The behavior of the Antarctic Ice Sheet system has major implications for understanding past climates and global sea-level changes. James Ross Island, located in the cooler and drier lee side of the Antarctic Peninsula, preserves glacial and marine records spanning at least the late Pleistocene and Holocene. To reconstruct past environmental conditions during the last ∼50,000 years, we carry out new morphostratigraphic surveys, geomorphological mapping, and 75 radiocarbon and 4 luminescence analyses.The new records show that significant glacier retreat into the marine embayments and inner fjords occurred at least twice during the last ∼50,000 years: between 45,000 and 40,000 calendar years before present (yr BP), and again in the Holocene, as early as 11,200 yr BP, with the latter documenting the emergence of landscapes on the east side of the Antarctic Peninsula following the Last Glacial Maximum. The findings suggest that the local Last Glacial Maximum began after 40,000 yr BP and persisted until 11,200 yr BP, followed by the transition from ice sheet to alpine glaciation on James Ross Island.Additionally, we identify at least five glacier advances during the Holocene, at ∼7200, ∼5800, ∼5300, ∼4300, and after ∼500 yr BP, based on the new 14C data along with previously published cosmogenic surface exposure ages. When compared with paleoclimate records from lower latitudes, these glacier expansions appear broadly coincident with colder conditions associated with lower latitude northward shifts of Subantarctic climates and the Southern Westerly Winds. In contrast, intervals of overall reduced glacier extent, notably between ∼4000 and 2000 yr BP, likely reflect relatively warmer regional climates. Finally, we present a new record of Holocene marine-limit observations documenting relative sea-level change, with a sea-level highstand reaching ∼14–16 m a.s.l. at ∼7100 yr BP, followed by continuous sea-level fall from ∼3 mm yr−1 to ∼0.6 mm yr−1. This record captures both overall isostatic rebound after deglaciation and coastal uplift changes preserved around James Ross Island likely affected by regional glacier advance and retreat.

The contribution of the Greenland Ice Sheet (GrIS) to sea-level rise is accelerating and there is an urgent need to characterize which sectors of the ice sheet are the most vulnerable. Estimating the volume of Greenland ice that was lost during past warm periods can support efforts to constrain the ice sheet's response to future warming. Sub-ice sediment and bedrock, retrieved from deep ice core campaigns or targeted drilling efforts, yield critical and direct information about past ice-free conditions. However, it is challenging to scale the few available sub-ice point measurements to the geometry of the entire ice sheet. Here, we provide a framework for assessing sea-level potential, which we define within an ensemble of ice-sheet model simulations as the amount the GrIS has contributed to sea level when a particular location in Greenland is ice free. An assessment of dominant sources of uncertainty in our paleo ice-sheet modelling, including climate forcing, ice-sheet initialization, and solid-Earth properties, reveals spatial patterns in the sensitivity of the ice sheet to these processes and related feedbacks. We find that the sea-level potential of central Greenland is most sensitive to lithospheric feedbacks and ice-sheet initialization, whereas the ice-sheet margins are most sensitive to climate forcing parameters. We map the GrIS response to warming, in order to (1) estimate of the region(s) of GrIS that likely contributed to the first meter(s) of global sea-level change across a range of plausible deglaciation scenarios, (2) guide future sub-glacial access efforts that can provide targeted information about the response of the ice sheet to past warming, and (3) contextualize existing and future datasets within a glaciologically coherent, full-geometry framework to establish the minimum GrIS contribution to past sea level when a particular location is ice-free. Through our ensemble approach, we can assign a plausible range of GrIS contributions to global sea level for deglaciated conditions at any site. Our results identify primarily areas in southwest Greenland, and secondarily north Greenland, as best-suited for subglacial access drilling that seeks to constrain the response of the ice sheet to past and future warming.

