Browsing by Author "Storey, BC"

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    A 2 million year glacial chronology of the Hatherton Glacier, Antarctica and implications for the size of the East Antarctic Ice Sheet at the Last Glacial Maximum
    (Pergamon-Elsevier Science Ltd, 2014-01-01) Joy, K; Fink, D; Storey, BC; Atkins, C
    A series of distinct glacial deposits flanking the margins of the upper Hatherton Glacier, an outlet glacier in the central Transantarctic Mountains, are used to constrain the behaviour of the Antarctic ice-sheets. Cosmogenic exposure ages of 18 erratics from four glacial drifts covering the ice free Dubris and Bibra valleys, range in age from 5 to 1997 ka. Our results document four glacial advance and retreat events superimposed on an overall long-term ice thickness reduction of about 500 m since the mid-Pleistocene. The lack of field evidence and absence of LGM exposure ages in the glacial deposits of the Hatherton Glacier supports our conclusion that at the LGM the East Antarctic Ice Sheet was of similar size, or may have been slightly smaller, than present. Minimum exposure ages from the oldest two glacial events, represented by the Isca and Danum drifts, are similar to 1-2 Ma and similar to 0.5 Ma respectively. The Britannia-II Drift, previously assumed to mark the maximum extent of the Last Glacial Maximum advance, has a mean Be-10 age of 126 +/- 3.2 ka (n = 5). Ages from the younger Britannia-I Drift suggest that since the mid-Holocene (6.5 +/- 1.2 ka, n = 5), approximately 200 m of additional ice has been lost. © 2014, Elsevier Ltd.
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    Constraints on ice volume changes of the WAIS and Ross Ice Shelf since the LGM based on cosmogenic exposure ages in the Darwin-Hatherton glacial system of the Transantarctic Mountains
    (Copernicus Publications, 2010-05-02) Fink, D; Storey, BC; Hood, D; Joy, K; Shulmeister, J
    Quantitative assessment of the spatial and temporal scale of ice volume change of the West Antarctic ice sheet (WAIS) and Ross Ice Shelf since the last glacial maximum (LGM) ~20 ka is essential to accurately predict ice sheet response to current and future climate change. Although global sea level rose by approximately 120 metres since the LGM, the contribution of polar ice sheets is uncertain and the timing of any such contribution is controversial. Mackintosh et al (2007) suggest that sectors of the EAIS, similar to those studied at Framnes Mountains where the ice sheet slowly calves at coastal margins, have made marginal contributions to global sea-level rise between 13 and 7 ka. In contrast, Stone et al (2003) document continuing WAIS decay during the mid-late Holocene, raising the question of what was the response of the WAIS since LGM and into the Holocene. Terrestrial evidence is restricted to sparse coastal oasis and ice free mountains which archive limits of former ice advances. Mountain ranges flanking the Darwin-Hatherton glaciers exhibit well-defined moraines, weathering signatures, boulder rich plateaus and glacial tills, which preserve the evidence of advance and retreat of the ice sheet during previous glacial cycles. Previous studies suggest a WAIS at the LGM in this location to be at least 1,000 meters thicker than today. As part of the New Zealand Latitudinal Gradient Project along the Transantarctic, we collected samples for cosmogenic exposure dating at a) Lake Wellman area bordering the Hatherton Glacier, (b) Roadend Nunatak at the confluence of the Darwin and Hatherton glaciers and (c) Diamond Hill which is positioned at the intersection of the Ross Ice Shelf and Darwin Glacier outlet. While the technique of exposure dating is very successful in mid-latitude alpine glacier systems, it is more challenging in polar ice-sheet regions due to the prevalence of cold-based ice over-riding events and absence of outwash processes which removes glacially transported debris. Our glacial geomorphic survey from ice sheet contact edge (~850 masl) to mountain peak at 1600 masl together with a suite of 10Be and 26Al exposure ages, documents a pre-LGM ice volume at least 800 meters thicker than current ice levels which was established at least 2 million years ago. However a complex history of exposure and re-exposure of the ice free regions in this area is seen in accordance with advance and retreat of the ice sheets that feeds into the Darwin –Hatherton system. A cluster of mid-altitude boulders, located below a prominent moraine feature mapped previously as demarcating the LGM ice advance limits, have exposure ages ranging from 30 to 40 ka. Exposure ages for boulders just above the ice contact range from 1to 19 ka and allow an estimate of inheritance. Hence, we conclude that LGM ice volume was not as large as previously estimated and actually little different from what is observed today. These results raise rather serious questions about the implications of a reduced WAIS at the LGM, its effect on the development of the Ross Ice Shelf, and how the Antarctic ice sheets respond to global warming.
