Glacier Expansion Research Articles

Ice-marginal ridge relief complex in northern Kola Peninsula (NW Russia): morphology, structure, and genetic interpretation

A widely spread ridge relief complex was formed by the last ice cover in the northeastern part of the Kola Peninsula. The complex belongs to the ice-marginal formations of the ice streams of the north-eastern Fennoscandian Ice Sheet. The applied morphometric research technique (including the analysis of the digital elevation model) has allowed identifying the ridge relief complex to make a sub-longitudinal belt. The belt comprises frontal and radial ridges, ridges and hills of the distal part of the belt, and complex-shaped ridges. These landforms were studied in eight outcrops and trenches. The frontal and some complex-shaped ridges consist of basal and ablation tills and glaciofluvial deposits deformed by the east- and north-eastward advancing glacier. The radial ridges composed of glaciofluvial sediments are the eskers. Glaciofluvial deposits with a thin cover of ablation and flow tills form the ridges on the distal part of the belt. They mark the limits of glacier expansion at an individual glacial stage. Some complex-shaped ridges are composed only of the ablation melt-out till and formed in crevasses of dead ice massifs. The ridge relief complex shows morphological similarities with the Veiki moraine in North Sweden, Pulju moraine in Finland, and ridges of the “ice-walled-lake plains” in North America. The location of the moraine ridge landforms is controlled by the topography of crystalline bedrock. During the last glaciation, the glacier retreated in several stages marked by belts of the ridge landforms. Each stage was followed by a series of oscillations corresponding to chains of frontal moraine ridges. The correlation of the ice-marginal forms in other parts of the Kola and Karelia regions allows the authors to refer them to the Neva Stage (other names are Keiva I, Syamozero), which took place in the Older Dryas Stadial.

Mineralogical and magnetic variations of periglacial loess in SE Tibet reveal mid-Pleistocene expansion of Tibetan glacial activity

The formation and evolution of the cryosphere on the Tibetan Plateau is of great significance in understanding the Earth's carbon and climatic system. Periglacial loess deposits in southeastern Tibet offer a means to constrain this history as they contain critical information on glacial grinding and frost shattering processes in high-altitude mountain regions through time, which yield lithogenic fractions of largely loess silts and sands. Based on combined analyses of lithogenic magnetic properties and mineralogical composition, here we find that increasing high mountain production and supply of fresh detrital components since the mid-Pleistocene climate transition (MPT, 1.2–0.7 Ma) led to a substantial increase of the lithogenic susceptibility and decrease in chemical weathering intensity of periglacial loess in southeastern Tibet. The agreement of these findings with similar results from eolian loess on the northern margins of the Tibetan Plateau suggests a plateau-wide glacier expansion during the MPT. Enhanced glacial erosion and freeze-thaw activities occurred in the high-altitude mountain regions of the plateau during the MPT, thereby providing vast amounts of fresh detritus for the formation of loess deposits. High and constant values of lithogenic magnetic parameters in the loess deposits after 0.7–0.6 Ma further indicate that the Middle Pleistocene is a critical period for the establishment of modern-like glacial and periglacial landforms on the Tibetan Plateau. Our results further suggest that enhanced Quaternary glaciation in SE Tibet occurred earlier than in the north, which we attribute to climate cooling combined with regional seasonal snowline lowering. As such, a close relationship exists between global climate changes, development of pan-Tibetan glaciations, and large-scale dust emission.

Anti-phase glacier fluctuations on the millennial-scale on the southern Tibetan Plateau and New Zealand during the last glacial period

The sparsity of high-resolution 10Be chronologies in the Northern Hemisphere makes it difficult to determine whether the global fluctuations in glacier extent during the last glacial occurred simultaneously. This limits our understanding of the past mechanisms driving global climate changes. We compiled and reanalyzed 476 10Be exposure ages from the southern Tibetan Plateau for the last glacial and compared them with coeval 10Be ages from the Southern Alps. The results indicate an anti-phase relationship between the glacier expansions in these two regions on the millennial-scale during the last glacial period. Comparison with a glacier-derived temperature reconstruction suggests that maintaining a stable glacier state in both regions required a similar cooling magnitude. We speculate that variability of the Atlantic Meridional Overturning Circulation, which induced poleward/equatorward shifts in atmospheric and oceanic circulation, was the primary driving mechanism of this anti-phase relationship. Our findings provide glacial geological evidence to support the bipolar seesaw hypothesis.