Projections of future sea-level rise benefit from understanding the response of past ice sheets to warming during past Quaternary interglacials. Constraints on the extent of inland Greenland Ice Sheet retreat during the Middle Holocene (~8–4 thousand years before present) are limited because geological records of a smaller-than-modern phase largely remain beneath the modern ice sheet. We drilled through 509 metres of firn and ice at Prudhoe Dome, northwestern Greenland, to obtain sub-ice material yielding direct evidence for the response of the northwest Greenland ice sheet to Holocene warmth. Here we present infrared stimulated luminescence measurements from sub-ice sediments that indicate that the ground below the summit was exposed to sunlight 7.1 ± 1.1 thousand years ago. This proposed complete deglaciation of Prudhoe Dome, coeval to reduced extent at other ice caps across northern Greenland, is consistent with interglacial-only δ18O values from the Prudhoe Dome ice column and ice depth–age modelling. Our results point to a substantial response of the northwest Greenland ice sheet to early Holocene warming, estimated to be +3–5 °C from palaeoclimate data. This range of summer temperatures is similar to projections of warming by 2100 CE. The ~500-metre-thick Prudhoe Dome in northwestern Greenland completely deglaciated 7,000 years ago, highlighting the sensitivity of the ice sheet to mid-Holocene warming, according to luminescence and geochemical data from sub-ice sediments and ice cores.

The lack of geological constraints on past ice-sheet change in marine-based sectors of the Greenland Ice Sheet (GrIS) following the Last Glacial Maximum limits our ability to assess (1) the drivers of ice-sheet change, and (2) the performance of ice-sheet models that are benchmarked against the paleo-record of GrIS change. Here, we provide new in situ 10Be surface exposure chronologies of ice-sheet margin retreat from the outer Scoresby Sund and Storstrømmen Glacier regions in eastern and northeastern Greenland, respectively. Ice retreated from Rathbone Island, east of Scoresby Sund, by ∼ 14.1 ka, recording some of the earliest documentations of terrestrial deglaciation in Greenland. The mouth of Scoresby Sund deglaciated by ∼ 13.2 ka, and retreated at an average rate of ∼ 43 m yr−1 between 13.2 and 9.7 ka. Storstrømmen Glacier retreated from the outer coast to within ∼ 3 km of the modern ice margin between ∼ 12.7 and 8.6 ka at an average rate of ∼ 28 m yr−1. Retreat then slowed or reached a stillstand as ice retreated ∼ 3 km between ∼ 8.6 ka to the modern ice margin at ∼ 8.0 ka. These retreat rates are consistent with late glacial and Holocene estimates for marine-terminating outlet glaciers across East Greenland, and comparable to modern retreat rates observed at the largest ice streams in northeastern, and northwestern Greenland.

We used mapping of bedrock lithology, bedrock fractures, and lake density in Inglefield Land, northwestern Greenland, combined with cosmogenic nuclide (10Be and 26Al) measurements in bedrock surfaces, to investigate glacial erosion and the ice sheet history of the northwestern Greenland Ice Sheet. The pattern of eroded versus weathered bedrock surfaces and other glacial erosion indicators reveal temporally and spatially varying erosion under cold- and warm-based ice. All of the bedrock surfaces that we measured in Inglefield Land contain cosmogenic nuclide inheritance with apparent 10Be ages ranging from 24.9 ± 0.5 to 215.8 ± 7.4 ka. The 26Al/10Be ratios require minimum combined surface burial and exposure histories of ∼ 150 to 2000 kyr. Because our sample sites span a relatively small area that experienced a similar ice sheet history, we attribute differences in nuclide concentrations and ratios to varying erosion during the Quaternary. We show that an ice sheet history with ∼ 900 kyr of exposure and ∼ 1800 kyr of ice cover throughout the Quaternary is consistent with the measured nuclide concentrations in most samples when sample-specific subaerial erosion rates are between 0 and 2 × 10−2 mm yr−1 and subglacial erosion rates are between 0 and 2 × 10−3 mm yr−1. These erosion rates help to characterize Arctic landscape evolution in crystalline bedrock terrains in areas away from focused ice flow.

