| 1. |
- Blomdin, Robin, et al.
(författare)
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Evaluating the timing of former glacier expansions in the Tian Shan : A key step towards robust spatial correlations
- 2016
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 153, s. 78-96
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Tidskriftsartikel (refereegranskat)abstract
- The timing of past glaciation across the Tian Shan provides a proxy for past climate change in this critical area. Correlating glacial stages across the region is difficult but cosmogenic exposure ages have considerable potential. A drawback is the large observed scatter in Be-10 surface exposure data. To quantify the robustness of the dating, we compile, recalculate, and perform statistical analyses on sets of 10Be surface exposure ages from 25 moraines, consisting of 114 new and previously published ages. We assess boulder age scatter by dividing boulder groups into quality classes and rejecting boulder groups of poor quality. This allows us to distinguish and correlate robustly dated glacier limits, resulting in a more conservative chronology than advanced in previous publications. Our analysis shows that only one regional glacial stage can be reliably correlated across the Tian Shan, with glacier expansions occurring between 15 and 281 a during marine oxygen isotope stage (MIS) 2. However, there are examples of older more extensive indicators of glacial stages between MIS 3 and MIS 6. Paleoglacier extent during MIS 2 was mainly restricted to valley glaciation. Local deviations occur: in the central Kyrgyz Tian Shan paleoglaciers were more extensive and we propose that the topographic context explains this pattern. Correlation between glacial stages prior to late MIS 2 is less reliable, because of the low number of samples and/or the poor resolution of the dating. With the current resolution and spatial coverage of robustly-dated glacier limits we advise that paleoclimatic implications for the Tian Shan glacial chronology beyond MIS 2 are speculative and that continued work toward robust glacial chronologies is needed to resolve questions regarding drivers of past glaciation in the Tian Shan and Central Asia.
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| 2. |
- Blomdin, Robin, 1986-, et al.
(författare)
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Glacial geomorphology of the Altai and Western Sayan Mountains, Central Asia
- 2016
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Ingår i: Journal of Maps. - : Informa UK Limited. - 1744-5647. ; 12:1, s. 123-136
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we present a map of the glacial geomorphology of the Altai andWestern Sayan Mountains, covering an area of almost 600,000 km2. Although numerous studies provide evidence for restricted Pleistocene glaciations in this area, others have hypothesized the past existence of an extensive ice sheet. To provide a framework for accurate glacial reconstructions of the Altai and Western Sayan Mountains, we present a map at a scale of 1:1,000,000 based on a mapping from 30 m resolution ASTER DEM and 15 m/30 mresolution Landsat ETM+ satellite imagery. Four landform classes have been mapped: marginal moraines, glacial lineations, hummocky terrain, and glacial valleys. Our mapping reveals an abundance of glacial erosional and depositional landforms. The distribution of these glacial landforms indicates that the Altai and Western Sayan Mountains have experienced predominantly alpine-style glaciations, with some small ice caps centred on the higher mountain peaks. Large marginal moraine complexes mark glacial advances in intermontane basins. By tracing the outer limits of present-day glaciers, glacial valleys, and moraines, we estimate that the past glacier coverage have totalled to 65,000 km2 (10.9% of the mapped area), whereas present-day glacier coverage totals only 1300 km2 (0.2% of the mapped area). This demonstrates the usefulness of remote sensing techniques for mapping the glacial geomorphology in remote mountain areas and for quantifying the past glacier dimensions. The glacial geomorphological map presented here will be used for further detailed reconstructions of the paleoglaciology and paleoclimate of the region.
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| 3. |
- Blomdin, Robin, 1986-, et al.
(författare)
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Paleoglaciation on opposite flanks of the Ikh-Turgen Mountains, Central Asia : Importance of style of moraine deposition for 10-Be surface exposure dating
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The ages of marginal moraines that record extensive glacier expansions across the Altai Mountains of Central Asia are poorly documented. We present 18 10Be exposure ages from moraines in valleys on opposite flanks of the Ikh-Turgen Mountains. On the eastern side, exposure ages from a latero-frontal moraine indicate deglaciation during MIS 3 (45.3±2.7 ka) and MIS 2 (22.8±3.5 ka). Corresponding exposure ages, from the western side, indicate a more complex story with large scatter (~14-53 ka). Owing to their close proximity, the paleoglaciers should have responded similarly to climate forcing, yet they exhibited a distinctly different behavior. We propose that differences in glacier dynamics caused differences in ice-marginal depositional environments, explaining the scatter in exposure ages on the western side. This study shows the importance of style of deposition in chronological studies of glacial landforms and demonstrates that certain moraine types can be difficult to use as paleoclimate proxies.
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| 4. |
- Blomdin, Robin, et al.
