Search

The causes underlying Holocene glacier fluctuations remain elusive, despite decades of research efforts. Cosmogenic nuclide dating has allowed systematic study and thus improved knowledge of glacier-climate dynamics during this time frame, in part by filling in geographical gaps in both hemispheres. Here we present a new comprehensive Holocene moraine chronology from Mt. San Lorenzo (47°S) in central Patagonia, Southern Hemisphere. Twenty-four new 10Be ages, together with three published ages, indicate that the Río Tranquilo glacier approached its Holocene maximum position sometime, or possibly on multiple occasions, between 9,860 ± 180 and 6,730 ± 130 years. This event(s) was followed by a sequence of slightly smaller advances at 5,750 ± 220, 4,290 ± 100 (?), 3,490 ± 140, 1,440 ± 60, between 670 ± 20 and 430 ± 20, and at 390 ± 10 years ago. The Tranquilo record documents centennial to millennial-scale glacier advances throughout the Holocene, and is consistent with recent glacier chronologies from central and southern Patagonia. This pattern correlates well with that of multiple moraine-building events with slightly decreasing net extent, as is observed at other sites in the Southern Hemisphere (i.e., Patagonia, New Zealand and Antarctic Peninsula) throughout the early, middle and late Holocene. This is in stark contrast to the typical Holocene mountain glacier pattern in the Northern Hemisphere, as documented in the European Alps, Scandinavia and Canada, where small glaciers in the early-to-mid Holocene gave way to more-extensive glacier advances during the late Holocene, culminating in the Little Ice Age expansion. We posit that this past asymmetry between the Southern and Northern hemisphere glacier patterns is due to natural forcing that has been recently overwhelmed by anthropogenic greenhouse gas driven warming, which is causing interhemispherically synchronized glacier retreat unprecedented during the Holocene.

We here report the results of luminescence and cosmogenic exposure dating of the Idre marginal moraine, located in the southern Scandinavian Mountains. This particular moraine is targeted because it is morphologically distinct and marks the margin of a former ice sheet. The till in the moraine contains erratics that provide strong evidence of flow from an ice sheet centred over Norway. The area immediately outside the moraine margin is an older residual soil. Luminescence ages of three samples taken from a sand lense within the moraine indicate that it formed at around 55 ka, during the early warm part of Marine Isotope Stage (MIS) 3. Median exposure ages (10Be) of ten samples from boulders embedded in the surface till indicate that about 30 ka of ice-free time have elapsed since formation of the moraine. The difference between the age of the ridge and the duration of exposure provides a measure of the time of ice-cover in the ice sheet core area. Previous research indicates that final deglaciation of the site occurred at approximately 10 ka ago, which in combination with our results implies that the area around the Idre marginal moraine was ice free for ca. 20 ka, i.e. from around 55 ka to around 35 ka. Thereafter, the area was glaciated and the marginal moraine was covered by the Late Weichselian ice sheet for around 25 ka without experiencing any significant erosion or morphological destruction. While earlier studies have already pointed towards MIS 3 ice free conditions in northern and central Sweden, this study contributes a measurement-based duration estimate for the MIS 3 interstadial.

Cosmogenic nuclide dating of glacial landforms may lead to ambiguous results for ice retreat histories. The persistence of significant cosmogenic concentrations inherited from previous exposure may increase the apparent exposure ages for polished bedrocks affected by limited erosion under ice and for erratic boulders transported by glaciers and previously exposed in high‐altitude rock walls. In contrast, transient burying by moraines, sediments and snow decreases the apparent exposure age. We propose a new sampling strategy, applied to four sites distributed in the Arc and Arve valleys in the Western Alps, to better constrain the factors that can bias exposure ages associated with glacial processes. We used the terrestrial cosmogenic nuclide 10Be (TCN) to estimate the exposure time from paired sampling of depth profiles in polished bedrock and on overlying erratic boulders. For a given sampling site, the exposure ages for both the polished bedrock and boulder are expected to be the same. However, in six cases out of seven, boulders had significantly higher 10Be surface concentrations than those of the associated polished surfaces. In present and past glacial processes, the 10Be distribution with depth for boulders and bedrocks implies the presence of an inheritance concentration of 10Be. Our study suggests that 10Be concentrations in erratic boulders and in polished bedrocks provide maximum and minimum exposure ages of the glacial retreat, respectively. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd [ABSTRACT FROM AUTHOR]

