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Direct observations of the size of the Greenland Ice Sheet during Quaternary interglaciations are sparse yet valuable for testing numerical models of ice-sheet history and sea level contribution. Recent measurements of cosmogenic nuclides in bedrock from beneath the Greenland Ice Sheet collected during past deep-drilling campaigns reveal that the ice sheet was significantly smaller, and perhaps largely absent, sometime during the past 1.1 million years. These discoveries from decades-old basal samples motivate new, targeted sampling for cosmogenic-nuclide analysis beneath the ice sheet. Current drills available for retrieving bed material from the US Ice Drilling Program require < 700 m ice thickness and a frozen bed, while quartz-bearing bedrock lithologies are required for measuring a large suite of cosmogenic nuclides. We find that these and other requirements yield only ∼ 3.4 % of the Greenland Ice Sheet bed as a suitable drilling target using presently available technology. Additional factors related to scientific questions of interest are the following: which areas of the present ice sheet are the most sensitive to warming, where would a retreating ice sheet expose bare ground rather than leave a remnant ice cap, and which areas are most likely to remain frozen bedded throughout glacial cycles and thus best preserve cosmogenic nuclides? Here we identify locations beneath the Greenland Ice Sheet that are best suited for potential future drilling and analysis. These include sites bordering Inglefield Land in northwestern Greenland, near Victoria Fjord and Mylius-Erichsen Land in northern Greenland, and inland from the alpine topography along the ice margin in eastern and northeastern Greenland. Results from cosmogenic-nuclide analysis in new sub-ice bedrock cores from these areas would help to constrain dimensions of the Greenland Ice Sheet in the past.

Glacial erosion creates diagnostic landscapes and vast amounts of sediment. Yet, knowledge about the rate by which glaciers erode and sculpt bedrock and the proportion of quarried (plucked) versus abraded material is limited. To address this, we quantify subglacial erosion rates and constrain the ratio of quarrying to abrasion during the 19th/20th century overriding of a bedrock surface fronting Jakobshavn Isbræ, Greenland, by combining 10Be analyses, a digital terrain model, and field observations. Cosmogenic 10Be measurements along a 1.2-m-tall quarried bedrock step reveal a triangular wedge of quarried rock. Using individual 10Be measurements from abraded surfaces across the study area, we derive an average abrasion rate of 0.13±0.08 mm yr-1. By applying this analysis across a ~1.33 km2 study area, we estimate that the Greenland Ice Sheet quarried 378±45 m3 and abraded 322±204 m3 of material at this site. These values result in an average total erosion rate of 0.26±0.16 mm yr-1 with abrasion and quarrying contributing in roughly equal proportions within uncertainty. Additional cosmogenic 10Be analysis and surface texture mapping indicate that many lee steps are relict from the prior glaciation and were not re-quarried during the recent overriding event. These new observations of glacier erosion in a recently exposed landscape provide one of the first direct measurements of quarrying rates and indicate that quarrying accounts for roughly half of total glacial erosion in representative continental shield lithologies.

Over the last century, northwestern Canada experienced some of the highest rates of tropospheric warming globally, which caused glaciers in the region to rapidly retreat. Our study seeks to extend the record of glacier fluctuations and assess climate drivers prior to the instrumental record in the Mackenzie and Selwyn Mountains of northwestern Canada. We collected 27 10Be surface exposure ages across nine cirque and valley glacier moraines to constrain the timing of their emplacement. Cirque and valley glaciers in this region reached their greatest Holocene extents in the latter half of the Little Ice Age (1600–1850 CE). Four erratics, 10–250 m distal from late Holocene moraines, yielded 10Be exposure ages of 10.9–11.6 ka, demonstrating that by ca. 11 ka, alpine glaciers were no more extensive than during the last several hundred years. Estimated temperature change obtained through reconstruction of equilibrium line altitudes show that since ca. 1850 CE, mean annual temperatures rose 0.2–2.3 °C. We use our glacier chronology and the Open Global Glacier Model (OGGM) to estimate that since 850 CE, glaciers in this region reached a maximum total volume of 34–38 km3 between 1765–1855 CE and have lost nearly half their ice volume by 2019 CE. OGGM was unable to produce modeled glacier lengths that match the timing or magnitude of the maximum glacier extent indicated by the 10Be chronology. However, when applied to the entire Mackenzie and Selwyn Mountain region, past-millennium OGGM simulations using the Max Planck Institute Earth System Model (MPI-ESM) and the Community Climate System Model 4 (CCSM4) yield late Holocene glacier volume change temporally consistent with our moraine and remote sensing record, while the Meteorological Research Institute Earth System Model 2 (MRI-ESM2) and the Model for Interdisciplinary Research on Climate (MIROC) fail to produce modeled glacier change consistent with our glacier chronology. Finally, OGGM forced by future climate projections under varying greenhouse gas emissions scenarios predict 85 to over 97 % glacier volume loss by the end of the 21st century. The loss of glaciers from this region will have profound impacts to local ecosystems and communities that rely on meltwaters from glacierized catchments.

