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Reconstructing past climate seasonality is fundamental to understanding the nature of past climate changes. This is especially true in the Arctic, where climate is intensely seasonal and proxies that can distinguish climate conditions of multiple seasons in a single year are relatively rare. We propose that submerged aquatic mosses, which are abundant subfossils in some Arctic lake sediments and have distinctive seasonal growth morphologies, can be used to estimate past lake water oxygen isotope composition (δ18O lw) across multiple seasons. Aquatic mosses are abundant, well preserved, and grow continuously in Arctic lakes whenever light is available, with some species displaying unique seasonal morphologies influenced by water temperature. Although Greenland paleorecords suggest that aquatic moss oxygen isotope values (δ18O om) reflect the δ18O values of lake water, no modern calibration between δ18O om and δ18O lw exists in Greenland. We present a modern δ18O om vs. δ18O lw calibration using multiple moss species or morphotypes from eight lakes and ponds near Pituffik (Thule), northwest Greenland. We find strong linear relationships (r2 = 0.76-0.85) between the δ18O om and δ18O lw values of multiple species or morphotypes across the range of relatively low δ18O lw values at Pituffik, and our results indicate isotopic fractionations are similar to those found previously at lower latitudes. To assess the potential of mosses as archives of seasonal δ18O lw values, we analyzed δ18O om in season-specific segments of moss strands, with seasons identified based upon growth morphology. Moss inferred lake water δ18O values (δ18O lwom) are higher in autumn than spring or summer, likely due to increasing contributions of 18O enriched precipitation and the cumulative effects of lake water evaporation throughout the ice-free season. For moss subsampled throughout summer, δ18O lwom values generally increased through the season in parallel with observed δ18O lw values. Potential temperature dependent fractionation effects during biosynthesis, however, remain unconstrained and should be further addressed with future research. Overall, these findings suggest that aquatic mosses from lake sediments could be used to directly resolve climate seasonality of the past. • Aquatic moss strand δ18O values reflect lake water values through multiple seasons. • Summer subsampled moss strands show weekly to monthly evolution of lake water δ18O. • Aquatic moss vs. lake water δ18O calibrations are similar for species tested here. • Aquatic moss δ18O needs testing down core to evaluate past seasonal signals. • Temperature-dependent fractionation and pre-treatment effects need more research. [ABSTRACT FROM AUTHOR]

Holocene paleotemperature records from ice-free margins of Greenland suggest spatiotemporal heterogeneity in the timing of key climate transitions following retreat of the Greenland Ice Sheet. However, the paucity of high-resolution climate records from this region limits our understanding of the timing, spatial variation, and drivers of Holocene climate variability. Here, we present a middle to late Holocene climate reconstruction based on δ18O of aquatic invertebrate (chironomid and cladoceran) remains and sediment geochemistry from lake sediments to elucidate millennial to submillennial-scale drivers of climate in southwestern Greenland. We establish that our site, Arrowhead Lake, is a through-flowing basin with an integrated signal of annual meteoric water with no evidence of significant evaporative enrichment. Core sediment geochemistry captures the transition from minerogenic-dominated to organic-rich sediments ∼8 cal ka BP. Chitin-based δ18O measurements of both chironomid head capsules and ephippia exhibit similar temporal variability through the record, broadly decreasing from 8.2 cal ka BP to present, concurrent with decreasing summer insolation and regional Neoglacial cooling. A simplified assumption that temperature is the sole driver of changes in isotopes of precipitation yields an estimated average temperature change from the middle to late Holocene at Arrowhead Lake of 2.1–3.0 °C, comparable to existing estimates of middle to late Holocene temperature decline in western Greenland. Depleted δ18O values after 3.3 cal ka BP correspond to the onset of Neoglacial cooling and independent evidence for a slowdown of the West Greenland Current, and suggests that both temperature and sea-ice variability were important controls on isotopic variability at this site. Highly depleted isotopic values at 8.2 cal ka BP followed by high isotopic variability in the early part of the middle Holocene suggests that our record may capture regional 8.2 ka cooling. This new isotope record provides insight into climate influences during the middle and late Holocene along the western Greenland margin that are important for understanding how ongoing melt of the Greenland Ice Sheet and amplified warming in the Arctic may impact the climate system. • A new δ18O record offers insight into 8200 years of climate change in SW Greenland. • Data suggest ∼2.1–3.0 °C Neoglacial cooling, consistent with regional records. • Decreasing magnitude of temperature from north to south in western Greenland. • Highly depleted isotopic values are consistent with the 8.2 ka cooling. [ABSTRACT FROM AUTHOR]

Investigations of chronology play a key role in the majority of archaeological research endeavors and are particularly pertinent to examinations of culture-environment relationships, especially during periods characterized by rapid and marked climatic variability and environmental reorganization. Rigorous evaluations of available data and robust methods are required if one wishes to reconstruct reliable chronologies, and this is especially the case when examining periods that are associated with a relatively few radiometric measurements. Such is the case for the Upper Paleolithic archaeological record documented in present-day France from 32,000 to 21,000 calibrated years BP. We take into account critically examined radiocarbon measurements from contextually secure archaeological contexts and employ a recently-developed method of Hierarchical Bayesian Modeling to reconstruct the chronology of archaeological cultures from the Middle Gravettian to the Badegoulian. The calculated chronological intervals for each typo-technologically defined culture phase are compared to the Greenland ice core climatic record and a terrestrial paleoenvironmental record from Bergsee Lake (Southern Germany)—itself expressed in calendar years calculated with the same calibration curve employed in our age model—thereby permitting each archaeological culture to be correlated accurately with documented paleoclimatic variability. • Robust chronologies are needed to correlate past cultures with climate variability. • A recently-developed method of Hierarchical Bayesian Modeling is employed. • Temporal intervals for archaeological cultures are determined with this method. • Arguments are presented as to why this new Bayesian method is preferable. [ABSTRACT FROM AUTHOR]

Ravine slopes at the recently discovered Nesseltalgraben site in southeastern Germany provide a unique last glacial sediment record for the Northern Calcareous Alps. The 21 m-long profile is dominated by fine-grained lacustrine-palustrine sediments overlain by several metres of glacifluvial gravels and lodgement tills of the Last Glacial Maximum and underlain by a diamicton. The age model includes 29 radiocarbon analyses and one paleomagnetic anomaly (Laschamp event) together providing a modelled age range from c. 59 to 29.6 ka cal BP, i.e. Marine Isotope Stage (MIS) 3. Apart from a description of the lithofacies, X-ray-fluorescence (XRF) scanning and elemental analyses provide high-resolution records of the geochemical composition. Multivariate analyses of XRF data separate Ca from other major elements. Carbonate contents, represented by Ca and total inorganic carbon, reach maxima in repeatedly occurring calcareous silty to sandy layers and are related to glacigenic origin. These indicate repeated inner-alpine local glaciations during stadials of MIS 3. Scanning electron microscopy and XRF data confirm the detrital origin of these layers. In contrast, organic matter and elements more resistant to chemical weathering (Si, Ti, Zr) accumulated during interstadials and concurrently elevated Rb/Sr ratios indicate intensified weathering. The high-frequency proxy variations determined for Nesseltalgraben reflect interstadial-stadial climate variability comparable with oxygen-isotope records from Greenland ice cores and Alpine speleothems. Thus, Nesseltalgraben is among the very few independently dated sediment records from continental Europe covering the entire MIS 3 and reflecting the full Dansgaard-Oeschger climate variability. • A 21 m sediment profile from the northern Alps provides a complete MIS 3 record. • Repeated inner Alpine glaciations are indicated by calcareous silt layers. • Geochemical variations reflect interstadials and stadials. • The Nesseltalgraben record resembles Dansgaard-Oeschger climate variability. [ABSTRACT FROM AUTHOR]

