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Understanding the timing of past glacial advances in Patagonia is of global climatic importance because of the insight this can provide into the influence on glacier behaviour of changes in temperature and precipitation related to the Southern Westerlies. In this paper we present new luminescence ages determined using single grains of K-feldspar from proglacial outwash sediments that were deposited by the Patagonian Ice Sheet around Lago Buenos Aires (∼46 °S), east of the contemporary Northern Patagonian Icefield. The new luminescence ages indicate that major outwash accumulations formed around ∼110 ± 20 ka to 140 ± 20 ka and that these correspond to the Moreno I and II moraine ridges, which were previously dated using cosmogenic isotope dating to 150 ± 30 ka. Luminescence dating at Lago Buenos Aires has also identified outwash sediments that were deposited during glacial advances ∼30.8 ± 5.7 ka and ∼34.0 ± 6.1 ka (MIS 3) that are not recorded in the moraine record. Younger outwash accumulations were then deposited between ∼14.7 ± 2.1 and 26.2 ± 1.6 ka which correspond to the Fenix I – V moraine ridges. The combined chronology suggests that glacial advances occurred ∼110 ± 20 ka to 150 ± 30 ka (MIS 6), ∼30.8 ± 5.7 ka to ∼34.0 ± 6.1 ka (MIS 3), and ∼14.7 ± 2.1 to 26.2 ± 1.6 ka (MIS 2) at Lago Buenos Aires. Overall luminescence dating using single grains of K-feldspar has excellent potential to contribute towards the ever-increasing geochronological dataset constraining the timings of glacial advances in Patagonia. [ABSTRACT FROM AUTHOR]

Abstract: Predicting the future response of the Antarctic Ice Sheet to climate change requires an understanding of the ice streams that dominate its dynamics. Here we use cosmogenic isotope exposure-age dating (26Al, 10Be and 36Cl) of erratic boulders on ice-free land on James Ross Island, north-eastern Antarctic Peninsula, to define the evolution of Last Glacial Maximum (LGM) ice in the adjacent Prince Gustav Channel. These data include ice-sheet extent, thickness and dynamical behaviour. Prior to ∼18 ka, the LGM Antarctic Peninsula Ice Sheet extended to the continental shelf-edge and transported erratic boulders onto high-elevation mesas on James Ross Island. After ∼18 ka there was a period of rapid ice-sheet surface-lowering, coincident with the initiation of the Prince Gustav Ice Stream. This timing coincided with rapid increases in atmospheric temperature and eustatic sea-level rise around the Antarctic Peninsula. Collectively, these data provide evidence for a transition from a thick, cold-based LGM Antarctic Peninsula Ice Sheet to a thinner, partially warm-based ice sheet during deglaciation. [Copyright &y& Elsevier]

Abstract: Ice-free areas Antarctica reveal a multi-million year history of landscape evolution, but most attention up to now has focused on the Transantarctic Mountains. The Amery Oasis in the northern Prince Charles Mountains borders the Lambert Glacier—Amery Ice Shelf System that drains 1millionkm2 of the East Antarctic Ice Sheet, and therefore provides a record of fluctuations of both local and regional ice since the ice sheet first formed in early Oligocene time. This glacial record has been deciphered by (i) geomorphological mapping from aerial photographs and on the ground, (ii) documenting the relationship between thick well-dated, uplifted glaciomarine strata and the underlying palaeolandscape, (iii) examining surficial sediment facies, and (iv) surface-exposure dating using 10Be and 26Al. The SE Amery Oasis records at least 10 million years of landscape evolution beginning with a pre-late Miocene phase of glacial erosion, followed by deposition of glaciomarine strata of the Battye Glacier Formation (Pagodroma Group) in late Miocene time. A wet-based ice sheet next expanded over the SE Amery Oasis, following which deposition of the glaciomarine Pliocene Bardin Bluffs Formation (Pagodroma Group) took place. Both formations were uplifted; by at least 500 and 200m, respectively. Their tops are characterised by geomorphological surfaces upon which intensive periglacial activity took place. Higher-level bedrock areas were subjected to deep weathering and tor-formation. Early Pleistocene time was characterised by expansion of a cold-based ice sheet across the whole area, but it left little more than patches of sandy gravel and erratic blocks. Late Pleistocene expansion of local ice (the Battye Glacier) saw deposition of moraine-mound complexes on low ground around Radok Lake and ice-dammed lake phenomena. Subglacial drainage of the lake escaped to the east exhuming the sediment-filled gorges. Holocene landscape modification has been relatively superficial. Overall, the landscape of the Amery Oasis evolved primarily under the influence of wet-based (probably polythermal) glaciers in Miocene and Pliocene times, whereas the Quaternary Period was characterised mainly by cold-based glaciers that had comparatively little impact on the landscape. [Copyright &y& Elsevier]