In the Cordillera Darwin, southernmost South America, we used 10Be and 14C dating, dendrochronology, and historical observations to reconstruct the glacial history of the Dalla Vedova valley from deglacial time to the present. After deglacial recession into northeastern Darwin and Dalla Vedova, by ~16 ka, evidence indicates a glacial advance at ~13 ka coeval with the Antarctic Cold Reversal. The next robustly dated glacial expansion occurred at 870 ± 60 calendar yr ago (approximately AD 1150), followed by less-extensive dendrochronologically constrained advances from shortly before AD 1836 to the mid-twentieth century. Our record is consistent with most studies within the Cordillera Darwin that show that the Holocene glacial maximum occurred during the last millennium. This pattern contrasts with the extensive early- and mid-Holocene glacier expansions farther north in Patagonia; furthermore, an advance at 870 ± 60 yr ago may suggest out-of-phase glacial advances occurred within the Cordillera Darwin relative to Patagonia. We speculate that a southward shift of westerlies and associated climate regimes toward the southernmost tip of the continent, about 900–800 yr ago, provides a mechanism by which some glaciers advanced in the Cordillera Darwin during what is generally considered a warm and dry period to the north in Patagonia.

Sometime during the middle to late Holocene (8.2 ka to ∼ 1850–1900 CE), the Greenland Ice Sheet (GrIS) was smaller than its current configuration. Determining the exact dimensions of the Holocene ice-sheet minimum and the duration that the ice margin rested inboard of its current position remains challenging. Contemporary retreat of the GrIS from its historical maximum extent in southwestern Greenland is exposing a landscape that holds clues regarding the configuration and timing of past ice-sheet minima. To quantify the duration of the time the GrIS margin was near its modern extent we develop a new technique for Greenland that utilizes in situ cosmogenic 10Be – 14C – 26Al in bedrock samples that have become ice-free only in the last few decades due to the retreating ice-sheet margin at Kangiata Nunaata Sermia ( n=12 sites, 36 measurements; KNS), southwest Greenland. To maximize the utility of this approach, we refine the deglaciation history of the region with stand-alone 10Be measurements ( n=49 ) and traditional 14C ages from sedimentary deposits contained in proglacial–threshold lakes. We combine our reconstructed ice-margin history in the KNS region with additional geologic records from southwestern Greenland and recent model simulations of GrIS change to constrain the timing of the GrIS minimum in southwest Greenland and the magnitude of Holocene inland GrIS retreat, as well as to explore the regional climate history influencing Holocene ice-sheet behavior. Our 10Be – 14C – 26Al measurements reveal that (1) KNS retreated behind its modern margin just before 10 ka , but it likely stabilized near the present GrIS margin for several thousand years before retreating farther inland, and (2) pre-Holocene 10Be detected in several of our sample sites is most easily explained by several thousand years of surface exposure during the last interglaciation. Moreover, our new results indicate that the minimum extent of the GrIS likely occurred after ∼5 ka , and the GrIS margin may have approached its eventual historical maximum extent as early as ∼2 ka . Recent simulations of GrIS change are able to match the geologic record of ice-sheet change in regions dominated by surface mass balance, but they produce a poorer model–data fit in areas influenced by oceanic and dynamic processes. Simulations that achieve the best model–data fit suggest that inland retreat of the ice margin driven by early to middle Holocene warmth may have been mitigated by increased precipitation. Triple 10Be – 14C – 26Al measurements in recently deglaciated bedrock provide a new tool to help decipher the duration of smaller-than-present ice over multiple timescales. Modern retreat of the GrIS margin in southwest Greenland is revealing a bedrock landscape that was also exposed during the migration of the GrIS margin towards its Holocene minimum extent, but it has yet to tap into a landscape that remained ice-covered throughout the entire Holocene.

Direct observations of the size of the Greenland Ice Sheet during Quaternary interglaciations are sparse yet valuable for testing numerical models of ice-sheet history and sea level contribution. Recent measurements of cosmogenic nuclides in bedrock from beneath the Greenland Ice Sheet collected during past deep-drilling campaigns reveal that the ice sheet was significantly smaller, and perhaps largely absent, sometime during the past 1.1 million years. These discoveries from decades-old basal samples motivate new, targeted sampling for cosmogenic-nuclide analysis beneath the ice sheet. Current drills available for retrieving bed material from the US Ice Drilling Program require < 700 m ice thickness and a frozen bed, while quartz-bearing bedrock lithologies are required for measuring a large suite of cosmogenic nuclides. We find that these and other requirements yield only ∼ 3.4 % of the Greenland Ice Sheet bed as a suitable drilling target using presently available technology. Additional factors related to scientific questions of interest are the following: which areas of the present ice sheet are the most sensitive to warming, where would a retreating ice sheet expose bare ground rather than leave a remnant ice cap, and which areas are most likely to remain frozen bedded throughout glacial cycles and thus best preserve cosmogenic nuclides? Here we identify locations beneath the Greenland Ice Sheet that are best suited for potential future drilling and analysis. These include sites bordering Inglefield Land in northwestern Greenland, near Victoria Fjord and Mylius-Erichsen Land in northern Greenland, and inland from the alpine topography along the ice margin in eastern and northeastern Greenland. Results from cosmogenic-nuclide analysis in new sub-ice bedrock cores from these areas would help to constrain dimensions of the Greenland Ice Sheet in the past.

