[1] This paper presents the first assessment of the Uummannaq ice stream system (UISS) in West Greenland. The UISS drained~6% of the Greenland ice sheet (GrIS) at the Last Glacial Maximum (LGM). The onset of the UISS is a function of a convergent network of fjords which feed a geologically controlled trough system running offshore to the shelf break. Mapping, cosmogenic radiogenic nuclide (CRN) dating, and model output reveal that glacially scoured surfaces up to 1266 m above sea level (asl) in fjord-head areas were produced by warm-based ice moving offshore during the LGM, with the elevation of warm-based ice dropping westwards to~700 m asl as the ice stream trunk zone developed. Marginal plateaux with allochthonous blockfields suggest that warm-based ice produced till and erratics up to~1200 m asl, but CRN ages and weathering pits suggest this was pre-LGM, with only cold-based ice operating during the LGM. Deglaciation began on the outer shelf at~14.8 cal. kyrs B.P., with Ubekendt Ejland becoming ice free at~12.4 ka. The UISS then collapsed with over 100 km of retreat by~11.4 ka-10.8 cal. kyrs B.P., a rapid and complex response to bathymetric deepening, trough widening, and sea-level rise coinciding with rapidly increasing air temperatures and solar radiation, but which occurred prior to ocean warming at~8.4 cal. kyrs B.P. Local fjord constriction temporarily stabilized the unzipped UISS margins at the start of the Holocene before ice retreat inland of the current margin at~8.7 ka.

Citation for published item:vneD FF nd oertsD hFrF nd eD fFF nd ¡ y gofighD gF nd ieliD eF nd od¡ esD eF @PHIRA 9gontrols upon the vst qlil wximum deglition of the northern ummnnq se trem ystemD est qreenlndF9D uternry siene reviewsFD WP F ppF QPREQRRF Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractThe Uummannaq ice stream system (UISS) was a convergent cross-shelf ice stream system that operated in West Greenland during the Last Glacial Maximum (LGM). This paper presents new evidence constraining the geometry and evolution of the northern sector of the UISS and considers the factors controlling its dynamic behaviour. Geomorphological mapping, 21 new terrestrial cosmogenic nuclide (TCN) exposure ages, and radiocarbon dating constrain LGM warm-based ice stream activity in the north of the system up to 1400 m a.s.l. Intervening plateaux areas either remained ice free, or were covered by cold-based icefields. Beyond the inner fjords, topography and bathymetry forced ice flow southwards into the Uummannaq Trough, where it coalesced with ice from the south, and formed the trunk zone of the UISS.Deglaciation of the UISS began at 14.9 cal. kyr BP. Rapid retreat from the LGM limit was forced by an increase in air temperatures and rising sea level, enhanced by the bathymetric over- Greenland, which suggest ice had retreated beyond its present margin by 9-7 kyr. This demonstrates the potential importance of topographic control on calving margin stability, and its ability to override climatic forcing.

Global audiences are captivated by climbers pushing themselves to the limits in the hypoxic environment of Mount Everest. However, air pressure sets oxygen abundance, meaning it varies with the weather and climate warming. This presents safety issues for mountaineers but also an opportunity for public engagement around climate change. Here we blend new observations from Everest with ERA5 reanalysis (1979-2019) and climate model results to address both perspectives. We find that plausible warming could generate subtle but physiologically relevant changes in summit oxygen availability, including an almost 5% increase in annual minimum VO 2 max for 2 C warming since pre-industrial. In the current climate we find evidence of swings in pressure sufficient to change Everest's apparent elevation by almost 750 m. Winter pressures can also plunge lower than previously reported, highlighting the importance of air pressure forecasts for the safety of those trying to push the physiological frontier on Mt. Everest.

In the Northern Hemisphere, most mountain glaciers experienced their largest extent in the last millennium during the Little Ice Age (1450 to 1850 CE, LIA), a period marked by colder hemispheric temperatures than the Medieval Climate Anomaly (950 to 1250 CE, MCA), a period which coincided with glacier retreat. Here, we present a new moraine chronology based on 36Cl surface exposure dating from Lyngmarksbræen glacier, West Greenland. Consistent with other glaciers in the western Arctic, Lyngmarksbræen glacier experienced several advances during the last millennium, the first one at the end of the MCA, in ~1200 CE, was of similar amplitude to two other advances during the LIA. In the absence of any significant changes in accumulation records from South Greenland ice cores, we attribute this expansion to multi-decadal summer cooling likely driven by volcanic and/or solar forcing, and associated regional sea-ice feedbacks. Such regional multi-decadal cold conditions at the end of the MCA are neither resolved in temperature reconstructions from other parts of the Northern Hemisphere, nor captured in last millennium climate simulations.

