Late Quaternary–Holocene evolution of Dun structure and the Himalayan Frontal Fault zone of the Garhwal Sub-Himalaya,NW India

Dun structures are common in the Sub-Himalayan zone of the Himalaya bounded by the Main Boundary Thrust (MBT) and the Himalayan Frontal Thrust (HFT). They are broad synclinal longitudinal valleys formed as a consequence of the exhumation of the range front of the Himalaya. In the Garhwal Sub-Himalaya, these structures have grown since 0.5 Ma, with the peak activity postdating ∼100 ka. A series of out-of-sequence deformation structures have been identified within the MBT-HFT-bounded Dun structures. They are identified on the basis of geomorphic, post-100 ka stratigraphic, and structural expressions, with activity as young as the early Holocene. To the south of the range front of the Himalaya, uplift has been observed in the Piedmont Zone, with peculiar active tectonic geomorphic expressions. Piedmont sediments of 15–5 ka, determined by Optically Simulated Luminescence (OSL), have been affected by the above uplift. The complete tectonic scenario has been analyzed and an attempt has been made to delineate the sequential evolution of these structures during the post-100 ka period (Late Quaternary–Holocene) in the Himalayan range front.     

Timing and extent of Holocene glaciations in the monsoon dominated Dunagiri valley (Bangni glacier), Central Himalaya,India

Field stratigraphy and optical and radiocarbon dating of lateral moraines in the monsoon dominated Dunagiri valley of the Central Himalaya provide evidence for three major glaciations during the last 12 ka. The oldest and most extensive glaciation, the Bangni Glacial Stage-I (BGS-I), is dated between 12 and 9 ka, followed by the BGS-II glaciation (7.5 and 4.5 ka) and the BGS-III glaciation (∼1 ka). In addition, discrete moraine mounds proximal to the present day glacier snout are attributed to the Little Ice Age (LIA). BGS-I started around the Younger Dryas (YD) cooling event and persisted till the early Holocene when the Indian Summer Monsoon (ISM) strengthened. The less extensive BGS-II glaciation, which occurred during the early to mid-Holocene, is ascribed to lower temperature and decreased precipitation. Further reduction in ice volume during BGS-III is attributed to a late Holocene warm and moist climate. Although the glaciers respond to a combination of temperature and precipitation changes, in the Dunagiri valley decreased temperature seems to be the major driver of glaciations during the Holocene.     

Reconstruction of Last Glacial to early Holocene monsoon variability from relict lake sediments of the Higher Central Himalaya,Uttrakhand, India

Proglacial lake sediments at Goting in the Higher Central Himalaya were analyzed to reconstruct the summer monsoon variability during the Last Glacial to early Holocene. Sedimentary structures, high resolution mineral magnetic and geochemical data suggest that the lacustrine environment experienced fluctuating monsoonal conditions. Optically stimulated luminescence (OSL) dating indicates that the lake sedimentation occurred before 25 ka and continued after 13 ka. During this period, Goting basin witnessed moderate to strengthened monsoon conditions around 25 ka, 23.5 ka–22.5 ka, 22 ka–18 ka, 17 ka–16.5 ka and after14.5–13 ka. The Last Glacial phase ended with the deposition of outwash gravel dated at ～11 ka indicating glacial retreat and the onset of Holocene condition. Additionally, centennial scale fluctuations between 16.5 ka and 12.7 ka in the magnetic and geochemical data are seen.A close correspondence at the millennial scale between our data and that of continental and marine records from the Indian sub-continent suggests that Goting basin responded to periods of strengthened monsoon during the Last Glacial to early Holocene. We attribute the millennial scale monsoon variability to climatic instability in higher northern latitudes. However, centennial scale abrupt changes are attributed to the result of albedo changes on the Himalaya and Tibetan plateau.     