Abstract We present 32 new cosmogenic 10Be exposure ages from a moraine sequence deposited during the Wisconsinan glaciation in the Swift River valley, Revelation Mountains, western Alaska Range. 10Be ages from an early Wisconsinan [Marine Isotope Stage 4] moraine average 59.7 ± 3.6 ka (n = 9; excluding one outlier), and 10Be ages from a late Wisconsinan [Marine Isotope Stage 2] terminal moraine, inboard moraines, and two recessional end moraines average 21.3 ± 0.8 ka (n = 3; excluding two outliers), 20.2 ± 1.0 ka (n = 7; excluding three young outliers), 19.6 ± 1.0 ka (n = 2; excluding one outlier) and 17.7 ± 0.8 ka (n = 4; excluding two outliers), respectively. The early Wisconsinan moraine age coincides with the close of MIS 4, consistent with previous chronologies from Beringia. Whereas Southern Hemisphere glaciers retreated prior to the onset of Heinrich Stadial 6 (64–60 ka), the MIS 4 glacier advance in the Swift River valley terminated at the close of Heinrich Stadial 6, possibly in response to abrupt North Atlantic warming. Our late Wisconsinan ages indicate significant initial glacier retreat between ca. 21.3–17.7 ka (prior to any significant increase in CO 2) likely in response to amplified warming from rising insolation. Preservation of MIS 4 moraines in Beringia has traditionally been ascribed to limited MIS 2 glacier advance modulated by low regional moisture availability, stemming from the exposed Bering Land Bridge. However, we hypothesize that atmospheric re-organization forced by the Laurentide Ice Sheet resulted in relatively higher temperatures and drier conditions in Beringia during MIS 2 than MIS 4, allowing for the preservation of early Wisconsinan moraines. Highlights • We present a new 10Be chronology of early and late Wisconsinan moraines from the Revelation Mountains, Alaska. • An early Wisconsinan [MIS 4] moraine dates to 59.7 ± 3.6 ka (n = 9). • Four late Wisconsinan [MIS 2] moraines date to 21.3 ± 0.8 ka, 20.2 ± 1.0 ka, 19.6 ± 1.0 ka, and 17.7 ± 0.8 ka. • Early Wisconsinan glaciation in Beringia culminated at the close of HS-6 possibly in response to North Atlantic warming. • Late Wisconsinan glaciation in Beringia culminated possibly in response to arctic amplification prior to the LGM. • Wisconsinan glaciation in Beringia is possibly controlled by atmospheric re-organization forced by the LIS during MIS 2. [ABSTRACT FROM AUTHOR]

ABSTRACT: Reconstructing the deglacial history of palaeo‐glaciers provides vital information on retreat processes, information which can inform predictions of the future behaviour of many of the world's glaciers. On this basis, this paper presents 170 Schmidt Hammer exposure ages from moraine boulders and glacially sculpted bedrock to reveal the post‐Last Glacial Maximum (LGM) history of the Wicklow Mountains, Ireland. These data suggest that large ice masses survived for 4–7 ka after retreat of the Irish Sea Ice Stream and were sustained by summit ice fields until ∼16.6 ka. Post‐LGM retreat was driven by climate and involved numerous short‐term ice front oscillations (≤1 ka), with widespread moraine deposition during Heinrich Stadial 1. In contrast, marked asynchroneity in the timing of Younger Dryas deglaciation is closely linked to snow redistribution which demonstrates the sensitivity of small cirque glaciers (≤1 km2) to local topography. This result has important implications for palaeoclimate reconstructions as cirque glacier dynamics may be (at least partly) decoupled from climate. This is further complicated by post‐depositional processes which can result in moraine ages (e.g. 10Be) which post‐date retreat. Future palaeoclimate studies should prioritize cirques where snow‐contributing areas are small and where post‐depositional disturbance of moraines is limited. [ABSTRACT FROM AUTHOR]

The response of the Greenland Ice Sheet to future climate change is relatively unconstrained. Determining the extents and rates of ice-margin fluctuations during the Holocene provides a longer-term perspective on ice-sheet changes and offers an analogue of how the ice-sheet may respond to future changes. Here, we present sixteen new 10Be ages of boulders on moraines, boulders perched on bedrock, and bedrock surfaces that mark the timing of ice-margin fluctuations during the Holocene in the Kangerlussuaq region of southern west Greenland. We show that the Keglen moraines date to 8.0 ± 0.3 ka (n = 6) and that the average ice-margin retreat rate slowed from about 49 to 13 m yr−1 after about 8.0 ka, likely in response to the ice margin retreating onto land at the head of the fjord Kangerlussuaq at this time. The average retreat rate further slowed to less than 1 m yr−1 between 6.8 ka and 4.2 cal kyr BP, a time when nearby paleoclimate records document warm summers and increased precipitation. Finally, we show that the historical advances of the ice margin occurred during the past 200 years, likely in response to cooler summer temperatures.