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    Cosmogenic 10Be ages from the Meirs and Garwood Valleys, Denton Hills, West Antarctica, suggest an absence in LGM Ice Sheet expansion
    (EGU General Assembly, 2014-04-27) Fink, D; Joy, K; Carson, N; Storey, BC
    It has been hypothesised that during interglacials, thinning of the Ross Ice Shelf allowed a more open water environment with increased local precipitation. This resulted in outlet glaciers, which drain the Transantarctic Mountains and fed by the East Antarctic Ice Sheet, advancing during moist warmer periods, apparently out of phase with colder arid dry periods. Significantly the ice core record during these warm periods also shows increased accumulation continent wide The geomorphology of the Denton Hills in the Royal Society Range, West Antarctica, is a result of Miocene fluvial incision reworked by subsequent glacial advances throughout the Quaternary. The Garwood and Miers glacial valleys drain ice across the Denton Hills into the Shelf, and should thus show maximum extent during interstadials. To understand the chronology of late Quaternary glaciations, 15 granitic boulders from terminal moraines were sampled for 10Be and 26Al cosmogenic dating. Obtaining reliable exposure ages of erratics within moraines that represent timing of deposition (i.e. glacial advances) is problematic in polar regions, where glacial activity is principally controlled by ice sheet dynamics. Recycling of previously exposed debris, uncertainty in provenance of glacially transported boulders and a lack of a post-depositional hydrologic process to remove previously exposed material from a valley system, leads to ambiguities in multiple exposure ages from a single coeval glacial landform. More importantly, cold-based ice advance can leave a landform unmodified resulting in young erratics deposited on bedrock that shows weathering and/or inconsistent age-altitude relationships. Primarily, inheritance becomes a difficulty in qualifying exposure ages from polar regions. Preliminary results from the Garwood and Miers Valleys indicate that glaciers in the Denton Hills had begun to retreat from their last maximum positions no later than 23-37 ka, and thus the local last glacial maximum occurred prior to the Antarctic LGM (18-22 ka). No evidence based on cosmogenic ages for post-LGM or Holocene advances were found. These results support an extensive exposure age data set from the nearby Darwin-Hatherton Glacier system that indicates an absence of EAIS expansion across the Transantarctic Mnts during the global LGM period.
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    Cosmogenic evidence for limited local LGM glacial expansion, Denton Hills, Antarctica
    (Elsevier, 2017-12-15) Joy, K; Fink, D; Storey, BC; De Pascale, GP; Quigley, M; Fujioka, T
    The geomorphology of the Denton Hills provides insight into the timing and magnitude of glacial retreats in a region of Antarctica isolated from the influence of the East Antarctic ice sheet. We present 26 Beryllium-10 surface exposure ages from a variety of glacial and lacustrine features in the Garwood and Miers valleys to document the glacial history of the area from 10 to 286 ka. Our data show that the cold-based Miers, Joyce and Garwood glaciers retreated little since their maximum positions at 37.2 ± 6.9 (1σ n = 4), 35.1 ± 1.5 (1σ, n = 3) and 35.6 ± 10.1 (1σ, n = 6) ka respectively. The similar timing of advance of all three glaciers and the lack of a significant glacial expansion during the global LGM suggests a local LGM for the Denton Hills between ca. 26 and 51 ka, with a mean age of 36.0 ± 7.5 (1σ, n = 13) ka. A second cohort of exposure ages provides constraints to the behaviour of Glacial Lake Trowbridge that formerly occupied Miers Valley in the late Pleistocene. These data show active modification of the landscape from ∼20 ka until the withdrawal of ice from the valley mouths, and deposition of Ross Sea Drift, at 10–14 ka. © 2017 Elsevier Ltd.
