Browsing by Author "Wilson, GS"

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    Antiphase dynamics between cold-based glaciers in the Dry Valleys region and ice extent in the Ross Sea, Antarctica during MIS 5
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Anderson, JTH; Fink, D; Fujioka, T; Wilson, GS; Wilcken, KM; Abramov, A; Demidov, N
    During interglacial conditions in Marine Isotope Stage (MIS) 5, outlet and alpine glaciers in the Dry Valleys region, Antarctica, appear to have advanced in response to increased open ocean in the Ross Sea. However, the timing and extent of antiphase behaviour between these glaciers and ice in the Ross Sea is poorly resolved. Here, we report the antiphase behaviour through retreat of a peripheral lobe of Taylor Glacier in Pearse Valley, an area that was glaciated during MIS 5. First, we measured cosmogenic ¹⁰ Be and ²⁶ Al in 3 granite cobbles from thin, patchy drift (Taylor 2 Drift) in Pearse Valley to constrain the timing of retreat of Taylor Glacier. Assuming simple continuous exposure, our exposure ages suggest Taylor Glacier had partially retreated from Pearse Valley no later than 71 ka. Timing of retreat after 71 ka, until the Last Glacial Maximum (LGM), when Taylor Glacier was at a minimum position, remains unresolved. Second, we measured paired ¹⁰ Be and ²⁶ Al depth profiles to ~3 metres in permafrost in proximity to the cobble sampling sites at Pearse Valley and neighbouring Lower Wright Valley. The ¹⁰ Be and ²⁶ Al depth profiles from both sites show no clear exponential attenuation trend which suggest that both deposits are too young for the most recent exposure (≥71 ka for Pearse Valley and LGM – early Holocene for Lower Wright Valley) to alter the profile, and measured nuclide concentrations are essentially dominated by inheritance. Using ¹⁰ Be depth profile data from Pearse Valley we calculate a maximum age of ~100 ka for surface layer permafrost formation. The cobble exposure-ages and depth profile constrain surface permafrost formation in Pearse Valley to between ~71 – 102 ka, following the retreat of the Taylor Glacier from Pearse Valley. These new data are consistent with geochronology from central Taylor Valley, and suggest changes in moisture delivery over Taylor Dome during MIS 5c and 5a appear to be associated with the extent of the Ross Ice Shelf and sea ice in the Ross Sea. Our ²⁶ Al/¹⁰ Be concentration ratios for all depth profile samples also exhibit relatively constant and suppressed ratios of 4.3 and 5.2 for Pearse and Wright valleys, respectively, indicating that prior to surface permafrost formation, these sediments experienced a significant complex prior exposure history. Assuming a simple burial scenario, the observed ²⁶ Al/¹⁰ Be ratios are equivalent to a total exposure-burial history of ~1.2 Ma, somewhat consistent with the Packard dune field in Victoria Valley. Our new data corroborate antiphase behaviour between outlet and alpine glaciers in the Dry Valleys region and ice extent in the Ross Sea, and imply a causal mechanism with cold-based glacier advance and retreat being controlled by moisture availability and drying, respectively due to ice retreat and expansion in the Ross Sea. © The Authors
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    Cosmogenic nuclides constrain surface fluctuations of an East Antarctic outlet glacier since the Pliocene
    (Elsevier, 2017-12-05) Jones, JS; Norton, KP; Mackintosh, AN; Anderson, JTH; Kubik, P; Vockenhuber, C; Wittmann, H; Fink, D; Wilson, GS; Golledge, NR; McKay, RM
    Understanding past changes in the Antarctic ice sheets provides insight into how they might respond to future climate warming. During the Pliocene and Pleistocene, geological data show that the East Antarctic Ice Sheet responded to glacial and interglacial cycles by remaining relatively stable in its interior, but oscillating at its marine-based margin. It is currently not clear how outlet glaciers, which connect the ice sheet interior to its margin, responded to these orbitally-paced climate cycles. Here we report new ice surface constraints from Skelton Glacier, an outlet of the East Antarctic ice sheet, which drains into the Ross Ice Shelf. Our multiple-isotope (10Be and 26Al) cosmogenic nuclide data indicate that currently ice-free areas adjacent to the glacier underwent substantial periods of exposure and ice cover in the past. We use an exposure-burial model driven by orbitally-paced glacial–interglacial cycles to determine the probable ice surface history implied by our data. This analysis shows that: 1) the glacier surface has likely fluctuated since at least the Pliocene; 2) the ice surface was >200 m higher than today during glacial periods, and the glacier has been thicker than present for ∼75–90% of each glacial–interglacial cycle; and 3) ice cover at higher elevations possibly occurred for a relatively shorter time per Pliocene cycle than Pleistocene cycle. Our multiple-nuclide approach demonstrates the magnitude of ice surface fluctuations during the Pliocene and Pleistocene that are linked to marine-based ice margin variability. © 2017 Elsevier B.V.