Abstract: The Greenland Ice Sheet is a major component of the Arctic cryosphere and the magnitude of its response to future climate changes remains uncertain. Longer-term records of climate near the ice sheet margin provide information about natural climate variability and can be used to understand the causes of past changes in the Greenland Ice Sheet. As a proxy for Holocene climate near the ice sheet margin, we reconstruct the fluctuations of Bregne ice cap in the Scoresby Sund region of central east Greenland. Bregne is a small ice cap (2.5 km2 in area) and responds sensitively to summer temperatures. We employ a multi-proxy approach to reconstruct the ice cap fluctuations using geomorphic mapping, 10Be ages of boulders and bedrock and lake sediment records. Past extents of Bregne ice cap are marked by moraines and registered by sediments in downvalley lakes. 10Be ages of bedrock and boulders outboard of the moraines indicate that Bregne ice cap was within ∼250 m of its present-day limit by at least 10.7 ka. Multi-proxy data from sediments in Two Move lake, located downvalley from Bregne ice cap, indicate that the ice cap likely completely disappeared during early and middle Holocene time. Increasing magnetic susceptibility and percent clastic material from ∼6.5 to ∼1.9 cal ka BP in Two Move lake sediments suggest progressively colder conditions and increased snow accumulation on the highlands west of the lake. Laminated silt deposited at ∼2.6 cal ka BP and ∼1.9 cal ka BP to present registers the onset and persistence of Bregne ice cap during the late Holocene. 10Be ages of boulders on an unweathered, unvegetated moraine in the Bregne ice cap forefield range from 0.74 to 9.60 ka. The youngest 10Be age (0.74 ka) likely represents the age of the moraine whereas older ages may be due to 10Be inherited from prior periods of exposure. This late Holocene moraine marks the second largest advance of the ice cap since deglaciation of the region at the end of the last ice age. The oldest moraine in the forefield dates to ≤2.6 cal ka BP. The fluctuations of Bregne ice cap were likely influenced by Northern Hemisphere summer insolation throughout the Holocene and abrupt late Holocene cold events. [Copyright &y& Elsevier]

ABSTRACT We present 34 new cosmogenic 10Be exposure ages that constrain the Lateglacial (Bølling-Preboreal) history of the Scandinavian Ice Sheet in the Lysefjorden region, south-western Norway. We find that the classical Lysefjorden moraines, earlier thought to be entirely of Younger Dryas age, encompass three adjacent moraines attributed to at least two ice sheet advances of distinctly different ages. The 10Be age of the outermost moraine (14.0 ± 0.6 ka; n = 4) suggests that the first advance is of Older Dryas age. The innermost moraine is at least 2000 years younger and was deposited near the end of the Younger Dryas (11.4 ± 0.4 ka; n = 7). After abandonment of the innermost Lysefjorden Moraine, the ice front receded quickly towards the head of the fjord, where recession was interrupted by an advance that deposited the Trollgaren Moraine at 11.3 ± 0.9 ka ( n = 5). 10Be ages from the inboard side of the Trollgaren Moraine suggest final retreat by 10.7 ± 0.3 ka ( n = 7). The late culmination of the Younger Dryas advance contrasts with other sectors of the Scandinavian Ice Sheet where the margin appears to have culminated earlier during the Younger Dryas stadial, followed by retreat during the middle and late part of the Younger Dryas. [ABSTRACT FROM AUTHOR]

