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Abstract Be isotopes are a useful tracer of sediment source and transport pathways but have not been widely tested in glacio-marine environments. We measured Be isotopes in a range of depositional environments from open marine, sub-ice shelf and subglacial settings throughout Prydz Bay, one of Antarctica's largest ice drainage systems. We find that strong sub-ice shelf and bottom current circulations can advect 10Be-rich open marine sediments into an ice shelf cavity, and 10Be-poor terrestrial sediments onto the continental shelf at the ice shelf outflow, meaning that 10Be concentrations reflect sub-ice shelf circulation patterns rather than depositional environment. However, HCl-extractable 10Be/9Be ratios can provide a more robust discrimination of sediment deposited in open marine and sub-ice shelf settings. Thus, Be isotopes are a useful tracer of both environmental setting and sub-ice shelf circulation strength in both modern and paleo-ice sheet margins. Highlights • Be-10 is advected underneath ice shelves by sub-shelf currents. • Be-10/9 ratios may be a proxy for past ice shelf geometries in sediments. • Ice sheet extent may influence Be-isotope delivery ratios to the deep ocean. [ABSTRACT FROM AUTHOR]

Cataclysmic outburst floods transformed landscapes and caused abrupt climate change during the last deglaciation. Whether such events have also characterized previous deglaciations is not known. Arctic marine cores hint at megafloods prior to Oxygen Isotope Stage (OIS) 2, but the overprint of successive glaciations means that geomorphological traces of ancient floods remain scarce in Eurasia and North America. Here we present the first well-constrained terrestrial megaflood record to be linked with Arctic archives. Based on cosmogenic-nuclide exposure dating and optically stimulated luminescence dating applied to glacial-lake sediments, a 300-m deep bedrock spillway, and giant eddy-bars > 200-m high, we reconstruct a history of cataclysmic outburst floods from glacial Lake Vitim, Siberia, to the Arctic Ocean over the past 60,000-years. Three megafloods have reflected the rhythm of Eurasian glaciations, leaving traces that stretch more than 3500 km to the Lena Delta. The first flood was coincident with deglaciation from OIS-4 and the largest meltwater spike in Arctic marine-cores within the past 100,000 years (isotope-event 3.31 at 55.5 ka). The second flood marked the lead up to the local Last Glacial Maximum, and the third flood occurred during the last deglaciation. This final 3000 km 3 megaflood stands as one of the largest freshwater floods ever documented, with peak discharge of 4.0–6.5 million m 3 s −1 , mean flow depths of 120–150 m, and average flow velocities up to 21 m s −1 . [ABSTRACT FROM AUTHOR]

Mountain glaciers at ∼26–19 ka, during the global Last Glacial Maximum near the end of the last 10 5 yr glacial cycle, are commonly considered on the basis of dating and field mapping in several well-studied areas to have been the largest of the late Quaternary and to have advanced synchronously from region to region. However, a numerical sensitivity model (Rupper and Roe, 2008) predicts that the fraction of ablation due to melting varies across Central Asia in proportion to the annual precipitation. The equilibrium-line altitude of glaciers across this region likely varies accordingly: in high altitude, cold and arid regions sublimation can ablate most of the ice, whereas glaciers fed by high precipitation cannot ablate completely due to sublimation alone, but extend downhill until higher temperatures there cause them to melt. We have conducted field studies and 10 Be dating at five glaciated sites along a precipitation gradient in Mongolia to test the Rupper/Roe model. The sites are located in nearby 1.875 × 1.875° cells of the Rupper/Roe model, each with a different melt fraction, in this little-studied region. The modern environment of the sites ranges from dry subhumid in the north (47.7° N) to arid in the south (45° N). Our findings show that the maximum local advances in the dry subhumid conditions predated the global Last Glacial Maximum and were likely from MIS 3. However, we also found that at ∼8–7 ka a cirque glacier in one mountain range of the arid Gobi desert grew to a magnitude comparable to that of the local maximum extent. This Holocene maximum occurred during a regional pluvial period thousands of years after the retreat of the Pleistocene glaciers globally. This asynchronous behavior is not predicted by the prevailing and generally correct presumption that glacier advances are dominantly driven by temperature, although precipitation also plays a role. Our findings are consistent with and support the Rupper/Roe model, which calls for glaciation in arid conditions only at high altitudes of sub-freezing temperatures, where the melt fraction in ablation is low. We expect a heterogeneous pattern of glacial responses to a changing modern climate in cold arid regions; an individual glacier advance should not be necessarily interpreted as evidence of cooling climate. [ABSTRACT FROM AUTHOR]

This paper presents data from 42 new samples yielding Late Pleistocene cosmogenic 10 Be and 36 Cl exposure ages of moraine boulders across a series of glaciated valleys in the Toubkal Massif (4167 m a.s.l.), High Atlas, Morocco. This represents the first comprehensive Pleistocene glacial chronology in North Africa and one of the largest datasets from the Mediterranean region. The timing of these glacier advances has major implications for understanding the influence of Atlantic depressions on moisture supply to North Africa and the Mediterranean basin during the Pleistocene. The oldest and lowest moraines which span elevations from ∼1900 to 2400 m a.s.l. indicate that the maximum glacier advance occurred from MIS 5 to 3 with a combined mean 10 Be and 36 Cl age of 50.2 ± 19.5 ka (1 SD; n = 12, 7 outliers). The next moraine units up-valley at higher elevations (∼2200–2600 m a.s.l.) yielded exposure ages close to the global Last Glacial Maximum (LGM) with a combined mean 10 Be and 36 Cl age of 22.0 ± 4.9 ka (1 SD; n = 9, 7 outliers). The youngest exposure ages are from moraines that were emplaced during the Younger Dryas with a combined mean 10 Be and 36 Cl age of 12.3 ± 0.9 ka (1 SD; n = 7, no outliers) and are found in cirques at the highest elevations ranging from ∼2900 to 3300 m a.s.l. From moraines predating the Younger Dryas, a large number of young outliers are spread evenly between 6 and 13 ka suggesting a continuing process of exhumation or repositioning of boulders during the early to mid-Holocene. This attests to active seismic processes and possibly intense erosion during this period. [ABSTRACT FROM AUTHOR]