The Glacier‐Climate Interaction Over the Tibetan Plateau and Its Surroundings During the Last Glacial Maximum

AbstractGlacier growth affects the local climate, and in turn, can either promote or prohibit its own growth. Such feedback has not been considered in modeling the glaciers of the Tibetan Plateau and its surroundings (TPS) during the Last Glacial Maximum (LGM; ∼28–23 ka). We find that the volume/area of the glaciers simulated by a coupled glacier‐climate model is 20%/10% less than that by a standalone glacier model forced with fixed climate fields; glaciers advance toward their western rims and yet decrease in the interior of TPS. Such changes in spatial patterns improve model‐data comparison. Moreover, the expansion of glaciers warms the winter surface temperature of the eastern TPS and decreases precipitation almost everywhere. These effects are primarily due to the added surface elevation, which blocks the water vapor brought by westerlies and south‐westerlies, reducing precipitation and increasing surface temperatures to the east and northeast of the newly grown glaciers.

Coupling of river discharges and alpine glaciers in arid Central Asia

Water resource is the primary factor impacting socio-economic development and security in arid Central Asia where high water stress occurs. Therefore, understanding the mechanism of water resource, particularly its associations with global warming, has unique importance for regional sustainable development. However, the dynamics of water resource is far from constrained in arid Central Asia indicated by the observed heterogenous trends of both alpine glaciers in high mountains (water tower) and river runoffs (dominant freshwater sources). Both meltwater and precipitations have been assumed to be the major contribution to the river runoff. Here, we make a systematic analysis on the 10Be exposure ages of the moraines in the high mountains and river terraces across Central Asia (n = 1057) to characterize the past changes of alpine glaciers and river discharges. The results show that the high river discharges are coupled with the alpine glacier expansions on both orbital and millennial scales, indicating a dominant contribution of meltwater to the freshwater supply. Both high river discharges and alpine glacier expansions occurred during the cold periods of the past 130 ka in Central Asia, indicating relatively low water stress under low-temperature conditions. This characteristic suggests that the water stress would increase with the decrease in both water reservoir and river discharges, and thus the environment would become drying with global warming in Central Asia.

Mid-Pleistocene links between Asian dust, Tibetan glaciers, and Pacific iron fertilization

Increasing Asian dust fluxes, associated with late Cenozoic cooling and intensified glaciations, are conventionally thought to drive iron fertilization of phytoplankton productivity in the North Pacific, contributing to ocean carbon storage and drawdown of atmospheric CO2. During the early Pleistocene glaciations, however, productivity remained low despite higher Asian dust fluxes, only displaying glacial stage increases after the mid-Pleistocene climate transition (~800ka B.P.). We solve this paradox by analyzing an Asian dust sequence, spanning the last 3.6 My, from the Tarim Basin, identifying a major switch in the iron composition of the dust at ~800ka, associated with expansion of Tibetan glaciers and enhanced production of freshly ground rock minerals. This compositional shift in the Asian dust was recorded synchronously in the downwind, deep sea sediments of the central North Pacific. The switch from desert dust, containing stable, highly oxidized iron, to glacial dust, richer in reactive reduced iron, coincided with increased populations of silica-producing phytoplankton in the equatorial North Pacific and increased primary productivity in more northerly locations, such as the South China Sea. We calculate that potentially bioavailable Fe2+ flux to the North Pacific was more than doubled after the switch to glacially- sourced dust. These findings indicate a positive feedback between Tibetan glaciations, glaciogenic production of dust with enhanced iron bioavailability, and changes in North Pacific iron fertilization. Notably, this strengthened link between climate and eolian dust coincided with the mid-Pleistocene transition to increased storage of C in the glacial North Pacific and more intense northern hemisphere glaciations.