Constraining the timing of past ice-sheet change is important for assessing the cryospheric expression of climate change and improving our understanding of ice sheet dynamics. Geochronology used to construct past ice-sheet reconstructions, however, can be ineffective in polar environments where ice sheets were polythermal and left varying imprints on landscapes. Cosmogenic-nuclide exposure dating, for example, is especially hampered by the lack of ice-sheet erosion and resultant cosmogenic nuclide inheritance. Here, we apply in situ cosmogenic 10Be, 14C and 26Al methods to decipher various elements of the Laurentide Ice Sheet history of north-central Baffin Island. A clearly defined erosion boundary across the landscape reveals the transition in basal ice-sheet conditions as ice flow became channelized into northern Baffin Island fiords. 10Be and 26Al concentrations indicate that the boundary represents a juxtaposition of sliding, erosive ice and cold-bedded ice that preserved ancient bedrock that has not been significantly impacted by the ice sheet in perhaps one to two million years. We combine 10Be measurements from ice-sculpted bedrock with measurements of in situ 14C, which has no inheritance due to its quick decay during ice-sheet cover, to determine the local timing of deglaciation. The average 10Be and in situ 14C ages for upland deglaciation in north-central Baffin Island are 7.7 ± 0.9 and 8.4 ± 1.4 ka, respectively. Finally, in situ 14C measurements from surfaces being uncovered by present-day retreat of small ice caps mantling uplands within the study area have concentrations too low to be compatible with continuous post-glacial exposure. These samples require shielding by ice for a significant portion of the Holocene, and more burial than during the Little Ice Age alone. Simple exposure-burial modeling suggests that 2400–2900 yr of total ice cover during Neoglaciation is required to explain measured in situ 14C inventories. Combined, multiple cosmogenic nuclides with varying half-lives can be used to decipher many aspects of the history in landscapes occupied by polythermal ice sheets. [ABSTRACT FROM AUTHOR]

Due to rising sea levels and warming ocean currents, marine-based sectors of the Greenland and Antarctic ice sheets are particularly vulnerable to warming climate. Reconstructions of the timing of marine-based ice margin fluctuations in Greenland during the early Holocene can provide context for historical and modern observations of ice-sheet change. Here, we generate a 10Be chronology of ice-sheet retreat through Disko Bugt, western Greenland. Our new chronology, consisting of twelve 10Be ages from sites surrounding and within Disko Bugt, fills a gap in the history of the western margin of the Greenland Ice Sheet and allows for a continuous composite record of ice-margin recession between the continental shelf break and the current margin. We constrain the onset of ice-margin retreat from outer Disko Bugt to 10.8 ± 0.5 ka. When combined with previous chronologies, these results place the final Greenland Ice Sheet retreat out of Disko Bugt onto land at Jakobshavn Isfjord and Qasigiaanguit at 10.1 ± 0.3 ka, and later at 9.2 ± 0.1 ka in southeastern Disko Bugt. The rate of retreat during this time period is between ∼50–450 m a−1 for central Disko Bugt and ∼50–70 m a−1 along the southern coast of Disko Bugt. Deglaciation of Disko Bugt occurred ∼1000 years later than in neighboring Uummannaq Fjord to the north. This asynchrony in the timing of deglaciation suggests that local ice dynamics played an important role in the retreat of the Greenland Ice Sheet from large marine embayments in western Greenland. [ABSTRACT FROM AUTHOR]

The chronology and configuration of the Svalbard Barents Sea Ice Sheet (SBSIS) during the Late Weichselian (LW) are based on few and geographically scattered data. Thus, the timing and configuration of the SBSIS has been a subject of extensive debate. We present provenance data of erratic boulders and cosmogenic 10Be ages of bedrock and boulders from Northwest Spitsbergen (NWS), Svalbard to determine the thickness, configuration and chronology during the LW. We sampled bedrock and boulders of mountain summits and summit slopes, along with erratic boulders from coastal locations around NWS. We suggest that a local ice dome over central NWS during LW drained radially in all directions. Provenance data from erratic boulders from northern coastal lowland Reinsdyrflya suggest northeastward ice flow through Liefdefjorden. 10Be ages of high-elevation erratic boulders in central NWS (687–836 m above sea level) ranging from 18.3 ± 1.3 ka to 21.7 ± 1.4 ka, indicate that the centre of a local ice dome was at least 300 m thicker than at present. 10Be ages of all high-elevation erratics (>400 m above sea level, central and coastal locations) indicate the onset of ice dome thinning at 25–20 ka. 10Be ages from erratic boulders on Reinsdyrflya ranging from 11.1 ± 0.8 ka to 21.4 ± 1.7 ka, indicate an ice cover over the entire Reinsdyrflya during LW and a complete deglaciation prior to the Holocene, but apparently later than the thinning in the mountains. Lack of moraine deposits, but the preservation of beach terraces, suggest that the ice covering this peninsula possibly was cold-based and that Reinsdyrflya was part of an inter ice-stream area covered by slow-flowing ice, as opposed to the adjacent fjord, which possibly was filled by a fast-flowing ice stream. Despite the early thinning of the ice sheet (25–20 ka) we find a later timing of deglaciation of the fjords and the distal lowlands. Several bedrock samples (10Be) from vertical transects in the central mountains of NWS pre-date the LW, and suggest either ice free or pervasive cold-based ice conditions. Our reconstruction is aligned with the previously suggested hypothesis that a complex multi-dome ice-sheet-configuration occupied Svalbard and the Barents Sea during LW, with numerous drainage basins feeding fast ice streams, separated by slow flowing, possibly cold-based, inter ice-stream areas. [ABSTRACT FROM AUTHOR]