We present 33 new Be-10 exposure ages on boulders rooted in moraines in the Calluqueo valley in central Patagonia. The former glacier flowed westward off the Monte San Lorenzo massif and was expanded from similar to 6,900 until similar to 6,700 years ago; and at 5,620 +/- 200, 5,140 +/- 150, 4,660 +/- 180, 4,100 +/- 140, 3,610 +/- 200, 3,120 +/- 110 years ago (n=2 for these groups), and repeatedly during the last similar to 600 years. Glaciers may have advanced earlier in the Holocene, but additional effort is needed to elucidate the timing. Also taking into account a record in the nearby Tranquillo Valley, we see that at Monte San Lorenzo glaciers were expanded often between similar to 7 and similar to 3 ka, and after similar to 1.4 ka. During the middle Holocene moraines were built on average every similar to 500 years. The largest expansions of the last millennium were at similar to 1400-1500 CE. We also date boulders on the innermost moraine terrain to 1810 CE +/- 20 and 1870 CE +/- 20 years. A last phase of stability existed from similar to 1800 to 1940 CE, with pronounced ongoing retreat since after 1940 CE. The Monte San Lorenzo chronologies allow us to compare Holocene records between central and southernmost Patagonia. Throughout Patagonia, there is a similar glacier-climate history, with nested moraine sets and the largest glaciers generally in the mid-early Holocene. In most places, a marked change in glacier behavior and climate occurred around 7 ka, but some sites exhibit evidence of earlier Holocene activity. Over the last millennium, a net decrease in extent of advances occurred from similar to 1400 to similar to 1800 CE. However, there are some differences across Patagonia. In central Patagonia (similar to 44-49 degrees S), glaciers expanded between 4 and 3 ka, while from 3 to 2 ka moraines are not preserved; the pattern appears reversed to the south (i.e. south of similar to 49 degrees S). We hypothesize that Subantarctic or high latitude climates strongly impacted at least as far as northern Patagonia throughout the Holocene, including centennial and millennial changes in cold phases reflecting shifts in the Southern Hemisphere Westerlies and associated air masses. One exception perhaps is between 4 and 3 ka, where moraines are not observed to the south, possibly reflecting closer proximity to Antarctica where this interval may be generally warm. Regardless of secondary differences across southern South America, glacier records in central Patagonia are unlike those in the Northern Hemisphere, but similar to other records in the Southern Hemisphere. For comparison, anthropogenic climate change has caused climate, and thus glacier, behavior to be more in sync between the hemispheres, whereas longer-term Holocene records show distinct differences in histories even regionally within South America.

Understanding basal thermal regimes of paleo-ice sheets is fundamental to provide constraints on ice sheet dynamics and geometry, subglacial hydrology and sediment fluxes, landscape evolution, and long-term climate responses. While various methods have characterized glacial terrains from a range of subglacial conditions, the relationship between landsystem mapping and terrestrial cosmogenic nuclides (TCNs) remains largely unexplored. Here, we investigate a continuum of relict polythermal landsystems and surrounding warm-based terrains mapped in areas formerly covered by the Keewatin Ice Divide by utilizing paired 10Be and 26Al cosmogenic nuclide analyses on bedrock, boulder, and till samples in the eastern Keewatin region of Nunavut, northern Canada. Exposure ages in low-elevation warm-based landscapes cluster at 8.2 f 0.6 ka and align with the timing of deglaciation (7.7 f 1 ka) indicating relatively high (deep) glacial erosion under dominantly warm-based conditions. Moderate nuclide abundances and apparent mean ages of 23.5 f 4.6 ka (surface tills) and 21.8 f 2.1 ka (bedrock trimlines at marine limit) in relict intermediate landsystems extending across the ice divide migration zone above 200 m elevation reflect moderate erosion during transient cold-based and warm-based conditions. High nuclide abundances and apparent mean 10Be ages of 53.7 f 4.6 ka (bedrock and boulder) in relict cold-based landsystems, predominant where the ice divide was anchored in the uplands above 400 m elevation, are consistent with low erosion and persistent cold-based conditions partially preserving surfaces weathered prior to the last glaciation. The apparent exposure ages in the relict terrains, significantly exceeding expected deglacial ages, and the relatively long periods of burial derived from 26Al/10Be ratios, indicate widespread TCN inheritance and reflect differential erosion under polythermal basal ice regimes as inferred from landsystem mapping. Our findings emphasize the importance of geomorphological mapping and landsystem analysis to inform the TCN sampling plan and highlight the need for caution in interpreting exposure ages within predominantly warm-based glacial landscapes in a core region of the Laurentide Ice Sheet where relict weathered terrains are recognized.