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    Cosmogenic nuclide exposure age constraints on the glacial history of the Lake Wellman area, Darwin Mountains, Antarctica
    (Cambridge University Press, 2010-12) Storey, BC; Fink, D; Hood, D; Joy, K; Shulmeister, J; Riger-Kusk, M; Stevens, MI
    We present direct terrestrial evidence of ice volume change of the Darwin and Hatherton glaciers which channel ice from the Transantarctic Mountains into the Ross Ice Shelf. Combining glacial geomorphology with cosmogenic exposure ages from 25 erratics indicates a pre-LGM ice volume at least 600 m thicker than current Hatherton ice elevation was established at least 2.2 million years ago. In particular, five erratics spread across a drift deposit at intermediate elevations located below a prominent moraine feature mapped previously as demarcating the LGM ice advance limits, give a well-constrained single population with mean 10Be age of 37.0 ± 5.5 ka (1σ). At lower elevations of 50–100 m above the surface of Lake Wellman, a further five samples from within a younger drift deposit range in exposure age from 1 to 19 ka. Our preferred age model interpretation, which is partly dependent on the selection of a minimum or maximum age-elevation model, suggests that LGM ice volume was not as large as previously estimated and constrains LGM ice elevation to be within ± 50 m of the modern Hatherton Glacier ice surface, effectively little different from what is observed today. © 2010, Cambridge University Press
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    Darwin / Hatherton glacial system: preliminary results of geomorophological mapping and cosmogenic sampling in 2009/10.
    (University of Canterbury, 2010-07-05) Joy, K; Atkins, C; Storey, BC; Fink, D
    The role that Antarctica played in post-glacial global sea level rise and the configuration of the LGM ice margins are poorly understood and are the subject of much debate. The Darwin / Hatherton Glacial System (79.5° S, 158° E) in the Transantarctic Mountains contains an important archive of glacial recession during this period in the form of well-preserved glacial landforms. These represent the former extent of ice masses and have been previously used to support numeric models of Antarctic ice volume. By using this glacial system as a proxy for the East and West Antarctic Ice Sheets, the timing and magnitude of the LGM recession can be quantified. In situ cosmogenic nuclide dating combined with detailed geomorphological mapping of glacial landforms is being used at a number of sites along the downstream profile of the glaciers to create isochronous surfaces. These represent the ice sheet margins post LGM. Aluminum-26 and Beryllium-10 are two common radionuclides produced within quartz from the interaction of high energy cosmic particles with atoms of Oxygen and Silicon in the rocks. The production rate of these nuclides is known under given conditions, allowing an “exposure” age to be calculated based on their measured concentration. As the age of various glacial landforms and the retreat of ice can be correlated, cosmogenic dating allows the temporal and spatial distribution of ice to be analysed. During the 2009/10 field season, a series of well preserved moraines was mapped and several cosmogenic sampling transects were carried out in the Dubris/Bibra valleys area on the southern side of the Hatherton Glacier. This work confirmed the general distribution of known drift sheets and moraines mapped by Bockheim et al (1989) but also recognised that cold based glaciers have produced a subtle and complex glacial record due to simultaneous deposition and /or reworking of some drifts and in some cases protection and preservation of relict surfaces. These previously unrecognised cold based glacial events have significant implications for interpreting cosmogenic ages of deposits and glacial history of the area. The use of cosmogenic dating viewed through the lens of cold based ice will provide new data about the size and behaviour of the Antarctic ice sheets. Combined with numeric modelling, a new understanding of how Antarctica reacted to a warming climate post LGM may be gained. This in turn may lead to predictions of ice sheet response to current and future climate change and its effect on sea level rise.
