Surface-exposure ages of Front Range moraines that may have formed during the Younger Dryas, 8.2 cal ka,and Little Ice Age events

Surface-exposure (¹⁰Be) ages have been obtained on boulders from three post-Pinedale end-moraine complexes in the Front Range, Colorado. Boulder rounding appears related to the cirque-to-moraine transport distance at each site with subrounded boulders being typical of the 2-km-long Chicago Lakes Glacier, subangular boulders being typical of the 1-km-long Butler Gulch Glacier, and angular boulders being typical of the few-hundred-m-long Isabelle Glacier. Surface-exposure ages of angular boulders from the Isabelle Glacier moraine, which formed during the Little Ice Age (LIA) according to previous lichenometric dating, indicate cosmogenic inheritance values ranging from 0 to ∼3.0 ¹⁰Be ka.¹ Subangular boulders from the Butler Gulch end moraine yielded surface-exposure ages ranging from 5 to 10.2 ¹⁰Be ka. We suggest that this moraine was deposited during the 8.2 cal ka event, which has been associated with outburst floods from Lake Agassiz and Lake Ojibway, and that the large age range associated with the Butler Gulch end moraine is caused by cosmogenic shielding of and(or) spalling from boulders that have ages in the younger part of the range and by cosmogenic inheritance in boulders that have ages in the older part of the range. The surface-exposure ages of eight of nine subrounded boulders from the Chicago Lakes area fall within the 13.0–11.7 ¹⁰Be ka age range, and appear to have been deposited during the Younger Dryas interval. The general lack of inheritance in the eight samples probably stems from the fact that only a few thousand years intervened between the retreat of the Pinedale glacier and the advance of the Chicago Lakes glacier; in addition, bedrock in the Chicago Lakes cirque area may have remained covered with snow and ice during that interval, thus partially shielding the bedrock from cosmogenic radiation.     

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.     

Cosmogenic 10Be and 36Cl ages from Late Pleistocene terminal moraine complexes in the Taylor River drainage basin,central Colorado,USA

Cosmogenic surface-exposure ages from boulders on a terminal moraine complex establish the timing of the local last glacial maximum (LGM) in the Taylor River drainage basin, central Colorado. Five zero-erosion ¹⁰Be ages have a mean of 19.5±1.8 ka while that for three ³⁶Cl ages is 20.7±2.3 ka. Corrections for modest rates (∼1 mm ka⁻¹) of boulder surface erosion result in individual and mean ages that are generally within 2% of their zero-erosion values. Both the means and the range in ages of individual boulders are consistent with those reported for late Pleistocene moraines elsewhere in the southern and middle Rocky Mountains, and thus suggest local LGM glacier activity was regionally synchronous. Two anomalously young (?) zero-erosion ¹⁰Be ages (mean 14.4±0.8 ka) from a second terminal moraine are tentatively attributed to the boulders having been melted out during a late phase of ice stagnation.     

Glacial retreat history of Nanhuta Shan (north-east Taiwan) from preserved glacial features: the cosmic ray exposure perspective.

Taiwan, located at the junction of the Pacific Ocean, the Eurasian continent, and the South China marginal Sea, is of particular interest for reconstructing paleoclimate periods in Eastern Asia. This study reports the first cosmic ray exposure dating (CRE) of glacial features in Taiwan. Among the areas where glacial relicts have been described in Taiwan, the Nanhuta Shan range is probably the place where glacial landforms are best preserved. We consequently focused on this area combining glacial geomorphology observations together with CRE dating using in situ produced ¹⁰Be of erratic boulders and ice-sculpted surfaces. When combined with the geomorphic characteristics of the sampled areas, the obtained minimum CRE ages suggest that the glacial retreat in the Nanhuta Shan commenced about 10±3 ka ago and retreat was complete by 7±1 ka ago. This is consistent with the Holocene warming trend deduced from other biological and physico-chemical paleoclimatic records for the region. Estimates of local bedrock surface denudation rates either directly from in situ produced ¹⁰Be measurements or from geomorphic considerations are employed to determine the preservation of such glacial features within the highly dynamic setting of Taiwan.     

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.     