Citation for published item:vneD FF nd oertsD hFrF nd eD fFF nd ¡ y gofighD gF nd ieliD eF @PHISA 9gontrols on suglil edrok edform development t the se of the ummnnq se tremD est qreenlndF9D qeomorphologyFD PQI F ppF QHIEQIQF Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. This paper investigates the controls on the formation of subglacially eroded bedrock bedforms 17 beneath the topographically confined region upstream of the Uummannaq Ice Stream (UIS). During 18 the last glacial cycle, palaeoglaciological conditions are believed to have been similar for all sites in 19 the study, characterised by thick, fast-flowing ice moving over a rigid bedrock bed. Classic bedrock 20 bedforms indicative of glacially eroded terrain were mapped, including p-forms, roches moutonnées, 21 and whalebacks. Bedform long axes and plucked face orientations display close correlation (parallel 22 and perpendicular) to palaeo-ice flow directions inferred from striae measurements. Across all sites, 23 elongation ratios (length to width) varied by an order of magnitude between 0.8:1 and 8.4:1. 24Bedform properties (length, height, width, and long axis orientation) from four subsample areas, 25 *Revised manuscript with no changes marked Click here to view linked References 2 form morphometrically distinct populations, despite their close proximity and hypothesised 26 similarity in palaeoglaciological conditions. 27 28Variations in lithology and geological structures (e.g., joint frequency; joint dip; joint orientation; 29 bedding plane thickness; and bedding plane dip) provide lines of geological weakness, which focus 30 the glacial erosion, in turn controlling bedform geometries. Determining the relationship(s) between 31 bedding plane dip relative to palaeo-ice flow and bedform shape, relative length, amplitude, and 32 wavelength has important ramifications for understanding subglacial bed roughness, cavity 33 formation, and likely erosion style (quarrying and/or abrasion) at the ice-bed interface. This paper 34 demonstrates a direct link between bedrock bedform geometries and geological structure and 35 emphasises the need to understand bedrock bedform characteristics when reconstructing 36 palaeoglaciological conditions. 37 38Keywords: ice stream; glacial erosion; bedrock bedform; abrasion; quarrying; Greenland ice sheet 39 3 Introduction 40 41 Importance of glacial bedforms 42An understanding of past ice sheet dynamics can significantly improve our understanding of current 43 and potential future ...

Despite an increasing interest in Greenlandic mountain glaciers over recent decades, their evolution during the Lateglacial and Holocene still needs to be better constrained. Here we present 25 10Be cosmic‐ray exposure (CRE) ages of boulders collected on moraines from three glaciers located on Clavering Island (northeastern Greenland). CRE ages span 16.29±0.79 to 0.37±0.05 ka and reveal three periods of moraine formation during the Lateglacial, the Early and the Late Holocene. Data show a multi‐modal distribution of the ages during the Lateglacial with exposure ages spanning from 16.29±0.79 to 12.31±1.3 ka. At least two glaciers experienced a greater expansion at the beginning of the Holocene than at the end of the Holocene, dated to 11.3±0.3 and 10.8±0.6 ka, respectively. At the end of the Holocene, glacial advances occurred during the Dark Ages Cold Period and during the Little Ice Age (LIA), synchronous with glacial advances documented in nearby lake sediments. This new CRE chronology highlights that the LIA extent is not the largest glacier advance in the Late Holocene in Clavering Island. This broadly corresponds with other mountain glaciers of western and northern Greenland, and does not appear to reflect northern high latitude summer insolation that would suggest progressive temperature decrease, but instead mimics recent regional continental temperature reconstructions that show a long term warming driven by different forcing.

Understanding Arctic glacier sensitivity is key to predicting future response to air temperature rise. Previous studies have used proglacial lake sediment records to reconstruct Holocene glacier advance–retreat patterns in South and West Greenland, but high‐resolution glacier records from High Arctic Greenland are scarce, despite the sensitivity of this region to future climate change. Detailed geochemical analysis of proglacial lake sediments close to Zackenberg, northeast Greenland, provides the first high‐resolution record of Late Holocene High Arctic glacier behaviour. Three phases of glacier advance have occurred in the last 2000 years. The first two phases (c. 1320–800 cal. a BP) occurred prior to the Little Ice Age (LIA), and correspond to the Dark Ages Cold Period and the Medieval Climate Anomaly. The third phase (c. 700 cal. a BP), representing a smaller scale glacier oscillation, is associated with the onset of the LIA. Our results are consistent with recent evidence of pre‐LIA glacier advance in other parts of the Arctic, including South and West Greenland, Svalbard, and Canada. The sub‐millennial glacier fluctuations identified in the Madsen Lake succession are not preserved in the moraine record. Importantly, coupled XRF and XRD analysis has effectively identified a phase of ice advance that is not visible by sedimentology alone. This highlights the value of high‐resolution geochemical analysis of lake sediments to establish rapid glacier advance–retreat patterns in regions where chronological and morphostratigraphical control is limited.

The oldest Oldowan tool sites, from around 2.6 million years ago, have previously been confined to Ethiopia’s Afar Triangle. We describe sites at Nyayanga, Kenya, dated to 3.032 to 2.581 million years ago and expand this distribution by over 1300 kilometers. Furthermore, we found two hippopotamid butchery sites associated with mosaic vegetation and a C 4 grazer–dominated fauna. Tool flaking proficiency was comparable with that of younger Oldowan assemblages, but pounding activities were more common. Tool use-wear and bone damage indicate plant and animal tissue processing. Paranthropus sp. teeth, the first from southwestern Kenya, possessed carbon isotopic values indicative of a diet rich in C 4 foods. We argue that the earliest Oldowan was more widespread than previously known, used to process diverse foods including megafauna, and associated with Paranthropus from its onset.