Millennial-scale Dansgaard Oeschger (DO) variability at northern high latitudes has influenced climatic and environmental conditions in the Mediterranean during the last glacial period. There is evidence that the hemispheric transmission of the DO variability occurred at the end of DO event 25; however, the exact timing and the trigger that activated the environmental response in the Mediterranean remains incompletely understood. Here, we provide evidence that the clear millennial-scale teleconnection between Greenland and the Mediterranean started at ∼111.4 ka BP and was initiated by a sub-millennial scale cooling in Greenland (GI-25b). High-resolution sediment proxies and the pollen record of Lago Grande di Monticchio (MON), Italy, reflect climatic instability during the last millennium of the last interglacial, which was characterised by a first and short cooling episode (MON 1) at 111.44 ± 0.69 ka BP, coinciding with the Greenland cold sub-event GI-25b in duration and timing (within dating uncertainties). MON and Greenland (NorthGRIP ice core) also agree in recording a subsequent warm rebound phase that abruptly culminated in the stadial MON 2/GS-25, marking the transition into the last glacial period. Our results show that the GI-25b triggered an early environmental response at MON to centennial-scale climate change in Greenland as a prelude to the millennial-scale teleconnection that was maintained during the glacial period. • Annual-resolution study of the transition from the Last Interglacial period to the last Glacial period. • Evaluation of the differences in proxy response to sub-millennial-scale climate variability. • Chronological discussion based on comparison of independent chronologies. [ABSTRACT FROM AUTHOR]

In this study, we present the results of independent component analysis (ICA) of previously published Lake Van data covering the last 250 kyr BP, to shed light on the precipitation and temperature regime in eastern Anatolia. The data processed were the element intensities of Ca, Fe, K, Mn, and Si analyzed by XRF core scanner; concentrations of TOC and CaCO 3 content; and B* (color reflectance) from the Ahlat Ridge sediment record. Our analysis is based on application of ICA on the data by changing the initial random unit vector several times and clustering possible independent components through average-link agglomeration. As components extracted by ICA do not have a hierarchy, mutual information, which is a measure of information content between two random variables, is used as a measure of similarity by which to select candidate components. As a result, we argue, the independent component (Van-IC8), which shows the highest similarity to the Greenland δ 18 O record and visually similar to other regional temperature indicating data, can be read as a proxy for temperature variability. We also assert that the independent component (Van-IC7) which has the highest similarity to B* and visually similar to other regional precipitation proxies, and with the lake level reconstruction from another sediment profile from Lake Van is a proxy of precipitation variability across the region. Our results show that the region's temperature approximately maps onto global records, i.e. warm during interglacials and cold during stadials. However, the precipitation proxy reveals that the region was not dry, or at least as wet as it is today, during the end of the MIS 6 and the LGM. The MIS 5e/c and Holocene were characterized by a wet period followed by dry intervals and Dansgaard/Oeschger events are characterized as being warm and wet. [ABSTRACT FROM AUTHOR]

Abstract We present new sedimentological and environmental magnetic records spanning ∼3.2–2.2 Ma, during the intensification of Northern Hemisphere glaciation, from North Atlantic Integrated Ocean Drilling Program Site U1307 on Eirik Drift. Our new datasets and their high-fidelity age control demonstrate that while inland glaciers – and potentially also at times restricted iceberg-calving margins – have likely existed on southern Greenland since at least ∼3.2 Ma, persistent and extensive iceberg-calving glacial margins were only established in this region at 2.72 Ma, ∼300 kyr later than in northeastern and eastern Greenland. Despite a dramatic increase in Greenland-sourced ice-rafted debris deposition on Eirik Drift at this time, contemporaneous changes in the bulk magnetic properties of Site U1307 sediments, and a reduction in sediment accumulation rates, suggest a decrease in the delivery of Greenland-sourced glaciofluvial silt to our study site. We attribute these changes to a shift in depositional regime from bottom-current-dominated to glacial-IRD-dominated between ∼2.9 and 2.7 Ma, in response to a change in the depth of the flow path of the Western Boundary Undercurrent relative to our study site. Highlights • New high-fidelity RPI-based age model for Site U1307. • Orbital-resolution history of Greenland IRD deposition on Eirik Drift during iNHG. • Persistent marine-terminating margins established in southern Greenland from 2.7 Ma. • Potentially ∼300 ka later than in northeastern and eastern Greenland. • Major reduction in flow speed of bottom currents bathing Site U1307 during iNHG. [ABSTRACT FROM AUTHOR]

Abstract According to the findings of a complex radiocarbon dated sedimentological, geochemical, anthracological, phytolite, malacological study implemented on an open 1036 cm wind-blown sand, loess, sandy loess and fossil soils profile of western part of brickyard at Katymár village in Hungary. Increased boreal mixed-leaved forest steppe and temperate grassland cover characterized the interstadials in the SE Great Hungarian Plain during the terminal phase of MIS3 stage and MIS2 stage. These interstadials correlate well with the Dansgaard-Oeschger (DO) interstadials 8, 7, 6, 5, 4, 3, 2 and the post LGM warm interval (DO1) seen in the Greenland ice core oxygen isotope records. Intervening cold phases, on the other hand, their start correlating with Heinrich event 1, 2, 3, 4 and the LGM. These data overall confirm that millennial scale climate variability during MIS3 and MIS2 stages had profound effect on the terrestrial ecosystems in the continental interior of SE Europe leading to periodic mixed-leaved boreal forest steppe within mosaic structure expansions in the interstadias and cold steppe, taiga and tundra like spots mosaic and mixed vegetation expansion in the stadial phases. 1400–1500 year long drier interstadial and humid, extended vegetation covered stadial periods interchanged at Katymár sequence, therefore the vegetation and fauna development was different from the Atlantic and Central European schemes and inferred an independent local and regional South Carpathian Basin trend. [ABSTRACT FROM AUTHOR]