The Greenland Ice Sheet (GIS) is losing mass at a high rate1. Given the short-term nature of the observational record, it is difficult to assess the historical importance of this mass-loss trend. Unlike records of greenhouse gas concentrations and global temperature, in which observations have been merged with palaeoclimate datasets, there are no comparably long records for rates of GIS mass change. Here we reveal unprecedented mass loss from the GIS this century, by placing contemporary and future rates of GIS mass loss within the context of the natural variability over the past 12,000 years. We force a high-resolution ice-sheet model with an ensemble of climate histories constrained by ice-core data2. Our simulation domain covers southwestern Greenland, the mass change of which is dominated by surface mass balance. The results agree favourably with an independent chronology of the history of the GIS margin3,4. The largest pre-industrial rates of mass loss (up to 6,000 billion tonnes per century) occurred in the early Holocene, and were similar to the contemporary (ad 2000–2018) rate of around 6,100 billion tonnes per century5. Simulations of future mass loss from southwestern GIS, based on Representative Concentration Pathway (RCP) scenarios corresponding to low (RCP2.6) and high (RCP8.5) greenhouse gas concentration trajectories6, predict mass loss of between 8,800 and 35,900 billion tonnes over the twenty-first century. These rates of GIS mass loss exceed the maximum rates over the past 12,000 years. Because rates of mass loss from the southwestern GIS scale linearly5 with the GIS as a whole, our results indicate, with high confidence, that the rate of mass loss from the GIS will exceed Holocene rates this century. Rates of ice-mass loss from southwestern Greenland this century will exceed the maximum rate over the past 12,000 years, and would not be the result of natural variation.

Glaciers provide an excellent natural laboratory for reconstructing the climate of the past as they respond sensitively to climate oscillations with advance or retreat. Therefore, we study glacier systems and their behavior during the transition from colder to warmer climate episodes in glaciated valleys of the Silvretta Massif in the Austrian Alps. Using a combination of geomorphological mapping and beryllium-10 surface exposure dating, we reconstruct ice extents of the past and find that glaciers stabilized during the Pre-Bølling to Bølling transition (14.4 ± 1.0 ka, n=3), during the Younger Dryas (ca. 12.9-11.7 ka; n=7), and during the earliest Holocene (ca. 12-10 ka; n=2). The first, (pre)-Bølling age group indicates a stable ice margin that postdates the Gschnitz stadial (ca. 17-16 ka) and predates the Younger Dryas. It shows that local inner-alpine glaciers prevailed until the onset of the Bølling warm phase (ca. 14.6 ka) or possibly even into the Bølling. The second Younger Dryas age group captures the spatial and temporal fine structure of glacier retreat during the Egesen stadial prior to Holocene warming. It evidences ice surface lowering of several tens of meters throughout the Younger Dryas, which is indicative of milder climate conditions at the end of the stadial compared to its beginning. The third age group falls into a period of substantial warming, the Younger Dryas-Holocene transition. The deposition of moraines during a period of abrupt warming implies centennial-scale cold snaps that were probably caused by feedback in the climate system. An explanation proposed in the Younger Dryas-Holocene context is the deglaciation of ice sheets in the Northern hemisphere and resulting freshwater input into the Atlantic ocean, which in turn slowed down ocean circulations and thus reduced heat transport toward (Northern) Europe.The new geochronologies synthesized with pre-existing moraine records from the Silvretta Massif show that the transition from glacial to interglacial climate conditions occurred within a few centuries and illustrate the sensitive response of Silvretta glaciers to abrupt warming events in the past. Our ice-margin reconstructions provide an example of the response of glaciers and the climate system in a warming world.

Alpine glaciers are sensitive indicators of changes in climate, and their ubiquity in mountainous regions make them valuable proxies for terrestrial climate reconstructions worldwide. However, the timing and extent of glacier change across the South American mid-latitudes through the Holocene are still poorly constrained relative to their counterparts in the Northern Hemisphere. Here we report a new 10Be surface exposure-based chronology of moraines recording a series of progressively less-extensive glacier advances of Glaciar Torre (Argentina, 49.3°S/73.0°W) since the Last Glacial Maximum, with expansions culminating at 17,600 ± 900, 13,500 ± 500, 9700 ± 400, 6900 ± 200, 6100 ± 300, 4500 ± 200, and 530 ± 60 yr BP. The declining magnitude of Holocene glacier expansions parallels a gradual rise in local summer insolation intensity during the Holocene, while individual advances occurred during inferred negative Southern Annular Mode (SAM)-like states at centennial to millennial timescales. These observations suggest that (i) summer insolation intensity modulated antiphased trends in glacier extent in the polar hemispheres during the Holocene, and that (ii) centennial-scale ‘SAM-like’ temperature and precipitation anomalies paced glacier fluctuations throughout Patagonia. Given the persistence of the inferred ’SAM-like’ anomalies throughout the Holocene, the modern measured trend towards positive SAM index conditions could mark the onset of a fundamental shift in the climate of the Southern Hemisphere midlatitudes that warrants consideration in projections of future climate.

We undertook geomorphological mapping in conjunction with 10Be surface-exposure dating in a previously unstudied sector of the left-lateral moraine sequence of the ice-age Pukaki glacier in the Southern Alps of New Zealand. The mapping and dating approach enabled the identification of six distinct moraine belts that were formed during maxima of glacier extent during the last glaciation. The chronology implies that ice recession occurred during Northern Hemisphere Heinrich stadials, while expansion occurred between Heinrich stadials. The ages of the moraine belts identified here are 44,000 ± 1000 yrs; 41,800 ± 1100 yrs; 36,450 ± 940 yrs 26,730 ± 740 yrs; 20,030 ± 460 yrs; and 18,000 ± 400 yrs. This moraine chronology is consistent with previous dating results from other sectors of the Pukaki moraine sequence, except that the c. 44,000 yr old moraine belt has not previously been detected elsewhere in the Pukaki moraines. Collectively with previously published 10Be chronologies from the Pukaki glacier, and the adjacent Ohau glacier valley, the results demonstrate that there were several millennial-scale episodes of ice advance to full-glacial extent, and subsequent ice recession, during Marine Isotope Stages 3 and 2. This millennial-scale pulsebeat of oscillations of the Pukaki and Ohau glaciers in sympathy with the North Atlantic Heinrich episodes is further emphasized by rapid ice recession in the Southern Alps early in the last glacial termination, coeval with the onset of Heinrich stadial 1 (HS 1) in the Northern Hemisphere. That this pattern is widespread in mid-latitudes of the Southern Hemisphere is highlighted by similar chronologies of glacier variation for Andean ice lobes in the Chilean Lake District of South America.

