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The alpine topography observed in many mountainous regions is thought to have formed during repeated glaciations of the Quaternary period. Before this time, landscapes had much less relief. However, the spatial patterns and rates of Quaternary exhumation at high latitudes-where cold-based glaciers may protect rather than erode landscapes-are not fully quantified. Here we determine the exposure and burial histories of rock samples from eight summits of steep alpine peaks in northwestern Svalbard (79.5° N) using analyses of 10Be and 26Al concentrations. We find that the summits have been preserved for at least the past one million years. The antiquity of Svalbard's alpine landscape is supported by the preservation of sediments older than one million years along a fjord valley, which suggests that both mountain summits and low-elevation landscapes experienced very low erosion rates over the past million years. Our findings support the establishment of northwestern Svalbard's alpine topography during the early Quaternary. We suggest that, as the Quaternary ice age progressed, glacial erosion in the Arctic became inefficient and confined to ice streams, and high-relief alpine landscapes were preserved by minimally erosive glacier armour. [ABSTRACT FROM AUTHOR]

Glacial denudation can significantly perturb terrestrial cosmogenic nuclide depth profiles and, if this is not corrected for, derived apparent denudation rates will overestimate the actual denudation rates. Here we determine how much 10Be-derived denudation rates - calculated under the assumption of steady state - deviate from actual denudation rates as a function of three parameters: (1) the total amount of glacial denudation, (2) the post-glacial denudation rate and (3) the time elapsed since deglaciation. We provide correction lines for the full parameter space explored (glacial denudation: 0.01-100 m; post-glacial denudation rate: 1-1000 mm/ka; deglaciation: 1-100 ka before present), to evaluate and, if necessary, correct denudation rates for the impact of glacial denudation. Applied to 10Be-derived catchment-averaged denudation rates for formerly glaciated catchments in the Black Forest, Germany, we find that uncorrected denudation rates overestimate actual rates by up to a factor of three. [ABSTRACT FROM AUTHOR]

Abstract: Glacial chronologies from the Pamir may not only provide insights into past changes in temperature, but also into past changes in precipitation related to the northern-hemispheric westerlies and the monsoonal circulation. We present 18 new exposure ages from the Bogchigir Valleys that complement and refine our previous studies in these valleys. The most extensive dated glaciation in the area occurred ~100ka, during Marine Oxygen Isotope Stage (MIS) 5, and indicates increased precipitation likely from both the westerlies and the monsoonal circulation. A subsequent glacier advance, which deposited characteristic ‘chukur’ moraine lobes, occurred at ~80–75ka. Circumstantial evidence points to glacial advances at ~65 and 40ka, the latter likely also documenting increased monsoonal moisture supply during MIS 3. Less extensive glacial advances occurred during MIS 2 at ~28 and 24ka and reflect the aridization trend during the course of the last glacial cycle. Deglaciation started ~21ka, interrupted by minor stillstands or readvances at ~16 and 12ka. Local calibration sites and glacier-climate modeling would be very helpful to reduce the systematic methodological uncertainties (still at least 10%) and to draw more detailed paleoclimatic conclusions. [Copyright &y& Elsevier]

Abstract: Although glacial landscapes have previously been used for the reconstruction of late Quaternary glaciations in the Central Andes, only few data exist for the Eastern Cordillera in Bolivia. Here, we present results from detailed morphostratigraphic mapping and new data of surface exposure dating (SED), optically stimulated luminescence (OSL), and radiocarbon dating (14C) from the Huara Loma Valley, Cordillera de Cochabamba (Bolivia). Discrepancies between individual dating methods could be addressed within the context of a solid geomorphic framework. We identified two major glaciations. The older is not well constrained by the available data, whereas the younger glaciation is subdivided into at least four major glacial stages. Regarding the latter, a first advance dated to ~29–25ka occurred roughly contemporaneous with the onset of the global last glacial maximum (LGM) and was followed by a less extensive (re-)advance around 20–18ka. The local last glacial maximum (LLGM) in the Huara Loma Valley took place during the humid lateglacial ~17–16ka, followed by several smaller readvances until ~10–11ka, and complete deglaciation at the end of the Early Holocene. [Copyright &y& Elsevier]

