Search

In this paper, we present a reconstruction of climate conditions during the Last Glacial Maximum on a karst plateau Snežnik, which lies in Dinaric Mountains (southern Slovenia) and bears evidence of glaciation. The reconstruction merges geomorphological ice limits, classified as either clear or unclear, and a computer modelling approach based on the Parallel Ice Sheet Model (PISM). Based on extensive numerical experiments where we studied the agreements between simulated and geomorphological ice extent, we propose using a combination of a high-resolution precipitation model that accounts for orographic precipitation combined with a simple elevation-based temperature model. The geomorphological ice extent can be simulated with climate to be around 6 °C colder than the modern day and with a lower-than-modern-day amount of precipitation, which matches other state-of-the art climate reconstructions for the era. The results indicate that an orographic precipitation model is essential for the accurate simulation of the study area, with moist southern winds from the nearby Adriatic Sea having a predominant effect on the precipitation patterns. Finally, this study shows that transforming climate conditions towards wetter and warmer or drier and colder does not significantly change the conditions for glacier formation. [ABSTRACT FROM AUTHOR]

This study presents the first continuously measured transfer functions that quantify the age difference between the Greenland ice-core chronology 2005 (GICC05) and the U–Th timescale during the last glacial period. The transfer functions were estimated using an automated algorithm for Bayesian inversion that allows inferring a continuous and objective synchronization between Greenland ice-core and East Asian summer monsoon speleothem data, and a total of three transfer functions were inferred using independent ice-core records. The algorithm is based on an alignment model that considers prior knowledge of the GICC05 counting error but also samples synchronization scenarios that exceed the differential dating uncertainty of the annual-layer count in ice cores, which are currently hard to detect using conventional alignment techniques. The transfer functions are on average 48 % more precise than previous estimates and significantly reduce the absolute dating uncertainty of the GICC05 back to 48 kyr ago. The results reveal that GICCC05 is, on average, systematically younger than the U–Th timescale by 0.86 %. However, they also highlight that the annual-layer counting error is not strictly correlated over extended periods of time and that within the coldest Greenland Stadials the differential dating uncertainty is likely underestimated by up to ∼13 %. Importantly, the analysis implies for the first time that during the Last Glacial Maximum GICC05 may overcount ice layers by ∼10 % – a bias possibly attributable to a higher frequency of sub-annual layers due to changes in the seasonal cycle of precipitation and mode of dust deposition to the Greenland Ice Sheet. The new timescale transfer functions provide important constraints on the uncertainty surrounding the stratigraphic dating of the Greenland age scale and enable an improved chronological integration of ice cores as well as U–Th-dated and radiocarbon-dated paleoclimate records on a common timeline. The transfer functions are available as a Supplement to this study. [ABSTRACT FROM AUTHOR]

During the Last Glacial Period, the climate shift to cold conditions associated with changes in atmospheric circulation and vegetation cover resulted in the development of large aeolian systems in Europe. On a regional scale, many factors may have influenced dust dynamics, such as the latitudinal difference between the various aeolian systems and the variability of the sources of wind-transported particles. Therefore, the assumption that the timing of aeolian deposition is strictly synchronous in Europe does not seem to be the most plausible hypothesis and needs to be evaluated. To test this assumption, the chronology of loess deposition in different European regions was investigated by studying 93 luminescence-dated loess–palaeosol sequences with their data recalculated and compiled in a single comma separated values (*.csv) file: the ChronoLoess database. Our study shows that the two major aeolian systems, the Northern European Loess Belt (NELB) on the one hand and the systems associated with the rivers draining the Alpine Ice Sheet on the other hand, developed asynchronously. The significant deposition started at about 32 kyr b2k for the NELB vs. 42 kyr b2k for the perialpine loess and peaked about 2 millennia later for the former (21.8 vs. 23.9 kyr b2k, respectively). This shift resulted mainly from the time lag between the maxima of the Alpine and Fennoscandian ice sheets, which acted as the primary sources of fine-grained particles through glacial abrasion. The major geomorphic changes that resulted from the development and decay of the Fennoscandian and British–Irish ice sheets also played an important role. Particularly, ice sheet coalescence during the Last Glacial Maximum (LGM) diverted meltwater fluxes through the Channel River and provided vast amounts of glacial particles available for deflation in the western NELB. The period during which the maximum mass accumulation rate was reached for each loess–palaeosol sequence is relatively homogeneous in the NELB and ranges from 30 to 19 kyr b2k, whereas it is more scattered in the perialpine systems (>60 to 14 kyr b2k). This probably resulted from a combination of factors, including the asynchrony of maximum valley glacier advances and local geomorphic factors. The ChronoLoess database is available at 10.5281/zenodo.7728616 (Bosq et al., 2023). [ABSTRACT FROM AUTHOR]

Knowledge of microparticle geometry is essential for accurate calculation of ice core volume-related dust metrics (mass, flux, and particle size distributions) and subsequent paleoclimate interpretations, yet particle shape data remain sparse in Antarctica. Here we present 41 discrete particle shape measurements, volume calculations, and calibrated continuous particle time series spanning 50–16 ka from the South Pole Ice Core (SPC14) to assess particle shape characteristics and variability. We used FlowCAM, a dynamic particle imaging instrument, to measure aspect ratios (width divided by length) of microparticles. We then compared those results to Coulter counter measurements on the same set of samples as well as high-resolution laser-based (Abakus) data collected from SPC14 during continuous flow analysis. The 41 discrete samples were collected during three periods of millennial-scale climate variability: Heinrich Stadial 1 (18–16 ka , n=6 ; ∼250 years per sample), the Last Glacial Maximum (LGM) (27–18 ka , n=19 ; ∼460 years per sample), and during both Heinrich Stadial 4 (42–36 ka , n=8 ; ∼620 years per sample) and Heinrich Stadial 5 (50–46 ka , n=8 ; ∼440 years per sample). Using FlowCAM measurements, we calculated different particle size distributions (PSDs) for spherical and ellipsoidal volume estimates. Our calculated volumes were then compared to published Abakus calibration techniques. We found that Abakus-derived PSDs calculated assuming ellipsoidal, rather than spherical, particle shapes provide a more accurate representation of PSDs measured by Coulter counter, reducing Abakus to Coulter counter flux and mass ratios from 1.82 (spherical assumption) to 0.79 and 1.20 (ellipsoidal assumptions; 1 being a perfect match). Coarser particles (>5.0 µm diameter) show greater variation in measured aspect ratios than finer particles (<5.0 µm). While fine particle volumes can be accurately estimated using the spherical assumption, applying the same assumption to coarse particles has a large effect on inferred particle volumes. Temporally, coarse and fine particle aspect ratios do not significantly change within or among the three time periods (p value >0.05), suggesting that long-range transport of dust is likely dominated by clay minerals and other elongated minerals. [ABSTRACT FROM AUTHOR]