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    Defining past volume of grounded ice in the Ross Sea
    (Geological Society of New Zealand, 2009-11-26) Lilly, K; Wilson, GS; Fink, D; Levy, R; Mifsud, C
    A large portion of global sea-level increase over the last glacial cycle is believed to originate from reduction in the volume of West Antarctic ice including ice grounded across the Ross Sea. The evidence for this comes from observation of glacigene sediments in the Ross Embayment, both onshore and offshore, indicating a much greater ice extent in the past. However, much of this evidence is not dated directly. Marine geophysical surveys show that the Antarctic Ice Sheet did in many locations ground out to the continental shelf edge, but it is not clear whether this happened at the Last Glacial Maximum. On land, our understanding of former ice extent in the Ross Sea region comes primarily from a glacial sedimentary deposit known as the Ross Sea Drift. The limit of these sediments has been used to define the volume of grounded ice in the Ross Sea and by further inference in the adjacent West Antarctic, representing an ice volume of some 9 million km3, or 14 m sea level equivalent. However, the Ross Sea Drift is defined by common processes and facies rather than as a time restricted unit and conflicting interpretations from different locations suggest different timing and different ice configurations. The geographic area of the southern McMurdo Ice Shelf (between Black Island, Minna Bluff and Mount Discovery) is identified as a location where the reconstructions are in greatest conflict. We present new constraints on the age of formation of these moraines from the application of cosmogenic exposure dating on 16 sandstone erratics collected from moraines on the flanks of Minna Bluff and Mount Discovery. These ice shelf marginal moraines have traditionally been included in the Ross Sea Drift. The sandstone erratics themselves are ideal targets for exposure dating as they include large blocks (> 1 m) that sit proud of the surrounding drift, they are quartz rich and are from an Eocene formation for which there is no known outcrop. While the origin of the erratics is not confirmed, each of the available reconstructions infers them to have been exhumed by advancing ice grounded in the Ross Sea. Thus we can assume that their exposure age relates to glacial erosion and deposition.
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    Ice surface lowering of Skelton Glacier, Transantarctic Mountains, since the Last Glacial Maximum: implications for retreat of grounded ice in the western Ross Sea
    (Elsevier, 2020-06-01) Anderson, JTH; Wilson, GS; Jones, RS; Fink, D; Fujioka, T
    Quantifying the contribution of the East Antarctic Ice Sheet (EAIS) to sea-level rise during the last deglaciation is complicated by the limited opportunities to constrain ice-sheet models. The nunatak, Escalade Peak, provides a gauge for past ice surface elevation changes and behaviour throughout the last glacial cycle. Geomorphological mapping, geological evidence and 10Be cosmogenic-nuclide exposure dating at Escalade Peak, provide new constraints on the ice surface history of the Skelton Névé since the Last Glacial Maximum (LGM). An elevation transect from the eastern margin of Escalade Peak indicates that the ice surface of the Skelton Névé was at least 50 m and perhaps >120 m higher than present during the LGM. In contrast, surface-exposure ages from a suite of inner moraines (blue-ice moraines) adjacent to Escalade Peak do not provide independent ice surface elevation constraints, but may provide an indirect constraint on the timing of thinning due to exhumation-ablation processes. Maximum simple exposure ages from the inner moraines suggest ice surface ablation was initiated by 19.2 ka, but the majority of ice surface lowering at Escalade Peak likely occurred after ∼15 ka and reached the present-day ice level at ∼6 ka. These findings suggest that slow flowing inland sites of EAIS outlet glaciers, such as southern Skelton Névé, experienced minimal ice surface elevation change since the LGM and record an EAIS outlet glacier and western Ross Sea retreat signature rather than widespread Ross Sea retreat. The ice surface lowering is likely to have been in response to retreat of the grounded ice in the western Ross Embayment causing a reduction in buttressing of the Skelton Glacier and draw down into the Ross Sea. © 2020 Elsevier Ltd.
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    Late glacial and Holocene climate change in the subantarctic Auckland Islands
    (American Geophysical Union (AGU), 2017-12-14) Gilmer, G; Moy, CM; Vandergoes, MJ; Gadd, PS; Riesselman, CR; Jacobsen, GE; Wilson, GS; Visinand, C
    Situated within the core of the Southern Hemisphere westerly winds, and between the subtropical and subantarctic fronts, the New Zealand subantarctic islands are uniquely positioned to evaluate past ocean and atmospheric change in the middle to high southern latitudes. We collected a series of sediment cores from Auckland Island fjords to produce a high-resolution record of climate change following the Last Glacial Maximum. Physical property and organic geochemical data, Itrax XRF, and visual core descriptions indicate the cores capture several phases of sedimentation. From these studies, we identify four primary sedimentary facies: 1) a deglacial facies exhibiting mm-scale laminae defined by magnetic susceptibility and density contrasts and high counts of elements associated with terrigenous sources; 2) a lacustrine facies defined by very low density, high organic carbon concentrations and low counts of lithophilic elements; 3) a marine transgression facies with moderate density, moderate bioturbation and alternating marine and lacustrine sedimentary components; 4) a marine facies that contains biogenic carbonate. Radiocarbon results indicate deglacial sedimentation was underway in the basin by approximately 19,000 cal yr BP. Lacustrine deposition in ice-free conditions began around 15,600 cal yr BP and continued until marine transgression at approximately 9,500 cal yr BP. During the early Holocene between 11 and 9.5 ka, we observe elevated n-alkane δD values and an overall increase in redox-sensitive elements that signal a combination of warmer atmospheric temperatures and reduced westerly wind strength that drives fjord stratification. Poleward-shifted westerlies south of the Auckland Islands could accommodate these results, but there are few records to corroborate this interpretation. We will discuss these results within the context of developing New Zealand and subantarctic paleoclimate records in order to provide a more comprehensive record of past change.