The sensitivity of mountain glaciers to small-scale climate fluctuations makes records of their past extent among the best proxies for identifying spatio-temporal climate variability. Here we build on the few existing Holocene records of local glacier change in Greenland by using three independent geochronological methods—proglacial lake sediment analysis, cosmogenic 10Be surface-exposure dating, and in situ 14C burial modeling—to reconstruct continuous records of Holocene glacier variability on Nuussuaq, West Greenland. 10Be ages of perched boulders indicate eastern Nuussuaq was deglaciated between ∼11.0 and 10.5 ka. Radiocarbon-dated sediments from two lakes on Nuussuaq contain mineral-rich layers between ∼9.6 and 9.0 and ∼8.7–8.0 cal ka BP that may be correlative with nearby ice sheet moraines deposited in the early Holocene. Multiple proxies for glacier size indicate frequent, high-amplitude glacier fluctuations superimposed on net glacier growth during the late Holocene, with significant ice expansion phases at ∼3.7 ka, 2.8 ka, and throughout the past ∼2 ka. Mean 10Be ages from five nested moraine crests confirm that local glacier extents on Nuussuaq culminated during both the Little Ice Age [∼1470 C.E. (n = 3) and 1750 C.E. (n = 3)] and the preceding centuries (∼520–1320 C.E.; n = 11). Results reveal that local glaciers on Nuussuaq episodically advanced and retreated at centennial timescales throughout the Holocene, most likely in response to regional climate changes in West Greenland superimposed on the progressive insolation-driven cooling trend in the Northern Hemisphere. Our new 10Be moraine chronologies coupled with other glacier-size proxies corroborate an emerging pattern of significant summer cooling and glacier expansion in the centuries prior to the Little Ice Age in the Arctic.

Since the Last Glacial Maximum ∼20,000 years ago, the Antarctic Ice Sheet has undergone extensive changes, resulting in a much smaller present-day configuration. Improving our understanding of basic physical processes that played important roles during that retreat is critical to providing more robust model projections of future retreat and sea-level rise. Here, a limited-area nested ice sheet model was applied to the last deglacial retreat of the West Antarctic Ice Sheet in the Amundsen Sea Embayment (ASE), at 5 km resolution. The ice sheet response to climate and sea-level forcing was examined at two sites along the flowlines of Pine Island Glacier and Pope Glacier, close to the Hudson Mountains and Mount Murphy respectively, and the simulated responses compared with ice sheet thinning histories derived from glacial-geological data. The sensitivity of results to selected model parameters was also assessed. The model simulations predict a broadly similar response to ocean forcing in both the central and eastern ASE, with an initial rapid phase of thinning followed by a slower phase to the modern configuration. Although there is a mismatch of up to 5,000 years between the timing of simulated and observed thinning, the modeling suggests that the upstream geological records of ice surface elevation change reflect a response to retreat near the grounding line. The model-data mismatch could potentially be improved by accounting for regional variations in mantle viscosity, sea-surface heights and basal sliding properties across the continental shelf.

Glaciers preserve climate variations in their geological and geomorphological records, which makes them prime candidates for climate reconstructions. Investigating the glacier–climate system over the past millennia is particularly relevant first because the amplitude and frequency of natural climate variability during the Holocene provides the climatic context against which modern, human-induced climate change must be assessed. Second, the transition from the last glacial to the current interglacial promises important insights into the climate system during warming, which is of particular interest with respect to ongoing climate change. Evidence of stable ice margin positions that record cooling during the past 12 kyr are preserved in two glaciated valleys of the Silvretta Massif in the eastern European Alps, the Jamtal (JAM) and the Laraintal (LAR). We mapped and dated moraines in these catchments including historical ridges using beryllium-10 surface exposure dating (10Be SED) techniques and correlate resulting moraine formation intervals with climate proxy records to evaluate the spatial and temporal scale of these cold phases. The new geochronologies indicate the formation of moraines during the early Holocene (EH), ca. 11.0 ± 0.7 ka (n = 19). Boulder ages along historical moraines (n = 6) suggest at least two glacier advances during the Little Ice Age (LIA; ca. 1250–1850 CE) around 1300 CE and in the second half of the 18th century. An earlier advance to the same position may have occurred around 500 CE. The Jamtal and Laraintal moraine chronologies provide evidence that millennial-scale EH warming was superimposed by centennial-scale cooling. The timing of EH moraine formation coincides with brief temperature drops identified in local and regional paleoproxy records, most prominently with the Preboreal Oscillation (PBO) and is consistent with moraine deposition in other catchments in the European Alps and in the Arctic region. This consistency points to cooling beyond the local scale and therefore a regional or even hemispheric climate driver. Freshwater input sourced from the Laurentide Ice Sheet (LIS), which changed circulation patterns in the North Atlantic, is a plausible explanation for EH cooling and moraine formation in the Nordic region and in Europe.