The extent and distribution of glaciers on the Swiss Plateau during the Last Glacial Maximum (LGM) can be determined from the geological record. However, similar reconstructions for the glaciations that preceded the LGM are far more difficult to be made due to the destruction of suitable sedimentary records through recurring glaciations or due to the inaccessibility of preserved records. Here, we explored Quaternary sediments that were deposited during the Marine Isotope Stage (MIS) 8 glaciation at least around 250 ka, and which were recovered in a drilling that was sunk into an overdeepened bedrock trough west of Bern (Switzerland). We analyzed the sediment bulk chemical composition of the deposits to investigate the supply of the material to the area by either the Aare Glacier, the Saane Glacier, or the Valais Glacier, and we complement this investigation with the results of heavy mineral analyses and geochemical information from detrital garnet. The potential confluence of the Valais and the Aare glaciers in the Bern area makes this location ideal for such an analysis. We determined the sediment bulk chemical signal of the various lithological units in the central Swiss Alps where the glaciers originated, which we used as endmembers for our provenance analysis. We then combined the results of this fingerprinting with the existing information on the sedimentary succession and its deposition history. This sedimentary suite is composed of two sequences, Sequence A (lower) and Sequence B (upper), both of which comprise a basal till that is overlain by lacustrine sediments. The till at the base of Sequence A was formed by the Aare Glacier. The overlying lacustrine deposits of an ice-contact lake were mainly supplied by the Aare Glacier. The basal till in Sequence B was also formed by the Aare Glacier. For the lacustrine deposits in Sequence B, the heavy mineral and garnet geochemical data indicate that the sediment was supplied by the Aare and the Saane glaciers. We use these findings for a paleogeographic reconstruction. During the time when Sequence A and the basal till in Sequence B were deposited, the Aare Glacier dominated the area. This strongly contrasts with the situation during the LGM, when the Aare Glacier was deflected by the Valais Glacier towards the northeast. The Valais Glacier was probably less extensive during MIS 8, but it was potentially present in the area, and it could have been essential for damming a lake in which the material supplied by the Aare and the Saane glaciers accumulated. In conclusion, combining provenance with sedimentological data, we could document how sediment was supplied to the investigated overdeepened basin during the MIS 8 glacial period and how glaciers were arranged in a way that was markedly different from the LGM. Kurzfassung: Die Gletscherstände und die Verbreitung der Gletscher im Schweizer Mittelland während des letztglazialen Maximums (LGM) lassen sich aus den erhaltenen Ablagerungen und der Oberflächenmorphologie ableiten. Ähnliche Rekonstruktionen für die dem LGM vorangegangenen Vergletscherungen sind ungleich schwerer anzustellen, da entsprechende Ablagerungen durch die wiederkehrenden Gletschervorstöße zerstört wurden oder da entsprechende Sedimentsequenzen unzugänglich sind. In der vorliegenden Arbeit untersuchten wir Quartäre Sedimente, die während des marinen Isotopenstadiums (MIS) 8 abgelagert wurden. Erbohrt wurden diese Sedimente in einem übertieften Trog, der ins Molassegestein westlich von Bern (Schweiz) erodiert wurde. An diese Stelle konnte Sediment möglicherweise durch einen von drei Gletschern, den Aaregletscher, den Saanegletscher oder den Wallisergletscher transportiert werden. Um zu ermitteln, welche der Gletscher Sediment in den Trog lieferten, untersuchten wir die chemische Zusammensetzung der Ablagerungen und ergänzten diese Untersuchung mit Daten aus der Analyse der Schwermineralzusammensetzung sowie der Analyse detritischer Granate. Da hier möglicherweise der Aare– und der Wallisergletscher zusammenflossen, bietet sich die Gegend um Bern für eine solche Untersuchung an. Um den Ursprung des Sediments feststellen zu können, definierten wir verschiedene lithologische Einheiten der zentralen Schweizer Alpen, in denen die Gletscher sich bildeten, als Endglieder unserer Provenienzanalyse und bestimmten ebenfalls deren chemische Zusammensetzung. Die Ergebnisse aus der Untersuchung dieser chemischen Fingerabdrücke ergänzten wir anschließend mit den bereits vorhandenen Informationen über die Sedimentationsabfolge und deren Ablagerungsverhältnisse. In dieser Abfolge können zwei Sequenzen unterschieden werden, eine untere Sequenz A und eine obere Sequenz B. Beide Sequenzen bestehen aus einer Grundmoräne, die von lakustrischem Sediment überlagert wird. Der Aaregletscher lagerte die Moräne an der Basis der Sequenz A ab. Die Sedimente, die sich anschließend in einem Eisrandsee bildeten, wurden ebenfalls hauptsächlich vom Aaregletscher geliefert. Die basale Moräne der Sequenz B wurde ebenfalls durch den Aaregletscher gebildet. Daraufhin wurde das Seebecken mit Sediment aufgefüllt, das vermutlich durch den Aare– sowie den Saanegletscher herantransportiert wurde, wie die Schwermineralzusammensetzung und Granatgeochemie zeigen. Anhand dieser Ergebnisse erstellen wir eine paläogeographische Rekonstruktion. Es zeigt sich darin die Dominanz des Aaregletschers im Gebiet um Bern während des Ablagerungszeitraums der unteren Sequenz A sowie der Moräne an der Basis der Sequenz B. Dieses Bild der Verbreitung der Gletscher im Raum Bern steht in starkem Kontrast zur Situation während des LGM, als der Aaregletscher vom Wallisergletscher in Richtung Nordost abgedrängt wurde. Augenscheinlich war der Wallisergletscher während der MIS 8 Vergletscherung weniger weit ausgedehnt. Jedoch kann hier die vollständige Abwesenheit des Wallisergletschers nicht ausgeschlossen werden und möglicherweise war er sogar essenziell, um einen See in der Gegend um Bern aufzustauen, in welchen der Aare– und der Saanegletscher ihr mitgeführtes Material schütteten. Letztlich zeichnen die hier präsentierten Ergebnisse, eine Kombination aus Provenienzanalyse und sedimentologischen Daten, ein Bild des Sedimenttransportes in den hier untersuchten übertieften Trog während des MIS 8 Glazials, und den deutlichen Unterschied zur Gletscherverbreitung während des LGM. [ABSTRACT FROM AUTHOR]

The young moraine area to the south-east of Berlin was repeatedly overrun and covered by Scandinavian ice sheets (SISs). The last glaciation took place during the Last Glacial Maximum (LGM), when the last/most recent SIS reached its furthest southern extent. An incompletely formed chain of terminal moraines marks the Brandenburg ice stage. The most recent glacier had its greatest environmental impact due to the large quantities of released meltwaters. Many subglacial channels, massive proglacial sands and huge meltwater streamways (Urstromtäler) were formed at that time. During the Holocene, the landscape was finally shaped mainly by the rivers Dahme and Spree. [ABSTRACT FROM AUTHOR]