Abstract Lake Sihailongwan in Jilin province, NE China, provides the first continuous and almost entirely seasonally laminated sediment record on the East Asian mainland comprising the complete Holocene, the Late-glacial period, and large parts of the Last Glacial. Sediment and palynological proxy data provide a finely resolved regional environmental history of the East Asian monsoon. A varve-based chronology (shl-vc2) has been established for the last 65,000 years and allows a detailed comparison with other long regional and global palaeoclimate records. Vegetation density of the study area depends, on the long run, on precessionally forced insolation changes, with superimposed millennial-scale variability during the Last Glacial. Periodic increase of organic carbon content and thermophilous tree species like Ulmus and Fraxinus and contemporary decrease of shrub Alnus precisely mirror millennial-scale climatic variations primarily known from Greenland ice-cores as Dansgaard-Oeschger cycles, as well as Late-glacial period climate changes. Percentages of trees & shrubs pollen and in particular lake productivity-related data reveal substantial differences between interstadial intensities, with those between 50 and 60 ka BP being more pronounced than the following ones. Highlights • A varved lake sediment record covers the last 65 ka of East Asian monsoon history. • Influence of local environmental thresholds and climate change on proxy data. • Strong similarities between East Asian monsoon and Dansgaard-Oeschger cycles. • Week East Asian Monsoon during Heinrich events. [ABSTRACT FROM AUTHOR]

Abstract A stalagmite (FR16) from Frasassi Cave, located near the Adriatic coast of the Italian peninsula, offers a 16 kyr petrographic and stable isotope record spanning from 112.8 ± 1.5 ka to 96.6 ± 1.0 ka, corresponding to the interval from marine isotope stage (MIS) 5c to MIS 5d. The physical characteristics of FR16 calcite, allowed for a thorough understanding of the processes controlling isotopic changes, because fabrics as well are controlled by the environmental parameters within the cave that reflect external climate forcing. The FR16 δ13C profile matches fabric changes where columnar fabric usually corresponds to more negative values and micrite/microsparite layers to less negative δ13C values, and with the North Greenland Ice-core Project (NGRIP) δ18O record with more negative δ13C values during interstadials GI24 and GI23. This suggests a hydrological sensitivity for the two proxies, and their variability can be linked to recharge changes. On the other hand, the response to Greenland events appears subdued in the δ18O record and the trend mimics instead the Northern Hemisphere (NH) summer insolation with more negative δ18O values corresponding to the maximum insolation centred at ca. 105 ka. This behaviour can be explained by the higher sensitivity of δ18O to rainfall seasonality, moisture source and trajectories, whose combined effect attenuated the stadials/intersadials signal in the stalagmite. Highlights • 16 kyr stable isotope and petrographic stalagmite record from Frasassi cave (Italy), covering the last glacial inception. • Petrographic observations benchmark the interpretation of the δ13C profile. • Stalagmite δ13C shows a general increasing trend with short-lived more positive shifts coinciding with NGRIP stadials. • The δ18O profile trend follows the NH summer insolation, with the most negative values recorded at higher insolation. • The δ18O signal of the stalagmite seems to be primarily controlled by moisture provenance and rain shadow effects. [ABSTRACT FROM AUTHOR]

Abstract Newly acquired U Th dates on gypsum sands contained within Pleistocene lake sediments allow us to extend the record of climatic change in the Estancia Basin of central New Mexico back to ∼69 ka from a previous limit of ∼29 ka. Using a hydrologic balance index (HBI) that reflects variations in sediment mineralogy and bedding characteristics, we find strong similarities to speleothem oxygen isotopic records for the southwestern United States as well as to isotopic variations in Greenland ice cores. Intervals of wetter climate in the Estancia Basin generally appear to correlate to colder conditions in the North Atlantic and conversely. The existence of a pronounced dry period from 18.1 to 17 ka matches in timing the Extrapolar Climate Reversal of Asmerom et al. (2017) at Fort Stanton cave in southern New Mexico and confirms a different origin for this stadial-like event. Furthermore, the new U Th dates support the existing Estancia Basin interpretation of a dry Bølling/Allerød followed by a wet Younger Dryas, a result consistent with speleothem and wet meadow evidence from New Mexico and Arizona (Asmerom et al., 2010, 2017; Polyak et al., 2004; Hall et al., 2012; Wagner et al., 2010) but in conflict with an interpretation of speleothem evidence from central Texas (Feng et al., 2014). Highlights • U Th dates extend the record of climatic change in the Estancia Basin of New Mexico to ∼69 ka. • The dates were acquired from gypsum sands produced during lowstands of pluvial Lake Estancia. • A new U Th date provides support for a wet Younger Dryas interval in central New Mexico. • A dry period from 18.1 to 17 ka matches in timing the Extrapolar Climate Reversal at Stanton Cave. • An Estancia Basin hydrologic balance index shows similarities to the Greenland ice sheet record. [ABSTRACT FROM AUTHOR]

The investigation of trough mouth fans (TMFs), important paleoclimatic archives on mid- and high-latitude continental margins, has so far mainly been based on the integration of various types of acoustic data supplemented with short sediments cores. In consequence, sedimentological and chronological data about parts of TMFs deposited prior to the Last Glacial Maximum remains sparse. Here, we re-evaluate the upper part of ODP Site 987 drilled on the distal part of the Scoresby Sund TMF on the east Greenland continental margin, which records the former dynamics of the Scoresby Sund sector of the Greenland Ice Sheet. Based on a more detailed sedimentological description than previously available we find that lithological unit I, deposited over the last ~ 2.14 Ma, can be divided into two parts, a lower part dominated by glacimarine and marine deposits including some scattered, sandy turbidites and an upper part of debris flow deposits interbedded with sandy turbidites. The transition between these parts occurred at about 0.99 Ma, i.e. at the same time when the mode of ice-sheet variation changed globally, the average ice sheet size increased significantly and the periodicity of ice-volume variation increased from around 41 ka to approximately 100 ka (the “Mid-Pleistocene Transition”). On the distal Scoresby Sund TMF, this change appears to be reflected through a marked increase in the abundance of sandy turbidity flows accompanied by a longer run-out of some of the debris flows due to the delivery of larger sediment volumes during longer-lasting glacial maxima. This suggests that long sediment cores from TMFs have the potential to record the major climatic trends occurring during the Pleistocene. [ABSTRACT FROM AUTHOR]

Astronomical forcing (obliquity and precession) has been thought to modulate Dansgaard-Oeschger (DO) events, yet the detailed quantification of such modulations has not been examined. In this study, we apply the novel Holo-Hilbert Spectral Analysis (HHSA) to five polar ice core records, quantifying astronomical forcing's time-varying amplitude modulation of DO events and identifying the preferred obliquity phases for large amplitude modulations. The unique advantages of HHSA over the widely used windowed Fourier spectral analysis for quantifying astronomical forcing's nonlinear modulations of DO events is first demonstrated with a synthetic data that closely resembles DO events recorded in Greenland ice cores (NGRIP, GRIP, and GISP2 cores on GICC05 modelext timescale). The analysis of paleoclimatic proxies show that statistically significantly more frequent DO events, with larger amplitude modulation in the Greenland region, tend to occur in the decreasing phase of obliquity, especially from its mean value to its minimum value. In the eastern Antarctic, although statistically significantly more DO events tend to occur in the decreasing obliquity phase in general, the preferred phase of obliquity for large amplitude modulation on DO events is a segment of the increasing phase near the maximum obliquity, implying that the physical mechanisms of DO events may be different for the two polar regions. Additionally, by using cross-spectrum and magnitude-squared analyses, Greenland DO mode at a timescale of about 1400 years leads the Antarctic DO mode at the same timescale by about 1000 years. [ABSTRACT FROM AUTHOR]