Glacial history of Pyramid Trough, southern McMurdo Sound, Antarctica: Constraints on Koettlitz Glacier during the last glacial maximum and termination

Reconstructions of past glacier extent and timing afford perspective on the efficacy of mechanisms thought to control ice-sheet fluctuations. Here, we present data concerning the interactions between the Antarctic Ice Sheet and a local glacier (Koettlitz Glacier) in the McMurdo Sound region of the western Ross Embayment and use this information to gain insight into driving forces of ice expansion in this sector during the last glacial maximum (LGM; 24–18 ka) and termination (18–13 ka). Our data suggest that a grounded ice sheet in McMurdo Sound at the LGM resulted not from expansion of local glaciers, such as Koettlitz, from the continent but rather from flow of marine-based ice into the sound from the Ross Sea. We infer that the relative importance of different forcing mechanisms, such as sea-level rise, ocean-temperature change, and accumulation variations, explains the contrasting behavior of the grounded marine ice sheet in the Ross Sea and local glaciers adjacent to McMurdo Sound, with Ross Sea ice responding primarily to marine forcing and local glaciers influenced strongly by accumulation.

Holocene deglaciation of the northern Fildes Peninsula, King George Island, Antarctica

AbstractThe timing and magnitude of Holocene glacial oscillations in most currently ice‐free areas of Antarctica remain unknown. This work focuses on the recent deglaciation in the northern sector of the Fildes Peninsula, King George Island, northern Antarctic Peninsula. The ice cap covering ca. 90% of the island has receded since the Last Glacial Maximum and exposed ca. 29 km2 of ice‐free land. We reconstruct its glacial history based on a dataset of 12 36Cl exposure ages obtained through cosmic‐ray exposure (CRE) dating of moraine boulders, polished surfaces and erratic boulders surrounding the peninsula's northern plateau. Results reveal that the deglaciation of the northern Fildes Peninsula took place during the Holocene Thermal Maximum at 7–6 ka, when warm conditions promoted a massive glacial retreat. The present arrangement of ice‐free areas was in place by 6 ka. Small cirque moraines suggest the subsequent occurrence of favourable climate conditions for glacial expansion fed by intense snow deflation at 4.6 and 1 ka at the foot of the northern plateau. The deglaciation pattern of the Fildes Peninsula resulted from the combined shrinkage of different ice masses, rather than of the long‐term retreat of the King George Ice Cap. No evidence of glacier expansion during more recent cold periods (i.e. the Little Ice Age) was found. These results fit well with regional deglacial histories inferred from lacustrine sediments and raised beaches and complement the existing chronological framework to help better understand the peninsula's Holocene geoecological dynamics.

Sedimentary features and sequence stratigraphy of the successions around the Carboniferous–Permian boundary in the Ordos Basin: links to glacial and volcanic impacts

The sedimentary successions around the Carboniferous–Permian boundary (CPB) in the Ordos Basin were investigated using extensive outcrop, borehole, well logging, thin section, and geochemistry data to study sedimentary and sequence stratigraphic responses to glaciation and volcanism in paleotropical transitional strata. Within the studied interval, five distinct lithofacies have been identified, including bauxite, coal, and carbonaceous shale (No. 8 + 9 coal seams), sandstone (Qiaotou), limestone (Baode), and mudstone, which can be classified into three lithofacies associations. The most complete lithofacies association is composed of bauxite, coal, carbonaceous shale, sandstone, limestone/mudstone or their combinations from the bottom to the top, while coal and carbonaceous shale, as well as sandstone, are absent locally, resulting in the formation of the other two types of lithofacies associations. The occurrence of bauxite indicates shelf exposure and weathering, the occurrence of coal and carbonaceous shale indicates swampiness of the shelf, and the occurrence of sandstone reveals river rejuvenation; all of these are thought to be sedimentary responses to the transcontinental glacier expansion in Gondwana around the CPB. The presence of limestone and mudstone indicates carbonate platform and lagoon deposition, respectively, in the context of the earliest Asselian transgression caused by volcanism-induced glacier melting. The lithofacies associations record the regressive–transgressive cycles that occurred because of glaciation and volcanism near the CPB. The top surface of bauxite can be used as a sequence boundary, while the lowstand systems tract consists of the No. 8 + 9 coal seams and the Qiaotou sandstone, and the transgressive systems tract consists of the overlying Baode limestone and laterally equivalent mudstone. The lowstand systems tract, which contains source rock and hydrocarbon reservoirs, and the overlying transgressive systems tract, which serves as cap rock, form an excellent source-reservoir-seal combination.