Projections of future sea-level rise benefit from understanding the response of past ice sheets to interglacial warmth. Constraints on the extent of inland Greenland Ice Sheet (GrIS) recession during the Middle Holocene (~8 – 4 ka) are limited because geological records of a smaller-than-modern phase largely remain beneath the modern ice sheet. We drilled through 509 m of firn and ice at Prudhoe Dome (PD), northwest Greenland to obtain sub-ice material yielding direct evidence for the response of the NW GrIS to Holocene warmth. Our infrared stimulated luminescence measurements from sub-ice sediments indicates that the ground below the summit was exposed to sunlight at 7.1 ± 1.1 ka. This complete deglaciation of PD, coeval to reduced extent at other ice caps across Northern Greenland, is further supported by interglacial-only δ18O values from the PD ice column as well as ice depth-age modeling. Our results point to a significant response of the NW GrIS to early Holocene warming, estimated to be +3–5 ℃ from paleoclimate data. This range of summer temperatures is similar to projections of warming by 2100 CE.

We describe and analyze the glacial geomorphology and new 10Be cosmogenic surface exposure ages from moraines deposited before Marine Isotope Stage (MIS) 2 around Nevado de Cha & ntilde;i (24 degrees 4 ' S, 65 degrees 45 ' W), a north-south-trending massif located in the arid subtropical mountains of northwestern Argentina. We combine these data with previously published ages in order to establish a glacier chronology around the massif and the central Andes. The results show at least three phases of glacier expansions occurred before the global Last Glacial Maximum, (i) during MIS 6, (ii) close to the transition from MIS 4 to MIS 3, and (iii) during mid-late MIS 3. Based on a comparison of the timing of glacier advances with other glacial and paleoclimatic proxies elsewhere, we infer that glaciers grew in this arid region of the subtropical Andes during periods of reduced temperatures and wetter conditions, ultimately due to intensification of the South American Summer Monsoon. In contrast, during MIS 5 no glacial activity was recorded around the massif, and we infer that even if wetter conditions prevailed in the region the temperature was not sufficiently low to support glaciations.

Up until now, the cosmogenic radioisotope 39Ar has not been used for surface exposure or burial dating of minerals due to its low concentration in rocks and the large sample size requirements for its detection by low-level counting. The novel analytical method Atom Trap Trace Analysis (ATTA) – already well established for gas samples from groundwater, ocean water or ice cores – can measure the isotopic ratio of 39Ar to stable Ar in the range of 10-16 on just a few ml STP of argon and therefore opens up new possibilities for applying 39Ar. This talk will report on the initial steps taken towards using 39Ar as a geochronometer. Calculations of production rates of 39Ar in typical continental rocks, exposed to cosmic radiation at the Earth surface, show that sample sizes of the order of 100 g of rock should yield a sufficient number of 39Ar atoms (order 103 to 104) for detection by ATTA. However, the amount of 40Ar in such samples – and therefore the total extractable Ar amount - is much lower than what is typically extracted from ice and water samples, which contain atmosphere-derived Ar. The 40Ar content in rock stems from 40K-decay and depends on the rock formation age and the potassium content. Dilution with 39Ar-free Ar results in sufficient total argon volumes for the standard ATTA analysis. Gas extractions from heated rock samples indeed show 39Ar isotope abundances 2-3 orders of magnitude above the atmospheric ratio, well within the measurement range of ATTA after dilution. In order to check the feasibility of exposure dating of rocks, several samples were taken for comparison from boulders of glacier moraines, previously dated with 10Be, in the Jamtal valley in Austria. Additionally, 10Be-dated samples from other moraine sites are to be analysed for 39Ar for further validation of 39Ar as a tool for exposure dating. As of now it remains to be seen whether reliable agreement between the dating methods can be achieved. Due to its relatively short half-life of 268 years, 39Ar would be a useful addition in multi-tracer studies on geologic processes within the last two millennia.