Lateglacial and early Holocene dynamics of adjacent valley glaciers in the Western Swiss Alps

The Alps play a pivotal role for glacier and climate reconstructions within Europe. Detailed glacial chronologies provide important insights into mechanisms of glaciation and climate change. We present 26 ¹⁰Be exposure dates of glacially transported boulders situated on moraines and ice‐moulded bedrock samples at the Belalp cirque and the Great Aletsch valley, Switzerland. Weighted mean ages of ～10.9, 11.1, 11.0 and 9.6 ka for the Belalp, on up to six individual moraine ridges, constrain these moraines to the Egesen, Kartell and Schams stadials during Lateglacial to early Holocene times. The weighted mean age of ～12.5 ka for the right‐lateral moraine of the Great Aletsch correlates with the Egesen stadial related to the Younger Dryas cooling. These data indicate that during the early Holocene between ～11.7 and ～9.2 ka, glaciers in the Swiss Alps seem to have been significantly affected by cold climatic conditions initiated during the Younger Dryas and the Preboreal Oscillation. These conditions resulted in glacier margin oscillations relating to climatic fluctuations during the second phase of the Younger Dryas – and continuing into Boreal times – as supported by correlation of the innermost moraine of the Belalp Cirque to the Schams (early) Holocene stage. Copyright © 2011 John Wiley & Sons, Ltd.     

10Be ages from central east Greenland constrain the extent of the Greenland ice sheet during the Last Glacial Maximum

Traditional ice sheet reconstructions have suggested two distinctly different ice sheet regimes along the East Greenland continental margin during the Last Glacial Maximum (LGM): ice to the shelf break south of Scoresby Sund and ice extending no further than to the inner shelf at and north of Scoresby Sund. We report new ¹⁰Be ages from erratic boulders perched at 250 m a.s.l. on the Kap Brewster peninsula at the mouth of Scoresby Sund. The average ¹⁰Be ages, calculated with an assumed maximum erosion rate of 1 cm/ka and no erosion (respectively, 17.3±2.3 ka and 15.1±1.7 ka) overlap with a period of increased sediment input to the Scoresby Sund fan (19–15 ka). The results presented here suggest that ice reached at least 250 m a.s.l. at the mouth of Scoresby Sund during the LGM and add to a growing body of evidence indicating that LGM ice extended onto the outer shelf in northeast Greenland.     

The deglacial history of NW Alexander Island,Antarctica, from surface exposure dating

Recent changes along the margins of the Antarctic Peninsula, such as the collapse of the Wilkins Ice Shelf, have highlighted the effects of climatic warming on the Antarctic Peninsula Ice Sheet (APIS). However, such changes must be viewed in a long-term (millennial-scale) context if we are to understand their significance for future stability of the Antarctic ice sheets. To address this, we present nine new cosmogenic ¹⁰Be exposure ages from sites on NW Alexander Island and Rothschild Island (adjacent to the Wilkins Ice Shelf) that provide constraints on the timing of thinning of the Alexander Island ice cap since the last glacial maximum. All but one of the ¹⁰Be ages are in the range 10.2–21.7 ka, showing a general trend of progressive ice-sheet thinning since at least 22 ka until 10 ka. The data also provide a minimum estimate (490 m) for ice-cap thickness on NW Alexander Island at the last glacial maximum. Cosmogenic ³He ages from a rare occurrence of mantle xenoliths on Rothschild Island yield variable ages up to 46 ka, probably reflecting exhumation by periglacial processes.     

Readvance of the last British–Irish Ice Sheet during Greenland Interstade 1 (GI-1): the Wester Ross Readvance,NW Scotland

Fourteen samples obtained from Torridon sandstone boulders on four moraines marking the limit of the Wester Ross Readvance (WRR) in NW Scotland yielded tightly clustered ¹⁰Be exposure ages confirming contemporaneous or penecontemporaneous moraine deposition. Collectively, the 14 samples yield mean ages of 13.5 ± 1.2 ka to 14.0 ± 1.7 ka, depending on choice of geomagnetic scaling and sampling surface erosion rates. All fourteen moraine ages are significantly younger than an age of ca 16.3 ka previously proposed for the WRR, and also younger than most samples obtained from rock outcrops within the WRR limits. The ages obtained for the WRR moraines appear to confirm that a substantial cover of glacier ice persisted over low ground in NW Scotland during at least the early part of the Lateglacial Interstade (≈Greenland Interstade 1). We infer that the WRR probably occurred in response to rapid short-lived cooling during the Older Dryas climatic reversal (≈Greenland Interstade 1d), though the possibilities that the WRR represents ice-margin response to a later climatic reversal during the Lateglacial Interstade or stabilization and readvance of the ice margin following rapid offshore calving cannot be discounted.     