Quaternary glaciation of Mount Everest

The Quaternary glacial history of the Rongbuk valley on the northern slopes of Mount Everest is examined using field mapping, geomorphic and sedimentological methods, and optically stimulated luminescence (OSL) and ¹⁰Be terrestrial cosmogenic nuclide (TCN) dating. Six major sets of moraines are present representing significant glacier advances or still-stands. These date to >330 ka (Tingri moraine), >41 ka (Dzakar moraine), 24–27 ka (Jilong moraine), 14–17 ka (Rongbuk moraine), 8–2 ka (Samdupo moraines) and ～1.6 ka (Xarlungnama moraine), and each is assigned to a distinct glacial stage named after the moraine. The Samdupo glacial stage is subdivided into Samdupo I (6.8–7.7 ka) and Samdupo II (～2.4 ka). Comparison with OSL and TCN defined ages on moraines on the southern slopes of Mount Everest in the Khumbu Himal show that glaciations across the Everest massif were broadly synchronous. However, unlike the Khumbu Himal, no early Holocene glacier advance is recognized in the Rongbuk valley. This suggests that the Khumbu Himal may have received increased monsoon precipitation in the early Holocene to help increase positive glacier mass balances, while the Rongbuk valley was too sheltered to receive monsoon moisture during this time and glaciers could not advance. Comparison of equilibrium-line altitude depressions for glacial stages across Mount Everest reveals asymmetric patterns of glacier retreat that likely reflects greater glacier sensitivity to climate change on the northern slopes, possibly due to precipitation starvation.     

Glaciations and paleoclimate of Mount Erciyes,central Turkey,since the Last Glacial Maximum,inferred from 36Cl cosmogenic dating and glacier modeling

Forty-four boulders from moraines in two glacial valleys of Mount Erciyes (38.53°N, 35.45°E, 3917 m), central Turkey, dated with cosmogenic chlorine-36 (³⁶Cl), indicate four periods of glacial activity in the past 22 ka (1 ka = 1000 calendar years). Last Glacial Maximum (LGM) glaciers were the most extensive, reaching 6 km in length and descending to an altitude of 2150 m above sea level. These glaciers started retreating 21.3 ± 0.9 ka (1σ) ago. They readvanced and retreated by 14.6 ± 1.2 ka ago (Lateglacial), and again by 9.3 ± 0.5 ka ago (Early Holocene). The latest advance took place 3.8 ± 0.4 ka ago (Late Holocene). Using glacier modeling together with paleoclimate proxy data from the region, we reconstructed the paleoclimate at these four discrete times. The results show that LGM climate was 8–11 °C colder than today and moisture levels were somewhat similar to modern values, with a range between 20% more and 25% less than today. The analysis of Lateglacial advance suggests that the climate was colder by 4.5–6.4 °C based on up to 1.5 times wetter conditions. The Early Holocene was 2.1–4.9 °C colder and up to twice as wet as today, while the Late Holocene was 2.4–3 °C colder and its precipitation amounts approached to similar conditions as today. Our paleoclimate reconstructions show a general trend of warming for the last 22 ka, and an increase of moisture until Early Holocene, and a decrease after that time. The recent glacier terminates at 3450 m on the northwest side of the mountain. It is a remnant from the last advance (possibly during the Little Ice Age). Repeated measurements of glacier length between 1902 and 2008 reveal a retreat rate of 4.2 m per year, which corresponds to a warming rate of 0.9–1.2 °C per century.     

Moraine dam related to late Quaternary glaciation in the Yulong Mountains,southwest China,and impacts on the Jinsha River

The Yulong Mountain massif is tectonically active during Quaternary and contains the southernmost glacierized mountains in China, and all of Eurasia. Past glacial remnants remain preserved on the east and west sides of the Yulong Mountains. A ridge of moraine protruded into the Jinsha River at the Daju Basin, damming the river, and forming a lake at the head of the Jinsha River. Cosmogenic ¹⁰Be and ²⁶Al provide exposure age dates for the moraine-based fluvial terraces left behind after the dam breached, and for moraine boulders on both the eastern and western sides of the Yulong Mountains. Our results yield exposure ages for the terraces that range from 29 ka to 8 ka, and a downcutting rate of 7.6 m/ka. The preservation of the remaining dam for over 10,000 years suggests stability of the moraine dam and gradual erosion of the dam during drainage of the dammed lake. From the relationship between exposure ages and elevations of the fluvial terraces located in different walls of the Daju fault, we obtain a late Quaternary dip-slip rate of about 5.6 m/ka for the Daju fault. The exposure ages of 10.2 ka and 47 ka for moraine boulders located in the east and west sides of the Yulong Mountains, respectively, coincide with warm periods in the late Quaternary. This implies that precipitation provides the major control for glaciations on the Yulong Mountains, a domain of the southwest Asian monsoon.     