(författare)
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Timing and dynamics of glaciation in the Ikh Turgen Mountains, Altai region, High Asia
- 2018
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Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 47, s. 54-71
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Tidskriftsartikel (refereegranskat)abstract
- Spanning the northern sector of High Asia, the Altai region contains a rich landform record of glaciation. We report the extent, chronologies, and dynamics of two paleoglaciers on opposite flanks of the Ikh Turgen mountains (In Russian: Chikhacheva Range), straddling the border between Russia and Mongolia, using a combination of remote sensing-based glacial geomorphological mapping, 10Be surface exposure dating, and geomorphometric analysis. On the eastern side (Mongolia), the Turgen-Asgat paleoglacier, with its potential for developing a large accumulation area (∼257 km2), expanded 40 km down valley, and mean ages from a latero-frontal moraine indicate deglaciation during marine oxygen isotope stage (MIS) 3 (45.1 ± 1.8 ka, n = 4) and MIS 2 (22.8 ± 3.3 ka, n = 5). These minimum age constraints are consistent with other 10Be glacial chronologies and paleoclimate records from the region, which indicates glacier culmination during cold and wet conditions coinciding with MIS 3 (piedmont-style glaciation; inferred for a few sites across the region) and glacier culmination during cold and dry conditions coinciding with MIS 2 (mainly valley-style glaciation; inferred from several sites across the region). On the western side (Russia), the Boguty paleoglacier had a smaller accumulation area (∼222 km2), and advanced 30 km down valley across a low gradient forefield. Surface exposure ages from two moraine complexes on this side of the mountains exhibit wide scatter (∼14–53 ka, n = 8), making paleoclimate inferences and comparison to other proxies difficult. Ice surface profile reconstructions imply that the two paleoglaciers likely shared an ice divide. © 2018 Elsevier B.V.
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| 5. |
- Blomdin, Robin, et al.
(författare)
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Topographic and climatic controls on paleoglaciation patterns across the Tian Shan and Altai Mountains, Central Asia
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Reconstructing spatial patterns of the extents and dynamics of paleoglaciers across Central Asia is key in understanding the mechanisms of global environmental change. The Tian Shan and Altai Mountains are located in the continental interior of Eurasia, at the confluence of several major climate systems. In order to test hypothesized patterns in paleoglacier extent, and to test the role of paleoclimate and mountain topography in modulating the evolution of these glacial systems, we perform a domain-wide terrain analysis. We first divide the Tian Shan and the Altai Mountains into six physiographic regions delineated by major drainage divides and outlining generalised climate zones. Thereafter we mine published datasets on the distribution of glaciers and glacial landforms, calculate their area-elevation distributions (hypsometry), and extract present-day regional equilibrium line altitudes (ELAs) and long-term average ELAs (paleo-ELAs). We show that the use of glacial landform hypsometry is an effective tool to quantify broad-scale paleoglaciation patterns and find that there is a regional variability in glacier extents across the Tian Shan and Altai Mountains. Reconstructed ELAs show pronounced spatial gradients; increasing ELAs from northern to southern Tian Shan, and increasing ELAs from the northern to both the southeastern and southwestern Altai Mountains. In contrast, maximum paleoglaciation patterns and paleo-ELAs were more uniform across the two mountain systems, with inter-regional topographic variability influencing moraine distributions and thus complicating regional paleo-ELA determinations. Because estimated paleo-ELAs were relatively uniform across the Tian Shan and Altai Mountains, the paleo-ELA lowering were most pronounced in the more continental southern and eastern regions. Our current data is insufficient to explain whether this observation is the result of a different regional paleoclimatic regime than today, or if paleoglaciers responded dynamically different to a paleoclimate forcing of the same magnitude. Our ELA reconstructions also lack temporal constraints, so we furthermore propose that future studies systematically compare hypsometry-derived ELA reconstructions with those stemming from surface energy mass balance models, other proxy records (i.e. lake- and ice core records), and from chronologically constrained ice-marginal moraines.
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| 6. |
- Codilean, A. T., et al.