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    Late Pleistocene and Holocene climate and environmental evolution of a subantarctic fjord ingression basin in the southwest Pacific
    (Elsevier, 2021-02-01) Greer, G; Moy, CM; Riesselman, CR; Vandergoes, MJ; Jacobsen, GE; Gorman, AR; Tidey, EJ; Wilson, GS
    Subantarctic islands are located at a critical latitude for reconstructing past changes in ocean-atmosphere interactions. Currently, there is a lack of high-resolution records from the Pacific sector of the Southern Ocean that can be used to reconstruct climate since the Last Glacial Maximum (LGM). Here, we present a reconstruction of environmental change from a fjord ingression basin at New Zealand’s subantarctic Auckland Islands (50.5°S) over the last ∼19 ka cal BP. Using sedimentological and geochemical analysis of cores collected along a depth transect in Norman Inlet we find evidence for four different stages of environmental history: deglacial, lacustrine, marine transgression, and marine. Glaciers retreated from their maximum extent before 19.4 ka cal BP during a period of ice retreat that appears synchronous across the Pacific basin, likely due to southward migration of the Subtropical Front. However, in contrast to other glaciated regions, we see no evidence for ice re-advance, and a proglacial lake was present in the basin until 15.7 ka cal BP. Following deglaciation, organic-rich sedimentation dominated the lacustrine environment until post-glacial sea-level rise flooded the depositional basin at 8.8 ka cal BP. Deposition of organic-rich sediment continued during the Antarctic Cold Reversal and we find no evidence for a glacial re-advance. Mixing of terrestrial and marine organic matter during the marine transgression (8.8–6.7 ka cal BP) indicates significant erosion and re-working of sediment in the catchment as seawater overtopped the sill. Modern fjord circulation commenced ∼6.7 ka cal BP when sea level reached its maximum in the early Holocene. This well-dated, high-resolution record constrains the timing of deglaciation, sea-level rise, and subantarctic environmental change following the LGM that expands our understanding of the key drives of climate change in the middle to high southern latitudes. © 2020 Elsevier Ltd.
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    Reconciling marine and terrestrial evidence for post LGM ice sheet retreat in southern McMurdo Sound, Antarctica
    (Elsevier, 2017-02-01) Anderson, JTH; Wilson, GS; Fink, D; Lilly, K; Levy, RH; Townsend, D
    Retreat of the Antarctic ice sheets since the Last Glacial Maximum (LGM) contributed to sea-level rise, but the location, amount, and timing of ice mass loss has been controversial. This paper presents new 10Be exposure ages from glacially transported erratics which record post LGM retreat of grounded ice in the western Ross Sea. Ice elevation in southern McMurdo Sound was ≥520 m above present day sea level on the eastern side of Mount Discovery during the LGM, and the onset of major deglaciation in the region was after 14 ka. The ice surface lowered from ∼520 to 234 m above present day sea level between 14.0 ka and 10.3 ka and from 234 m to ∼30 m between 10.3 ka and 7.4 ka. This late-glacial and Holocene deglaciation chronology from southern McMurdo Sound is consistent with other records on the margins of the Ross Embayment, and implies that the western margins of the Ross Sea Ice Sheet (RSIS) experienced most mass loss during the early to middle Holocene. These 10Be exposure ages coupled with sediment provenance define a two-stage ice flow scenario for McMurdo Sound subdividing differing reconstructions into an early and late phase. Prior to Termination I, an expanded Koettlitz Glacier flowed north and northeast between Brown Peninsula and Mount Discovery and coalesced with northward flowing ice fed from the Skelton and Mulock Glaciers. Thinning and retreat of the Koettlitz Glacier and perhaps other outlet glaciers flowing through the Royal Society Range allowed ice grounded in the Ross Sea to flow westward and northward, north of Brown Peninsula. Grounding-line recession in the Ross Sea during the late-glacial and Holocene was likely driven by Southern Ocean warming and sea-level rise from the retreat of the Northern Hemisphere ice sheets and the outer margins of the Antarctic ice sheets.© 2016 Elsevier Ltd.