The onset of dune formation in the Strzelecki Desert,South Australia

This study is concerned with the Late Quaternary climatic chronology of the Strzelecki Desert dunefields in central Australia. The sand ridges comprise layers of quartz sand, some of which include palaeosol horizons with carbonated rootlets providing excellent opportunity for dating of alternations of dune building and stability by using optically stimulated luminescence (OSL). Deduced from the OSL age of the oldest aeolian layer dated, we conclude that the onset of aridity dates back to at least ∼65 ka. Older phases of aeolian activity though, following a fluvial depositional phase 160 ka ago, cannot be excluded, although no aeolian layers giving evidence for this have been found in the two dunes dated here. Unconsolidated dune sands in the upper part of one section with Late Holocene (4 ka to modern) depositional ages indicate a reactivation of the dunefield in recent times.From the crosscheck of ¹⁴C ages of the carbonated rootlets with OSL results it is concluded that under the given environmental conditions radiocarbon dating of the calcareous rootlets is not able to provide reliable ages for the phase of soil development.     

Determination of slip rate by optical dating of fluvial deposits from the Wangsan fault,SE Korea

The time-integrated slip rate in fault zones can be determined if the deformed deposits are reliably dated. Here, we report optically stimulated luminescence (OSL) ages of Late Pleistocene fluvial deposits cut by the Wangsan fault, southeastern Korea, which displaces a hanging wall block of about 28 m. Five sandy samples of the deformed Quaternary deposits were dated by quartz OSL using the single aliquot regenerative-dose (SAR) protocol. Three samples taken from the footwall block show stratigraphically consistent OSL ages of 54±7, 76±5 and 90±6 ka, from top to bottom. Two samples collected from the same layer in the hanging wall block show reproducible OSL ages of 81±5 and 82±5 ka, which are also in good agreement with the stratigraphic relationships. Our OSL ages yield an average sedimentation rate of the Quaternary deposits as around 0.04 mm a⁻¹, and a minimum value of time-integrated slip rate as 0.52 mm a⁻¹. This minimum slip rate is considerably higher than those reported earlier for Quaternary faults in southeastern Korea. The youngest OSL age (54±7 ka) constrains the maximum value of the recurrence interval of the fault movement.     

Glacial geomorphology and chronology of deglaciation,South Georgia,sub-Antarctic

We mapped and dated the glacial geomorphology of north-east South Georgia, in the maritime sub-Antarctic. The aim was to examine the timing of deglaciation of the island in the context of inter-hemispheric phasing of climate change. Former glacier limits are restricted to the inner fjords, and our detailed mapping of them has demonstrated a consistent geomorphological pattern that is similar across several different glacier types and sizes. The pattern comprises three suites of moraines (categories “a–c”), not all of which are represented at every site because the outer suite is often overridden by younger suites. Category “a” is an outer wide, low amplitude moraine ridge, category “b” comprises 2–4 sharp-crested, bouldery moraines that are often located close to or even over-riding “a”, and category “c” is a series of lower amplitude moraines with overprinted streamlined landforms such as flutings. Analysis of in situ cosmogenic ¹⁰Be in boulders on these moraines has allowed us to determine a deglacial chronology for the older two moraine groups. The age of the inner (youngest) group has been estimated from soil development. The cosmogenic nuclide ages show that the outermost moraine was deposited ca 12.2±1.5 ka BP, but that a subsequent readvance in the mid-Holocene (ca 3.6±1.1 ka BP) reached and, in places, over-rode this earlier moraine. This latter advance coincides with the “Mid Holocene Hypsithermal”. A final Late Holocene advance reached closely similar limits to the previous two fluctuations and is estimated from soil data to have an age of ca 1.1 ka BP. We suggest that the close concordance of Late-Glacial and interglacial limits (in this case associated with warming) can be explained by a change in dominant forcing. During glacials, extensive sea-ice limits precipitation availability and so glaciers are restricted to the inner fjords. During interglacials precipitation is not limited in the same way by sea-ice cover and so during warming precipitation increases and tidewater glaciers on the island have responded by advancing. This study emphasises the importance of a clear understanding of geomorphology in order to interpret chronological information.     