(författare)
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OCTOPUS database (v.2)
- 2022
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Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 14:8, s. 3695-3713
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Tidskriftsartikel (refereegranskat)abstract
- OCTOPUS v.2 is an Open Geospatial Consortium (OGC) compliant web-enabled database that allows users to visualise, query, and download cosmogenic radionuclide, luminescence, and radiocarbon ages and denudation rates associated with erosional landscapes, Quaternary depositional landforms, and archaeological records, along with ancillary geospatial (vector and raster) data layers. The database follows the FAIR (Findability, Accessibility, Interoperability, and Reuse) data principles and is based on open-source software deployed on the Google Cloud Platform. Data stored in the database can be accessed via a custom-built web interface and via desktop geographic information system (GIS) applications that support OGC data access protocols. OCTOPUS v.2 hosts five major data collections. CRN Denudation and ExpAge consist of published cosmogenic Be-10 and Al-26 measurements in modern fluvial sediment and glacial samples respectively. Both collections have a global extent; however, in addition to geospatial vector layers, CRN Denudation also incorporates raster layers, including a digital elevation model, gradient raster, flow direction and flow accumulation rasters, atmospheric pressure raster, and CRN production scaling and topographic shielding factor rasters. SahulSed consists of published optically stimulated luminescence (OSL) and thermoluminescence (TL) ages for fluvial, aeolian, and lacustrine sedimentary records across the Australian mainland and Tasmania. SahulArch consists of published OSL, TL, and radiocarbon ages for archaeological records, and FosSahul consists of published late-Quaternary records of direct and indirect non-human vertebrate (mega)fauna fossil ages that have been systematically quality rated. Supporting data are comprehensive and include bibliographic, contextual, and sample-preparation- and measurement-related information. In the case of cosmogenic radionuclide data, OCTOPUS also includes all necessary information and input files for the recalculation of denudation rates using the open-source program CAIRN. OCTOPUS v.2 and its associated data curation framework allow for valuable legacy data to be harnessed that would otherwise be lost to the research community. The database can be accessed at https://octopusdata.org (last access: 1 July 2022). The individual data collections can also be accessed via their respective digital object identifiers (DOIs) (see Table 1).
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| 7. |
- Dalton, April S., et al.
(författare)
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Deglaciation of the north American ice sheet complex in calendar years based on a comprehensive database of chronological data: NADI-1
- 2023
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Ingår i: QUATERNARY SCIENCE REVIEWS. - 0277-3791 .- 1873-457X. ; 321
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Tidskriftsartikel (refereegranskat)abstract
- The most recent deglaciation of the North American Ice Sheet Complex (NAISC: comprising the Innuitian, Cordilleran, and Laurentide ice sheets) offers a broad perspective from which to analyze the timing and rate of ice retreat, deglacial sea-level rise, and abrupt climate change events. Previous efforts to portray the retreat of the NAISC have been focused largely on minimum-limiting radiocarbon ages and ice margin location(s) tied to deglacial landforms that were not, for the most part, chronologically constrained. Here, we present the first version of North American Deglaciation Isochrones (NADI-1) spanning 25 to 1 ka in calendar years before present. Key new features of this work are (i) the incorporation of cosmogenic nuclide data, which offer a direct constraint on the timing of ice recession; (ii) presentation of all data and time-steps in calendar years; (iii) optimal, minimum, and maximum ice extents for each time-step that are designed to capture uncertainties in the ice margin position, and; (iv) extensive documentation and justification for the placement of each ice margin. Our data compilation includes 2229 measurements of Be-10, 459 measurements of Al-26 and 35 measurements of Cl-36 from a variety of settings, including boulders, bedrock surfaces, cobbles, pebbles, and sediments. We also updated a previous radiocarbon dataset (n = 4947), assembled luminescence ages (n = 397) and gathered uranium-series data (n = 2). After scrutiny of the geochronological dataset, we consider >90% of data to be reliable or likely reliable. Key findings include (i) a highly asynchronous maximum glacial extent in North America, occurring as early as 27 ka to as late as 17 ka, within and between ice sheets. In most marine realms, extension of the ice margin to the continental shelf break at 25 ka is somewhat speculative because it is based on undated and spatially scattered ice stream and geomorphic evidence; (ii) detachment of the Laurentide and Cordilleran ice sheets took place gradually via southerly and northerly 'unzipping' of the ice masses, starting at 17.5 ka and ending around 14 ka; (iii) the final deglaciation of Hudson Bay began at 8.5 ka, with the collapse completed by 8 ka. The maximum extent of ice during the last glaciation occurred at 22 ka and covered 15,470,000 km(2). All North American ice sheets merged at 22 ka for the first time in the Quaternary. The highly asynchronous Last Glacial Maximum in North America means that our isochrones (starting at 25 ka) capture ice advance across some areas, which is based on limited evidence and is therefore somewhat speculative. In the Supplementary Data, the complete NADI-1 chronology is available in PDF, GIF and shapefile format, together with additional visualizations and spreadsheets of geochronological data. The NADI-1 shapefiles are also available at https://doi.org/10.5281/zenodo.8161764.
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| 8. |
- Fu, Ping, 1982-, et al.
