Browsing by Author "Hodgson, DA"
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- ItemAssessing 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, DAAnimals 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of these studies were undertaken after rabbits were introduced, and no pre-introduction data exist beyond some limited historical documents after its discovery in 1810.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
- ItemA community-based geological reconstruction of Antarctic ice sheet deglaciation since the last glacial maximum(Elsevier, 2014-09-15) Bentley, MJ; O'Cofaigh, C; Anderson, JB; Conway, H; Davies, B; Graham, AGC; Hillenbrand, CD; Hodgson, DA; Jamieson, SSR; Larter, RD; Mackintosh, AN; Smith, JA; Verleyen, E; Ackert, RP; Bart, PJ; Berg, S; Brunstein, D; Canals, M; Colhoun, EA; Crosta, X; Dickens, WA; Domack, E; Dowdeswell, JA; Dunbar, R; Ehrmann, W; Evans, J; Favier, V; Fink, D; Fogwill, CJ; Glasser, NF; Gohl, K; Golledge, NR; Goodwin, I; Gore, DB; Greenwood, SL; Hall, BL; Hall, K; Hedding, DW; Hein, AS; Hocking, EP; Jakobsson, M; Johnson, JS; Jomelli, V; Jones, RS; Klages, JP; Kristoffersen, Y; Kuhn, G; Leventer, A; Licht, K; Lilly, K; Lindow, J; Livingstone, SJ; Massé, G; McGlone, MS; McKay, RM; Melles, M; Miura, H; Mulvaney, R; Nel, W; Nitsche, FO; O'Brien, PE; Post, AL; Roberts, SJ; Saunders, KM; Selkirk, PM; Simms, AR; Spiegel, C; Stolldorf, TD; Sugden, DE; van der Putten, N; van Ommen, TD; Verfaillie, D; Vyverman, W; Wagner, B; White, DA; Witus, AE; Zwartz, DA robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community. © 2014 The Authors. CC BY license
- ItemEcosystem impacts of feral rabbits on World Heritage sub-Antarctic Macquarie Island: a palaeoecological perspective(Elsevier, 2013-11) Saunders, KM; Harrison, JJ; Hodgson, DA; de Jong, R; Mauchle, F; McMinn, AThe introduction and establishment of non-indigenous species through human activities often poses a major threat to natural biodiversity. In many parts of the world management efforts are therefore focused on their eradication. The environment of World Heritage sub-Antarctic Macquarie Island has been severely damaged by non-indigenous species including rabbits, rats and mice, introduced from the late AD 1800s. An extensive eradication programme is now underway which aims to remove all rabbits and rodents. To provide a long-term context for assessing the Island's pre-invasion state, invasion impacts, and to provide a baseline for monitoring its recovery, we undertook a palaeoecological study using proxies in a lake sediment core. Sedimentological and diatom analyses revealed an unproductive catchment and lake environment persisted for ca. 7100 years prior to the introduction of the invasive species. After ca. AD 1898, unprecedented and statistically significant environmental changes occurred. Lake sediment accumulation rates increased >100 times due to enhanced catchment inputs and within-lake production. Total carbon and total nitrogen contents of the sediments increased by a factor of four. The diatom flora became dominated by two previously rare species. The results strongly suggest a causal link between the anthropogenic introduction of rabbits and the changes identified in the lake sediments. 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 monitor the recovery of the ecosystem and natural biodiversity following successful non-indigenous species eradication programmes. © 2014 Elsevier Ltd.