The accelerated melting of ice on the Antarctic Peninsula and islands in the sub-Antarctic suggests that the cryosphere is edging towards an irreversible tipping point. How unusual is this trend of ice loss within the frame of natural variability, and to what extent can it be explained by underlying climate dynamics? Here, we present new high-resolution reconstructions of long-term changes in the extents of three glaciers on the island of South Georgia (54°S, 36°W), combining detailed analyses of glacial-derived sediments deposited in distal glacier-fed lakes and cosmogenic exposure dating of moraines. We document that the glaciers of South Georgia have gradually retracted since the Antarctic cold reversal (ACR, 14.5–12.8 ka), culminating in the disappearance of at least one of the reconstructed glaciers. The glacier retreat pattern observed in South Georgia suggests a persistent link to summer insolation at 55°S, which intensified during the period from the ACR to approximately 2 ka. It also reveals multi-decadal to centennial climate shifts superimposed on this long-term trend that have resulted in at least nine glacier readvances during the last 10.5 ka. Accompanying meridional changes in the Southern Hemisphere westerlies and their interconnection with local topography may explain these glacier readvances.

Mountain glaciers and their preserved moraine records provide important insights into periods when climate conditions favored glacier advance or stabilization. Comprehensive mapping of moraines in glacier forefields elucidates the spatial distribution of former ice margins. Numerical age dating of moraines, in turn, constrains the timing of moraine formation intervals. A combination of both methods allows reconstructing the evolution of mountain glaciers across time and space and links today’s alpine geomorphology with climate of the past.Here, we present glacier reconstructions from two adjacent valleys in the northern Silvretta Massif (Austrian Alps). Both, the Jamtal and the Laraintal, exhibit multiple prominent moraine ridges outboard the Little Ice Age (LIA) moraine and inboard presumable Late Glacial ice margins. By applying 10Be surface exposure dating to these moraines, we decipher the response of Silvretta glaciers to the transition from glacial to interglacial climatic conditions.Pronounced double-ridge structures in lateral and terminal positions outside the LIA moraines were dated and yield landform ages of 11.3 ±0.8 kyrs (n=12) and 10.8 ±0.8 kyrs (n=9). This age pattern is consistent across both valleys and implies two significant moraine formation intervals during the earliest Holocene that overlap within uncertainties. Additional samples (n=6) were collected along presumable LIA ice margins. Four of them indeed produced LIA ages with three of them suggesting a culmination in the second half of the 18th century CE (mean age: 260 ±25 yrs). This result is in good agreement with 10Be ages from a recent study at an adjacent site, which indicate a LIA advance around 260 ±30 yrs. The remaining two ages coincide with a phase of cooler temperatures and increased precipitation in Europe from the 4th to 6th century, a climate episode, which is often associated with the fall of the Roman Empire and with the migration period in Europe.We interpret the sets of Early Holocene moraines as evidence of brief cold lapses, which punctuated the general warming trend at the beginning of the Holocene, with the Preboreal Oscillation (PBO; c. 11,300 to 11,150 cal BP) being the most prominent one. Moraine formation intervals during the Early Holocene have been reported in the wider Alpine region and at other places in the northern hemisphere (e.g. North America, Scandinavia, Greenland). Annual mean temperatures certainly differed at each of these places, but synchronous phases of glacier advances or stabilization are recorded across the northern hemisphere during the Early Holocene. We suggest that freshwater input into the Atlantic Ocean caused phases of temporary weakening of the Atlantic Meridional Overturning Circulation (AMOC), which lead to episodes of relative cooling in the northern hemisphere. This cooling phases are preserved in the Early Holocene moraine sets that we mapped and dated in the Silvretta region.

Understanding the history of the Greenland Ice Sheet (GrIS) is critical for determining its sensitivity to warming and contribution to sea level; however, that history is poorly known before the last interglacial. Most knowledge comes from interpretation of marine sediment, an indirect record of past ice-sheet extent and behavior. Subglacial sediment and rock, retrieved at the base of ice cores, provide terrestrial evidence for GrIS behavior during the Pleistocene. Here, we use multiple methods to determine GrIS history from subglacial sediment at the base of the Camp Century ice core collected in 1966. This material contains a stratigraphic record of glaciation and vegetation in northwestern Greenland spanning the Pleistocene. Enriched stable isotopes of pore-ice suggest precipitation at lower elevations implying ice-sheet absence. Plant macrofossils and biomarkers in the sediment indicate that paleo-ecosystems from previous interglacial periods are preserved beneath the GrIS. Cosmogenic 26 Al/ 10 Be and luminescence data bracket the burial of the lower-most sediment between 0.7 to 1.4 Ma. In the upper-most sediment, cosmogenic 26 Al/ 10 Be data require exposure within the last 1.0 ± 0.1 My. The unique subglacial sedimentary record from Camp Century documents at least two episodes of ice-free, vegetated conditions, each followed by glaciation. The lower sediment derives from an Early Pleistocene GrIS advance. 26 Al/ 10 Be ratios in the upper-most sediment match those in subglacial bedrock from central Greenland, suggesting similar ice-cover histories across the GrIS. We conclude that the GrIS persisted through much of the Pleistocene but melted and reformed at least once since 1.1 Ma., info:eu-repo/semantics/published