We present a chronology of late Pleistocene deglaciation and Neoglaciation for two valleys in the north-central Brooks Range, Alaska, using cosmogenic 10Be exposure dating. The two valleys show evidence of ice retreat from the northern range front before ∼16-15 ka, and into individual cirques by ∼14 ka. There is no evidence for a standstill or re-advance during the Lateglacial period, indicating that a glacier advance during the Younger Dryas, if any, was less extensive than during the Neoglaciation. The maximum glacier expansion during the Neoglacial is delimited by moraines in two cirques separated by about 200 km and dated to 4.6 ± 0.5 and 2.7 ± 0.2 cal ka BP. Both moraine ages agree with previously published lichen-inferred ages, and confirm that glaciers in the Brooks Range experienced multiple advances of similar magnitude throughout the late Holocene. The similar extent of glaciers during the middle Holocene and the Little Ice Age may imply that the effect of decreasing summer insolation was surpassed by increasing aridity to limit glacier growth as Neoglaciation progressed. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: We surveyed fluvial terraces to decipher the Quaternary increment of crustal shortening and shortening rate in the on-shore Makran Accretionary Wedge. We focused on three major catchment basins and associated fold systems. Terrace profiles reconstructed from differential GPS measurements combined with DEM revealed two regional dominant wavelengths, about 5km in the northern part of the study area and about 15km to the south. These two wavelengths suggest the existence of two active décollement layers at two rooting depths. The average shortening rate due to folding is estimated at 0.8–1.2mm/a over the last 130ka. This accounts for 10–15% of the shortening rate (∼8mm/a) given by kinematic GPS measurements between Chabahar and Bazman and 3% of the convergence between Arabia and Eurasia, across the Makran subduction zone. Despite active deformation and a relatively high shortening rate, the geophysical record shows nearly absent seismic activity in Makran. We propose that strain accumulated in folds over intermediate décollement levels within a thick, incompletely lithified sedimentary cover explains the essentially aseismic, recent tectonics in this region. The importance of folds points to imperfect Coulomb behaviour of the wedge. [Copyright &y& Elsevier]

Abstract: Although Greenland ice core records register relatively stable Holocene climate conditions, the lower elevation margins of the Greenland Ice Sheet (GrIS) experienced significant Holocene fluctuations. These fluctuations include ice sheet recession during the Holocene Thermal Maximum (9–5 ka) and advance during the Little Ice Age (LIA; ∼A.D. 1350–1880). Determining the extent and timing of these fluctuations is important for understanding the response of the GrIS to interglacial climate conditions both warmer and colder than at present and for developing accurate ice sheet models. Sets of moraines marking past extents of the southwestern GrIS margin occur in the Kangerlussuaq region. We focus on the Ørkendalen moraines, a prominent moraine set located within 2 km of the modern ice margin and just outboard of the LIA moraines. We present the first 10Be ages of the Ørkendalen moraines indicating they were deposited at 6.8 ± 0.3 ka. The geomorphic relationship between the Ørkendalen and LIA moraines indicates that the ice sheet margin was inboard of its Ørkendalen extent between ∼6.8 ka and the culmination of the LIA. The age of the Ørkendalen moraines provides an important constraint on the extent of the southwestern GrIS during the middle Holocene. [Copyright &y& Elsevier]