We present speleothem fluid inclusion δ18 O f and δ2 H f values from Larga Cave, Puerto Rico, that cover the interval between 46.2 and 15.3 ka on the millennial scale, including the Last Glacial Maximum (LGM) and several stadial and interstadial cycles. The data set can be divided in two main clusters of stable isotope compositions of the fluid inclusion water with respect to the global meteoric water line (GMWL), which coincide with strong variations in the water content of the stalagmite. In particular, this clustering is found to be climate related, where one cluster comprises samples from cold and dry periods, such as the Heinrich and Greenland stadials (HSs and GSs), as well as parts of the LGM, which exhibit very high δ18 O f and δ2 H f values. We interpret this enrichment as being caused by evaporation inside the cave due to enhanced cave ventilation during these colder and drier times. In contrast, in most samples corresponding to warmer and wetter Greenland interstadials (GIs), but also for some from HS 2 and 3, the δ18 O f and δ2 H f values plot on the meteoric water line and modification of fluid inclusion water due to "in-cave" evaporation are found to be negligible. Consequently, variations of recent glacial hydro-climate and temperatures in the western tropical Atlantic can be constrained. In general, δ18 O f values from fluid inclusions are up to 3 ‰ higher than those of modern drip water, which is interpreted as a weaker atmospheric convective activity during the last glacial period. In addition, reconstructed temperatures suggest an average cooling of 2–3 ∘ C during the LGM compared to modern cave temperatures. Reconstructed cave temperatures yield an average cooling of - 1.4 ± 2.8 ∘ C for HS 2 and - 3.6 ± 2.2 ∘ C for HS 3. Higher δ18 O f values of these samples further suggest that the drip water was dominated by orographic rainfall and/or cold fronts, along with weak or even absent convective activity. In contrast, during interstadial phases, reconstructed temperatures reached nearly modern values, and convective activity was comparable to or only slightly weaker than today. [ABSTRACT FROM AUTHOR]

We investigate the sensitivity of a distributed glacier surface mass and energy balance model using a variance-based analysis, for two distinct periods of the last glacial cycle: the present day (PD) and the Last Glacial Maximum (LGM). The results can be summarized in three major findings: the sensitivity towards individual model parameters and parameterizations is as variable in space as it is in time. The model is most sensitive to uncertainty related to atmospheric emissivity and the down-welling longwave radiation. While the turbulent latent heat flux has a sizable contribution to the surface mass balance uncertainty in central Greenland today, it dominates over the entire ice sheet during the cold climate of the LGM, in spite of its low impact on the overall surface mass balance of the Greenland ice sheet in the modern climate. We conclude that quantifying the model sensitivity is very helpful for tuning free model parameters because it clarifies the relative importance of individual parameters and highlights interactions between them that need to be considered. [ABSTRACT FROM AUTHOR]

Unanswered questions about the glacier and climate history preceding the global Last Glacial Maximum (LGM) in the southern temperate latitudes remain. The Marine Isotope Stage (MIS) 3 is normally understood as a global interstadial period; nonetheless its climate was punctuated by conspicuous variability, and its signature has not been resolved beyond the polar realms. In this paper, we compile a 10Be depth profile, single grain infrared (IR) stimulated luminescence dating and 14C samples to derive a new glacier record for the principal outwash plain complex, deposited by the western Patagonian Ice Sheet (PIS) during the last glacial period (Llanquihue Glaciation) on the Isla de Chiloé, southern Chile (42 ∘ S). In this region, the Golfo de Corcovado Ice Lobe left a distinct geomorphic and stratigraphic imprint, suitable for reconstructing former ice dynamics and timing of past climate change. Our data indicate that maximum glaciation occurred by 57.8±4.7 ka without reaching the Pacific Ocean coast. Ice readavanced and buttressed against the eastern side of the Cordillera de la Costa again by 26.0±2.9 ka. Our data further support the notion of a large ice extent during parts of the MIS 3 in Patagonia and New Zealand but appear to contradict near contemporaneous interstadial evidence in the southern midlatitudes, including Chiloé. We propose that the PIS expanded to its full-glacial Llanquihue moraines, recording a rapid response of southern mountain glaciers to the millennial-scale climate stadials that punctuated the MIS 3 at the poles and elsewhere. Kurzfassung: Hinsichtlich der Glazial- und Klimageschichte vor dem letztglazialen Maximum (LGM) in den temperierten Breiten der Südhemisphäre sind derzeit vielen Fragen noch unbeantwortet. Das Marine Isotopenstadium (MIS) 3 wird gemeinhin als globale interstadiale Phase verstanden, die jedoch durch phasenweise starke Variabilität gekennzeichnet war, deren Verlauf jenseits der Polargebiete jedoch noch nicht aufgelöst werden konnte. In dieser Studie werden ein 10Be Tiefenprofil, Datierungsergebnisse von Einzelkorn-Lumineszenz-Messungen mittels infraroter (IR) Stimulation und Alter von 14C Datierungen kompiliert, um für den Haupt-Sander-Komplex, der vom westlichen Patagonischen Eisschild (PIS) während des letzten Glazials (Llanquihue Vereisung) auf der Isla de Chiloé (südliches Chile, 42 ∘ S) aufgebaut wurde, eine neue Vereisungschronologie aufzubauen. In dieser Region ermöglichen die deutliche geomorphologische und stratigraphische Prägung durch den Golfo de Corcovado Lobus die Rekonstruktion von vergangener Eisdynamik und der Zeitstellung klimatischer Veränderungen. Unsere Ergebnisse besagen, dass sich die maximale Eisausdehnung um 57.8±4.7 ka einstellte. Der Pazifik wurde hierbei nicht erreicht. Ein erneuter Eisvorstoß entlang der östlichen Flanke der Cordillera de la Costa kann um 26.0±2.9 ka nachgewiesen werden. Unsere Daten unterstützen damit die Auffassung von der Existenz großer Eisausdehnungen im MIS 3 in Patagonien und Neuseeland, aber scheinen jedoch zeitgleiche Erkenntnisse aus benachbarten Regionen zum Interstadial der südlichen Mittelbreiten, einschließlich Chiloé, zu konterkarieren. Wir erklären die Ausdehnung des PIS zu den Llanquihue Endmoränen als schnelle, kurzfristige Reaktion südlicher Gebirgsgletscher auf kurze (tausendjährige Zeitskale) stadiale Phasen innerhalb des MIS 3 Interstadials, die bereits an den Polen und andernorts nachgewiesen werden konnten. [ABSTRACT FROM AUTHOR]