The northern Swiss Alpine Foreland exemplifies a highly transient landscape characterized by multiple knickzones along the trunk valleys and distinct bedrock straths at their junction with tributary valleys. This landscape has evolved as a result of fast base level changes in response to repeated glaciations during the Quaternary. As the archives related to the evolution of this transient landscape are scarce, available quantitative information is limited, especially for the early and middle Pleistocene. In order to track the pace of the landscape evolution in the northern Swiss Alpine Foreland during the Pleistocene, in this study, we focus on the Deckenschotter sequences, the oldest Quaternary terrestrial sedimentary archives on the northern margin of the Central European Alps. These deposits have been morphostratigraphically divided into two: Höhere (Higher; HDS) and Tiefere (Lower; TDS) Deckenschotter. We analyzed seven different sites extending from Basel in the west to Schaffhausen in the east of Switzerland for the provenance signal, and we dated these archives by depth-profile and isochron-burial dating techniques with 10Be, 26Al, and 36Cl. Investigations on the petrographic compositions of the deposits revealed distinct provenances for the HDS and TDS deposits. During HDS time, the Alpine Rhine drained through Lake Constance and into the Danube River. Rerouting of the river toward the west and into the Upper Rhine Valley occurred between the end of HDS and the beginning of TDS accumulation. The results of the depth-profile and isochron-burial dating suggest that the HDS deposits accumulated at around 2 Ma as a result of a first widespread Alpine glaciation, whereas the TDS was deposited at around 1 Ma. Based on the provenance and the chronological information, we propose a scenario where the Rhine River captured the Alpine sources of the Danube and thus increased its runoff and enhanced its baseline lowering. Consequently, the landscape evolution has been accelerated possibly in response not only to the larger runoff but also to the climate change associated with the mid-Pleistocene revolution. [ABSTRACT FROM AUTHOR]

Our study in the Başyayla Valley in northeastern Anatolia showed evidence of four glacier advances that built terminal and lateral moraines. Surface exposure dating of boulders on these moraines showed that the Maximum Ice Extent (MIE) was asynchronous with the global Last Glacial Maximum (LGM; 22.1 ± 4.3 thousand years; ka). The local MIE took place at least 57.0 ± 3.5 ka ago. The extent of the Başyayla Glacier during this advance is not known exactly because the boulders are only preserved on a lateral moraine. The next advance was prior to 41.5 ± 2.5 ka, and it descended down the valley to approximately 2320 m above sea level (m a.s.l.), with a glacier length of 5.3 km. During the early global LGM, the Başyayla Glacier extended for a distance of 4.9 km down to approx. 2430 m a.s.l. The last recorded advance occurred during the global LGM. This extension was 0.7 km smaller than the local MIE and its terminus reached 2490 m a.s.l. only. The exposure ages of boulders in a retreat position at an altitude of approx. 3045 m a.s.l. indicate that the valley has remained ice-free since the Lateglacial period. Therefore, the Lateglacial extent was limited to the cirque system in the uppermost part of the catchment. Furthermore, Holocene glacier oscillations seem to be either absent or restricted to solifluction in the whole catchment and to rock glacier movements in the southern tributary of the Başyayla Valley system. [ABSTRACT FROM AUTHOR]

Abstract: The Indus, one of Earth's major rivers, drains large parts of the NW Himalaya and the Transhimalayan ranges that form part of the western Tibetan Plateau margin. In the western Himalayan syntaxis, where local topographic relief exceeds 7 km, the Indus has incised a steep bedrock gorge at rates of several mm yr−1. Upstream, however, the upper Indus and its tributaries alternate between bedrock gorges and broad alluvial flats flanked by the Ladakh and Zanskar ranges. We review the late Quaternary valley history in this region with a focus on the confluence of the Indus and Zanskar Rivers, where vast alluvial terrace staircases and lake sediments record major episodes of aggradation and incision. New absolute dating of high-level fluvial terrace remnants using cosmogenic 10Be, optically and infrared stimulated luminescence (OSL, IRSL) indicates at least two phases of late Quaternary valley infilling. These phases commenced before ∼200 ka and ∼50–20 ka, judging from terrace treads stranded >150 m and ∼30–40 m above modern river levels, respectively. Numerous stacks of lacustrine sediments that straddle the Indus River >200 km between the city of Leh and the confluence with the Shyok River share a distinct horizontal alignment. Constraints from IRSL samples of lacustrine sequences from the Leh-Spituk area reveal a protracted lake phase from >177 ka to 72 ka, locally accumulating >50-m thick deposits. In the absence of tectonic faulting, major lithological differences, and stream capture, we attribute the formation of this and other large lakes in the region to natural damming by large landslides, glaciers, and alluvial fans. The overall patchy landform age constraints from earlier studies can be reconciled by postulating a major deglacial control on sediment flux, valley infilling, and subsequent incision that has been modulated locally by backwater effects of natural damming. While comparison with Pleistocene monsoon proxies reveals no obvious correlation, a late- or post-glacial sediment pulse seems a more likely source of this widespread sedimentation that has partly buried the dissected bedrock topography. Overall, the long residence times of fluvial, alluvial and lacustrine deposits in the region (>500 ka) support previous studies, but remain striking given the dominantly steep slopes and deeply carved valleys that characterise this high-altitude mountain desert. Recalculated late Quaternary rates of fluvial bedrock incision in the Indus and Zanskar of 1.5 ± 0.2 mm yr−1 are at odds with the longevity of juxtaposed valley-fill deposits, unless a lack of decisive lateral fluvial erosion helps to preserve these late Pleistocene sedimentary archives. We conclude that alternating, ∼104-yr long, phases of massive infilling and incision have dominated the late Quaternary history of the Indus valley below the western Tibetan Plateau margin. [Copyright &y& Elsevier]