Cosmogenic 10Be insights into the extent and chronology of the last deglaciation in Wester Ross,northwest Scotland

Cosmogenic ¹⁰Be surface exposure ages for bedrock sites around Torridon and the Applecross Peninsula in Wester Ross, northwest Scotland, provide new insights into the Lateglacial transition. Accounting for postglacial weathering, six statistically comparable exposure ages give a late Younger Dryas (G‐1) exposure age of 11.8 ± 1.1 ka. Two further outliers are tentative pre‐Younger Dryas exposure ages of 13.4 ± 0.5 ka in Torridon, and 17.5 ± 1.2 ka in Applecross. The Younger Dryas exposure ages have compelling implications for the deglaciation of marginal Loch Lomond Stadial ice fields in Torridon and Applecross. Firstly, they conflict with predictions of restricted ice cover and rapid retreat based on modelling experiments and climate proxies, instead fitting a model of vertically extensive and prolonged ice coverage in Wester Ross. Secondly, they indicate that >2 m of erosion took place in the upper valleys of Torridon and Applecross during the Younger Dryas, implying a dominantly warm‐based glacial regime. Finally, the exposure ages have clarified that corrie (cirque) glaciers did not readvance in Wester Ross, following final deglaciation. Copyright © 2011 John Wiley & Sons, Ltd.     

Cosmogenic Be dating of the Salpausselkä I Moraine in southwestern Finland

We determined in situ cosmogenic ¹⁰Be ages for nine boulders sampled on the Salpausselkä I (Ss I) Moraine. Previous dating of this moraine indicated that it formed during the Younger Dryas Stadial along the southern margin of the Scandinavian Ice Sheet in southern Finland. Our new exposure ages range from 10.9±1.0 to 13.5±1.2 ¹⁰Be ka, with an error-weighted mean age of 12.4±0.7 ¹⁰Be ka. Our results confirm four previous ¹⁰Be ages obtained 40 km northeast of our sample location. The combined data (n=13) indicate that retreat from the Ss I Moraine occurred at 12.5±0.7 ¹⁰Be ka, in excellent agreement with an age of 12.1 ka for retreat from the Ss I Moraine based on varve chronologies. These results identify the Ss I Moraine as among the best-dated margins associated with Late Quaternary ice sheets.     

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.     

Deglaciation and landscape history around Annapurna,Nepal, based on 10Be surface exposure dating

The High Himalaya is a key area for tectonic, geomorphological and climate studies, because of its extreme relief and location at the transition zone between areas with abundant monsoonal precipitation and the arid/semiarid Tibetan Plateau. We present ¹⁰Be surface exposure ages on 22 boulders from the Annapurna area in Nepal. The ages improve understanding of the Late Quaternary landscape history and the geomorphological processes operating in this part of the Himalaya.Although our study is reconnaissance in nature, it highlights the importance of catastrophic events, such as landslides and debris flows, for denudation of high mountains. Holocene exposure ages for the Dhampu–Chooya landslide (～4.1 ± 0.6 ka) and for 600 m of alluviation in Kali Gandaki Valley (～2.1 ± 0.6 ka), for example, indicate the frequent occurrence and extent of catastrophic events and their implications for natural hazards. We also offer an explanation for the differences in Late Quaternary glacial chronologies at closely spaced study sites in the Nepal Himalaya. Topographically controlled and spatially variable precipitation in the Himalaya determines the sensitivity of glaciers to changes in temperature and precipitation. Accordingly, some glaciers advanced in-phase with Northern Hemisphere ice sheets, whereas others reached their maximum extent at times of increased monsoonal precipitation during Marine Isotope Stage 3 and the early Holocene.     

Surface exposure dating of the Great Aletsch Glacier Egesen moraine system,western Swiss Alps,using the cosmogenic nuclide 10Be