Iron (Fe) is a key element in the Earth climate system, as it can enhance marine primary productivity in the high-nutrient low-chlorophyll (HNLC) regions where, despite a high concentration of major nutrients, chlorophyll production is low due to iron limitation. Eolian mineral dust represents one of the main Fe sources to the oceans; thus, quantifying its variability over the last glacial cycle is crucial to evaluate its role in strengthening the biological carbon pump. Polar ice cores, which preserve detailed climate records in their stratigraphy, provide a sensitive and continuous archive for reconstructing past eolian Fe fluxes. Here, we show the Northern Hemisphere Fe record retrieved from the NEEM ice core (Greenland), which offers a unique opportunity to reconstruct the past Fe fluxes in a portion of the Arctic over the last 108 kyr. Holocene Fe fluxes (0.042–11.7 ka, 0.5 mg m -2 yr -1) at the NEEM site were 4 times lower than the average recorded over the last glacial period (11.7–108 ka, 2.0 mg m -2 yr -1), whereas they were greater during the Last Glacial Maximum (LGM; 14.5–26.5 ka, 3.6 mg m -2 yr -1) and Marine Isotope Stage 4 (MIS 4; 60–71 ka, 5.8 mg m -2 yr -1). Comparing the NEEM Fe record with paleoceanographic records retrieved from the HNLC North Pacific, we found that the coldest periods, characterized by the highest Fe fluxes, were distinguished by low marine primary productivity in the subarctic Pacific Ocean, likely due to the greater sea ice extent and the absence of major nutrients upwelling. This supports the hypothesis that Fe fertilization during colder and dustier periods (i.e., LGM and MIS 4) was more effective in other regions, such as the midlatitude North Pacific, where a closer relationship between marine productivity and the NEEM Fe fluxes was observed. [ABSTRACT FROM AUTHOR]

Anthropogenic climate change raises growing concerns about its potential catastrophic impacts on both ecosystems and human societies. Yet, several studies on damage induced on the economy by unmitigated global warming have proposed a much less worrying picture of the future, with only a few points of decrease in the world gross domestic product (GDP) per capita by the end of the century, even for a global warming above 4 ∘ C. We consider two different empirically estimated functions linking GDP growth or GDP level to temperature at the country level and apply them to a global cooling of 4 ∘ C in 2100, corresponding to a return to glacial conditions. We show that the alleged impact on global average GDP per capita runs from -1.8 %, if temperature impacts GDP level, to +36 %, if the impact is rather on GDP growth. These results are then compared to the hypothetical environmental conditions faced by humanity, taking the Last Glacial Maximum as a reference. The modeled impacts on the world GDP appear strongly underestimated given the magnitude of climate and ecological changes recorded for that period. After discussing the weaknesses of the aggregated statistical approach to estimate economic damage, we conclude that, if these functions cannot reasonably be trusted for such a large cooling, they should not be considered to provide relevant information on potential damage in the case of a warming of similar magnitude, as projected in the case of unabated greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Anthropogenic climate change raises growing concerns about its potential catastrophic impacts on both ecosystems and human societies. Yet, several studies on damages induced on the economy by unmitigated global warming have proposed a much less worrying picture of the future, with only a few points decrease in the world GDP per capita by the end of the century, even for a global warming above +4 °C. We consider here two different empirically estimated functions linking GDP growth or GDP level to temperature at the country level and apply them to a global cooling of -4 °C in 2100, corresponding to a return to glacial conditions. We show that the alleged impact on global average GDP per capita runs from -1.8 %, if temperature impacts GDP level, to +36 %, if the impacts are rather on GDP growth. These results are then compared to the hypothetical environmental conditions faced by humanity, taking the last glacial maximum as a reference. The modeled impacts on the world's GDP appear strongly underestimated given the magnitude of climate and ecological changes recorded for that period. After discussing the weaknesses of the aggregated statistical approach to estimate economic damages, we conclude that, if these functions cannot reasonably be trusted for such a large cooling, they should also not be considered as providing relevant information on potential damages in the case of a warming of similar magnitude, as projected in the case of unabated greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Climate change in Siberia is currently receiving a lot of attention because large permafrost-covered areas could provide a strong positive feedback to global warming through the release of carbon that has been sequestered there on glacial–interglacial timescales. Geological evidence and climate model experiments show that the Siberian region also played an exceptional role during glacial periods. The region that is currently known for its harsh cold climate did not experience major glaciations during the last ice age, including its severest stages around the Last Glacial Maximum (LGM). On the contrary, it is thought that glacial summer temperatures were comparable to the present day. However, evidence of glaciation has been found for several older glacial periods. We combine LGM experiments from the second and third phases of the Paleoclimate Modelling Intercomparison Project (PMIP2 and PMIP3) with sensitivity experiments using the Community Earth System Model (CESM). Together, these climate model experiments reveal that the intermodel spread in LGM summer temperatures in Siberia is much larger than in any other region of the globe and suggest that temperatures in Siberia are highly susceptible to changes in the imposed glacial boundary conditions, the included feedbacks and processes, and to the model physics of the different components of the climate model. We find that changes in the circumpolar atmospheric stationary wave pattern and associated northward heat transport drive strong local snow and vegetation feedbacks and that this combination explains the susceptibility of LGM summer temperatures in Siberia. This suggests that a small difference between two glacial periods in terms of climate, ice buildup or their respective evolution towards maximum glacial conditions can lead to strongly divergent summer temperatures in Siberia, allowing for the buildup of an ice sheet during some glacial periods, while during others, above-freezing summer temperatures preclude a multi-year snowpack from forming. [ABSTRACT FROM AUTHOR]

In this study, the dead carbon fraction (DCF) variations in stalagmite M1-5 from Socotra Island in the western Arabian Sea were investigated through a new set of high-precision U-series and radiocarbon (14C) dates. The data reveal an extreme case of very high and also climate-dependent DCF. For M1-5, an average DCF of 56.2±3.4 % is observed between 27 and 18 kyr BP. Such high DCF values indicate a high influence of aged soil organic matter (SOM) and nearly completely closed-system carbonate dissolution conditions. Towards the end of the last glacial period, decreasing Mg/Ca ratios suggest an increase in precipitation which caused a marked change in the soil carbon cycling as indicated by sharply decreasing DCF. This is in contrast to the relation of soil infiltration and DCF as seen in stalagmites from temperate zones. For Socotra Island, which is influenced by the East African–Indian monsoon, we propose that more humid conditions and enhanced net infiltration after the Last Glacial Maximum (LGM) led to dense vegetation and thus lowered the DCF by increasing 14CO2 input into the soil zone. At the onset of the Younger Dryas (YD) a sudden change in DCF towards much higher, and extremely variable, values is observed. Our study highlights the dramatic variability of soil carbon cycling processes and vegetation feedback on Socotra Island manifested in stalagmite DCF on both long-term trends and sub-centennial timescales, thus providing evidence for climate influence on stalagmite radiocarbon. This is of particular relevance for speleothem studies that aim to reconstruct past atmospheric 14C (e.g., for the purposes of 14C calibration), as these would rely on largely climate-independent soil carbon cycling above the cave. [ABSTRACT FROM AUTHOR]