During the middle to late Holocene (8.2 ka BP to present), the Greenland Ice Sheet (GrIS) was smaller than its current configuration. Determining the exact dimensions of the Holocene ice-sheet minimum and the duration that the ice margin rested inboard of its current position remains challenging. Contemporary retreat of the GrIS from its historical maximum extent in southwestern Greenland is exposing a landscape that holds clues regarding the configuration and timing of past ice-sheet minima. To quantify the duration of the time the GrIS margin was near its modern extent we develop a new technique on Greenland that utilizes in situ cosmogenic 10Be-14C-26Al in bedrock samples that have become ice free only in the last few decades by the retreating ice-sheet margin at Kangiata Nunaata Sermia (n = 12 sites; KNS), southwest Greenland. To maximize the utility of this approach, we refine the deglaciation history of the region with stand-alone 10Be measurements (n = 49) and traditional 14C ages from sedimentary deposits contained in proglacial-threshold lakes. We combine our reconstructed ice-margin history in the KNS region with additional geologic records from southwestern Greenland and recent model simulations of GrIS change, to constrain the timing of the GrIS minimum in southwest Greenland, the magnitude of Holocene inland GrIS retreat, and explore the regional climate history influencing Holocene ice-sheet behavior. Our 10Be-14C-26Al measurements reveal that 1) KNS retreated behind its modern margin just before 10 ka, but likely stabilized near the present GrIS margin for several thousand years before retreating farther inland, and 2) pre-Holocene 10Be detected in several of our sample sites is most easily explained by several thousand years of surface exposure during the Last Interglaciation. Moreover, our new results indicate that the minimum extent of the GrIS likely occurred after ~ 5 ka, and the GrIS margin may have approached its eventual historical maximum extent as early as ~ 2 ka. Recent simulations of GrIS change are able to match the geologic record of ice-sheet change in regions dominated by surface mass balance, but produce a poorer model-data fit in areas influenced by oceanic and dynamic processes. Simulations that achieve the best model-data fit suggest that inland retreat of the ice margin driven by early to middle Holocene warmth may have been mitigated by increased precipitation. Triple 10Be-14C-26Al measurements in recently deglaciated bedrock provide a new tool to help decipher the duration of smaller-than-present ice over multiple timescales. Modern retreat of the GrIS margin in southwest Greenland is revealing a bedrock landscape that was also exposed during the migration of the GrIS margin towards its Holocene minimum extent, but has yet to tap into a landscape that remained ice covered throughout the entire Holocene.

Graphical abstract, Alpine glaciers, with their valuable combination of highly sensitive response to climate and near-global extent, are powerful tools for investigating previous and present climate changes. They also represent critical water resources for areas around the globe, with the potential for far-reaching effects in a warming world. Advancements to understand and model glacial changes and the variables influencing them are therefore paramount. Many glacier models fall into one of two endmembers: either highly complex transient models requiring careful tuning of multiple parameters to individual glaciers, or basic empirical correlations of glacier area and length with few considerations for local and regional variations in characteristics. Here we detail a physical steady-state model for alpine glaciers relating directly to glacier mass balance (via the equilibrium line altitude) while retaining the simplicity of other morphology methods, and simultaneously including error estimates. We provide custom MATLAB functions as a user-friendly and generally-applicable method to estimate glacier equilibrium line altitudes from only a limited number of glacier bed topography and glacier width measurements. As a test of the model’s efficacy, we compare the model results for present-day glaciers in the Swiss Alps with previously published estimates of equilibrium line altitudes and intermediate model outputs.•The method estimates glacier equilibrium line altitudes from a limited set of bed topography measurements and constraints on glacier width.•The method is based on continuity equations, reducing the need for empirical coefficients tuned with measured data.•The method uses Monte Carlo sampling and bootstrapping to generate uncertainty bounds on the equilibrium line altitude estimates.

The production of 10Be in the atmosphere in the high latitudes is modulated by solar variability. Time-series records of 10Be from ice cores therefore provide important information on variations in solar activity through time, which is fundamental to understanding climate variability. However, deposition of 10Be to the ice surface is also influenced by variability in atmospheric circulation and deposition processes, and thus, many 10Be ice core records remain difficult to interpret.South Pole is arguably the best available location for minimizing the influence of variable atmospheric circulation on 10Be deposition. The single existing 10Be record from South Pole covers the last millennium and ends in CE 1982.We present a new South Pole 10Be record from the late Holocene, together with examplary measurements from the last glacial period, complemented by climate modeling experiments of atmospheric 10Be production, transport and deposition physics. Our continuous one-meter resolution record covers so far the last three millennia. The data from the last millennium agree well with the existing 10Be record by Raisbeck et al. (1990). The 10Be data from the South Pole ice core matches the historic sunspot records strikingly, providing a robust calibration between sunspot number and 10Be deposition. The coincident timing of major shifts in sunspot number and 10Be provides an independent confirmation of the South Pole ice core timescale.Independently, our model simulations of both internannual variablity and glacial vs. interglacial 10Be production, transport and deposition indicate that 10Be in South Pole snow is robust even to significant climate changes, suggesting that the measured 10Be primarily reflect changes of solar activity over that period. In turn, our model-data comparison allows to evaluate potential shifts in solar activity through the late Holocene, and during the glacial-interglacial transition.