In three cirques in the western Olympus Range of the McMurdo Dry Valleys, Antarctica, previous advances of cirque glaciers are recorded by a sequence of three drifts in each of the cirques. We dated drift limits and the deposits on modern glaciers in two of these cirques, Dean and Dipboye, via cosmogenic He-3 in pyroxene from 41 dolerite boulders, Cl-36 in pyroxene from 12 of those dolerites, and Be-10 in quartz from 11 sandstone boulders. Exposure age scatter is high on all deposits. The He-3 exposure ages across all deposits range from similar to 35 to similar to 2300 ka and Be-10 exposure ages range from similar to 7 to similar to 435 ka. Coupled Cl-36/He-3 from dolerites support constant exposure with erosion for nine of the 12 samples, while the other three might have experienced complex exposure-burial histories. Due to the mesa-butte topography and slow bedrock erosion rates, nuclide inheritance is the primary cause of age scatter in dolerites, accounting for >1 Myr of exposure age error. Mean exposure ages from sandstones are 2-7 times younger than those from dolerites for the same deposits, indicating that inheritance is less common in sandstones in this region. Weathering analyses of sandstone boulders show an increase in average siliceous crust thickness and rock strength with deposit age, an example of case hardening. Based on both relative and exposure age dating, drift age increases with distance from the modern glaciers in both Dean and Dipboye cirques, with three advances during the past <700 ka. However, due to high exposure age scatter, it cannot be determined if the three drifts are temporally correlated across the two cirques and therefore the drifts might record different glacial advances in Dean Cirque vs. Dipboye Cirque despite the apparent stratigraphic correlation of the drifts. This study has implications for drift depositional processes of cold-based glaciers and the importance of source-bedrock lithology and geomorphology on nuclide inheritance in Antarctica.

ABSTRACT The final deglaciation stages of the Laurentide Ice Sheet in northern Quebec–Labrador were marked by the incursion of the d'Iberville Sea into the coastal areas of Ungava Bay. Remote and field mapping of raised marine strandlines along the Ungava Peninsula east coast show that the maximum marine limit decreases from south (165 m) to north (100 m), reflecting differential uplift linked to an ice mass remnant located to the southwest of the bay. Reconstruction of the uppermost marine limit in two east–west transects extending into the Peninsula interior reveals distinct sea‐level stands with limited extents towards the west, indicating that the early stages of the marine incursion occurred in contact with the ice margin. The reconstruction also identifies the maximum eastward extent of ice‐dammed lakes that occupied the Arnaud River and Aux‐Feuilles River valleys. 10 Be surface exposure dating of marine strandlines yielded consistent 10 Be ages that indicate a rapid deglaciation of Ungava Bay between 8900 ± 200 a (north) and 7900 ± 200 a (south). These results provide constraints on the position of the Labrador Sector eastern and western ice margins during the late deglaciation, in addition to the timing of ice and meltwater discharges from the Ungava Bay region.