Chronologies for Late Quaternary barchan dune reactivation in the southeastern Arabian Peninsula

The Liwa region of the United Arab Emirates contains some of the largest and most areally extensive megabarchanoid sand dunes on a global scale. Here we present optical dating results on samples of aeolian sediment from deep drill cores extracted from the largest dune field of the Liwa area. Optical dating of these core sediments using the single aliquot regeneration protocol indicates Mid–Late Holocene phases of rapid dune deposition, the most recent period of reactivation began at ca 2.8 ka. This event was preceded by a period of deposition at ca 5 ka. These results suggest that the dune systems of the southeastern Arabian Peninsula are closely linked to changes in Late Quaternary global climate, particularly linked to the intensity and spatial extent of palaeomonsoon rainfall. Since the last precessional maxima at ca 9 ka, at which time a peak in monsoonal rainfall has been recognised, a significant environmental transition to widespread desert conditions occurred in an apparently abrupt fashion. During the initial period of aridification, large quantities of sand were transported and deposited in the form of large and very large (up to 160 m high) scale aeolian bedforms. Following the initial phase of aeolian accumulation, the system appears to have remained in stasis.     

Latest Pleistocene glacial chronology of the Uinta Mountains: support for moisture-driven asynchrony of the last deglaciation

Recent estimates of the timing of the last glaciation in the southern and western Uinta Mountains of northeastern Utah suggest that the start of ice retreat and the climate-driven regression of pluvial Lake Bonneville both occurred at approximately 16 cal. ka. To further explore the possible climatic relationship of Uinta Mountain glaciers and the lake, and to add to the glacial chronology of the Rocky Mountains, we assembled a range-wide chronology of latest Pleistocene terminal moraines based on seventy-four cosmogenic ¹⁰Be surface-exposure ages from seven glacial valleys. New cosmogenic-exposure ages from moraines in three northern and eastern valleys of the Uinta Mountains indicate that glaciers in these parts of the range began retreating at 22–20 ka, whereas previously reported cosmogenic-exposure ages from four southern and western valleys indicate that ice retreat began there between 18 and 16.5 ka. This spatial asynchrony in the start of the last deglaciation was accompanied by a 400-m east-to-west decline in glacier equilibrium-line altitudes across the Uinta Mountains. When considered together, these two lines of evidence support the hypothesis that Lake Bonneville influenced the mass balance of glaciers in southern and western valleys of the range, but had a lesser impact on glaciers located farther east. Regional-scale variability in the timing of latest Pleistocene deglaciation in the Rocky Mountains may also reflect changing precipitation patterns, thereby highlighting the importance of precipitation controls on the mass balance of Pleistocene mountain glaciers.     

Evidence for prolonged El Nino-like conditions in the Pacific during the Late Pleistocene: a 43 ka noble gas record from California groundwaters

Information on the ocean/atmosphere state over the period spanning the Last Glacial Maximum – from the Late Pleistocene to the Holocene – provides crucial constraints on the relationship between orbital forcing and global climate change. The Pacific Ocean is particularly important in this respect because of its dominant role in exporting heat and moisture from the tropics to higher latitudes. Through targeting groundwaters in the Mojave Desert, California, we show that noble gas derived temperatures in California averaged 4.2 ± 1.1 °C cooler in the Late Pleistocene (from ～43 to ～12 ka) compared to the Holocene (from ～10 to ～5 ka). Furthermore, the older groundwaters contain higher concentrations of excess air (entrained air bubbles) and have elevated oxygen-18/oxygen-16 ratios (δ¹⁸O) – indicators of vigorous aquifer recharge, and greater rainfall amounts and/or more intense precipitation events, respectively. Together, these paleoclimate indicators reveal that cooler and wetter conditions prevailed in the Mojave Desert from ～43 to ～12 ka. We suggest that during the Late Pleistocene, the Pacific ocean/atmosphere state was similar to present-day El Nino-like patterns, and was characterized by prolonged periods of weak trade winds, weak upwelling along the eastern Pacific margin, and increased precipitation in the southwestern U.S.     