Cavernous tafoni-type weathering is a common and conspicuous global feature, creating artistic sculptures, which may be relevant for geochemical budgets. Weathering processes and rates are still a matter of discussion. Field evidence in the type locality Corsica revealed no trend of size variability from the coast to subalpine elevations and the aspect of tafoni seems to be governed primarily by the directions of local fault systems and cleavage, and only subordinately by wind directions or the aspect of insulation. REM analysis of fresh tafone chips confirmed mechanical weathering by the crystallization of salts, as conchoidal fracturing of quartz is observed. The salts are only subordinately provided by sea spray, as calcium and sodium sulfates rather than halite dominate even close to the coast. Characteristic element ratios compare well with aerosols from mixed African and European air masses. Sulfates are largely derived from Sahara dust, indicated by their sulfur isotopic composition. Salt crystals form by capillary rise within the rock and subsequent crystallization in micro-cracks and at grain boundaries inside rain-protected overhangs. Siderophile bacteria identified by raster electron microscopy (REM) analysis of tafone debris contribute to accelerated weathering of biotite and tiny sulfide ore minerals. By applying Be-exposure dating, weathering rates of large mature tafone structures were found to be about an order of magnitude higher than those on the exposed top of the affected granite blocks. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Catastrophic partial drainage of Pangong Tso, one of the largest lakes in Tibet, is supported by the geomorphology of the Tangtse Valley, Ladakh, northern India and cosmogenic 10Be nuclide ages of roche moutonnées, strath terraces, and a flood deposit downstream from the former spillway. The former spillway for Pangong Tso is ~20-m-high and likely allowed ~18km3 of water to drain catastrophically down the Tangtse Valley over a period of about 2days sometime during the latest Pleistocene to early Holocene. The largest flood deposit, composed of imbricated granitic boulders up to 4.5m in length, is present ~33km downvalley of the spillway. These boulders have a cosmogenic 10Be exposure age of 11.1±1.0ka, the age of the outburst flood. The minimum calculated discharge was ~110,000m3 s−1. One set of strath terraces, upvalley of the flood deposit along the flood''s drainage path, shows that the rate of fluvial incision 0.3±0.1mmy−1 during 122–10.5ka increased to 1.5±0.5mmy−1 during 10.5ka to the present. The temporal overlap of this increase in the rate of fluvial incision with the main flood deposit suggests that the flood was important in defining the incision along the Tangste valley. A second set of strath terraces shows little change in incision, from ~0.6–0.9 to ~0.9–1.4mmy−1, sometime between 18 and 27ka. Roche moutonnées, upvalley from strath terraces, yield a cosmogenic 10Be age of 35.8±3.0ka, defining the time when glaciers last occupied the Tangtse valley. However, the lack of glacial sediment along the Tangste valley suggests that the flood eroded glacial depositional landforms and sediments resulting in high sediment loads in the floodwater, which in turn increased fluvial incision to form strath terraces. Much of the eroded glacial sediment was subsequently redeposited as the main flood deposit. The catastrophic drainage of Pangong Tso may be the result of breaching of the Pangong–Tangste spillway during very high lake levels in a period of intensified monsoon (10.7–9.6ka) and/or possibly the consequence of seismic activity along the Karakoram Fault that is associated with the initial formation of Pangong Tso. [Copyright &y& Elsevier]

Based on results of nannofossil analysis and 10Be dating in ferromanganese crusts M1-1 and A1-1 (no nannofossils were found in it), from the western and central Pacific respectively, it is found that the crust growth ages from nannofossil biostratigraphy agree well with those based on 10Be isotope analysis. Both crusts have three growth layers, and the oldest layer was deposited in Miocene at about 12.80 Ma. The maximum, minimum, and average growth rates of crust A1-1 (from the central Pacific) are 8.11, 1.92 and 3.47 mm/Ma, and those of crust M1-1 (from the western Pacific) are 2.93, 0.47, and 0.94 mm/Ma. [ABSTRACT FROM AUTHOR]