The "inverse modelling through iterative forward modelling" (IMIFM) approach is used to reconstruct the last deglaciation climates from central equatorial African mountains. Unlike other approaches that use statistical models, it directly incorporates the effects of changes in atmospheric CO 2 concentrations on vegetation through a process-based vegetation model, but the results strongly depend on the model used. Therefore, two generally related but different equilibrium vegetation models are used for evaluating the dependence of the results on the choice of vegetation model. Our climate reconstructions show that long-term temperature increases during the last deglaciation, as seen in Greenland, were absent from many of the target sites. Moreover, there are few common long-term trends of climatic responses during the last deglaciation among central equatorial African mountains' sites despite the relatively close of those sites. No systematic climate responses were also found between the eastern and western sides of the Congo basin. While there is consistency in the long-term trends and their amplitudes regarding temperature reconstructions with both models, there are large differences between the sites in the long-term hydroclimatic reconstructions, particularly during arid periods. This difference may be attributed to the carbon-water use efficiency in the vegetation models. This study implies that the IMIFM approach is effective for climate reconstructions in equatorial African mountains, where modern pollen samples are not plentiful. Although low atmospheric CO 2 concentrations do not largely influence temperature reconstructions for the last deglaciation, they significantly affect the hydroclimate reconstructions, especially when drought-tolerant biomes are dominant. • Pollen-based climate reconstruction using an inverse-vegetation modelling approach. • Climate changes at the central equatorial African mountain sites were inconsistent. • Hydroclimate reconstructions strongly depend on the vegetation model used. [ABSTRACT FROM AUTHOR]

Ice core records have long indicated that the Younger Dryas began and ended with large, abrupt climate shifts over Greenland. Key climatic features remain unknown, including the magnitude of warming during the Younger Dryas-Holocene transition along with the seasonality and spatial variability of Younger Dryas climate changes across Greenland. Here, we use geochemical and paleoecological proxies from lake sediments at Lake N14 in south Greenland to address these outstanding questions. Radiocarbon dating and diatom assemblages confirm early deglaciation and isolation of Lake N14 before ∼13,600 cal yr BP, consistent with previous work. Oxygen isotope ratios (δ18O) of chironomid head capsules, bulk aquatic moss, and aquatic moss-derived cellulose are used to reconstruct oxygen isotopes of past lake water and annual precipitation. Oxygen isotope proxies indicate annual precipitation δ18O values increased by 5.9–7.7‰ at the end of the Younger Dryas. Following the Younger Dryas, moss and cellulose δ18O values show a clear decline in precipitation δ18O values of 2–3‰ from ∼11,540–11,340 cal yr BP that may correspond with the Preboreal Oscillation. Reconstructed precipitation δ18O values then gradually increased from 11,300–10,100 cal yr BP. All three aquatic organic materials register similar shifts in precipitation δ18O values over time, and they closely parallel the δ18O shifts observed in ice cores. This evidence strongly supports the utility of these methods for reconstructing lake water δ18O, and furthermore precipitation δ18O values where lake water reflects precipitation. The relatively large shift in isotopic composition of precipitation at Lake N14 suggests that shifts in temperature, precipitation seasonality, and/or moisture sources at the end of the Younger Dryas were even larger in south Greenland than they were in central Greenland, most likely because of the proximity to major changes in North Atlantic Ocean circulation. The annual air temperature change estimated at Lake N14 at the end of the Younger Dryas is also very large (∼18 ± 7 °C) compared to the summer warming previously inferred from chironomid species assemblages there (∼6 °C). This indicates that the strongest warming at the end of the Younger Dryas occurred in the winter season, consistent with past observations of intensified Younger Dryas seasonality at Lake N14 and elsewhere in Greenland. • Lake N14 in Greenland deglaciated and isolated from the sea by ∼13,600 cal yr BP. • Annual temperatures rose ∼18 °C and summer temperatures ∼6 °C at the end of the YD. • YD δ18O changes were larger at Lake N14 than at GISP2 and DYE3 ice core sites. • YD climate change varied seasonally and spatially, consistent with AMOC influence. [ABSTRACT FROM AUTHOR]

Millennial-scale climate oscillations of the last ice age registered in Greenland and Antarctic ice cores did not always vary in unison. A striking example is that the strongest Antarctic warming episodes occurred during Heinrich episodes in the North Atlantic region. Although the bipolar seesaw affords a possible explanation for such anti-phasing, it does not account for the equally striking observation that climate varied in unison between the hemispheres about half the time. Such phasing differences suggest the need for an alternative hypothesis in which the polar regions at times responded in unison to common forcing, and at other times left the impression of a bipolar seesaw. We posit that this impression arose from the effect of warmer-than-usual summers on continental ice sheets adjacent to the North Atlantic Ocean during each Heinrich episode. The relatively warm Heinrich summers produced discharges of meltwater and icebergs of sufficient volume to stimulate very cold winter conditions from widespread sea ice on a freshened ocean surface. The intervals between Heinrich episodes featured relaxation of sea-ice-induced winter severity from reduced summertime influx of meltwater and icebergs, indicating relatively cooler summer conditions. It is postulated that the causative variations in freshwater fluxes were driven by a climate signal most evident in Antarctic ice cores but also recognized in other paleoclimate records in both polar hemispheres. We suggest that this widespread signal arose from changes in the latitude and strength of the austral westerlies and the resulting effect on the western Pacific tropical warm pool, a mechanism dubbed the Zealandia Switch. • Bipolar synchrony of millennial-scale glacier melt during the last glaciation. • Interhemispheric glacier signal inconsistent with 'bipolar seesaw' hypothesis. • Northern 'stadials' attributed to warm summers paired with extremely cold winters. • Enhanced melt-induced northern seasonality obscured global ice-age climatic signature. • Differentiating summer from winter effects key to interpreting paleoclimatic proxies. [ABSTRACT FROM AUTHOR]