The Greenland Ice Sheet (GrIS) is melting in response to a rapidly warming climate. It is imperative to understand GrIS sensitivity to past climate, especially during periods when the ice sheet was smaller than present or possibly absent. The Camp Century ice core from NW Greenland, collected in 1966 and the first ice core to be drilled to the bed of the GrIS, revolutionized our understanding of global paleoclimate since 125 ka. However, basal sediment from the ice core was not fully explored and then sat in storage for decades – until it was re-discovered two years ago. We are now investigating these unique samples from the sub-glacial environment using modern analyses. Here, we present initial results from two samples, the upper and lower portions of >4 m of basal sediment. We applied an array of geochemical analyses to characterize paleoenvironment (lipid biomarkers, δ13C, δ15N), to infer past climatic conditions (δ18O, δD) from frozen pore water, and to determine the exposure and burial history of the sediments below the ice sheet (optically stimulated luminescence [OSL], cosmogenic 10Be, 26Al, and 21Ne). The sub-glacial sediment consists of poorly sorted, reddish-brown, quartz-rich diamict, with paleo-permafrost features in some layers. This material contains woody macrofossils, fungal sclerotia (Cenococcum geophilum), and mosses (Tomenthypnum nitens, Polytrichum juniperinum) that yield a 14C age >55 ka. Woody tissue from the upper and lower samples yield stable δ13C ratios of -26.7±0.1‰ and -29.6±0.1‰ and δ15N ratios of 2.4±0.8‰ and -2.3±0.8‰. Leaf wax (n-alkanoic acid) distributions are similar to modern Arctic shrubs. Frozen pore water yielded δ18O ratios of -23.06±0.08‰ and -21.49±0.08‰, enriched relative to all overlying ice (600 ka. In situ 10Be concentrations in quartz decrease with depth from 7.7±0.1 x104 atoms/g (500-850 µm) and 6.6±0.2 x104 (250-500 µm) in the upper sediment to 1.6±0.1 x104 atoms/g (500-850 µm) and 1.8±0.1 x104 (250-500 µm) in the lower sediment. The 26Al/10Be ratio also decreases with depth. In the upper sediment, 26Al/10Be ratios range between 4.2 and 4.9 indicating > 900 ka of burial. In the lower sediment, 26Al/10Be ratios range from 1.4 to 2.0 indicating >2 Ma of burial. Measured 21Ne/10Be ratios in quartz exceed 1000, which could indicate long-term burial and/or the presence of nucleogenic 21Ne.These results demonstrate that Camp Century basal sediment was exposed under ice-free conditions that supported vegetation similar to today. Cosmogenic data indicate the deeper sediment has been buried for most of the Pleistocene and the OSL date rules out surface exposure of the deeper material at MIS 11. Cosmogenic analysis indicates that the upper sample experienced less burial or more recent re-exposure. These data are consistent with a growing body of evidence indicating a dynamic Pleistocene GrIS, even under a pre-industrial climate system in which atmospheric CO2 concentrations did not exceed ~300 ppm.

The Camp Century Ice core, NW Greenland, recovered a 4.5 m basal section consisting of frozen sediments and debris-rich ice. This material was recently re-discovered in Danish ice core storage and visually logged. As part of a multi-disciplinary effort to unlock the climatic and paleo-environmental signal of this unique record, we have analysed detrital mineral composition and metamorphic ages. Bulk mineral analyses were performed at the Geological Survey of Denmark and Greenland on grain mounts from 2 core intervals using a SEM automated quantitative mineralogy (AQM) approach coupled to laser ablation ICP-MS analyses. This setup allows us to gain a full mineral description together with single-grain U-Pb dates for a large population of metamorphic components, e.g. apatite, rutile, titanite and zircon. In addition, amphibole grains were picked for 40Ar-39Ar dating performed at the LDEO Argon Isotope Lab. Mineralogical characterization was completed by X-Ray diffraction analysis of the fine fraction to determine the presence and nature of potential clay weathering products, and single-crystal X-ray diffraction was utilized to characterize the atomic arrangements of minerals that occur in solid solutions. The AQM results indicate that metamorphic minerals are present in sufficient amounts (100’s) for gaining statistically valid provenance data. Preliminary results show ages in the 1900 – 1700 Ma range (amphibole, rutile) and around 2700 Ma (zircon). This, along with the presence of swelling clays in the sediments, is consistent with weathering of the local bedrock, and/or sediments transported from the Inglefield orogenic belt north of the site. To gain information on the youngest thermal events of sediment sources, potentially revealing deep glacial incision, (U-Th-Sm)/He dating of single apatite grains is underway. Preliminary work on the 125-250 µm size fraction yield abundant subhedral-to-subrounded, euhedral apatite suitable for thermochronology. Here we report the results from the different methods and discuss the implications for understanding erosional processes and potential transport pathways of the Camp Century basal ice sediments.

Our knowledge about the glaciation history in the Russian Arctic has to a large extent been based on geomorphological mapping supplemented by studies of short stratigraphical sequences found in exp ...

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 CO2) 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.

The Svalbard-Barents ice sheet was predominantly a marine-based ice sheet and reconstructing the timing and rate of its decay during the last deglaciation can inform predictions of future decay of marine-based ice sheets (e.g. West Antarctica). Records of ice-sheet change are now routinely built with cosmogenic surface exposure ages, but in some regions, this method is complicated by the presence of isotopic inheritance yielding artificially old and erroneous exposure ages. Here, we present forty-six 1025 Be ages from bedrock (n = 38) and erratic boulders (n = 8) in southwestern Spitsbergen that, when paired with in situ 1427 C measurements (n = 5), constrain the timing of coastal deglaciation following the last glacial maximum. 10Be and 1428 C measurements from bedrock along a ~400 m elevation transect reveal inheritance-skewed 10Be ages, whereas 1429 C measurements constrain 400 m of ice-sheet thinning and coastal deglaciation at 17.4 ± 1.5 ka. Combined with three additional 10Be-dated coastal sites, we show that the southwestern margin of the Svalbard-Barents ice sheet retreated out of Norwegian Sea between ~18-16 ka. In situ 1432 C measurements can provide key chronological information on ice-sheet response to the last termination in cases where measurements of long-lived nuclides are compromised by isotopic inheritance.