Paleoseismic investigation along Nalagarh Thrust: Evidence of Late Pleistocene earthquake in Pinjaur Dun,Northwestern sub-Himalaya

The present article is the first time reporting of a paleoearthquake that occurred during Late Pleistocene time along the Nalagarh Thrust (NT) in the Pinjaur Dun in northwestern sub-Himalaya. Using CORONA satellite photographs, multi-spectral IRS satellite data, and aerial photographs, a prominent active fault has been identified at Nalagarh in Pinjaur Dun. This fault in the alluvial fan is located very close to the NT which borders the topographic front of the Tertiary rocks against Quaternary deposits. A trench excavation survey was carried out at Nalagarh for detailed paleoseismic studies across this thrust fault. Displacing all the lithologic units of the fan sequence, the fault plane has an average dip of 30° due ENE and a vertical displacement of 1.6 m and slip of ～2.5 m along the fault. The lithological units, consisting of alternating sand and gravel, show back tilting and asymmetrical tight folding. Based on Optically Stimulated Luminescence (OSL) ages, the oldest litho-unit in the trench is 85.83 ± 7.2 ka and the youngest is 67.05 ± 8.4 ka. The OSL age of the sample collected from the easterly exposure of the fault shows an age of 20 ka. The faulting and associated induced deformation features suggest occurrence of a Late Pleistocene large magnitude earthquake along NT in the Nalagarh region of the Pinjaur Dun following the deposition of the Quaternary sedimentary units. The Late Pleistocene fault substantiates the seismic potential of Pinjaur Dun and calls for more exhaustive study of paleoearthquakes in this fast developing industrial belt and highly populous mountainous region.     

Tropical glacier fluctuations in the Cordillera Blanca,Peru between 12.5 and 7.6 ka from cosmogenic 10Be dating

We report cosmogenic surface exposure ¹⁰Be ages of 21 boulders on moraines in the Jeullesh and Tuco Valleys, Cordillera Blanca, Peru (～10°S at altitudes above 4200 m). Ages are based on the sea-level at high-latitude reference production rate and scaling system of Lifton et al. (2005. Addressing solar modulation and long-term uncertainties in scaling secondary cosmic rays for in situ cosmogenic nuclide applications. Earth and Planetary Science Letters 239, 140–161) in the CRONUS-Earth online calculator of Balco et al. (2008. A complete and easily accessible means of calculating surface exposure ages or erosion rates from ¹⁰Be and ²⁶Al measurements. Quaternary Geochronology 3, 174–195). Using the Lifton system, large outer lateral moraines in the Jeullesh Valley have a ¹⁰Be exposure age of 12.4 ka, inside of which are smaller moraine systems dated to 10.8, 9.7 and 7.6 ka. Large outer lateral moraines in the Tuco Valley have a ¹⁰Be exposure age of 12.5 ka, with inner moraines dated to 11.3 and 10.7 ka. Collectively, these data indicate that glacier recession from the Last Glacial Maximum (LGM) in the Cordillera Blanca was punctuated by three to four stillstands or minor advances during the period 12.5–7.6 ka, spanning the Younger Dryas Chronozone (YDC; ～12.9–11.6 ka) and the cold event identified in Greenland ice cores and many other parts of the world at 8.2 ka. The inferred fluctuations of tropical glaciers at these times, well after their withdrawal from the LGM, indicate an increase in precipitation or a decrease in temperature in this region. Although palaeoenvironmental records show regional and temporal variability, comparison with proxy records (lacustrine sediments and ice cores) indicate that regionally this was a cold, dry period so we ascribe these glacier advances to reduced atmospheric temperature rather than increased precipitation.     

A luminescence dating study of the sediment stratigraphy of the Lajia Ruins in the upper Yellow River valley,China

Pedo-sedimentological fieldwork were carried out in the Lajia Ruins within the Guanting Basin along the upper Yellow River valley. In the eolian loess-soil sections on the second river terrace in the Lajia Ruins, we find that the land of the Qijia Culture (4.20–3.95 ka BP) are fractured by several sets of earthquake fissures. A conglomerated red clay covers the ground of the Qijia Culture and also fills in the earthquake fissures. The clay was deposited by enormous mudflows in association with catastrophic earthquakes and rainstorms. The aim of this study is to provide a luminescence chronology of the sediment stratigraphy of the Lajia Ruins. Eight samples were taken from an eolian loess-soil section (Xialajia section) in the ruins for optically stimulated luminescence (OSL) dating. The OSL ages are in stratigraphic order and range from (31.94 ± 1.99) ka to (0.76 ± 0.02) ka. Combined OSL and ¹⁴C ages with additional stratigraphic correlations, a chronological framework is established. We conclude that: (1) the second terrace of the upper part of Yellow River formed 35.00 ka ago, which was followed by the accumulation of the eolian loess-soil section; and (2) the eolian loess-soil section is composed of the Malan Loess of the late last glacial (MIS-2) and Holocene loess-soil sequences.     