- ItemEllsworth Subglacial Lake, West Antarctica: a review of its history and recent field campaigns(John Wiley & Sons, Inc, 2011-01-01) Ross, N; Siegert, MJ; Rivera, A; Bentley, MJ; Blake, D; Capper, L; Clarke, R; Cockell, CS; Corr, HFJ; Harris, W; Hill, C; Hindmarsh, RCA; Hodgson, DA; King, EC; Lamb, H; Maher, B; Makinson, K; Mowlem, M; Parnell, J; Pearce, DA; Priscu, J; Smith, AM; Tait, A; Tranter, M; Wadham, JL; Whalley, WB; Woodward, JCEllsworth Subglacial Lake, first observed in airborne radio echo sounding data acquired in 1978, is located within a long, deep subglacial trough within the Ellsworth Subglacial Highlands of West Antarctica. Geophysical surveys have characterized the lake, its subglacial catchment, and the thickness, structure, and flow of the overlying ice sheet. Covering 28.9 km2 , Ellsworth Subglacial Lake is located below 2.9 to 3.3 km of ice at depths of -1361 to -1030 m. Seismic reflection data have shown the lake to be up to 156 m deep and underlain by unconsolidated sediments. Ice sheet flow over the lake is characterized by low velocities (<6 m yr-1 ), flow convergence, and longitudinal extension. The lake appears to be in steady state, although the hydrological balance may vary over glacial-interglacial cycles. Direct access, measurement, and sampling of Ellsworth Subglacial Lake are planned for the 2012/2013 Antarctic field season. The aims of this access experiment are to determine (1) the presence, character, and maintenance of microbial life in Antarctic subglacial lakes and (2) the Quaternary history of the West Antarctic ice sheet. Geophysical data have been used to define a preferred lake access site. The factors that make this location suitable for exploration are (1) a relatively thin overlying ice column (~3.1 km), (2) a significant measured water depth (~143 m), (3) >2 m of sediment below the lake floor, (4) water circulation modeling suggesting a melting ice-water interface, and (5) coring that can target the deepest point of the lake floor away from marginal, localized sediment sources. © 2011 American Geophysical Union.
- ItemHolocene 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, DAThe 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
- ItemLate quaternary changes in the westerly winds over the Southern Ocean – a progress report(VII Southern Connection Congress 2016, 2016-01-18) Hodgson, DA; Roberts, S; Perren, B; Saunders, KM; Verleyen, E; van Nieuwenhuyze, W; Vyverman, W; Sime, LThe Southern Hemisphere westerly winds (SHW) are the strongest time-averaged oceanic winds. They drive the circulation of the Southern Ocean and changes in their strength and position are thought to modify the upwelling of carbon rich deep water, exerting significant control on the ocean-atmosphere balance of CO2. Thus changes in the SHW, such as the recently observed intensification, could influence whether the Southern Ocean acts as a net source or sink of atmospheric CO2, with major implications for global climate. At present the relationships between wind strength, CO2 and climate are poorly understood and there are very few studies within the core belt of the SHW in the sub-Antarctic zone c.46 to 60 deg South. We have been attempting to address this by producing centennial to decadal reconstructions of changes in SHW strength at sub-Antarctic islands in each of the major sectors of the Southern Ocean. In this talk we will show how lake sediments and peat deposits on the west coasts of these islands can yield proxy-based reconstructions of past changes in the SHW. We will review the statistical performance of our inference models, their application down selected sediment cores, and compare them with complimentary proxies of changes in wind strength based on precipitation and minerogenic inputs. The next phase of the project will use GCM simulations to help understand the patterns seen in the observational data and identify the drivers of past changes in the SHW.
- ItemPalaeoecological tools for improving the management of coastal ecosystems: a case study from Lake King (Gippsland Lakes) Australia(Springer, 2008-07) Saunders, KM; Hodgson, DA; Harrison, JJ; McMinn, ASince European settlement began over 200 years ago, many southeast Australian coastal lakes and lagoons have experienced substantial human impacts, including nutrient enrichment. Present day management and conservation efforts are often hampered by a lack of data on pre-impact conditions. We used a palaeoecological approach at Lake King, Gippsland Lakes, southeast Australia in order to determine its pre-impact condition and to establish the nature and direction of subsequent environmental changes, including responses to the construction of a permanent entrance to the sea in 1889. A 120 cm sediment core was analysed for diatoms, chlorophyll a, total carbon, nitrogen and sulphur, and dated using Pb-210. Past phosphate and salinity concentrations were reconstructed using diatom-phosphate and diatom-salinity transfer functions developed from a calibration set based on 53 sites from 14 southeast Australian coastal lakes and lagoons. Results show changes in the diatom assemblage that record a shift from a brackish-water to marine diatom flora since construction of the permanent entrance. Phosphate concentrations increased at the same time and experienced major peaks in the 1940s and 1950s to > 100 mu g/l. Chlorophyll a concentrations were generally below 24 mu g/l/gTOC in the core, but there has been a clear increase since the 1980s, peaking at 120 mu g/l/gTOC, likely associated with a recorded increase in the frequency of nuisance algal blooms. These results indicate that the Lake King environment is now very different to that present during early European settlement. We conclude that by identifying the nature and direction of environmental change, palaeoecological studies can contribute towards developing realistic and well-informed management, conservation and restoration strategies in Australian coastal ecosystems. © 2008, Springer.