A 10Be/9Be-based chronostratigraphy has been determined for ODP 181, Site 1121 sediment core, recovered from the foot of the Campbell Plateau, Southwest Pacific Ocean. This core was drilled through the Campbell ‘skin drift’ in ca. 4500 m water depth on the mid-western margin of the extensive Campbell Nodule Field, beneath the flow of the major cold-water Deep Western Boundary Current (DWBC). In the absence of detailed biostratigraphy, beryllium isotopes have provided essential time information to allow palaeo-environmental interpretation to be undertaken on the upper 7 m of the core. Measured 10Be/9Be ratios of sediment, and of ferromanganese nodules entrapped in the sediment, decrease systematically with depth in the core, in accordance with radioactive decay. However, the 10Be/9Be data diverge from ca. 3 m below the seafloor (mbsf) to the top of the core, giving rise to several possible geochronological models. The preferred model assumes that the measured 10Be/9Be ratios of the nodule rims reflect initial 10Be/9Be ratios equivalent to contemporary seawater, and that these can be used to derive the true age of the sediment where the nodules occur. The nodule rim ages can be then used to interpret the sediment 10Be/9Be data, which indicate an overall age to ca. 7 mbsf of ca. 17.5 Ma. The derived chronology is consistent with diatom biostratigraphy, which indicates an age of 2.2–3.6 Ma at 1 mbsf. Calculated sedimentation rates range from 8 to 95 cm m.y.−1, with an overall rate to 7 mbsf of ca. 39 cm m.y.−1. The lowest rates generally coincide with the occurrence of entrapped nodules, and reflect periods of increased bottom current flow causing net sediment loss. Growth rates of individual nodules decrease towards the top of the sediment core, similar to the observed decrease in growth rate from core to rim of seafloor nodules from the Campbell Nodule Field. This may be related to an overall increase in the vigour of the DWBC from ca. 10 Ma to the present. [Copyright &y& Elsevier]

To put recent Greenland Ice Sheet (GrIS) ice loss into a longer-term context, we must understand its behavior during late-glacial and Early Holocene warming. Previous results seem to suggest that there is a large contrast in the timing of deglaciation between South and Southeast Greenland. However, because of lack of available data, in particular in Southeast Greenland, it is difficult to assess how the ice sheet responded to major late-glacial and Early Holocene climate changes. In this study, we use 41 new 10Be ages to constrain the deglaciation chronology in 12 new locations from the coast to the present ice margin in South and Southeast Greenland. We find that South Greenland (south of 61.5°N) deglaciated between ∼14.8 and 11.9 ka, whereas Southeast Greenland (61.5°N to 68.2°N) deglaciated between ∼11.4 and 11.3 ka. The deglaciation of the coastal, low-intermediate topography in South Greenland coincides with increased air surface temperatures during the Bølling-Allerød with fjords continuing to deglaciate into the Early Holocene. In contrast, the ice sheet persisted at the coast until the late-glacial and Early Holocene in Southeast Greenland, likely because of increased precipitation in the high alpine topography and fjord geometry and bathymetry (e.g. width of fjords and presence of sills). This multi-phased deglaciation demonstrates a contrasting response of the southern GrIS to changes in climate and variations in topographic setting, and that the spatial deglaciation of the GrIS was complex and likely did not respond to a single external climate forcing. • Deglaciation began in South Greenland by 14.8 ka coeval with rising air temperature. • Warm Atlantic water likely drove deglaciation during the Younger Dryas. • Ice retreated from Southeast Greenland coast by 11.3 ka when air temperatures rose. • Evidence of a Neoglacial advance occurs in Southeast Greenland by ∼1.9 ka. • Local climate, topography and fjord geometry/bathymetry likely mediated ice retreat. [ABSTRACT FROM AUTHOR]