Antanas Karolis Giedraitis’ geological investigations in Lithuania

This work is dedicated to Antanas Karolis Giedraitis (Antoni Karol Giedroyć, A.K. Gedroïz, А.K. Гедройц) (1848–1909) geological research that he did in Lithuania territory for geological mapping. In the History of Science, A.K. Giedraitis is called the first professional geologist of Lithuania, who investigated geology of our and neighboring countries. In 1895 he compiled a geological map of very large territory – Russian Empire governorates of Vilnius, Kaunas, Suvalkai, Gardinas, and Minskas according to international standards. It is important to understand A.K. Giedraitis’ approach to the formation of Quaternary sediments and the theory of polyglacialism. He took at that time the bold position that this entire region two or even three times had been covered by a glacier that advanced from the North. Based on the weathering (wearing) of erratic boulders and glacial incisions, he tried to describe the limits of glacier expansion and the directions of its movement. A.K. Giedraitis’ professional achievements are well-known, they are evidenced by the detailed reports and publications of his geological research in German, Polish, and Russian, which were published in 1886, 1887, and 1894. A summary of all his research was published in 1895, together with a geological map to a scale of 1:420 000. Interestingly, research carried out nowadays has confirmed some of the more than 130-year-old insights of A.K. Giedraitis about the geological formation of our country.

Recent and Past Arboreal Change: Observational and Retrospective Studies Within a Subalpine, Birch-Dominated (Betula Pubescens Ssp. Czerepanovii) Mountain Valley in the Southern Swedish Scandes-Responses to Climate Change and Land Use

Multi-scale observations and reconstructions of treeline and associated plant cover changes are reviewed in this study. The main focus is on the dynamics of the treeline ecotone within a mountain valley in the southern Swedish Scandes. This area is well-researched for more than 100 years, with a background of historical studies covering the entire Holocene epoch. Trees were present on ice-free nunataks already during the Late-Glacial, 17 000-13 000 cal. a BP. Mountain birch (Betula pubescens ssp. czerepanovii), Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) then grew 400-700 m higher than their current treelines, indicative of summer temperatures 3 °C higher than present. In addition, the tree flora contained Siberian larch (Larix sibirica) and broad-leaf thermophilic and deciduous species, Quercus robur, Corylus avellana, Ulmus glabra and Alnus glutinosa. Eventually, the climate turned cooler, particularly enhanced around 5000 cal. a BP. This course of change initiated the Neoglacial period, when thermophilic species were extirpated. Concomitantly, mountain birch forest and spruce benefitted from this course of change. Pine, on the other hand was disfavored and regressed in the treeline elevation and general abundance on the landscape. These trends continued until the Mediaeval period AD 1000-1300, when temperature raised above present-day standards and the pine treeline locally shifted upslope by at least 100 m. This favourable epoch was discontinued quite abruptly by resurgence of Neoglacial cooling; the “Little Ice Age”, which prevailed until the late 19th century. Widespread glacier expansion, high-elevation arboreal decline and treeline retraction then occurred. With a gentle onset in the late 19th century or somewhat earlier, a modern and still prevailing warming period was accentuated by the late 1930s. Subsequently, slight cooling prevailed for 3-4 decades, whereupon warming was resumed with short interruptions until the present day. One distinct short-term cooling-conditioned setback occurred during the 1980s. Transient permafrost formed close to the treeline, and locally some treeline recession took place. Thereafter, warming has re-occurred and glaciers and permafrost have receded. Treeline rise and densification of the treeline ecotone are once again active processes in the mountainscape. Currently, most conspicuous is a process of pine reclamation of local ground lost during the Little Ice Age. Hereabouts, seed regeneration, still virtually without winter injuries, is taking place at an unprecedented rate and abundance. Mountain birch is gaining ground in snow rich depressions in the birch belt and is currently regressing in exposed and snow-poor sections of the local topography. Current biotic changes within the treeline ecotone are well within the ranges of inferred natural variabilty during the postglacial period.