Based on field investigations, we have mapped the extent of moraines in the Šara Range (Balkan peninsula) in order to reconstruct the altitude of the glacier equilibrium line (ELA) during the Last Glacial Maximum (LGM) and successive glacier advances. The age of moraine stabilisation was determined by 10Be exposure dating. With increasing altitude, late glacial and Holocene glacial depressions have been progressively filled with apparently inactive block glaciers in northerly exposure, indicating increasing seasonal dryness in more continental climate since the LGM. In southerly aspect, block glacier debris is rare and glacial cirques are poorly developed. The ELA during the LGM ranged between 1900 and 2000 m in NW to NE aspect, and 2100 to 2300 m in southerly aspect. The ELA of the Oldest Dryas is found 300 m higher in northerly aspect, and the ELA of the Younger Dryas about 50 m higher than that of the Oldest Dryas. Holocene niche glacier deposits have been found in well-protected cirques of three northexposed valleys. There was hardly any west-east gradient of the ELA within the Šara Range in the LGM but a minor decline by about 200 m towards the Albanian Alps in the west at about 42° northern latitude. The west-east gradient seems to have been roughly similar in the late glacial. Presently preserved niche glaciers in the Albanian Alps reflect a similar gradient of eastward decreasing winter precipitation, resulting from topographic barriers, matching the LGM gradient. In contrast to the studied west-east section of the Balkan peninsula, its western continuation along 42° northern latitude in the LGM shows that the western Mediterranean basin was much stronger affected by climate change. Frequent winterly meridional circulation in the Mediterranean triggered polar air outbreaks into the western Mediterranean basin which caused transport of air masses from the Sahara and admixed wet polar and subtropical air masses to the southern Balkan peninsula and further north towards the Fennoscandian ice shield. Westerly advection of moisture in the study area, however, was remarkably stable since the LGM, despite for strong temperature changes. [ABSTRACT FROM AUTHOR]

Extensive ice cover on the Tibetan Plateau would significantly influence Earth’s climate in general and the Asian monsoon system in particular, but extent and timing of Quaternary glaciations in Tibet remain highly controversial. We dated erratics on top of moraines in the climatic key areas of Central and East Tibet using cosmogenic 10Be, 26Al, and 21Ne. Consistent exposure ages obtained by various nuclides indicate a continuous period of exposure since the deposition of the samples. Our data imply that glacial advances were restricted to a few 10 km during the last 170 kyr in Central Tibet and during the peak of the last glaciation (∼24–13 kyr ago) in Eastern Tibet. Advances of Tibetan glaciers were much less prominent than elsewhere in the northern hemisphere most likely due to very arid conditions and high sublimation rates. A proposed ice-dome covering the entire Plateau can be excluded. Thus, albedo increase of Tibet most likely did trigger neither northern hemisphere ice ages nor paleomonsoon changes during the last two glacial cycles. The glacial advance during Marine Isotope Stage 2 in East Tibet and the absence of significant glacial events during the Holocene suggest a relation of snowline lowering in East Tibet to North Atlantic cooling events rather than to periods of high precipitation by an intensified monsoon. [Copyright &y& Elsevier]