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    Diamond Hill, Darwin Glacier. A proxy for the West Antarctic ice sheet?
    (Australasian Quaternary Association, 2010-07-16) Joy, K; Storey, BC; Fink, D; Shulmeister, J
    In the Ross Sea embayment during the Last Glacial Maximum (LGM, 18-22ka), the grounding line of the West Antarctic Ice Sheet (WAIS) advanced northwards into the Ross Ice Shelf (RIS). This effectively dammed the drainage of the Transantarctic Mountain outlet glaciers and caused significant downstream thickening of their glacier profiles (Conway et al 1999). The Darwin / Hatherton Glacial System (79.5° S, 158° E) provides a number of sites that contain geological evidence of WAIS fluctuations. Previous geomorphic and pedological studies in the area (Bockheim et al. 1989, Denton & Hughes 2000) have used these sites to constrain the timing and magnitude of the LGM ice sheet advances. As Diamond Hill lies at the confluence of the Darwin Glacier and RIS its glacial geomorphology should reflect the thickening caused by the advancing WAIS. Insitu cosmogenic nuclide dating has being used at sites along the Darwin/Hatherton as a proxy to recreate the timing and magnitude of both WAIS and EAIS advances. By measuring the concentrations of Beryllium-10 and Aluminium-26 in quartz rich lithologies, the time since the deposition of a moraine can be calculated. Early interpretations based on cosmogenic ages from the Lake Wellman area (Fink et al 2009, Storey, et al. 2010) show up to 800 meters of thickened ice approximately 2 million years ago. Moraines previously assumed to be the limit of LGM ice expansion, date to 30-40 ka. This suggests that while early EAIS Quaternary expansion was large; ice volume at the LGM may be little changed from the present. Two transects were sampled on Diamond Hill that cover an altitude range of 1100 meters. Preliminary 10Be cosmogenic dates show a similar trend to that seen further up glacier in Lake Wellman, in the case of Diamond Hill the WAIS was approximately 900 meters thicker than the current Rose Ice Shelf configuration at ~1.5Ma and with only small advances in the last 10ka. As with Lake Wellman no evidence of large scale LGM advances were found.
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    Diamond Hill, Darwin Glacier. A proxy for the West Antarctic ice sheet?
    (University of Canterbury, 2010-07-05) Joy, K; Storey, BC; Fink, D; Shulmeister, J
    In the Ross Sea embayment during the Last Glacial Maximum (LGM, 18-22ka), the grounding line of the West Antarctic Ice Sheet (WAIS) advanced northwards into the Ross Ice Shelf (RIS). This effectively dammed the drainage of the Transantarctic Mountain outlet glaciers and caused significant downstream thickening of their glacier profiles (Conway et al 1999). The Darwin / Hatherton Glacial System (79.5° S, 158° E) provides a number of sites that contain geological evidence of WAIS fluctuations. Previous geomorphic and pedological studies in the area (Bockheim et al. 1989, Denton & Hughes 2000) have used these sites to constrain the timing and magnitude of the LGM ice sheet advances. As Diamond Hill lies at the confluence of the Darwin Glacier and RIS its glacial geomorphology should reflect the thickening caused by the advancing WAIS. Insitu cosmogenic nuclide dating has being used at sites along the Darwin/Hatherton as a proxy to recreate the timing and magnitude of both WAIS and EAIS advances. By measuring the concentrations of Beryllium-10 and Aluminium-26 in quartz rich lithologies, the time since the deposition of a moraine can be calculated. Early interpretations based on cosmogenic ages from the Lake Wellman area (Fink et al 2009, Storey, et al. 2010) show up to 800 meters of thickened ice approximately 2 million years ago. Moraines previously assumed to be the limit of LGM ice expansion, date to 30-40 ka. This suggests that while early EAIS Quaternary expansion was large; ice volume at the LGM may be little changed from the present. Two transects were sampled on Diamond Hill that cover an altitude range of 1100 meters. Preliminary 10Be cosmogenic dates show a similar trend to that seen further up glacier in Lake Wellman, in the case of Diamond Hill the WAIS was approximately 900 meters thicker than the current Rose Ice Shelf configuration at ~1.5Ma and with only small advances in the last 10ka. As with Lake Wellman no evidence of large scale LGM advances were found.