Relative timing of last glacial maximum and late-glacial events in the central tropical Andes

Whether or not tropical climate fluctuated in synchrony with global events during the Late Pleistocene is a key problem in climate research. However, the timing of past climate changes in the tropics remains controversial, with a number of recent studies reporting that tropical ice age climate is out of phase with global events. Here, we present geomorphic evidence and an in-situ cosmogenic ³He surface-exposure chronology from Nevado Coropuna, southern Peru, showing that glaciers underwent at least two significant advances during the Late Pleistocene prior to Holocene warming. Comparison of our glacial-geomorphic map at Nevado Coropuna to mid-latitude reconstructions yields a striking similarity between Last Glacial Maximum (LGM) and Late-Glacial sequences in tropical and temperate regions.Exposure ages constraining the maximum and end of the older advance at Nevado Coropuna range between 24.5 and 25.3 ka, and between 16.7 and 21.1 ka, respectively, depending on the cosmogenic production rate scaling model used. Similarly, the mean age of the younger event ranges from 10 to 13 ka. This implies that (1) the LGM and the onset of deglaciation in southern Peru occurred no earlier than at higher latitudes and (2) that a significant Late-Glacial event occurred, most likely prior to the Holocene, coherent with the glacial record from mid and high latitudes. The time elapsed between the end of the LGM and the Late-Glacial event at Nevado Coropuna is independent of scaling model and matches the period between the LGM termination and Late-Glacial reversal in classic mid-latitude records, suggesting that these events in both tropical and temperate regions were in phase.     

New results on palaeoenvironmental conditions in equatorial Africa derived from alluvial sediments of Cameroonian rivers

The ReSaKo project undertook extended fieldwork across southern Cameroon to explore the palaeoenvironmental information recorded in the alluvial sediments of equatorial African rivers. 160 hand-corings reaching maximum depths of 550 cm were carried out on alluvial ridges and floodplains of major Cameroonian fluvial systems. These multilayered, sandy to clayey alluvia contain sedimentary form-units and palaeosurfaces, which provide excellent additional proxy data archives for the reconstruction of palaeoenvironmental conditions in western equatorial Africa. Coring transects and sedimentary profiles document grain-size shifts and distinguishable sedimentary units in the stratigraphic record, which evidence (fluvial-)morphological adjustments of the fluvial systems in response to external forcing and (river-) intrinsic variability. 76 ¹⁴C-(AMS)-dated samples from organic sediment and macro-rests (fossil organic remains like wood, leafs, etc.) embedded in these sedimentary units indicate Late Pleistocene to recent ages (uncalibrated ¹⁴C-ages: 48–0.2 ka BP). The tentative interpretation of the alluvial record yields excellent additional information on the complex feedbacks between climate, ocean, fluvial as well as ecological systems and human activity in a little-studied region with high sensitive tropical ecosystems. δ¹³C-values (?35.5 to ?18.0‰) of the dated samples indicate the persistence of C₃-dominated gallery forests across the rivers (‘fluvial rain forest refuges’) despite several climatic fluctuations (aridifications, e.g. Last Glacial Maximum around 20 ka BP, Younger Dryas 13–11 ka BP). This research complements earlier results from additional terrestrial and marine proxy data archives on the Late Quaternary history of monsoonal western equatorial Africa.     

Climatic and topographic controls on the style and timing of Late Quaternary glaciation throughout Tibet and the Himalaya defined by 10Be cosmogenic radionuclide surface exposure dating