This study explores the mechanisms behind the high glacial productivity in the southern Brazilian margin (SBM) during the last 70 kyr using planktonic foraminifera assemblage and subsurface temperature information derived using the modern analogue technique. We show that enhanced glacial productivity was driven by the synergy of two mechanisms operating in different seasons: (i) enhanced productivity in the upwelling region during short austral summer events; and (ii) the persistent presence of the Plata Plume Water (PPW) due to prolonged austral winter conditions. We suggest that the upwelling systems in the southern Brazilian margin were more productive during the last glacial period due to the enhanced Si supply for diatom production by high-Si thermocline waters preformed in the Southern Ocean. We hypothesize that orbital forcing did not have a major influence on changes in upwelling during the last glacial period. However, the more frequent northward intrusions of the Plata Plume Water were modulated by austral winter insolation at 60 ∘ S via changes in the strength of alongshore southwesterly winds. After the Last Glacial Maximum, the reduced Si content of thermocline waters decreased upwelling productivity, while lower austral winter insolation decreased the influence of the Plata Plume Water over the southern Brazilian margin, reducing regional productivity. [ABSTRACT FROM AUTHOR]

The New Zealand subantarctic islands of Auckland and Campbell, situated between the subtropical front and the Antarctic Convergence in the Pacific sector of the Southern Ocean, provide valuable terrestrial records from a globally important climatic region. Whilst the islands show clear evidence of past glaciation, the timing and mechanisms behind Pleistocene environmental and climate changes remain uncertain. Here we present a multidisciplinary study of the islands – including marine and terrestrial geomorphological surveys, extensive analyses of sedimentary sequences, a comprehensive dating programme, and glacier flow line modelling – to investigate multiple phases of glaciation across the islands. We find evidence that the Auckland Islands hosted a small ice cap 384 000 ± 26 000 years ago (384±26 ka), most likely during Marine Isotope Stage 10, a period when the subtropical front was reportedly north of its present-day latitude by several degrees, and consistent with hemispheric-wide glacial expansion. Flow line modelling constrained by field evidence suggests a more restricted glacial period prior to the LGM that formed substantial valley glaciers on the Campbell and Auckland Islands around 72–62 ka. Despite previous interpretations that suggest the maximum glacial extent occurred in the form of valley glaciation at the Last Glacial Maximum (LGM; ∼21 ka), our combined approach suggests minimal LGM glaciation across the New Zealand subantarctic islands and that no glaciers were present during the Antarctic Cold Reversal (ACR; ∼15 –13 ka). Instead, modelling implies that despite a regional mean annual air temperature depression of ∼5 ∘ C during the LGM, a combination of high seasonality and low precipitation left the islands incapable of sustaining significant glaciation. We suggest that northwards expansion of winter sea ice during the LGM and subsequent ACR led to precipitation starvation across the middle to high latitudes of the Southern Ocean, resulting in restricted glaciation of the subantarctic islands. [ABSTRACT FROM AUTHOR]

We present a new seafloor map for the northern Antarctic Peninsula (AP), including swath multibeam data sets from five national programs. Our map allows for the examination and interpretation of Last Glacial Maximum (LGM) paleo-ice-flow paths developed on the seafloor from the preservation of mega-scale glacial lineations, drumlinized features, and selective linear erosion. We combine this with terrestrial observations of flow direction to place constraints on ice divides and ice domes on the AP continental shelf during the LGM time interval. The results show a flow bifurcation as ice exits the Larsen B embayment. Flow emanating off the Seal Nunataks (including Robertson Island) is directed toward the southeast, then eastward as the flow transits toward the Robertson Trough. A second, stronger "streaming flow" is directed toward the southeast, then southward as ice overflowed the tip of the Jason Peninsula to reach the southern perimeter of the embayment. Our reconstruction also refines the extent of at least five other distinct paleo-ice-stream systems that, in turn, serve to delineate seven broad regions where contemporaneous ice domes must have been centered on the continental shelf at LGM. Our reconstruction is more detailed than other recent compilations because we followed specific ice-flow indicators and have kept tributary flow paths parallel. [ABSTRACT FROM AUTHOR]

During the last glacial cycle, the Antarctic Ice Sheet (AIS) has passed from an interglacial state, warmer than present day (PD), slowly into a glacial state, known as the Last Glacial Maximum (LGM) and then deglaciated on a faster timescale into the Holocene and PD conditions. Although we have proxy data of the size and extent of the ice sheet for the LGM, neither the oceanic temperatures of the Southern Ocean, nor the precipitation fields are well constrained. Also the time evolution of the ice volume during the glacial cycle is not fully clear. It is well assumed that it follows a sawtooth pattern, but from a modelling perspective different combinations of parameters and boundary conditions can give rise to plausible Antarctic configurations. Here we aim to study the uncertainty in AIS evolution resulting from ice-sheet model parameters, as well as the imposed climatic fields used as forcing. For this purpose we use the three-dimensional thermomechanical hybrid ice-sheet-shelf model Yelmo, which treats ice dynamics via the shallow-ce and shallow-shelf approximations, and accounts for basal melt below ice shelves and a subgrid parameterisation for treatment of the grounding line. We will focus on the effect of different climatic fields, such as precipitation and oceanic temperatures, as well as the effect of different enhancement factors and basal drag choices for reproducing consistent Antarctic configurations in the LGM and the PD. Improving our understanding of the effect of different ice-dynamics configurations in various climatic scenarios will help to better understand the past evolution of the AIS and potentially constrain its future evolution as well. [ABSTRACT FROM AUTHOR]

Marine Isotope Stage 2 (MIS 2) is the latest glacial period and includes the Last Glacial Maximum, which is known as the period when global ice volume reached its maximum and global temperature lower than today. An advantage of MIS 2 is the availability of radiocarbon dating to make it possible to compare sea-level data with other paleoclimatic proxies. However, the number and accuracy of sea-level records during MIS 2 is currently lacking. Here we present the history of MIS 2 sea-level and ice-sheet change as recorded in the Bonaparte Gulf, northwestern Australia, by reconstructing relative sea level and then modeling glacial isostatic adjustment. The isostatically-corrected global sea-level history indicates that sea-level plateaued around 23 cal kyr BP prior reaching its minimum (~19 cal kyr BP). These large changes in ice volume over such a short time indicates that the continental ice sheets never reached their isostatic equilibrium during the Last Glacial Maximum. [ABSTRACT FROM AUTHOR]