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    Glacial geomorphology and its links to ice sheet thicknesses, Diamond Hill, Transantarctic Mountains.
    (GNS Science, 2009-07-03) Joy, K; Storey, BC; Fink, D; Shulmeister, J
    An understanding of how the Antarctic continent has reacted to past climates is necessary to accurately predict the response of its ice sheets to current and future climate changes. The thickness and proximity of the peripheral ice to the continental margin are key to the discussion and relate directly to the volume of ice within the East and West Antarctica ice sheets and their melt water contribution to sea level rise since the LGM. The Darwin/Hatherton is an outlet glacial system that drains the East Antarctic Ice Sheet into the Ross Sea through the Transantarctic Mountains. At the confluence of the Darwin Glacier and Ross Ice Shelf, Diamond Hill a relatively ice free area, contains evidence of glacial advances at altitudes up to 850m above the current ice surface. Here both ice sheets have created landforms that will allow a reconstruction of ice thickness. Cosmogenic dating will be used to create a timeline of post-LGM glacial retreat in which the influence of cold based ice must also be evaluated. This work will contribute fundamental data to an important international debate on the scale of the glaciation in the last ice age. It will help validate ice thickness reconstructions for the ice sheets and it may give insight into the timing and nature of Antarctic contributions to global sea-levels.
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    Size of the West Antarctic ice sheet at the last glacial maximum: new constraints from the Darwin-Hatherton glacial system in the Transantarctic Mountains
    (University of Auckland, 2009-07-01) Storey, BC; Hood, D; Fink, D; Shulmeister, J; Riger-Kusk, M
    An understanding of how the Antarctic ice sheet has reacted to natural global warming since the last glacial maximum (LGM) 18 to 22 thousand years ago (kya) is essential to accurately predict the response of the ice sheets to current and future climate change. Although global sea level rose by approximately 120 metres since the LGM, the contribution from and rate of change of the Antarctic ice sheets is by no means certain. Mackintosh et al (2007) have suggested that the East Antarctic Ice Sheet (EAIS) made an insignificant contribution to global sea-level rise between 13 and 7 kya raising interesting questions about the initial extent and response of the West Antarctic Ice Sheet (WAIS) during that time frame. Terrestrial evidence of these changes is restricted to a few ice-free areas where glacial landforms, such as moraines, show the extent of former ice advances. One such area is the Darwin-Hatherton glacial system where spectacular moraines preserve the advance and retreat of the glacial system during previous glacial cycles. Previous researchers have suggested that the WAIS was more than 1000 metres thicker than it is today at this location at the LGM. As part of the Latitudinal Gradient Project, we mapped the moraines of the Lake Wellman area bordering the Hatherton Glacier and collected samples for cosmogenic nuclide dating, a technique that is widely used to calculate the exposure history of the glacial landscape and the amount of time that the glacial debris has been exposed to cosmic rays and not covered by ice or other glacial debris. While the technique is very successful in mid latitudes, it is more challenging in Polar Regions. Our mapping has shown that ice in the past was at least 800 metres thicker than current ice levels in this area. Our cosmogenic data suggest that this was at least 2 million years ago but for the most part our data record, as expected, a complex history of exposure and re exposure of the ice free regions in this area in accordance with advance and retreat of the ice sheets. However, a cluster of ages of 35 to 40 thousand years record a single exposure event and indicate that the ice in this area was not as thick as previous estimates for the extent of ice at the LGM. These ages are recorded from moraine boulders that are located below a prominent moraine feature mapped as representing the LGM. These results raise further questions about the size of the Antarctic ice sheets at the LGM, their contribution to global sea level change and how the Antarctic ice sheets respond to global warming.