The last glacial termination featured a major reconfiguration of Earth's climate and cryosphere, whose underlying cause remains unresolved. To investigate this problem, we combine Be-10 surface-exposure dating of moraines with former equilibrium line altitudes to determine the magnitude and timing of atmospheric temperature warming that ended the Last Glaciation in the Takap & omacr;/Tekapo valley in the central Southern Alps of New Zealand. We show mountain-valley glacier recession from a nearly full-glacial configuration to a near-interglacial configuration early in the termination between similar to 18,000 and similar to 17,000 yrs ago, commensurate with a net atmospheric warming of similar to 3.8 degreesC (from -6.25 degreesC to -2.5 degreesC cooler than present). Similar recession also affected mid-latitude mountain glaciers in South America. We suggest trans-South Pacific glacier withdrawal early in the termination resulted from a decisive poleward shift of the austral westerlies that increased the proportion of warm subtropical air masses flowing over southern mid-latitude mountains, markedly raising glacier ablation rates. Farther south, the poleward-shifted westerlies drove increased ocean upwelling and surface warming, outgassing of carbon dioxide, and progressive ocean destratification, together raising atmospheric temperature over the Antarctic Ice Sheet, but at a rate slower than over mid-latitude mountain glaciers. Overall, we consider that Southern Hemisphere middle-latitude glacier recession was linked to Antarctic warming by a poleward displacement in latitude and an increase in strength of the Southern Hemisphere westerlies.

We present 40 new 10Be exposure ages of moraines and other glacial deposits left behind by the southeastern sector of the Laurentide Ice Sheet (LIS) in southern New England and New York, summarize the regional moraine record, and interpret the dataset in the context of previously published deglaciation chronologies. The regional moraine record spans the Last Glacial Maximum (LGM), with the outermost ridge of the terminal complex dating to similar to 26-25 ka, the innermost ridge of the terminal complex dating to similar to 22 ka, and a series of smaller recessional limits within similar to 50 km of the terminal complex dating to similar to 21-20.5 ka. The chronology generally agrees with independent age constraints from radiocarbon and glacial varves. A few inconsistencies between ages from cosmogenic-nuclide measurements and those from other dating methods are explained by geological scatter, where several bedrock samples and boulders from the outer terminal moraine exhibit nuclide inheritance, while some exposure ages of large moraines are likely affected by postdepositional disturbance. The exposure age chronology places the southeastern sector of the LIS at or near its maximum extent, from similar to 26 to 21 ka, which is broadly consistent with the LGM sea-level lowstand, local and regional temperature indicators, and local summer insolation. The net change in LIS extent, represented by this chronology, occurred more slowly (< 5 to 25 m yr(-1)) than the subsequent retreat through the rest of New England, consistent with a slow general rise in insolation and modeled summer temperature. We conclude that the major pulse of LIS deglaciation and accelerated recession, recorded by dated glacial deposits north of the moraines discussed here, did not begin until after atmospheric CO2 increased around 18 ka, marking the onset of Termination I.

Alpine glacier-based temperature reconstructions spanning the last deglaciation provide critical constraints on local to regional climate change and have been reported from several formerly glaciated regions around the world yet remain sparse from high-northern-latitude regions. Using newly and previously 10Be-dated moraines, we report paleo-glacier equilibrium line altitudes (ELAs) for 15 time slices spanning the Last Glacial Maximum (LGM) to the Little Ice Age (LIA) for a valley in the western Alaska Range. We translate our ELA reconstructions into a proxy for summer temperature by applying a dry adiabatic lapse rate at each reconstructed ELA relative to the outermost LIA moraine. We observe ∼4 °C warming through the last deglaciation at our site that took place in two steps following initial gradual warming: ∼1.5 °C abrupt warming at 16 ka, ∼2 kyr after the onset of global CO2 rise, and ∼2 °C warming at ∼15 ka, near the start of the Bølling. Moraine deposition and modest summer cooling during Heinrich Stadial 1 and the early Younger Dryas (YD) suggest that despite these events being expressed more strongly in wintertime, the classic blueprint of North Atlantic climate variability extends to the western Arctic region.