Relict proglacial lake of Spituk (Leh), northwest (NW) Himalaya: A repository of hydrological changes during Marine Isotopic Stage (MIS)-2

In the northwestern Himalaya (Ladakh and Karakoram), the spatial and temporal changes in the late Quaternary glaciation were modulated by a combination of two contrasting moisture sources (viz., the Indian Summer Monsoon and the mid-latitude westerlies). The inferences about their relative contribution to glacier expansion are based on the ages obtained on moraines. Since the moraines suffer from poor preservation and chronological uncertainty, the present study, therefore, resorted to a near-continuous relict proglacial lake succession in order to reconstruct the continuous pattern of glacier fluctuations during Marine Isotopic Stage-2 (MIS-2). Since the AMS radiocarbon ages (both organic and inorganic matter) suffered from various complexities such as dead carbon contribution and hard water effect, the paleohydrological inferences in this study were drawn primarily based on optical ages (along with sedimentological and geochemical analysis).The proglacial lake sedimentation was modulated by the temporal changes in meltwater discharge. This is attributed to the waning and waxing of proximal valley glaciers. Evidence accrued from the lake sediment supported by the published moraine chronology suggests that valley glaciers expanded during the onset of MIS-2 and persisted until around the Last Glacial Maximum (LGM). The beginning of MIS-2 is marked by the onset of cooling (~ 30 ka), which led to a marginal advance in the glaciers. Additionally, early MIS-2 was characterised by millennial-scale climatic fluctuations. For example, a short-lived increase in humidity was observed between 30.2 ka and 29.3 ka, followed by a reversal towards a drier climate between 29.3 ka and 28.1 ka. During the early part of MIS-2, glaciers were driven by the decrease in temperature, whereas the enhanced moisture contribution during mid MIS-2 was responsible for extensive glacier growth. We hypothesise that the enhanced moisture was contributed by the mid-latitude westerlies, with subordinate contribution from the Indian Summer Monsoon (ISM). This we attribute to the southward positioning of the Intertropical Convergence Zone (ITCZ) during MIS-2.

Increase in seasonal precipitation over the Tibetan Plateau in the 21st century projected using CMIP6 models

Precipitation changes over the Tibetan Plateau (TP) substantially impact the downstream river runoff. However, future precipitation variation over the TP remains unclear. Here, we evaluated the historical (1961–2014) precipitation of 25 CMIP6 models based on the observations. The multi-model ensemble mean of the five best models (BMME) was in stronger agreement with observations than the single model. Then, seasonal precipitation changes in 2015–2099 were projected using the BMME under four Shared Socioeconomic Pathway (SSP) scenarios. The results showed that seasonal precipitation would increase over the TP in the 21st century, with a higher rate of precipitation increase under the higher emission scenarios. Precipitation is projected to increase by 29.3% (11.5%), 27.1% (12.7%), 23.2% (9.4%), and 16.7% (2.9%) in spring, summer, autumn, and winter by end of the 21st century relative to 1995–2014 under the high-emission SSP5‐8.5 (low-emission SSP1‐2.6) scenario, respectively. The largest precipitation increases in summer and autumn during 2040–2059 and 2080–2099 will occur in the southeastern TP, whereas the largest increases in winter and spring will appear in the Pamirs, where precipitation will increase by >40% during 2080–2099 relative to 1995–2014. The spatial discrepancy in seasonal precipitation changes indicates a potential glacier expansion over the Pamirs and increased flood risks over the southeastern TP.