(författare)
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Complex erosion patterns produced by the Haizishan paleo-ice cap
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Determining patterns and rates of glacial erosion is important in understanding landscape evolution, topographic relief production, geochemical cycles, climate change, and glacial thermal regimes of paleo glaciers and ice sheets. Combining in situ $^{10}$Be and $^{26}$Al apparent exposure age dating, geomorphological mapping, and field investigations, we examine glacial erosion patterns of the almost 4 000 km$^2$ Haizishan paleo-ice cap on the southeastern Tibetan Plateau. Our results show that ice caps developed several times on the low relief Haizishan Plateau and produced a zonal pattern of landscape modification. In locations where apparent exposure ages on bedrock are consistent with last deglaciation, complete resetting of the cosmogenic exposure age clock indicates that more than 2 m of glacial erosion occurred during the last major glaciation (which in this area correlates with the global Last Glacial Maximum (gLGM)). However, older apparent exposure ages on bedrock and in saprolites profiles in areas known to have been covered by the paleo ice cap during gLGM indicate inheritance and thus limited or no erosion by the last ice cap in several areas, including the central zone of the paleo ice cap and at the head of an outlet glacier. Similarly, cosmogenic radionuclide depth profiles in saprolites show erosion of $>$2 m in an outlet valley bottom and in the mountains that make up the northern border of the paleo ice cap, while samples from saprolites in areas of otherwise scoured terrain have a large nuclide inheritance indicating limited erosion. As patterns of glacial erosion intensity are largely driven by basal thermal regime, our results are consistent with a hypothesis of complex thermal regimes for the paleo Haizishan ice cap during gLGM that was proposed previously on the basis of landform patterns. Future work, including glaciological modeling, is required to fully understand the implications and mechanisms of the complex thermal regime of this paleo ice cap.
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| 9. |
- Fu, Ping, 1982-, et al.
(författare)
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Glacial geomorphology and paleoglaciation patterns in Shaluli Shan, the southeastern Tibetan Plateau — Evidence for polythermal ice cap glaciation
- 2013
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 182, s. 66-78
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Tidskriftsartikel (refereegranskat)abstract
- Glacial geomorphological mapping from satellite imagery and field investigations provide the basis for a reconstructionof the extent and style of glaciation of the Shaluli Shan, a mountainous area on the southeastern TibetanPlateau. Our studies provide evidence for multiple glaciations, including the formation of regional ice caps andvalley glaciers. The low-relief topographywithin the Shaluli Shan, the Haizishan Plateau, and Xinlong Plateau displayzonal distributions of glacial landforms that is similar to those imprinted by Northern Hemisphere ice sheetsduring the last glacial cycle, indicating the presence of regional, polythermal ice caps. Abundant alpine glaciallandforms occur on high mountain ranges. The pattern of glaciated valleys centered on high mountain rangesand ice-scoured low relief granite plateaus with distinctive patterns of glacial lineations indicate a strong topographiccontrol on erosional and depositional patterns by glaciers and ice caps. In contrast to the Shaluli Shan,areas farther north and west on the Tibetan Plateau have not yielded similar landform evidence for regionalice capswith complex thermal basal conditions. Such spatial differences across the Tibetan Plateau are the resultof variations in climate and topography that control the extent and style of glaciations and that reinforce the importanceof detailed geomorphological mapping for understanding paleoclimate variations and characteristics offormer glaciations.
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| 10. |
- Fu, Ping, et al.
(författare)
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Glacial geomorphology of the Haizi Shan area, SE Tibetan Plateau
- 2009
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Konferensbidrag (refereegranskat)abstract
- The Haizi Shan area on the SE Tibetan Plateau is characterized by an elliptical relatively low relief plateau surrounded by steeper fluvial valleys. Glacial deposits and erosive imprints are widely distributed indicating former glacier expansions of varying extents in a presently ice-free area. We have initiated a project on the glacial history of the Haizi Shan area and we here present some initial mapping results. Glacial landforms have been mapped based on remote sensing (SRTM digital elevation model, Landsat ETM+ satellite imagery, and Google Earth) and one short reconnaissance field season. Well-preserved moraines from different stages and distinctive U-shaped glacial valleys are abundant (Fig. 1). In the Daocheng Valley southwest of the Haizi Shan Plateau we have mapped glacial deposits in the form of discontinued moraine ridges at Sangdui village. This line, which might be the maximum Quaternary glacial extent, can be traced for several kilometers along the western side of the valley as dispersed erratic boulders. This implies that during the maximum glaciation, ice from the Haizi Shan Plateau crossed the valley and reached up to the piedmont of the opposite mountain. Smaller in extent than the former, numerous large moraine ridges reach down towards valley floors along the edges of the Haizi Shan Plateau. In several locations these valleys lack cirque heads indicating former outlet glaciers emanating from a Haizi Shan ice cap. We will use TCN and OSL dates of samples collected from numerous ice marginal moraines of the Haizi Shan Plateau to determine a glacial chronology. Hence, using remote sensing, field investigations and numerical dating techniques for the Haizi Shan we aim to advance our knowledge on Quaternary glaciations of the SE Tibetan Plateau.
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