Due to a general scarcity of archives and a lack of temporally highly resolved records, the response of Central European ecosystems to abrupt climate change during the Late Pleistocene – and notably the Last Glacial – has remained insufficiently explored. To contribute to a better understanding of the impact of short-term climate variability on ecosystems in Central Europe north of the Alps during that time, we present a new, near-continuous pollen record from Füramoos, southern Germany. Except for a hiatus from 28 to 20 ka BP, the record spans the past 130 kyrs in centennial-scale resolution. Our pollen dataset is augmented by sedimentological (i.e., XRF core scanning, loss on ignition, and maceral analysis) and macrobotanical data. This new record represents the yet most complete, temporally highest resolved reconstruction of terrestrial ecosystem dynamics in Central Europe for the Last Glacial period. Our results show that temperate forests thrived at Füramoos during full interglacial conditions (i.e., MIS 5e and MIS 1), boreal forests developed during the early glaciation (MIS 5 d–5a), and a tundra vegetation prevailed during full glacial conditions (MIS 4–2). Fourteen transient expansions (contractions) of tree and shrub populations that are synchronous with increases (decreases) in weathering intensity can be firmly attributed to specific Greenland Interstadials (Greenland Stadials) of the NGRIP ice-core record. By comparing individual expansions/contractions of tree and shrub populations with Greenland δ18O ice ice-core and North Atlantic sea-surface temperature (SST) data, we show that during interstadials vegetation dynamics in Central Europe were closely linked to SSTs in the North Atlantic and decoupled from the climate recorded in Greenland; during stadials, the opposite pattern prevailed. We attribute these patterns to changes in AMOC strength and associated latitudinal shifts of the polar front. • New, high-resolution palynological and element geochemical record for MIS 5e–1. • Most complete record of Central European ecosystem dynamics during the Last Glacial. • All Greenland (inter)stadials during MIS 4–3 characterized by abrupt biome shifts. • Ecosystem change during interstadials in response to atmospheric circulation change. • Forest composition during Greenland Interstadials depends on moisture availability. [ABSTRACT FROM AUTHOR]

Abstract: The Greenland Ice Sheet is a major component of the Arctic cryosphere and the magnitude of its response to future climate changes remains uncertain. Longer-term records of climate near the ice sheet margin provide information about natural climate variability and can be used to understand the causes of past changes in the Greenland Ice Sheet. As a proxy for Holocene climate near the ice sheet margin, we reconstruct the fluctuations of Bregne ice cap in the Scoresby Sund region of central east Greenland. Bregne is a small ice cap (2.5 km2 in area) and responds sensitively to summer temperatures. We employ a multi-proxy approach to reconstruct the ice cap fluctuations using geomorphic mapping, 10Be ages of boulders and bedrock and lake sediment records. Past extents of Bregne ice cap are marked by moraines and registered by sediments in downvalley lakes. 10Be ages of bedrock and boulders outboard of the moraines indicate that Bregne ice cap was within ∼250 m of its present-day limit by at least 10.7 ka. Multi-proxy data from sediments in Two Move lake, located downvalley from Bregne ice cap, indicate that the ice cap likely completely disappeared during early and middle Holocene time. Increasing magnetic susceptibility and percent clastic material from ∼6.5 to ∼1.9 cal ka BP in Two Move lake sediments suggest progressively colder conditions and increased snow accumulation on the highlands west of the lake. Laminated silt deposited at ∼2.6 cal ka BP and ∼1.9 cal ka BP to present registers the onset and persistence of Bregne ice cap during the late Holocene. 10Be ages of boulders on an unweathered, unvegetated moraine in the Bregne ice cap forefield range from 0.74 to 9.60 ka. The youngest 10Be age (0.74 ka) likely represents the age of the moraine whereas older ages may be due to 10Be inherited from prior periods of exposure. This late Holocene moraine marks the second largest advance of the ice cap since deglaciation of the region at the end of the last ice age. The oldest moraine in the forefield dates to ≤2.6 cal ka BP. The fluctuations of Bregne ice cap were likely influenced by Northern Hemisphere summer insolation throughout the Holocene and abrupt late Holocene cold events. [Copyright &y& Elsevier]

Abstract: The composition and evolution of the silicate Earth during Hadean/Eoarchean times are widely debated and largely unknown due to the sparse geological record preserved from Earthʼs infancy. The short-lived 146Sm–142Nd chronometer applied to 3.8–3.7 Ga old mantle-derived amphibolites from the Isua Supracrustal Belt (ISB) in southwest Greenland has revealed ubiquitous 142Nd excesses in these rocks compared to modern samples and terrestrial Nd standards. Because the parent isotope, 146Sm, was extant only during the first few hundred million years of Solar System history, this implies derivation of the Greenland samples from a source formed in the Hadean. This mantle source is the oldest yet identified on Earth and therefore provides key information about the nature and evolution of early-differentiated reservoirs. In contrast, modern mantle-derived rocks from around the world do not have 142Nd anomalies, suggesting that the primordial heterogeneities detected in Earthʼs early mantle have been erased over time. In order to better constrain the rate at which early mantle heterogeneities have been re-homogenized, we produced new 146Sm–142Nd data for both 3.8 and 3.3 Ga old mafic rocks from different tectonic domains of the ISB, accompanied by their corresponding 147Sm–143Nd and 176Lu–176Hf systematics. The 3.8 Ga suite yields 142Nd excesses comparable to those detected previously in 3.7 Ga old ISB amphibolites, indicating that Eoarchean mafic ISB lavas originated from sources with similar differentiation histories despite being from different juxtaposed tectonic segments. Conversely, 3.3 Ga old amphibolites from the ISB do not show resolvable 142Nd anomalies compared to terrestrial Nd standards. Since Rizo et al. (2012) reported 142Nd anomalies in 3.4 Ga old ISB samples, the present data suggest that the primordial 142Nd heterogeneities in the Isua mantle disappeared between 3.4 and 3.3 Ga. The present data set consists of samples from a unique location where 500 million years of history of the early terrestrial mantle have been preserved, hence offering an exceptional opportunity to gain new insight into the compositional evolution and dynamic workings of Earthʼs primordial mantle. [Copyright &y& Elsevier]

Geological evidence of paleoclimate conditions provide important constraints on paleoclimate models. Paleowinds are one of the central paleoclimate parameters in global circulation models used to reconstruct past climatic conditions. However, only a few climate proxies such as eolian dunes and shallow-water wave ripples provide information on paleowind directions. In this study, we present new paleoclimatic data based on lacustrine sediments with wave ripple marks in the Upper Triassic Fleming Fjord Group, central East Greenland deposited at very shallow water depth in the northern part of Pangaea in a mid-latitude, warm-temperate climate. Wave-ripple orientations are measured on 380 individual fossilized wave-rippled beds at four localities in the ~8500 km2 lacustrine basin. These ripple data are used to establish a geologic wind proxy and are compared to previously published general circulation models. Two wave ripple orientations are observed: The dominant ripple orientation and wave ripple characteristics indicate paleowinds from the Late Triassic SSE and NNW (154.5° and 334.5°), while a subordinate orientation indicate paleowinds from W or E (270° or 90°). This paleowind regime remained stable for at least ~7.5 million years during the mid-late Norian (218.5-211 Ma). These results correspond very well with some general circulation model results that suggest summer winds from the NNW and winter winds from the SSE. Based on the great compatibility between empirical data and general circulation model results, the wind pattern seems to have been greatly influenced by regional, Late Triassic mountain topography in the present-day Greenland and Norway channeling the paleowind in the northernmost part of the pre-Atlantic rift basin (the mid-Norwegian-east Greenland rift system). [ABSTRACT FROM AUTHOR]