The timing of glacier disappearance and rock glacier stabilization in the highest massifs of the Carpathians is still poorly documented. In this paper, we establish the extent and chronology of the final stages of glaciation and timing of stabilization of the uppermost rock glaciers in the Tatra Mountains, which are the highest (2654 m a.s.l.), northernmost (N 49°12′), and coldest range in the Carpathians. On the base of morphostratigraphic principles, Schmidt Hammer tests and glacier equilibrium line altitude (ELA) estimation, we assigned moraines and rock glaciers in the Mt. Kriváň massif (SW part of High Tatras) to a threefold stratigraphic sequence with glacial stages/advances from older to younger: Popradské pleso (Pp), Suchá važecká I (Sv I) and Suchá važecká II (Sv II). Landforms attributed to two younger advances, Sv I and Sv II, were sampled for the purpose of cosmogenic 10Be surface exposure dating. Our data show that Pp and Sv I glacial advances occurred during the Oldest Dryas climatic downturn. The younger advance (Sv I) occurred just before the Bølling-Allerød (B/A) warming at 14.9 ± 0.4 ka, at this time small glaciers occupied lower glacial cirques in the study area. The youngest Sv II advance was characterized by rock glaciers and small debris-covered glaciers confined to the highest cirques. The mean exposure age of four relict rock glaciers of this stage is 11.1 ± 0.9 ka but individual rock glacier mean ages spanned between 11.8 and 10.4 ka. Our research results show that the youngest moraines and rock glaciers in the Tatra Mountains were formed during the Younger Dryas (YD), but the final permafrost melting and rock glacier stabilization period was delayed until the early Holocene, but no later than 10.4 ka. In high elevation cirque bottoms (up to 2120 m a.s.l.), the YD glaciers and rock glaciers readvanced across land which was ice-free as early as 14.8–14.2 ka. Thus, it is likely that during the B/A interphase, glaciers completely disappeared in the Tatra Mountains. The YD was the last period of glacial/periglacial activity in the massif. As we investigated one of the highest-situated rock glaciers in the Tatras (up to 2220 m a.s.l.), we conclude that all rock glaciers in this massif are relict landforms which developed in response to severe Lateglacial climate conditions. The Lateglacial climate of the Tatra Mountains is discussed herein on the basis of glacier equilibrium line altitude (ELA) estimation and the vertical distribution of rock glacier belts. We argue that paleoclimate significance of the presented geomorphological record may match paleobotanical proxy reconstructions and the results of climate simulations, but only if the impact of enhanced temperature seasonality on glacier mass balance and rock glacier activity is taken into account. • Deglaciation in the High Tatras was almost completed before the B/A interphase. • During the Younger Dryas very limited, apron-type glaciation was renewed. • Highest located rock glaciers were stabilized in the YD/Early Holocene transition. • Increased temperature seasonality during the Lateglacial is discussed. [ABSTRACT FROM AUTHOR]

• The Aricota landslide dam is an enigmatic giant landslide of the hyper arid Andes • Its rock volume was 2 km3, producing a dam of 600 m height and a lake of 6 km long • 13 new 10Be exposure ages show two main events at 17.9 ± 0.7 and 12.1 ± 0.2 ka • This timing is consistent with periods of regional paleoprecipitation increases The central part of the Western Andes holds an exceptional concentration of giant paleolandslides involving very large volumes of rock material (v > km3). While those gravitational slope failures are interpreted consensually as an erosional response to the geodynamic activity of the Andes (relief formation and tectonic activity), the question of their triggering mechanisms remains enigmatic. To clarify the respective roles of climatic versus seismic forcing on the Andean landslides, new temporal constraints on paleo movements are essential. Here, we focus on one of those giant slope failures, the Aricota giant rockslide that damned the Locumba valley in southern Peru. We conducted fieldwork, high-resolution DEM analysis and cosmogenic nuclide dating to decipher its development history and failure mechanisms. Our results point to the occurrence of two successive events. A giant failure mobilizing a rock volume of ca. 2 km3 first produced a dam at 17.9 ± 0.7 ka. Considering its height of ca. 600 m, the Aricota rockslide dam is one of the three largest landslide dams worldwide. At 12.1 ± 0.2 ka, a second event produced ca. 0.2 km3 of material, and the rock-avalanche debris spread out over the dam. As the chronology of those two events is pointing to the two main paleoclimatic pluvial periods in this region (Heinrich Stadial 1a and Younger Dryas), we favor the interpretation of a climatic forcing. At a regional scale, the concomitant aggradation of alluvial terraces and fan systems along the nearby valleys highlights higher regional erosion, sediments supply and mass-wasting events during those paleoprecipitation events and strengthens this conclusion. [ABSTRACT FROM AUTHOR]

The response of the Greenland Ice Sheet to future climate change is relatively unconstrained. Determining the extents and rates of ice-margin fluctuations during the Holocene provides a longer-term perspective on ice-sheet changes and offers an analogue of how the ice-sheet may respond to future changes. Here, we present sixteen new 10Be ages of boulders on moraines, boulders perched on bedrock, and bedrock surfaces that mark the timing of ice-margin fluctuations during the Holocene in the Kangerlussuaq region of southern west Greenland. We show that the Keglen moraines date to 8.0 ± 0.3 ka (n = 6) and that the average ice-margin retreat rate slowed from about 49 to 13 m yr−1 after about 8.0 ka, likely in response to the ice margin retreating onto land at the head of the fjord Kangerlussuaq at this time. The average retreat rate further slowed to less than 1 m yr−1 between 6.8 ka and 4.2 cal kyr BP, a time when nearby paleoclimate records document warm summers and increased precipitation. Finally, we show that the historical advances of the ice margin occurred during the past 200 years, likely in response to cooler summer temperatures. [ABSTRACT FROM AUTHOR]