- ItemRecent environmental change and trace metal pollution in World Heritage Bathurst Harbour, southwest Tasmania, Australia(Springer Nature, 2013-08-22) Saunders, KM; Harrison, JJ; Butler, ECV; Hodgson, DA; McMinn, ABathurst Harbour in World Heritage southwest Tasmania, Australia, is one of the world’s most pristine estuarine systems. At present there is a lack of data on pollution impacts or long-term natural variability in the harbor. A ca. 350-year-old 210Pb-dated sediment core was analysed for trace metals to track pollution impacts from local and long-range sources. Lead and antimony increased from AD 1870 onwards, which likely reflects remote (i.e. mainland Australian and global) atmospheric pollution sources. Variability in the concentrations of copper and zinc closely followed the history of mining activities in western Tasmania, which began in the AD 1880s. Tin was generally low throughout the core, except for a large peak in AD 1989 ± 0.5 years, which may be a consequence of input from a local small-scale alluvial tin mine. Changes in diatom assemblages were also investigated. The diatom flora was composed mostly of planktonic freshwater and benthic brackish-marine species, consistent with stratified estuarine conditions. Since mining began, however, an overall decrease in the proportion of planktonic to benthic taxa occurred, with the exception of two distinct peaks in the twentieth century that coincided with periods of high rainfall. Despite the region’s remoteness, trace metal analyses revealed evidence of atmospheric pollution from Tasmanian and possibly longer-range mining activities. This, together with recent low rainfall, appears to have contributed to altering the diatom assemblages in one of the most pristine temperate estuaries in the world. © 2013 Springer Science+Business Media Dordrecht
- ItemRetreat history of the East Antarctic ice sheet since the last glacial maximum(Elsevier, 2014-09-15) Mackintosh, AN; Verleyen, E; O'Brian, PE; White, DA; Jones, RS; McKay, RM; Dunbar, R; Gore, DB; Fink, D; Post, AL; Miura, H; Leventer, A; Goodwin, ID; Hodgson, DA; Lilly, K; Crosta, X; Golledge, NR; Wagner, B; Berg, S; van Ommen, TD; Zwartz, D; Roberts, SJ; Vyverman, W; Massé, GThe East Antarctic Ice Sheet (EAIS) is the largest continental ice mass on Earth, and documenting its evolution since the Last Glacial Maximum (LGM) is important for understanding its present-day and future behaviour. As part of a community effort, we review geological evidence from East Antarctica that constrains the ice sheet history throughout this period (∼30,000 years ago to present). This includes terrestrial cosmogenic nuclide dates from previously glaciated regions, 14C chronologies from glacial and post-glacial deposits onshore and on the continental shelf, and ice sheet thickness changes inferred from ice cores and continental-scale ice sheet models. We also include new 14C dates from the George V Land – Terre Adélie Coast shelf. We show that the EAIS advanced to the continental shelf margin in some parts of East Antarctica, and that the ice sheet characteristically thickened by 300–400 m near the present-day coastline at these sites. This advance was associated with the formation of low-gradient ice streams that grounded at depths of >1 km below sea level on the inner continental shelf. The Lambert/Amery system thickened by a greater amount (800 m) near its present-day grounding zone, but did not advance beyond the inner continental shelf. At other sites in coastal East Antarctica (e.g. Bunger Hills, Larsemann Hills), very little change in the ice sheet margin occurred at the LGM, perhaps because ice streams accommodated any excess ice build up, leaving adjacent, ice-free areas relatively unaffected. Evidence from nunataks indicates that the amount of ice sheet thickening diminished inland at the LGM, an observation supported by ice cores, which suggest that interior ice sheet domes were ∼100 m lower than present at this time. Ice sheet recession may have started ∼18,000 years ago in the Lambert/Amery glacial system, and by ∼14,000 years ago in Mac.Robertson Land. These early pulses of deglaciation may have been responses to abrupt sea-level rise events such as Meltwater Pulse 1a, destabilising the margins of the ice sheet. It is unlikely, however, that East Antarctica contributed more than ∼1 m of eustatic sea-level equivalent to post-glacial meltwater pulses. The majority of ice sheet recession occurred after Meltwater Pulse 1a, between ∼12,000 and ∼6000 years ago, during a period when the adjacent ocean warmed significantly. Large tracts of East Antarctica remain poorly studied, and further work is required to develop a robust understanding of the LGM ice sheet expansion, and its subsequent contraction. Further work will also allow the contribution of the EAIS to post-glacial sea-level rise, and present-day estimates of glacio-isostatic adjustment to be refined. © 2014 The Authors. CC-BY Licence.
- 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.
- ItemWesterly 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, DAThe 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.
- 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).