Abstract: In recent years, increased awareness of the considerable potential offered by tephrochronology in palaeoclimatic studies has fuelled a renewed interest in the tephra record preserved within the Greenland ice-cores. This renewal has occurred in tandem with the development of continuous flow analysis techniques, which provide high-resolution volcanic aerosol records. These chemical records are of considerable value for identifying tephra horizons composed of glass shards and also provide the basis for a new high-precision ice-core timescale, thus allowing ages to be assigned to volcanic events. Tephra horizons of glass shards in the ice-cores play a critical role for (1) testing and building chronological frameworks for the ice-cores and other sequences, (2) synchronising disparate palaeoclimatic sequences and testing phase relationships, (3) atmospheric pathway reconstruction, and (4) verifying the source of volcanic aerosol peaks. Here we review the results of over 25years of research into tephra horizons in the GRIP, GISP2 and NGRIP cores. We provide high-precision ages for horizons based on recently developed timescales and draw together geochemical characterisations of the products of 45 volcanic events deposited on the Greenland ice sheet and identified in the cores. There is a clear disparity between the number of volcanic aerosol peaks and the number of tephra horizons of glass shards identified thus far. However, this synthesis highlights the critical role of the Greenland ice-cores, firstly in the reconstruction of the history of Icelandic volcanic eruptions, and secondly the considerable value of some tephra horizons in facilitating the correlation of these key climatic archives to North Atlantic marine sequences. Other noteworthy issues include the potential of these cores to preserve tephra horizons from more distal volcanic sources such as North America, to resolve the debate surrounding the Thera eruption, and the observation that some tephra horizons are preserved within the ice without coeval volcanic aerosol signals. [Copyright &y& Elsevier]

Abstract: Reconstructions of the palaeoclimate of the Early Cretaceous are controversial, varying from a warm-temperate greenhouse world to icehouse conditions. We studied calcareous nannofossil assemblages of sediments from North-East Greenland (Wollaston Forland and Kuhn Ø) of Late Ryazanian–Barremian age in order to better understand the palaeoclimate and palaeoceanography of the high latitudes. The calcareous nannofossil assemblages are characterized by abundant Crucibiscutum spp. and Watznaueria spp., Biscutum constans and other Boreal taxa. They show also influxes of Tethyan and low to mid latitudinal taxa like nannoconids (e.g. Nannoconus bermudezii, Nannoconus dolomiticus, Nannoconus steinmannii), pentaliths (Micrantholithus hoschulzii, Micrantholithus obtusus), conuspheres, Speetonia colligata and Cruciellipsis cuvillieri in the Upper Ryazanian and Lower Hauterivian. Reconstructed surface water conditions, indicated by fluctuations in the assemblage compositions, suggest cool conditions for the Late Ryazanian, a cold climate for the Valanginian, and warm climatic conditions for the Hauterivian–Barremian. High meridonial temperature gradients and cool–cold climatic conditions in the high latitudes caused supposedly the formation of deep water in the South Anyui Gulf in the Late Ryazanian–Valanginian. Palaeoceanographic changes, reflected in a counter-balanced ocean current system in the Greenland–Norwegian Seaway, allowed Tethyan biota to spread as far north as North-East Greenland during the Late Ryazanian. [Copyright &y& Elsevier]

Abstract: We present a palaeoclimatic reconstruction of the last glacial cycle in Iberia (ca. 120,000–11,600cal yrs BP) based on multi-proxy reconstructions from lake sediments with robust chronologies, and with a particular focus on abrupt climate changes. The selected lake sequences provide an integrated approach from northern Iberia exploring temperature conditions, humidity variations and land-sea comparisons during the most relevant climate transitions of the last glacial period. Thus, we present evidence that demonstrates: (i) cold but relatively humid conditions during the transition from MIS 5 to MIS 4, which prevailed until ca. 60,000cal yrs BP in northern Iberia; (ii) a general tendency towards greater aridity during MIS 4 and MIS 3 (ca 60,000 to 23,500cal yrs BP) punctuated by abrupt climate changes related to Heinrich Events (HE), (iii) a complex, highly variable climate during MIS 2 (23,500 to 14,600cal yrs BP) with the “Mystery Interval” (MI: 18,500 to 14,600cal yrs BP) and not the global Last Glacial Maximum (LGM: 23,000 to 19,000cal yrs BP) as the coldest and most arid period. The last glacial transition starts in synchrony with Greenland ice records at 14,600cal yrs BP but the temperature increase was not so abrupt in the Iberian records and the highest humidity was attained during the Allerød (GI-1a to GI-1c) and not during the Bølling (GI-1e) period. The Younger Dryas event (GS-1) is discernible in northern Iberian lake records as a cold and dry interval, although Iberian vegetation records present a geographically variable signal for this interval, perhaps related to vegetation resilience. [Copyright &y& Elsevier]

Abstract: West Greenland has been intensively studied to reconstruct and better understand past relative sea level changes and deglacial history. This study extends these efforts by linking sea level and deglacial history to the sedimentary infill successions of Kangerlussuaq Fjord and associated landward valleys. Based on published and new land- and sea-based geophysical data, radiocarbon dates and geological observations we have characterized the infill and reconstructed the sedimentation history during the Holocene. Based on a revised sea level curve and data presented in this paper we defined three depositional phases. Phase I (>7000 yr BP) is represented by dominant glaciomarine deposition associated with a tide-water glacier system. As the Greenland Ice Sheet (GIS) continued to retreat it became land based. During phase II (7000–1500 yr BP) two separate depocenters formed. Keglen delta depocenter arose from a temporary stabilization phase of the GIS and prograded rapidly over the glaciomarine deposits of Phase I. Further inland, proglacial lake formation and subsequent sedimentary infill associated with the ongoing GIS retreat is represents the second depocenter. The Watson River connected both depocenters by a flood plain which transferred sediment from the GIS to the Keglen delta. Ongoing sea level fall due to glacio-isostastic uplift combined with a gradually cooler and dryer climate resulted in terrace formation along the Watson River flood plain. Around 4000 yr BP, the GIS margin reached its most landward location and began to advance to its present location. The final phase (Phase III; <1500 yr BP) is represented by a stabilized GIS position and a relative sea level rise which led to aggrading conditions near the present-day delta plain of Watson River. Simultaneously, subaqueous channels were formed at the delta front by hyperpycnal flows associated with jökulhlaup events. [Copyright &y& Elsevier]

Abstract: We use an ice marginal "threshold lake", Lower Nordbosø, in southern Greenland to record episodes when the southern Greenland Ice Sheet (sGIS) was close to the present extent, represented by beds of clastic sediments whereas gyttja-deposition reflects periods when the glacier was behind the threshold, and no glacial meltwater input. The results show that the sedimentation was initiated at c. 10.6 cal ka BP when the ice margin had reached the present extent following the deglaciation. After this the ice margin remained close to the present extent until c. 6.9 cal ka BP when it retreated behind the threshold and first reappeared with a clear glacial signal at c. 3.0–2.8 cal. ka BP and from c. 0.5 cal ka BP until the present. An overall good correlation between clastic input into Lower Nordbosø and IRD events from Narsaq Sound suggests that they represent a general glacial proximity signal of the sGIS. Our data demonstrates that the sGIS behaved less vigorously to Holocene climate changes compared to previous reconstructions. The ice sheet only retreated behind the present ice extent from c. 6.9 to 3.0 cal ka BP and c. 2.8 to 0.5 cal ka BP in the mountainous southern Greenland, whereas the more sensitive low-lying Qassimiut lobe was behind its present margin from c. 9 ka until the Little Ice Age. Accordingly, the ice marginal behavior in southern Greenland is not only governed by climate changes but also strongly influenced by the local topographic setting. [Copyright &y& Elsevier]