Egesen moraines throughout the Alps mark a glacial advance that has been correlated with the Younger Dryas cold period. Using the surface exposure dating method, in particular the measurement of the cosmogenic nuclide ¹⁰Be in rock surfaces, we attained four ages for boulders on a prominent Egesen moraine of Great Aletsch Glacier, in the western Swiss Alps. The ¹⁰Be dates range from 10 460±1100 to 9040±1020 yr ago. Three ¹⁰Be dates between 9630±810 and 9040±1020 yr ago are based upon samples from the surfaces of granite boulders. Two ¹⁰Be dates, 10 460±1100 and 9910±970 yr ago, are based upon a sample from a quartz vein at the surface of a schist boulder. In consideration of the numerous factors that can influence apparently young ¹⁰Be dates and the scatter within the data, we interpret the weighted mean of four boulder ages, 9640±430 yr (including the weighted mean of two ¹⁰Be dates of the quartz vein), as a minimum age of deposition of the moraine. All ¹⁰Be dates from the Great Aletsch Glacier Egesen moraine are consistent with radiocarbon dates of nearby bog‐bottom organic sediments, which provide minimum ages of deglaciation from the moraine. The ¹⁰Be dates from boulders on the Great Aletsch Glacier Egesen moraine also are similar to ¹⁰Be dates from Egesen moraines of Vadret Lagrev Glacier on Julier Pass, in the eastern Swiss Alps. Both the morphology of the Great Aletsch Glacier Egesen moraine and the comparison with ¹⁰Be dates from the inner Vadret Lagrev Egesen moraine support the hypothesis that the climatic cooling that occurred during the Younger Dryas cold episode influenced the glacial advance that deposited the Great Aletsch Glacier Egesen moraine. Because of the large size and slow response time of Great Aletsch Glacier, we suggest that the Great Aletsch Glacier Egesen moraine was formed during the last glacial advance of the multiphased Egesen cold period, the Kromer stage, during the Preboreal chron. Copyright © 2004 John Wiley & Sons, Ltd.     

Late Quaternary glaciation of the Tianshan, Central Asia, using cosmogenic Be surface exposure dating

Glacial deposits are present at the head of the Ürümqi River valley, Tianshan, Central Asia. ¹⁰Be surface exposure ages of 15 boulders from three sites along a 12 km valley transect range from 9 to 21 ka suggesting emplacement by glacial retreat and advance commencing at the global last glacial maximum (LGM) and most likely abating in the early Holocene. Although the age spread for a given locality is not small, perhaps indicating post-depositional reworking, maximum ages per site are either coeval with or are post-LGM and inconsistent with previous pre-LGM electron spin resonance ages.     

Cosmogenic nuclide exposure ages for moraines in the Lago San Martin Valley, Argentina

At several times during the Quaternary, a major eastward-flowing outlet glacier of the former Patagonian Ice Sheet occupied the Lago San Martin Valley in Argentina (49°S, 72°W). We present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide (¹⁰Be) exposure ages (n = 10) of boulders on moraines and lake shorelines. There are five prominent moraine belts in the Lago San Martin Valley, associated with extensive sandar (glaciofluvial outwash plains) and former lake shorelines. Cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14.3 ± 1.7 ka, 22.4 ± 2.3 ka, 34.4 ± 3.4 ka to 37.6 ± 3.4 ka (and possibly 60 ± 3.5 ka), and 99 ± 11 ka (1σ). These dated glacier advances differ from published chronologies from the Lago San Martin Valley based on ¹⁴C age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges. The moraine boulder ages also point to possible pre-LGM glacial advances during the last glacial cycle and a key observation from our data is that the LGM glaciers were probably less extensive in the Lago San Martin Valley than previously thought.     

New data for Late Pleistocene Pinedale alpine glaciation from southwestern Colorado

New cosmogenic surface-exposure ages of moraine-crest boulders from southwestern Colorado are compared with published surface-exposure ages of boulders from moraine complexes in north-central Colorado and in west-central (Fremont Lake basin) Wyoming. ¹⁰Be data sets from the three areas were scaled to a single ¹⁰Be production rate of 5.4 at/g/yr at sea level and high latitude (SLHL), which represents the average ¹⁰Be production rate for two high-altitude, mid-latitude sites in the western United States (US) and Austria. Multiple nuclide ages on single boulders indicate that this ¹⁰Be production rate yields ages comparable to those calculated with a commonly used ³⁶Cl production scheme. The average age and age range of moraine-crest boulders on terminal moraines at the southwestern Colorado and Wyoming sites are similar, indicating a retreat from their positions ∼16.8 ³⁶Cl ka (Cosmogenic ages in this paper are labeled ¹⁰Be or ³⁶Cl ka or just ka when both ¹⁰Be or ³⁶Cl ages are being discussed; radiocarbon ages are labeled ¹⁴C ka, calibrated radiocarbon are labeled cal ka, and calendar ages are labeled calendar ka. Errors (±1σ) associated with ages are shown in tables. Radiocarbon ages were calibrated using the data of Hughen et al. (Science 303 (2004) 202). This suggests a near-synchronous retreat of Pinedale glaciers across a 470-km latitudinal range in the Middle and Southern Rocky Mountains. Hypothetical corrections for snow shielding and rock-surface erosion shifts the time of retreat to between 17.2 and 17.5 ¹⁰Be ka at Pinedale, Wyoming, and between 16.3 and 17.3 ³⁶Cl ka at Hogback Mountain, Colorado.     