Abstract: High-resolution topographic surveying is traditionally associated with high capital and logistical costs, so that data acquisition is often passed on to specialist third party organisations. The high costs of data collection are, for many applications in the earth sciences, exacerbated by the remoteness and inaccessibility of many field sites, rendering cheaper, more portable surveying platforms (i.e. terrestrial laser scanning or GPS) impractical. This paper outlines a revolutionary, low-cost, user-friendly photogrammetric technique for obtaining high-resolution datasets at a range of scales, termed ‘Structure-from-Motion’ (SfM). Traditional softcopy photogrammetric methods require the 3-D location and pose of the camera(s), or the 3-D location of ground control points to be known to facilitate scene triangulation and reconstruction. In contrast, the SfM method solves the camera pose and scene geometry simultaneously and automatically, using a highly redundant bundle adjustment based on matching features in multiple overlapping, offset images. A comprehensive introduction to the technique is presented, followed by an outline of the methods used to create high-resolution digital elevation models (DEMs) from extensive photosets obtained using a consumer-grade digital camera. As an initial appraisal of the technique, an SfM-derived DEM is compared directly with a similar model obtained using terrestrial laser scanning. This intercomparison reveals that decimetre-scale vertical accuracy can be achieved using SfM even for sites with complex topography and a range of land-covers. Example applications of SfM are presented for three contrasting landforms across a range of scales including; an exposed rocky coastal cliff; a breached moraine-dam complex; and a glacially-sculpted bedrock ridge. The SfM technique represents a major advancement in the field of photogrammetry for geoscience applications. Our results and experiences indicate SfM is an inexpensive, effective, and flexible approach to capturing complex topography. [Copyright &y& Elsevier]

In recent years luminescence dating has increasingly been applied to date glaciofluvial sediments, but uncertainties about the degree of bleaching of the luminescence signal at deposition make dating of such sediments challenging. Here we test a new approach for luminescence dating of glaciofluvial sediments, based on the analysis of rock cores drilled from granite cobbles, and compare the luminescence ages generated against independent age control. Luminescence measurements from rock slices in cobble-sized clasts can be used to reconstruct the extent of bleaching, thereby giving greater confidence in the ages produced. This study illustrates that another important advantage of using cobbles is that at depths of 2 mm or more below the cobble surface >90% of the total dose rate arises from the cobble itself, making the dose rate insensitive to the water content of the sediment matrix. Ordinarily, uncertainties in estimating water content during burial are one of the largest sources of uncertainty in luminescence dating methods, and hence reducing the reliance upon the dose rate could be particularly advantageous for glacial deposits, where water contents can potentially be large and highly variable. Measurements of cobbles from Orrisdale Head, Isle of Man, demonstrate that the luminescence signal was completely bleached to depths of up to 12 mm into the cobble. Sampling of orientated cobbles from lithofacies diagnostic of bar-top environments was used to maximise the chances of exposure to sunlight. The upper-faces of these orientated cobble surfaces appear to be bleached to a greater depth than the lowermost faces. Data from 45 rock slices from these cobbles were tightly clustered, yielding a mean age of 20.7 ± 0.3 ka that is in agreement with independent age control. One of the well-bleached cobbles shows evidence of two discrete exposure events, potentially recording both the advance at 26.2 ± 0.8 ka, and retreat at 20.7 ± 0.3 ka, of the Irish Sea Ice Stream. [ABSTRACT FROM AUTHOR]