Holocene water levels of Silver Lake, Montana, and the hydroclimate history of the Inland Northwest

AbstractThe wettest portion of the interior of western North America centers on the mountainous region spanning western Montana, Idaho, British Columbia, and Alberta. Inland ranges there capture the remnants of Pacific storms. Steep east–west hydroclimate gradients make the region sensitive to changes in inland-penetrating moisture that may have varied greatly during the Holocene. To investigate potential hydroclimate change, we produced a 7600-yr lake-level reconstruction from Silver Lake, located on the Montana–Idaho border. Ground-penetrating radar profiles and a transect of four shallow-water sediment cores that were dated using radiocarbon dating and tephrachronology revealed substantial changes in moisture through time. An organic-rich mud unit indicating wet and similar to modern conditions prior to 7000 cal yr BP is overlain by an erosional surface signifying drier than modern conditions from 7000–2800 cal yr BP. A subsequent time-transgressive increase in water levels from 2800–2300 cal yr BP is indicated by a layer of late Holocene muds, and is consistent with glacier expansion and increases in the abundance of mesic tree taxa in the region. Millennial-scale trends were likely driven by variations in orbital-scale forcing during the Holocene, but the regional outcomes probably depended upon factors such as the strength of the Aleutian Low, Pacific sea-surface temperature variability, and the frequency of atmospheric rivers over western North America.

Evolution and origin of global glaciers and their impacts on the environment

Glacier is one of the most important freshwater resources. However, the situation of glaciers is changed nowadays because of global warming. This study aimed at two types of glaciers, and analyzed their evolution, origin and impacts on the environment. As for typical melting glaciers, the Vatnajokull glacier and Urumqi Glacier No.1, Tianshan Mountains gradually melt over time. Their causes are related to atmospheric River events, black carbon pollutants, ice recycling, global warming, and human activities. The impacts of glacier retreat mainly include sea-level rise and can alleviate global warming and cause surface deformation. However, there are some “weird” glaciers because they are expanded in the past few years rather than shrinking. Those glaciers are highly concentrated in the Karakoram, Pamir Mountains, Svalbard, the Canadian Arctic islands, Alaska, and Iceland, which are called surged-type glaciers. Hydrological control, thermal regime, deformable bed hypothesis, and critical mass are reasons for glacier expansion. There is no clear and unified opinion on the advantages or disadvantages of glacier expansion.

Ice-sheet expansion from the Ross Sea into McMurdo Sound, Antarctica, during the last two glaciations

An understanding of Antarctic Ice Sheet (AIS) behavior is important for future sea-level predictions. Here, we examine past ice-sheet history in the McMurdo Sound region of the western Ross Sea over the last two glacial-interglacial cycles in order to gain insight into the drivers of ice-sheet change. Surficial mapping, along with radiocarbon dates of lacustrine algae and uranium-thorium disequilibrium dates of lacustrine carbonates from ice-dammed lakes, allow reconstruction of the timing and origin of grounded ice in McMurdo Sound during the last glacial maximum (LGM) and penultimate glaciation. During the LGM, ice-surface elevation profiles and distribution of erratics indicate ice flow into southern McMurdo Sound from the Ross Sea, rather than seaward expansion of local glaciers from the Royal Society Range. The grounded ice in McMurdo Sound flowed westward to block the mouths of valleys in the Royal Society Range and to dam proglacial lakes. In Marshall Valley, maximum ice extent during what is termed the Ross Sea glaciation, was achieved by 18 ka and remained close to this position until after 14 ka. The pattern of surficial deposits suggests that ice during the penultimate glaciation, locally named the Marshall glaciation, was slightly more extensive than that of the LGM but had a similar Ross Sea origin. Maximum ice extent in Marshall Valley occurred at ∼145–150 ka; the grounded ice may have receded from the valley mouth shortly after 138 ka. Both ice expansions occurred broadly during times of low Antarctic air temperatures, which have been linked to insolation minima. However, the lack of widespread surface melting ablation zones on the AIS indicates that the link between ice expansion and orbital forcing is likely to be indirect and possibly driven through the ocean. Closer examination of the precise timing of the glacial maxima in Marshall Valley shows that the Marshall glaciation occurred synchronously with the penultimate global maximum; ice recession took place during Termination II. In contrast, maximum ice extent during the Ross Sea glaciation along the Royal Society Range occurred after the global LGM, during Termination I. Deglaciation was primarily an early Holocene event. We attribute this delayed maximum and deglaciation (relative to global events) to the effect of rising accumulation on ice-sheet mass balance.