Abstract: A new centennial scale benthic foraminiferal record of late Holocene climate variability and oceanographic changes off West Greenland (Disko Bugt) highlights substantial subsurface water mass changes (e.g. temperature and salinity) of the West Greenland Current (WGC) over the past 3.6 ka BP. Benthic foraminifera reveal a long-term late Holocene cooling trend, which may be attributed to increased advection of cold, low-salinity water masses derived from the East Greenland Current (EGC). Cooling becomes most pronounced from c. 1.7 ka BP onwards. At this point the calcareous Atlantic benthic foraminiferal fauna decrease significantly and is replaced by an agglutinated Arctic fauna. Superimposed on this cooling trend, centennial scale variability in the WGC reveals a marked cold phase at c. 2.5 ka BP, which may correspond to the 2.7 ka BP cooling-event recorded in marine and terrestrial archives elsewhere in the North Atlantic region. A warm phase recognized at c. 1.8 ka BP is likely to correspond to the ‘Roman Warm Period’ and represents the warmest bottom water conditions. During the time period of the ‘Medieval Climate Anomaly’ we observe only a slight warming of the WGC. A progressively more dominant cold water contribution from the EGC on the WGC is documented by the prominent rise in abundance of agglutinated Arctic water species from 0.9 ka BP onwards. This cooling event culminates at c. 0.3 ka BP and represents the coldest episode of the ‘Little Ice Age’. Gradually increased influence of cold, low-salinity water masses derived from the EGC may be linked to enhanced advection of Polar and Arctic water by the EGC. These changes are possibly associated with a reported shift in the large-scale North Atlantic Oscillation atmospheric circulation pattern towards a more frequent negative North Atlantic Oscillation mode during the late Holocene. [Copyright &y& Elsevier]

Abstract: The revised study of stratotypes and key sections of the Karginsky regiostage in the West Siberian Plain with the use of 230Th/U dating determinations and advanced 14C dating indicated that many 14C ages obtained in the 1960–1970s were incorrect, and revealed the pre-Karginsky age of the Karginsky regional substage stratotypes adopted in the modern Pleistocene stratigraphic schemes of West Siberia. The available 230Th/U and 14C data along with the new paleobotanical record provided substantial refinement of the Late Pleistocene succession of paleoclimatic events in the West Siberian Plain. The 5e5 and 5e1 optima corresponding to climatic events of the Greenland ice core and 5e2 and 5e4 pessima are revealed in boreal West Siberia. The obtained 230Th/U dating determinations, even with their wide tolerance interval, make it possible to recognize not only the major but certain minor climatic events within the Kazantsevsky interglacial in boreal West Siberia. Beds corresponding to MIS 5c are recorded in the middle reaches of the Ob River. The preceding cooling was comparable with that of the later stages of the Zyryansky glaciation and is correlated with MIS 5d, which suggests the beginning of the Zyryansky glaciation occurred in the second half of MIS 5. The obtained records do not require elimination or reducing of the range of the Karginsky regiostage. However, the stratotypes of its regional sub-stages, chosen mainly in the 1960–1970s, appear to be invalid. [Copyright &y& Elsevier]

Abstract: Although progress has been made in recent years in reconstructing the environmental conditions at the Triassic/Jurassic Boundary (TJB), published records of atmospheric CO2 concentrations have been of low resolution and/or based on multi-taxon estimates. This is addressed here by reconstructing CO2 concentrations across the TJB using stomatal frequencies of four phylogenetically and ecologically distinct plant groups from two depositionally, geographically and taphonomically separate boundary sections in East Greenland and Northern Ireland, with stomatal proxy methods and regression analysis. The resulting CO2 records then are compared with an additional existing TJB record from a geological section in Sweden. The final results indicate that pre-TJB (Rhaetian), the CO2 concentration was approximately 1000ppm, that it started to rise steeply pre-boundary and had doubled to around 2000–2500ppm at the TJB. The CO2 concentration then remained elevated for some time post-boundary, before returning to pre-TJB levels in the Hettangian. These results are in very good accordance with published C-isotope, fire and leaf dissection records, and clearly indicate steeply rising and lingering CO2 concentration at the TJB. [Copyright &y& Elsevier]

Abstract: The present study is the first study on the stable oxygen isotope composition of the photosynthetic calcareous-walled dinoflagellate species Thoracosphaera heimii off NW Africa during the last 45,000yr. T. heimii based temperature estimates of sediment core GeoB 8507-3 were compared with those obtained from the stable oxygen isotopes of the planktic foraminifera Globigerina bulloides and Globigerinoides ruber (pink), and the Mg/Ca ratio of G. ruber (pink). We show that the isotopic composition of T. heimii and the temperature estimates based on the equation for inorganically precipitated calcite provide comparable results to those obtained from G. ruber (pink) isotopes and Mg/Ca ratios with exception of the Early Holocene and the Younger Dryas. The recently proposed palaeotemperature equation of Zonneveld et al. (2007), however, provides unrealistic temperature reconstructions that are about 16°C lower than those based on planktic foraminifera. Thus, this equation needs to be revised. The difference between T. heimii and G. bulloides isotopic and temperature reconstructions can be ascribed to differences in the ecology of both species, especially with regard to their depth habitat and/or seasonal production in the research area. All temperature proxies suggest comparable conditions during the last glacial and Holocene. Small differences between the reconstructed temperature values of T. heimii and the other proxies can be explained by differences in seasonal production of the individual species. The relatively low temperatures recorded by T. heimii at about 15,000 to 8,000yr BP are interpreted to reflect an increase in duration and/or intensity of the upwelling in the vicinity of the core site in comparison to the last glacial, with an abrupt and strong decrease of upwelling intensity and/or duration during the Early Holocene and the Younger Dryas. [Copyright &y& Elsevier]

Abstract: The chronology of late-glacial and Holocene ice fluctuations in East Greenland is important for documenting glacier response to climate change and for determining the mechanisms behind abrupt climate switches. Raised marine sediments and landforms suggest culmination of the late-glacial Milne Land Stade in Schuchert Dal alongside Scoresby Sund before ∼11,900–12,300calyr B.P. Ice in Schuchert Dal apparently receded during the later part of the Younger Dryas, consistent with the idea that this period was characterized by strong seasonality. A stillstand or slight readvance probably interrupted overall recession just prior to 11,000calyr B.P. In many locations, ice was back close to present positions by the start of the Holocene. The most extensive glacier advance of the Holocene occurred during the Little Ice Age and was restricted to within a few kilometers of present-day ice margins. [ABSTRACT FROM AUTHOR]