Temporal and spatial changes in glacier cover throughout the Late Quaternary in Tibet and the bordering mountains are poorly defined because of the inaccessibility and vastness of the region, and the lack of numerical dating. To help reconstruct the timing and extent of glaciation throughout Tibet and the bordering mountains, we use geomorphic mapping and ¹⁰Be cosmogenic radionuclide (CRN) surface dating in study areas in southeastern (Gonga Shan), southern (Karola Pass) and central (Western Nyainqentanggulha Shan and Tanggula Shan) Tibet, and we compare these with recently determined numerical chronologies in other parts of the plateau and its borderlands. Each of the study regions receives its precipitation mainly during the south Asian summer monsoon when it falls as snow at high altitudes. Gonga Shan receives the most precipitation (>2000 mm a⁻¹) while, near the margins of monsoon influence, the Karola Pass receives moderate amounts of precipitation (500–600 mm a⁻¹) and, in the interior of the plateau, little precipitation falls on the western Nyainqentanggulha Shan (∼300 mm a⁻¹) and the Tanggula Shan (400–700 mm a⁻¹). The higher precipitation values for the Tanggula Shan are due to strong orographic effects. In each region, at least three sets of moraines and associated landforms are preserved, providing evidence for multiple glaciations. The ¹⁰Be CRN surface exposure dating shows that the formation of moraines in Gonga Shan occurred during the early–mid Holocene, Neoglacial and Little Ice Age, on the Karola Pass during the Lateglacial, Early Holocene and Neoglacial, in the Nyainqentanggulha Shan date during the early part of the last glacial cycle, global Last Glacial Maximum and Lateglacial, and on the Tanggula Shan during the penultimate glacial cycle and the early part of the last glacial cycle. The oldest moraine succession in each of these regions varies from the early Holocene (Gonga Shan), Lateglacial (Karola Pass), early Last Glacial (western Nyainqentanggulha Shan), and penultimate glacial cycle (Tanggula Shan). We believe that the regional patterns and timing of glaciation reflect temporal and spatial variability in the south Asian monsoon and, in particular, in regional precipitation gradients. In zones of greater aridity, the extent of glaciation has become increasingly restricted throughout the Late Quaternary leading to the preservation of old (≫100 ka) glacial landforms. In contrast, in regions that are very strongly influenced by the monsoon (≫1600 mm a⁻¹), the preservation potential of pre-Lateglacial moraine successions is generally extremely poor. This is possibly because Lateglacial and Holocene glacial advances may have been more extensive than early glaciations and hence may have destroyed any landform or sedimentary evidence of earlier glaciations. Furthermore, the intense denudation, mainly by fluvial and mass movement processes, which characterize these wetter environments, results in rapid erosion and re-sedimentation of glacial and associated landforms, which also contributes to their poor preservation potential.     

A late Pleistocene glacial chronology from the Kitschi-Kurumdu Valley,Tien Shan (Kyrgyzstan), based on 10Be surface exposure dating

Surface exposure dating has become a helpful tool for establishing numeric glacial chronologies, particularly in arid high-mountain regions where radiocarbon dating is challenging due to limited availability of organic material. This study presents 13 new ¹⁰Be surface exposure ages from the Kitschi-Kurumdu Valley in the At Bashi Range, Tien Shan. Three moraines were dated to ~ 15, 21 and > 56 ka, respectively, and corroborate previous findings that glacial extents in the Tien Shan during Marine Oxygen Isotope Stage (MIS) 2 were limited compared to MIS 4. This likely documents increasingly arid conditions in Central Asia during the last glacial cycle. Morphological evidence in the Kitschi-Kurumdu Valley and a detailed review of existing numeric glacial chronologies from the Tien Shan indicate that remnants of the penultimate glaciation (MIS 6) are preserved, whereas evidence for MIS 5 glacier advances remains equivocal. Reviewed and recalculated exposure ages from the Pamir mountains, on the other hand, reveal extensive MIS 5 glacial extents that may indicate increased monsoonal precipitation. The preservation of MIS 3 moraines in the Tien Shan and the southern Pamir does not require any monsoonal influence and can be explained alternatively with increased precipitation via the westerlies.     

Postglacial climates inferred from a lake at treeline,southwest Yukon Territory,Canada

Pollen, chironomid, and ostracode records from a lake located at alpine treeline provide regional paleoclimate reconstructions from the southwest Yukon Territory, Canada. The pollen spectra indicate herbaceous tundra existed on the landscape from 13.6–11 ka followed by birch shrub tundra until 10 ka. Although Picea pollen dominated the assemblages after 10 ka, low pollen accumulation rates and Picea percentages indicate minimal treeline movement through the Holocene. Chironomid accumulation rates provide evidence of millennial-scale climate variability, and the chironomid community responded to rapid climate changes. Ostracodes were found in the late glacial and early Holocene, but disappeared due to chemical changes of the lake associated with changes in vegetation on the landscape. Inferred mean July air temperature, total annual precipitation, and water depth indicate a long-term cooling with increasing moisture from the late glacial through the Holocene. During the Younger Dryas (12.9–11.2 ka), cold and dry conditions prevailed. The early and mid-Holocene were warm and dry, with cool, wet conditions after 4 ka, and warm, dry conditions since the end of the Little Ice Age.