Abstract. The contribution of the Greenland Ice Sheet (GIS) to sea level rise (SLR) is accelerating and there is an urgent need to improve predictions of when and from what parts of the ice sheet Greenland will contribute its first meter. Estimating the volume of Greenland ice that was lost during past warm periods offers a way to constrain the ice sheet’s response to future warming. Sub-ice sediment and bedrock, retrieved from deep ice core campaigns or targeted drilling efforts, yield critical and direct information about past ice-free conditions. However, it is challenging to scale the few available sub-ice point measurements to the geometry of the entire ice sheet. Here, we provide a framework for assessing sea-level potential, which we define as the amount the GIS has contributed to sea level when a particular location in Greenland is ice-free, from an ensemble of ice-sheet model simulations representing a wide range of plausible deglaciation scenarios. An assessment of dominant sources of uncertainty in our paleo ice sheet modelling, including climate forcing, ice-sheet initialization, and solid-Earth properties, reveals spatial patterns in the sensitivity of the ice sheet to these processes and related feedbacks. We find that the sea-level potential of central Greenland is most sensitive to lithospheric feedbacks and ice-sheet initialization, whereas the ice-sheet margins are most sensitive to climate forcing parameters. Our framework allows us to quantify the local and regional uncertainty in sea-level potential, which we use to evaluate the GIS bedrock according to the usefulness of information sub-ice sediments and bedrock provide about past ice-sheet geometry. Through our ensemble approach, we can assign a plausible range of GIS contributions to global sea level for deglaciated conditions at any site. Our results identify primarily areas in southwest Greenland, and secondarily north Greenland, as best-suited for subglacial access drilling that seeks to constrain the response of the ice sheet to past and future warming.

Glacial erosion creates diagnostic landscapes and vast amounts of sediment. However, knowledge about the rate at 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 a recent, ∼ 200-year long overriding of a bedrock surface fronting, Sermeq Kujalleq (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 relicts 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 the total glacial erosion in representative continental shield lithologies.

From 10Be surface-exposure dating we make the case that classic late-glacial moraines in southwestern Norway, including the iconic Esmark moraine, and in the Southern Hemisphere middle latitudes, including the iconic Birch Hill moraine of the Southern Alps of New Zealand, were constructed coevally within dating uncertainties. This finding of simultaneous glacier resurgence in the two polar hemispheres carries the implication that the millennial-scale climate reversal of the last deglaciation was global and required a change in the energy budget of the earth's climate system.

The accelerated melting of ice in the polar regions 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? The SHIFTS project aimed to provide a new avenue for understanding how bi-polar climate varied during the Late Glacial and the Holocene by reconstructing primary features of atmospheric circulation and variability by using glaciers as climate indicators for both northern and southern hemisphere. In north, on the west coast of Troms and Finnmark we have mapped and sampled glacier forelands for cosmogenic dating. These results are combined with an extensive lake coring program targeting lakes with and without glacial input in Arctic Norway. At the Island of Arnøy, western Finnmark we mapped a glacier foreland to build a cosmogenic nuclide chronology from 71 moraine boulders deposited during the late glacial and the Holocene. Our record suggest that this Arctic Norway record reached its maximum late glacial extent about 14 ka ago, prior to the Younger Dryas. Following considerable retreat through the first part of the YD, glaciers re-stabilized in the mid-YD and showed slower oscillatory retreat through the latter part of the YD. This retreat pattern is confirmed from a lake sediment study at Andøya further south in Northern Norway. The sub-annually reconstruction show a glacier advance during the Intra Allerød cold period and thereafter a gradually retreat towards the end of the Younger Dryas when the glacier again did a re-advance. The results from the reconstructed Arctic glaciers during the late glacial show consistency to the glacier record from the southern hemisphere e.g., at South Georgia, New Zealand and in Patagonia. For the Holocene reconstruction we have used analyses of sediments deposited in distal glacier-fed lakes. We recorded several short-lived glacier advances in the early Holocene followed by a genera glacier retreat between 9000 and 7000 cal. yr BP, interrupted by a glacier advance 8200 years ago. Most glaciers were melted away between 7000 and 5200 cal. years BP. After this the glaciers advanced throughout the “Neoglacial”, until they reached its maximum extent during the “Little Ice Age”. The two “Little Ice Age” moraines in the upper valley of Rødhetta at the Island of Arnøy is dated to 480 and 390 yrs. BP using cosmogenic dating. This overall trend is coherent compared to other glacier reconstructions from Arctic Norway, however variations on multi-decadal time scales are observed that possibly reflect more local climatic changes and/or uncertainties associated with the methods employed in this study.