The maximal extent of the Laurentide Ice Sheet (LIS) on eastern Baffin Island during the Last Glacial Maximum (LGM; about 20 000 years ago) has been widely debated during the last decades as different palaeo-glaciological models have been proposed. Spatial and temporal variability of ice sheets extension during Quaternary glaciations complicate the establishment of a reliable reconstruction of the ice margin. Furthermore, the lack of geophysical data in most of the fjords, and seaward, makes it difficult to reconcile the proposed terrestrial and marine glacial margins. Here we use high-resolution swath bathymetry imagery, combined with acoustic stratigraphy data and sediment cores collected during various oceanographic expeditions, focusing on the ice dynamics in the area of Clyde Inlet since the LGM. Our data reveal possible positions of the maximal extent of the LIS near the continental shelf edge. The deglaciation on the shelf was rather slow and episodic, as indicated by the presence of grounding-zone wedges, recessional moraines, as well as time-transgressive glacial lineations. Ice retreat in the fjord occurred more rapidly, most likely due to increased water depths. However, the presence of multiple moraine systems reveals periods of ice-margin stabilizations. This study provides additional information to the terrestrial data and, thus, helps improve the models of glacial dynamics in the northeastern sector of the LIS. [ABSTRACT FROM AUTHOR]

A complex ice stream network occupied the European Alps during the last glacial maximum (LGM, MIS 2, Würmian Pleniglacial) with large valley glaciers extending as piedmont lobes into the northern and southern forelands. A completely different situation is reported for the easternmost Alps, where only a patchy pattern of isolated glaciers, confined to minor valleys, localized cirques and small plateaus could develop. Although the Alpine LGM glaciation was intensively studied, data sets vary considerably in the easternmost Alps (e.g concerning the numbers of local glaciers as well as extents) and systematic analyses of the glacial record are missing for the entire region. Consequently, equilibrium line altitudes (ELAs) and ELA depressions (ΔELAs) for these paleo glaciers remain unknown as well, though such data can be extremly useful to provide information on the variance of atmospheric circulation patterns over glacial to interglacial timescales. Characterized by relatively simple geometries and obviously rather simple source area relations (compared to the ice-stream network in the central Alps), they are most suitable for paleo-glacier reconstruction and ELA modelling – and can provide a robust dataset on ELA depression variabilities during the LGM. Such analysis is hardly possible for the ice-stream network occupying most of the central Alps at the same time.To fill this gap, we provide a new GIS-dataset of the LGM glaciation at the Eastern Alps based on the principal work of van Husen (1987), a number of case studies, geological maps, and the analyses of multiple orthophoto and DEM data. First systematic analyses on ELAs and ELA depressions of these low elevated isolated glaciers highlight the highly variable glacier response across the Eastern Alps to topographic and climatic forcing. [ABSTRACT FROM AUTHOR]

Geomorphological evidence shows that during the last glacial period glaciers reached far intothe foreland of the Alps. How frequent such advances took place, how long the glaciersremained in advanced position and how fast they advanced or retreated, however, is difficultto reconstruct from geomorphology. Models of glacier flow are increasingly used to assess icedynamics during the last glacial period. Driving such models relies on a series ofestimates, including ice rheology, the forcing climate and glacier mass balance.Thereby, the latter strongly depends on climate and the equations used to describe theirconnection. Here, we focus on reconstructing surface melt of the Rhine glacier (∼16,000 km2) at thelast glacial maximum (LGM). Given large uncertainties in our knowledge of the LGMclimate, we base our estimates on (i) analogies from Arctic present-day climate and massbalance and on (ii) theoretical considerations. Thereby we investigate which are the keyclimatic characteristics that need to be specified to simulate LGM glacier melt. We find thatchanges in the amplitude of annual air temperature substantially influence simulatedablation-area mass balance gradients db∕dz, and thus glacier-wide mass balance. While thisinfluence has been shown in earlier research, it has not yet been considered in reconstructionsof glacier mass balance during the last glacial. Paleoclimatic evidence from Central Europe suggests that during the LGM annualamplitude of air temperature was larger than today. We show that computing LGM glaciermass balance while assuming no change in amplitude compared to present-dayclimate can result in an overestimation of db∕dz (∼0.4 m w.e. (100 m)−1 yr−1 vs.∼0.55 m w.e. (100 m)−1 yr−1). It remains to be explored how these differing db∕dz couldinfluence simulated glacier dynamics during the last glacial. [ABSTRACT FROM AUTHOR]

We present a geomorphological assessment of the extent and dynamics of glaciation in the Wicklow Mountains, Ireland, during the Last Glacial Interglacial Transition (LGIT; ~ 20 – 11 ka BP). Previous research has established the existence of a local ice cap, confluent with regional ice at the Last Glacial Maximum (LGM; ~ 25 ka BP). However, there has been little consideration of ice retreat in response to climate amelioration during the LGIT. Here, we investigate ice dynamics during and after the transition from an ice cap to topographically restricted mountain glaciation. The geomorphological record indicates that initial ice cap recession was characterised by rapid retreat and large-scale disintegration, with ice masses only stabilising once topographically constrained within valleys. Following fragmentation of the LGM ice cap, three distinct landsystems were established in the Wicklow Mountains: (1) the large north-eastern sector of the region hosted a mountain icefield with multiple outlet glaciers; (2) a small plateau icefield existed in the central sector, with several outlet glaciers; and (3) several individual valley glaciers persisted in the south-western sector. Each of these landsystems document sustained retreat and subsequent stabilisation during the LGIT, prior to the Younger Dryas. Two-dimensional reconstructions of ice dynamics indicate variations in recession patterns throughout the region. Based on our ice margin reconstructions and the limited published dates for the region, we suggest that following the retreat of regional ice after the LGM, the local ice cap was relatively stable until the start of the LGIT (~20 ka BP). After this, ice experienced sustained thinning and ice margin retreat until ~ 17 ka BP. By this point, ice was topographically restricted and the three aforementioned landsystems established. A period of ice margin stabilisation occurred before further persistent retreat until ~ 15 ka BP, by which time ice had retreated into the upper reaches of valleys. It is likely that the plateau icefield and most of the mountain icefield had disappeared by ~15 ka BP, when the outlet glaciers of both landsystems had detached from their central accumulation areas and experienced sustained retreat. Following this, some small cirque glaciers experienced minor readvance before ice recession continued. The geomorphological record indicates that it is likely that glacial ice disappeared in the Wicklow Mountains during this period but was re-established, in a small number of cirques, during the Younger Dryas. [ABSTRACT FROM AUTHOR]