The geomorphology of the Denton Hills provides insight into the timing and magnitude of glacial retreats in a region of Antarctica isolated from the influence of the East Antarctic ice sheet. We present 26 Beryllium-10 surface exposure ages from a variety of glacial and lacustrine features in the Garwood and Miers valleys to document the glacial history of the area from 10 to 286 ka. Our data show that the cold-based Miers, Joyce and Garwood glaciers retreated little since their maximum positions at 37.2 ± 6.9 (1σ n = 4), 35.1 ± 1.5 (1σ, n = 3) and 35.6 ± 10.1 (1σ, n = 6) ka respectively. The similar timing of advance of all three glaciers and the lack of a significant glacial expansion during the global LGM suggests a local LGM for the Denton Hills between ca. 26 and 51 ka, with a mean age of 36.0 ± 7.5 (1σ, n = 13) ka. A second cohort of exposure ages provides constraints to the behaviour of Glacial Lake Trowbridge that formerly occupied Miers Valley in the late Pleistocene. These data show active modification of the landscape from ∼20 ka until the withdrawal of ice from the valley mouths, and deposition of Ross Sea Drift, at 10–14 ka. [ABSTRACT FROM AUTHOR]

Large earthquakes play a major role in the topographic evolution of active orogens. Earthquake induced landslides can alter the mass balance of mountain belts for decades to centuries depending on how landslide material is transported and stored. In this study, we analysed in-situ 10Be concentrations in fluvial sediments to capture a time series of post-earthquake denudation rates of the Tūtae Putaputa|Conway River catchment, which experienced ∼13 × 106 m3 of landsliding in the 2016 Kaikōura earthquake. 10Be concentrations were determined for detrital samples from the Conway River at the rangefront of the Seaward Kaikōura Mountains, South Island, New Zealand, and near the catchment outlet over three sampling intervals, including after significant precipitation events, 1-2 yr following the earthquake. Our results indicate somewhat higher apparent erosion rates at the rangefront (0.41-0.58 mm/yr) when compared to erosion rates incorporating lower-relief sub-catchments at the river outlet (∼0.28 mm/yr). No changes were found over the same time period in the Hurunui River, a neighbouring catchment that experienced negligible coseismic landsliding during the Kaikōura event. Apparent catchment-averaged erosion rates in the Conway River have remained similar to long-term exhumation rates from previously published thermochronology studies. To explain our results, we explore the observed controls on catchment-wide 10Be concentrations in our study area, such as the spatiotemporal variability in landslide connectivity to the channel and storage within the catchment. Our results highlight that using in-situ cosmogenic 10Be in fluvial deposits as a proxy for changes in sediment fluxes of earthquake-affected landscapes is complex and highly site-specific. • 10Be used to trace landslide sediment following 2016 M w 7.8 Kaikōura earthquake. • Nearly 13 M m3 of coseismic sediment released from hillslopes in the Conway River. • No detectable change in 10Be concentrations in quartz sands in the Conway River. • Erosion rates in the Conway River remain on pace with long term erosion rates. • Landslide properties influence 10Be concentrations in stream sediments. [ABSTRACT FROM AUTHOR]

Quantifying the contribution of the East Antarctic Ice Sheet (EAIS) to sea-level rise during the last deglaciation is complicated by the limited opportunities to constrain ice-sheet models. The nunatak, Escalade Peak, provides a gauge for past ice surface elevation changes and behaviour throughout the last glacial cycle. Geomorphological mapping, geological evidence and 10Be cosmogenic-nuclide exposure dating at Escalade Peak, provide new constraints on the ice surface history of the Skelton Névé since the Last Glacial Maximum (LGM). An elevation transect from the eastern margin of Escalade Peak indicates that the ice surface of the Skelton Névé was at least 50 m and perhaps >120 m higher than present during the LGM. In contrast, surface-exposure ages from a suite of inner moraines (blue-ice moraines) adjacent to Escalade Peak do not provide independent ice surface elevation constraints, but may provide an indirect constraint on the timing of thinning due to exhumation-ablation processes. Maximum simple exposure ages from the inner moraines suggest ice surface ablation was initiated by 19.2 ka, but the majority of ice surface lowering at Escalade Peak likely occurred after ∼15 ka and reached the present-day ice level at ∼6 ka. These findings suggest that slow flowing inland sites of EAIS outlet glaciers, such as southern Skelton Névé, experienced minimal ice surface elevation change since the LGM and record an EAIS outlet glacier and western Ross Sea retreat signature rather than widespread Ross Sea retreat. The ice surface lowering is likely to have been in response to retreat of the grounded ice in the western Ross Embayment causing a reduction in buttressing of the Skelton Glacier and draw down into the Ross Sea. • Ice was at least ∼50 m and perhaps >120 m higher than present during the LGM. • Inner moraines may provide an indirect constraint on the timing of thinning. • The majority of post-LGM ice surface lowering most likely occurred from ∼15 ka. • The retreat history suggests outlet glacier and western Ross Sea retreat signature. [ABSTRACT FROM AUTHOR]