Tandem dating methods constrain late Holocene glacier advances, southern Coast Mountains, British Columbia

Combined use of radiocarbon-dated subfossil wood within lateral moraines and surface exposure ages on moraine boulders provides an approach to better constrain times of glacier advance and onset of retreat. We test this method at Gilbert Glacier in the southern Coast Mountains of British Columbia where units of sediments associated with glacier expansion date to 4.8–4.6, 4.5–4.3, 4.0–3.9, 3.8–3.6, 3.4, 3.2–2.9, 2.7, and 0.5–0.3 kilo calendar years BP (ka; 2-sigma age range). Surface exposure (10Be) ages reveal times of moraine stabilization at 1.83–1.78, 1.38–1.28, 0.85–0.76, and 0.13–0.06 ka (interquartile range). Analysis of both datasets, as well as previously published regional advance records, narrows the age range of four late Holocene advances to 2.0–1.8, ∼1.5–1.3, ∼0.9–0.8, and 0.4–0.1 ka. We advocate for widespread use of our tandem approach at other sites throughout Earth's high mountains to narrow the uncertainties associated with glacier expansion and better understand how glaciers respond to climate change.

Geomorphology and 10Be chronology of the Last Glacial Maximum and deglaciation in northeastern Patagonia, 43°S-71°W

In southern South America, well-dated glacial geomorphological records constrain the last glacial cycle across much of the former Patagonian Ice Sheet, but its northeastern sector remains comparatively understudied and unconstrained. This knowledge gap inhibits our understanding of the timing of maximum glacier extent, the duration of the glacial maximum, the onset of deglaciation, and whether asynchronies exist in the behaviour of the former ice sheet with latitude, or with location (east or west) relative to the ice divide. Robust glacial reconstructions from this region are thus required to comprehend the mechanisms driving Quaternary glaciations at the southern mid-latitudes. We here present 10Be surface exposure ages from five moraine sets along with Bayesian age modelling to reconstruct a detailed chronology of Last Glacial Maximum expansions of the Río Corcovado glacier, a major former ice conduit of northern Patagonia. We find that the outlet glacier reached maximum expansion of the last glacial cycle during the global Last Glacial Maximum at ∼26.5–26 ka, and that at least four subsequent advances/stillstands occurred over a 2–3 ka period, at ∼22.5–22 ka, ∼22–21.5 ka, ∼21–20.5 ka and 20–19.5 ka. The onset of local ice sheet deglaciation likely occurred between 20 and 19 ka. Contrary to several other Patagonian outlet glaciers, including from similar latitudes on the western side of the Andes, we find no evidence for MIS 3/4 advances. Exposure dating of palaeo-shoreline cobbles reconstructing the timing of proglacial lake formation and drainage shifts in the studied region indicate three glaciolacustrine phases characterised by Atlantic-directed drainage. Phase one occurred from 26.4 ± 1.4 ka, phase two between ∼21 and ∼19 ka and phase three between ∼19 ka and ∼16.3 ka. Exposure dating of ice-moulded bedrock in the interior of the cordillera indicates local disintegration of the Patagonian Ice Sheet and the Atlantic-Pacific drainage reversal had occurred by ∼16.3 ka. We find that local Last Glacial Maximum glacier expansions were coeval with Antarctic and southern mid-latitude atmospheric and oceanic cooling signals, but out of phase with local summer insolation intensity. Our results indicate that local Patagonian Ice Sheet deglaciation occurred 1–2 ka earlier than northwestern, central eastern and southeastern Patagonian outlet glaciers, which could indicate high regional Patagonian Ice Sheet sensitivity to warming and drying during the Varas interstade (∼22.5–19.5 ka).