The last deglaciation of the Laurentide Ice Sheet in northern Quebec and Labrador led to the formation of several glacial lakes that drained into Ungava Bay and the nearby Labrador Sea. Assessing the potential impact of their drainage on ocean surface conditions and climate, however, is limited by the few existing age constraints on ice retreat and associated evolution of these lakes. Here we report 21 10Be ages from shorelines and an outburst flood landform formed by Lake Naskaupi, one of the largest glacial lakes in this region. The results indicate that the lake drained from its full extent at 8300 ± 300 a, suggesting that it may have contributed to the freshwater forcing initiated by the drainage of Lake Agassiz-Ojibway that caused the 8.2-ka cold event. Additionally, the results provide important constraints on the position of the ice margin of the Labrador Sector during its retreat across this region.

Iniciativa Cientifica Milenio NC120066 FONDECYT 11121280 1160488 1151469 CONICYT USA 2013-0035 NSF-BCS 1263474 Fulbright

Beryllium-10 has become the premiere cosmogenic nuclide for quantifying Earth-surface process. Routine measurement of 10Be at the ≤ 2–3% precision level, coupled with precise 10Be production-rate calibrations, now allow for 10Be-based records of glacier and ice-sheet change to be reliably compared to independent records of climate variability. Here, we review efforts over the last 10+ years to characterize the Holocene behavior of ice sheets and glaciers fringing Baffin Bay using in situ 10Be. Hundreds of 10Be measurements present a detailed picture of ice-margin migration through the early Holocene. Widespread net deglaciation was interrupted by ice-margin readvances or stillstands, marked by modes of moraine deposition, near the end of the Younger Dryas (12.9–11.7 ka BP), 10.4–10.2 ka BP, 9.3 ka BP, and 8.2 ka BP, with perhaps additional widespread moraine deposition occurring ca. 9.7 ka BP and 7.3 ka BP. Modes of moraine deposition encompass independent and glaciologically distinct ice masses – the Greenland and Laurentide ice sheets and local alpine glaciers situated on Baffin Island and western Greenland – providing a robust, albeit discontinuous, record of widespread climatic changes in the Baffin Bay region in the early Holocene. Periods of glacier advance coincide with abrupt cooling events documented in Summit Greenland ice cores indicating that i) Baffin Bay ice masses largely followed the pattern of temperature change displayed in Greenland ice cores, ii) abrupt cooling events were of sufficient magnitude and duration to briefly synchronize the behavior of independent and glaciologically distinct ice masses across Baffin Bay despite varying degrees of dynamical influence, and iii) centennial-scale synchronization of ice masses requires that abrupt temperature changes recorded at Summit Greenland also occurred during the summertime within glacier ablation zones. Advancements in 10Be methodology combined with an environment conducive towards developing 10Be-based records of ice-margin change has resulted in ice-margin reconstructions that identify a potentially fundamental negative feedback mechanism inherent to melting ice sheets in the Baffin Bay region – elevated and episodic meltwater delivery into the Labrador Sea results in a decrease in the Atlantic meridional overturning circulation and regional cooling, which, in turn, drives a brief reversal of deglaciation. Under the right conditions 10Be can be used to develop centennial-scale, climatically relevant records of glacier and ice-sheet change.

The Labrador Sector of the Laurentide Ice Sheet is characterized by a complex network of ice divides and an extensive landform record outlining two broad and opposing ice flows that are separated by a narrow Horseshoe Intersection Zone (HIZ). This geomorphic system gave rise to contrasting reconstructions, which reflect uncertainties on the temporal evolution of ice divides, the nature and age of the main landform systems and the overall pattern of ice retreat during the last deglaciation. Here, we address these issues through systematic mapping of glacial landforms and ice-flow indicators in a large area of northeastern Quebec and Labrador. The application of cosmogenic (10Be and 26Al) dating to esker-fed glaciomarine deltas and different rock surfaces brings new constraints on the chronological framework and insights on the subglacial thermal regime. Our results outline four main landform assemblages, two of which relating to a major system of opposite ice flows that delineate the position of the eastern Ancestral Labrador ice divide. Our reconstruction shows that the HIZ occurs several tens of km to the west of this divide and that these two features are genetically distinct. The HIZ relates to the late-glacial development of ice streams showing a massive convergent ice flow into Ungava Bay. The upstream extent of this ice flow system shows a strong coupling with the outline of Ungava Bay drainage divide, suggesting that the configuration of the HIZ could be the expression of a topographic control on the late-glacial ice sheet dynamics. Landforms also indicate a significant shift in the deglaciation mode, which evolved from an overall warm-based to an areally-confined cold-based ice retreat near the center of the former ice mass – a change in dynamics that also played a role in the configuration of the HIZ. Overall, areas indicative of cold-based ice conditions are limited to highly elevated terrains, thus ruling out models arguing for an extensive cold-based ice cover over Ungava Bay throughout the last deglaciation.