Latest insights from paleo-climatic research (Luetscher et al. 2015) and glacier modelling (Seguinot et al. 2018) suggest that ice build-up during the Last Glacial Maximum may not have been uniform across the European Alps. Favoured by predominant precipitation patterns and a steep topographic gradient, paleo-glaciers on the southern side of the Alps are believed to have reached their maximum extent earlier than glaciers that drained north. While reliable glacial chronologies based on radiocarbon and exposure dates are available for several of the major Italian amphitheatres, the LGM glaciation of the central part of the southern European Alps is a clear lack of knowledge. The latter's connection to the major Alpine ice domes makes understanding the Ticino/Toce glaciers behaviour especially critical. The present study aims on filling this gap of understanding with detailed mapping of the Toce/Ticino glacier combined with cosmogenic nuclide dating. A total of thirty rock samples for surface exposure dating has been collected from erratics deposited on the western shore of Lago Maggiore by the Ticino/Toce glacier. Preliminary Beryllium-10 results support an LGM extent larger than recently proposed (Bini et al. 2009). Next to LGM ages, the present data set together with field evidence also suggests a glacier re-advance following the LGM that ended with rapid down wasting of the glacier. ReferencesBini et al. 2009, Federal Office of Topography, Swisstopo.Luetscher et al. 2015, Nature Communications 7433. Seguinot et al. 2018, Cryosphere 12, 3265-3285. [ABSTRACT FROM AUTHOR]

Reconstruction of denudation rates through time is an important task to quantify andunderstand the impact of climate on landscape evolution. Cosmogenic nuclides have beenwidely used to infer denudation rates at the watershed scale from both present day sedimentsand past stratigraphic records. Here, we analyze the in situ 10Be cosmogenic concentrationin sediments of two long-piston cores that were collected offshore the Var River(Western Mediterranean Sea), precisely along the Var sedimentary ridge. Thesesedimentary archives have been well dated at a high resolution and analyzed forsediment provenance (Bonneau et al., 2017-EPSL) thus providing a unique record toreconstruct the denudation history of the Var catchment in the Southern French Alps overthe last 70 ka. This period covers the majority of the last glacial period and theassociated Dansgaard-Oeschger events, the last glacial maximum (LGM, 26-19 ka) andthe subsequent deglaciation (19-11 ka), and the Holocene, with all these eventsbeing precisely defined in the studied cores. Therefore, this setting offers the rareopportunity to study the impact of rapid climate fluctuations on denudation ratesin a mountainous glaciated catchment over a time scale that is not impacted bytectonics. We present 21 10Be paleo concentrations ranging from 1.24±0.51 x 104 atoms/gquartz to5.99±1.90 x 104 atoms/gquartz. The 10Be paleo concentrations overall are very similar topresent day 10Be concentrations (average of 4.20±0.67 x 104 atoms/gquartz at thewatershed&#x2019;s outlet in 2016, or a denudation rate of 0.20 ±0.03 mm/year). This suggestssimilar paleo denudation rates between today, the 0-17 ka period and the 27-70 kaperiod. Only the LGM shows a clear change in 10Be concentrations with much lowerconcentrations (average of 1.68±0.48 x 104 atoms/gquartz) suggesting high denudation ratesduring this period of maximum glacial extent in the French Alps. These results suggest that climatic settings have a limited impact on overall denudationrates and that glaciers in the Mediterranean Alps either weren&#x2019;t strong agents of erosionduring the MIS 3 (70-25 ka) or were smaller than previously thought. These results alsosuggest that only strong climatic fluctuations (such as the LGM) can induce meaningfulchanges in denudation rates. [ABSTRACT FROM AUTHOR]

Increased knowledge about anthropogenic climate change has raised growing concerns about its potential catastrophic impacts on both ecosystems and human societies. Yet, several studies on damages induced on the economy by unmitigated global warming have proposed a much less worrying image of the future, with only a few points decrease in the world GDP per capita by the end of the century, even for high levels of warming. Here we consider two different empirically estimated damage functions, linking GDP growth or GDP level to temperature, and apply them to a global cooling of -4°C in 2100, corresponding to a return to glacial conditions. We show that the alleged impact on average GDP per capita is comprised between -1.8% and +36%.These results are then compared to the living conditions on the planet during the last glacial maximum. The modeled impacts on the world GDP appear clearly unrealistic given the magnitude of climate and environmental changes recorded for that period. We therefore conclude that, if such damage functions cannot reasonably be trusted for a cooling outside their calibration range, nor should they be considered as plausible for the future climate projection under massive greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Resolving the timing and structure of glacial advances throughout the last glacial cycle is essential for understanding the underlying drivers of climate changes in the southern hemisphere. Our knowledge of glacial activity in the early stages of the last glacial cycle, however, is limited owing to the inherently incomplete preservation of the moraine record. Here, we present a 10Be-dated glacial chronology from Lago Belgrano (47.9°S) in central Patagonia that extends to the early last glacial. Our data reveal a major advance at the end of Marine Isotope Stage 5. A second, less-extensive advance occurred during the global Last Glacial Maximum at 25 ka. We suggest the pattern of ice advances reflects ice-divide migration during the build-up of the Patagonian Ice Sheet, which caused ice-flow re-routing, snow starvation, and less extensive glaciers at the site during peak glacial conditions. The timing of the early maximum coincides with cooling evident in Antarctic ice cores and marine proxies from the southern mid-latitudes. The early maximum at Lago Belgrano is likely an expression of hemisphere-wide oceanic and atmospheric cooling. [ABSTRACT FROM AUTHOR]

The volcanic island of Jan Mayen is situated on the southern part of the active Jan Mayen transform fault zone in the Norwegian – Greenland Sea. Jan Mayen hosts the world's northernmost active volcano, the spectacular Beerenberg which rises 2277 meter above sea level. Jan Mayen has an arctic – maritime climate influenced by the northwards flowing Atlantic current and the southwards flowing East Greenland current, suggesting that the island is sensitive to climatic changes. In 2015 we started a project to investigate the glacial and climate history of the island. In this presentation we focus on the glacial history of the island until the Last Glacial Maximum (LGM). Stratigraphic investigations in coastal cliffs indicate that the island was covered by ice also prior to the LGM. At several locations, glaciogenic diamictites at stratigraphic positions below the LGM are found in association with lava flows. Interaction between glaciers and volcanic eruptions cause complex sediment associations, but also provide opportunity for dating glacial events. 40Ar/39Ar and K/Ar dating are in progress in order to constrain pre-LGM glacial events, and results so far indicate that possible two ice advances may have taken place in Jan Mayen prior to the LGM. [ABSTRACT FROM AUTHOR]

