Browsing by Author "Woodward, JC"

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    36Cl exposure-age chronology of Late Pleistocene glaciations on Mount Tymphi, Pindus Mountains, northwest Greece
    (International Union for Quaternary Research (INQUA), 2019-07-27) Allard, JL; Hughes, PD; Woodward, JC; Fink, D; Simon, KJ; Wilcken, KM
    The mountains of Greece and the wider Balkans were glaciated during the Pleistocene. The most extensive glaciations occurred during the Middle Pleistocene when large ice caps and glaciers formed in several ranges including the Dinaric Alps and the Pindus Mountains. The Late Pleistocene in the Balkans, however, was characterised by smaller ice masses with glaciers restricted to the highest mountains. Nevertheless, these glaciers were important in shaping much of the high mountain landscapes that we see today and they supplied many rivers with outwash sediments. Here we present preliminary results from 36Cl terrestrial cosmogenic nuclide analyses. From samples collected in summer 2017, we have calculated exposure ages from moraine boulders and glaciated bedrock in the uppermost valleys and cirques of Mount Tymphi massif (2497 m) in northwest Greece. We address both a significant geographical gap in Mediterranean glacial chronologies and the temporal gap in the glacial history of this region by targeting the previously undated Late Pleistocene glacial record. Coupled with published U-series ages from lower elevation moraines, this is the first glacial chronology in the east-central Mediterranean based on multiple dating methods. On the southwest side of the massif, 18 exposure ages obtained from 3 moraines in the cirque and mouth of the Laccos Megalon Litharion valley and the mouth of the western cirque of Tsioumako (2155 m), indicate moraine formation between 1700 m and 2050 m a.s.l. during the Late Pleistocene. This complements previous U-series ages obtained from secondary calcites in glacial sediments below 1700 m (and elsewhere in the Balkans), which demonstrate more extensive glaciations dating to the Middle Pleistocene. At ~1430 m a.s.l. in the Laccos cirque on the northeast side of the massif, 6 exposure ages (5 boulders, 1 bedrock) from a pair of end moraines represent the first dates from this side of Mount Tymphi. They suggest small cirque glaciers persisted until at least the end of the Late Pleistocene, facilitated by avalanching snow and shading from the cliffs of Goura (2467 m). Understanding where, when and why glaciers reached their maxima during the last glacial cycle is not only important for understanding the dynamics of the glacial climate in this region, but also for the timing of sediment and meltwater delivery to river systems; the dynamics of Mediterranean refugia; and has implications for understanding the environmental context of nearby Middle and Upper Palaeolithic archaeological records.
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    Ellsworth 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, JC
    Ellsworth 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.
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    Late Pleistocene glacial chronologies in the Balkans: new 36Cl exposure-age dating from Montenegro and Greece
    (Copernicus GmbH, 2020-05-04) Allard, JL; Hughes, PD; Woodward, JC; Fink, D; Simon, KJ; Wilcken, KM; Tomkins, M
    The timing and extent of mountain glaciation during the Late Pleistocene shows considerable variability around the world. Identifying the nature and timing of glaciation is important for understanding landscape evolution and changing climatic conditions (precipitation and temperature). In the Balkans, glaciers were actually larger during the Middle Pleistocene when large ice caps formed in several mountain ranges including the Dinaric Alps, Montenegro, and the Pindus Mountains, Greece. Glaciations younger than Marine Isotope Stage 6 were characterised by smaller ice masses with glaciers mainly restricted to the highest mountains. The behaviour of Late Pleistocene glaciers in this region influenced the timing of sediment and meltwater delivery to river systems; the migration of modern humans across Europe; and the dynamics of biological refugia. However, dating control is limited for Late Pleistocene glaciers in the Balkans. Here we report new in-situ 36Cl terrestrial cosmogenic nuclide exposure ages from moraine boulders sampled in the Velika Kalica valley, in the Durmitor massif, Montenegro. This valley was targeted because it contains the Debeli Namet glacier - the last remaining glacier in Montenegro. We have sampled 25 limestone boulders from 5 moraines situated down-valley of the current glacier at altitudes between 1650–2000 m. AgCl targets for 36Cl assay were prepared at The University of Manchester and 36Cl concentrations were measured on the SIRIUS 6MV accelerator at the Centre for Accelerator Science at the Australian Nuclear Science and Technology Organisation. At the last local glacial maximum, the Debeli Namet glacier extended almost 3 km beyond its current position. These 36Cl analyses are part of a wider regional Mediterranean study, totalling >50 new exposure ages, which also includes Mount Tymphi in the Pindus Mountains, NW Greece. The project will address both a significant spatial and temporal gap in Mediterranean glacial chronologies by targeting the hitherto undated Late Pleistocene glacial record. The work in Montenegro will also shed light on the nature of Holocene glaciation in the Balkans. © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 Licence.
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    Late Pleistocene glaciers in Greece: a new 36Cl chronology
    (Elsevier, 2020-10-01) Allard, JL; Hughes, PD; Woodward, JC; Fink, D; Simon, KJ; Wilcken, KM
    Glaciers formed in the highest mountains of Greece during the Late Pleistocene, but the timing of glacier maxima is poorly understood. This paper presents 27 36Cl terrestrial cosmogenic nuclide exposure ages from glacial boulders on Mount Tymphi (2497 m a.s.l., 40oN) in Epirus, northwest Greece. These ages address both a significant geographical gap in Mediterranean glacial chronologies and a temporal gap in the glacial history of this region by targeting the previously undated Late Pleistocene record. Late Pleistocene glaciers were restricted to the cirques and upper valleys of Mount Tymphi. Terminal and lateral moraines between 1700 m and 2050 m a.s.l. mark the extent of Late Pleistocene glaciers on the southern side of Mount Tymphi. Moraines marking the maximum extent of Late Pleistocene glaciation date to 29.0 ± 3.0 ka and 25.7 ± 2.6 ka, taking the oldest ages as most representative of moraine emplacement. Glaciers had retreated to the high cirques by 24.5 ± 2.4 ka during Heinrich Stadial 2. Rock glaciers formed under cold and drier conditions during this period of glacier retreat. This 36Cl dataset complements published U-series ages from secondary calcites in glacial sediments below 1700 m elevation, which demonstrate more extensive Middle Pleistocene glaciations in MIS 6 and MIS 12. A Late Pleistocene glacier maxima on Mount Tymphi at 25.7–29 ka is in good agreement with well-preserved outwash sediments dating to 24–28 ka in the Voidomatis River record downstream and is consistent with the Ioaninna basin pollen record indicating cool and wet conditions, most favourable for glacier growth, at 25–30 ka. Crown Copyright © 2020 Published by Elsevier Ltd.