Last Glacial Maximum ice sheet dynamics in Arctic Canada inferred from young erratics perched on ancient tors

A long-standing debate regarding the reconstruction of former ice sheets revolves around the use of relative weathering of landscapes, i.e., the assumption that highly weathered landscapes have not been recently glaciated. New cosmogenic isotope measurements from upland bedrock surfaces and erratics along the northeastern margin of the Laurentide Ice Sheet (LIS) shed light on this debate. ¹⁰Be and ²⁶Al concentrations from three perched erratics, yielding cosmogenic exposure ages of 17–11 ka, are much lower than those measured in two unmodified, highly weathered tors upon which they lie, which yield cosmogenic exposure ages of >60 ka. These findings suggest that non-erosive ice covered weathered upland surfaces along the northeastern margin of the LIS during the last glacial maximum. These data challenge the use of relative weathering to define the margins of Pleistocene ice sheets. The juxtaposition of non-erosive ice over upland plateaus and erosive ice in adjacent fiords requires strong gradients in basal thermal regimes, suggestive of an ice-stream mode of glaciation.     

Glacial oscillations during the Bølling–Allerød Interstadial–Younger Dryas transition in the Ruda Valley,Central Pyrenees

The Upper Garonne Basin included the largest glacial system in the Pyrenees during the last glacial cycle. Within the long-term glacial retreat during Termination-1 (T-1), glacier fluctuations left geomorphic evidence in the area. However, the chronology of T-1 glacial oscillations on the northern slopes of the Central Pyrenees is still poorly constrained. Here, we introduce new geomorphological observations and a 12-sample dataset of ¹⁰Be cosmic-ray exposure ages from the Ruda Valley. This U-shaped valley, surrounded by peaks exceeding 2800 m a.s.l., includes a sequence of moraines and polished surfaces that enabled a reconstruction of the chronology of the last deglaciation. Following the maximum ice extent, warmer conditions prevailing at ~15–14 ka, during the Bølling–Allerød (B–A) Interstadial, favoured glacial retreat in the Ruda Valley. Within the B–A, glaciers experienced two phases of advance/stillstand with moraine formation at 13.5 and 13.0 ka. During the early Younger Dryas (YD), glacial retreat exposed the highest surfaces of the Saboredo Cirque (~2300–2350 m) at 12.7 ka. Small glaciers persisted only inside the highest cirques (~2470 m), such as in Sendrosa Cirque, with moraines stabilising at 12.6 ka. The results of this work present the most complete chronology for Pyrenean glacial oscillations from the B–A to the YD.     

Did large ice caps persist on low ground in north‐west Scotland during the Lateglacial Interstade?

Recent research based primarily on exposure ages of boulders on moraines has suggested that extensive ice masses persisted in fjords and across low ground in north‐west Scotland throughout the Lateglacial Interstade (≈ Greenland Interstade 1, ca. 14.7–12.9 ka), and that glacier ice was much more extensive in this area during the Older Dryas chronozone (ca. 14.0 ka) than during the Younger Dryas Stade (ca. 12.9–11.7 ka). We have recalibrated the same exposure age data using locally derived ¹⁰Be production rates. This increases the original mean ages by 6.5–12%, implying moraine deposition between ca. 14.3 and ca. 15.1 ka, and we infer a most probable age of ca. 14.7 ka based on palaeoclimatic considerations. The internal consistency of the ages implies that the dated moraines represent a single readvance of the ice margin (the Wester Ross Readvance). Pollen–stratigraphic evidence from a Lateglacial site at Loch Droma on the present drainage divide demonstrates deglaciation before ca. 14.0 ka, and therefore implies extensive deglaciation of all low ground and fjords in this area during the first half of the interstade (ca. 14.7–14.0 ka). This inference appears consistent with Lateglacial radiocarbon dates for shells recovered from glacimarine sediments and a dated tephra layer. Our revised chronology conflicts with earlier proposals that substantial dynamic ice caps persisted in Scotland between 14 and 13 ka, that large active glaciers probably survived throughout the Lateglacial Interstade and that ice extent was greater during the Older Dryas period than during the Younger Dryas Stade. Copyright © 2011 John Wiley & Sons, Ltd.