Continental shelves typically harbor reservoirs and aquifers, which provide vital resources such as oil, natural gas and freshwater. The existence of fresh groundwater has been recorded at several continental shelves around the world. The New Jersey shelf represents one of the best documented occurrences of this phenomenon. Two different hypotheses explaining the emplacement and survival of freshwater reservoirs offshore New Jersey are currently debated, either regarding them as active aquifers that are dynamically linked to onshore areas or as paleo freshwater lenses that were emplaced during past glacial periods. Here, we present results from numerical simulations on a geologically representative shelf model in order to understand the mechanisms and time scales of fresh groundwater emplacement and preservation at the New Jersey shelf. Utilizing 2D depth migrated seismic and well data, we built a detailed hydrogeological model, with a vertical resolution of 10 m and a horizontal extent of 127 km. Our model captures the highly heterogeneous shelf environment and incorporates porosity compaction trends measured on IODP 313 core data. Initial transient coupled simulations of groundwater flow, heat and salt transport were performed based on the assumption that submarine freshwater reservoirs existed after the last glacial period. Results provide insight into discharge and preservation of fresh groundwater during the Holocene period. We find that freshwater is preserved preferentially in low-permeability sediments and yield simulated borehole salinity profiles consistent with field observations. Further, our simulations show that freshwater intervals which extend tens of kilometers offshore may be have been preserved from the Last Glacial Maximum until today. We find that approximately 30 % of the initial freshwater volume remains preserved after 15 000 years, depending on the recharge boundary condition. Currently ongoing numerical simulations focus on the emplacement history of submarine freshwater reservoirs offshore New Jersey, incorporating a Pleistocene sea-level curve as a time-varying boundary condition. Finally, our results improve the understanding of submarine fresh groundwater through an interdisciplinary approach which integrates seismic imaging, hydrogeological modeling and high-performance numerical simulation. [ABSTRACT FROM AUTHOR]

Last Glacial Maximum reconstructions of former glacier in the European Alps shows large ice expansion on the northern side of the Alps, with wide piedmont lobes spreading over lowlands (synthese in Ehlers et al., 2011). The general chronological outline of the LGM in the Alps suggests a fairly synchronous glacial maximum around 26-20 ka (marine isotope stage 2; Wirsig et al., 2016), in line with global data from the Northern Hemisphere. However, a long lasting debate persists in French Alps regarding the timing of the Late Pleistocene maximum ice lobe extent in the Lyon area, varying from MIS 2 to MIS 4 based on indirect and contradictory radiocarbon ages (Mandier et al., 2003) and field constraints (Monjuvent and Nicoud, 1988). This debate was further rekindled by recent alpine ice modelling studies (Becker et al., 2016; Seguinot et al., 2018).A clear and robust chronological constrain of the Lyon glacial lobe extent is now critical as it would have major implication in terms of our understanding of past atmospheric circulation patterns. Traditional dating techniques such as radiocarbon and cosmogenic nuclides exposure are challenging in this area due to the scarcity of organic material incorporated within glacial deposits and the huge scarcity of in-place moraine boulders. In these circumstances, Optically Stimulated Luminescence (OSL) techniques, which allow the dating of buried sedimentary material, offer a promising alternative. In this study, we propose a new chronological reconstruction of the Lyon Lobe maximum extent during the Late Pleistocene. This chronology is based on new OSL data measured from fluvio-glacial deposits located in presently dry valleys only active during the Late Pleistocene maximum extent of the Lyon Lobe. Our preliminary results suggest that in fact, two major phases of glacial advance of similar extent occurred during the Last Glacial cycle, around the MIS 2 and around the MIS 4. These results not only bring a fresh contribution to the debate of the local paleoglacial history in the French Western Alps but may also have significant implications in terms of Late Pleistocene glaciations pattern and paleoclimate evolution in the Alps. [ABSTRACT FROM AUTHOR]

Ice sheets are both a clear physical representation of climate – fluctuating in response to temperature and precipitation – and a key contributor to climate variability, via feedbacks including albedo and meltwater input. Deciphering the scales of these respective roles from the geologic record of glaciation, however, requires glacial chronologies of sufficiently high resolution to be directly comparable to other, more continuous palaeoclimate records (e.g., ice and marine cores, speleothems). With the recent refinement of cosmogenic nuclide (CN) surface-exposure methods and, crucially, robust local calibration of CN production rates, glacial chronologies are now approaching this resolution. We present a new glacial-geologic record from the northern British Isles, constrained with cosmogenic 10Be and calculated using a new locally calibrated production rate, that documents the discrete pattern of ice sheet retreat in this part of the North Atlantic basin following the Last Glacial Maximum. This data set provides a nuanced view of phases during which the terrestrial cryosphere shrank, which we interpret as indicating strong atmospheric warming, and brief periods when the ice margin stabilised and/or readvanced, reflecting atmospheric cooling. Coupled with similar emerging glacial chronologies, these new data from northern Britain paint a terrestrial picture of stadial-interstadial climate during Termination 1 that contrasts with the traditional view of these severe climatic perturbations. Ultimately, our objective is to provide a robust terrestrial baseline for conceptual and computer models of cryosphere–climate interactions, both within and beyond the North Atlantic basin. [ABSTRACT FROM AUTHOR]

Groundwater is the main source of drinking water supply in Denmark. In southern Denmark, deep Miocene aquifers are increasingly considered as a resource of pristine high quality groundwater. Groundwater in these aquifers is up to several thousands of years old and the recharge conditions experienced significant changes in the past. Understanding the groundwater history is important to ensure sustainable groundwater use and protection from potential contamination.In this study we investigate large-scale changes in the groundwater flow system in southern Denmark during the Quaternary glacial/interglacial cycles with focus on the last (Weichselian) glaciation. Using a finite-difference groundwater flow model (MODFLOW) and a detailed geological representation we show that during the Weichselian glaciation groundwater flow patterns, directions and depths experienced a full reorganization in relation to the interglacial (modern) time as a result of high potentiometric heads imposed by the ice sheet. Of special interest are the feedback mechanisms between the groundwater flow and the ice sheet dynamics. Our simulations show that the drainage capacity of the ice-sheet bed was insufficient to evacuate all the meltwater from the glacier sole as groundwater flow, both under permafrost and no-permafrost conditions. This suggests a widespread decoupling of the ice sheet from the bed and high ice movement velocities by enhanced basal sliding on a layer of pressurized meltwater, which is in turn consistent with the presence of fast-flowing ice streams along the southern fringe of the Scandinavian Ice Sheet during the Last Glacial Maximum. To stabilize the ice sheet, the glacial system generated a system of deep tunnel valleys that drained the excess meltwater to the ice fore-field.Our study illustrates the advantages of a coupled palaeo-hydrological and glacio-geological approach in deciphering the behavior of past ice sheets and their impact on shaping the Earth's surface. [ABSTRACT FROM AUTHOR]