sea spray inputs to a small, exposed lake on the western edge of the Macquarie Island plateau, where the amount of sea spray is directly related to the strength of the westerlies. The reconstruction shows close agreement with the southern South America temperature (Past Global Changes) and SAM reconstructions for much of the last millennium, with the main feature being a decrease in wind strength ca. AD 1450 that coincides with a decrease in temperature at many sites around the Southern Hemisphere and transition to a more negative SAM phase. The combination of a modern climatological framework for understanding Macquarie Island’s current climate together with modelling and palaeoclimatological reconstructions of the westerlies, demonstrates that changes recorded at Macquarie Island are representative of wind, rainfall and temperature across the mid- to high-latitudes of the Southern Hemisphere. © The Authors.