A 2300-year record of glacier fluctuations at Skilak and Eklutna Lakes, south-central Alaska

Holocene glacier fluctuations in south-central Alaska reflect hydroclimate changes in a region strongly influenced by large-scale features of North Pacific climate. Glacier fluctuations over the past approximately 2300 years were inferred from multiple geophysical and geochemical properties of a new 13-m-long sediment core from proglacial Skilak Lake. The chronology is based on annual-layer (varve) counting, supported by radiocarbon ages and the identification of the 1912 CE Katmai tephra. Sediment density and accumulation rate show two prominent century-scale increases, one near the base of the cored sequence (around 270-370 BCE) and one near the top (around 1600–1900 CE, Little Ice Age). These two peaks, and the absence of such increases between them, coincide with sedimentation-rate changes as previously measured in multiple cores from Eklutna Lake, located 130 km northeast of Skilak Lake. The similarity between the two sedimentary sequences, despite their contrasting geomorphic settings and spatial scales, implies that regional climate change is the overriding control. Sediment with high bulk density and thick varves was deposited concurrently with the expansion of glaciers in the catchment and elsewhere in the region during the Little Ice Age. We likewise attribute the deposits with similar characteristics to expanded glaciers centered around 320 BCE, and the absence of such sediment during the intervening 1800 years to the lack of a major glacier advance. Climatologically, both periods of high sediment accumulation rate correspond with times of intensified Aleutian Low pressure, as recently reconstructed based on regional syntheses of oxygen-isotope records for the earlier period, and on sea-salt concentration in two Alaskan ice cores for the later period. Both periods also coincide with pronounced multi-decadal downturns in combined solar and volcanic global radiative forcing. The massive buildup of glaciers during the Little Ice Age might reflect the increased frequency of these downturns combined with millennial-scale decrease in orbitally driven insolation. Glaciolacustrine records from these two lakes add a new perspective on the multi-century variability of glaciers and hydroclimate in the North Pacific region.

Evidence of the largest Late Holocene mountain glacier extent in southern and southeastern Greenland during the middle Neoglacial from 10Be moraine dating

The timing of mountain glacier fluctuations is poorly constrained in some parts of Greenland during the Late Holocene. We present 31 10Be cosmic‐ray exposure ages (CRE) of boulders collected from three mountain glacier moraines located in the Tasilap valley, in southeastern Greenland, and 10 10Be CRE ages from one mountain glacier in the Isortup valley, in southern Greenland. For the first time in these areas, mountain glacier fluctuations are documented from moraine CRE for the Late Holocene period. Several glacier advances during the Late Holocene are revealed with exposure ages ranging from 3.90±0.26 to 0.4±0.04 ka. Moraines of three of the four glaciers investigated, dated to 3.75±0.13 ka (n = 3), 3.3±0.19 ka (n = 2) and 2.87±0.13 ka (n = 3), show a common timing of the largest glacier expansion during the Late Holocene. Evidence of at least one individual moraine deposited at ~1.2 ka was found on all glaciers. Finally, the most recent period of glacial advance during the Late Holocene is documented by one glacier in each valley at ~0.66–0.70 ka. The maximum glacier extent at ~3 ka differs from the Late Holocene glacier maximum extent usually reported during the Little Ice Age in east Greenland based on moraine dating and lake sediments. We suggest that the combination of a stronger East Greenland Current and a weaker Irminger Current, potentially associated with increased sea‐ice concentration, superimposed on the long‐term decrease in summer insolation during the Late Holocene could be responsible for this large glacial advance at ~3 ka in southern and southeastern Greenland.