Abstract: We present the mapping of glacial landforms and sediments from northernmost Greenland bordering 100 km of the Arctic Ocean coast. One of the most important discoveries is that glacial landforms, sediments, including till fabric measurements, striae and stoss-lee boulders suggest eastward ice-flow along the coastal plain. Volcanic erratic boulders document ice-transport from 80 to 100 km west of the study area. We argue that these findings are best explained by local outlet glaciers from the Greenland Ice Sheet and local ice caps that merged to form a shelf-based ice in the Arctic Ocean and possibly confirming an extensive ice shelf in the Lincoln Sea between Greenland and Ellesmere Island. It is speculated that the shelf-based ice was largely affected by the presence of thick multiyear sea ice in the Arctic Ocean that prevented it from breaking up and forced the outlet glaciers to flow eastwards. During the initial retreat the coastal area was dammed by the shelf-based ice and kame and glaciolacustrine sediments were deposited up to 50 m above the marine limit before the final deglaciation and marine transgression. The timing of the shelf-based ice is constrained on land by dating glaciolacustrine sediments with OSL and marine molluscs with radiocarbon and by re-evaluating IRD events in cores from the Fram Strait. Results show that the shelf-based ice started to build-up as early as 30 cal ka BP and reached a maximum during the Last Glacial Maximum (LGM). The shelf-based ice began to retreat ca 16 ka to 10.3 cal ka BP before the final break-up, which took place ca 10.1 cal ka BP probably as a combined result of increased inflow of warm Atlantic water through the Fram Strait, a shallower halocline and higher summer temperatures, corresponding to orbital maximum solar insolation at this time. The existence of extensive shelf-based ice north of Greenland provides an important contribution to the understanding of the LGM glaciation history of the Arctic Ocean. [Copyright &y& Elsevier]

Abstract: This paper presents the glacial stratigraphy and palaeoenvironmental evolution around Constable Bugt, Johannes V. Jensen Land, located on the north coast of Greenland. This is a land of extreme climate: polar desert conditions and a coast bound by a permanent sea ice cover. Our data covers the period from the Last Glacial Maximum (LGM, 18–22 cal ka BP) into the Holocene. It records the history of a shelf-based glaciation with ice flowing eastward along the coast as well as two local valley glacier advances from the south during the Holocene. With ice on the coastal plain during the LGM, glaciolacustrine basins formed in marginal positions and in ice-dammed valleys to the south into the mountainous area of Peary Land. With the break-up of shelf-based ice there was a gradual marine inundation at which the marine limit formed at ∼45 m a.s.l. This initial early Holocene ice advance from the south formed prominent valley mouth moraines, especially in Sifs valley. Here, both glaciolacustrine and marine sediments were remoulded and/or dislocated as thrust blocks into a moraine ridge spanning more than 1 km in width and >60 m in height. Radiocarbon ages of sediments incorporated in this moraine, as well as from on-lapping sediments, suggest that the moraine formed between 9.6 and 6.3 cal ka BP. Based on 14C dating results, the youngest ice advance phase can be narrowed down to 14C ages between ∼5.5–5.0 cal ka BP. The recorded ice advances took place during the Holocene Thermal Maximum (HTM) for North Greenland, the last one close to the beginning of the Neoglacial cooling. During the HTM we have recorded a period of ∼2500 years during which the north coast of Greenland – as opposed to today – experienced an absence to very restricted occurrence of land-fast or multi-year sea ice. This observation can be explained by the altitudinal and temporal distribution of beach-ridge complexes that must have formed by wave action and thus requiring at least partial open-water conditions. With a moisture source at hand, we propose that this lead to enhanced precipitation in the near-coastal areas which, coupled to documented HTM cold reversals, caused a lowered glaciation limit, and led to a positive mass balance and subsequent ice advance. [Copyright &y& Elsevier]

Abstract: East Asian monsoon (EAM) evolution during the last deglaciation has been shown repeatedly to be aligned with paleoclimatic changes in the North Atlantic, based on climate reconstructions comparing Asian speleothem records with Greenland ice cores. In contrast to this finding, paleoclimatic reconstructions based on Lake Suigetsu sediment cores suggest that past EAM variability in Japan was not always coherent with climatic variability recorded in Greenland ice cores. We resolve this discrepancy using an absolute-dated stalagmite δ 18O record that covers the period between 15.5 and 10.7 thousand years before present (ka, before AD 1950). This stalagmite record is from nearby Maboroshi cave, Japan, and shows climate changes that are synchronous with those of Chinese caves and Greenland ice cores. Our results support an effective teleconnection between low- and high-latitudinal climate systems during the transitions into the Bølling–Allerød (BA) warming at 14.6 ka and the Younger Dryas cooling at 12.8 ka in the North Atlantic. However, our results also indicate monsoonal intensification during the BA, coincident with decreasing temperatures in Greenland from 14.6 to 12.8 ka. We explain this decoupling as a result of the interhemispheric bipolar seesaw climate system. Discrepancies between Lake Suigetsu radiocarbon age data sets and other radiocarbon calibration archives can also be removed when our Maboroshi record is used to adjust the Lake Suigetsu age model, as well as resolving temporal ambiguities in the Lake Suigetsu paleoclimate record. [ABSTRACT FROM AUTHOR]

Abstract: Paleoclimatic records show that the Greenland Ice Sheet consistently has lost mass in response to warming, and grown in response to cooling. Such changes have occurred even at times of slow or zero sea-level change, so changing sea level cannot have been the cause of at least some of the ice-sheet changes. In contrast, there are no documented major ice-sheet changes that occurred independent of temperature changes. Moreover, snowfall has increased when the climate warmed, but the ice sheet lost mass nonetheless; increased accumulation in the ice sheet''s center has not been sufficient to counteract increased melting and flow near the edges. Most documented forcings and ice-sheet responses spanned periods of several thousand years, but limited data also show rapid response to rapid forcings. In particular, regions near the ice margin have responded within decades. However, major changes of central regions of the ice sheet are thought to require centuries to millennia. The paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur. The evidence suggests nearly total ice-sheet loss may result from warming of more than a few degrees above mean 20th century values, but this threshold is poorly defined (perhaps as little as 2°C or more than 7°C). Paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming, or changes may have been induced by factors other than temperature, without having been recorded. [Copyright &y& Elsevier]

Abstract: Two coeval stalagmites from Katerloch Cave show pronounced intervals of low δ 18O values around 8.2, 9.1, and 10.0kyr (all ages are reported before the year 2000 AD) and represent an inorganic U–Th dated climate archive from the southeast of the European Alps, a region where only very few well-dated climate records exist. The O isotope curves, providing near-annual resolution, allow a direct comparison to the Greenland ice core records, as temperature was the primary factor controlling the O isotopic composition of Katerloch speleothems. The 8.2kyr climate anomaly lasted about one century, from 8196 to 8100yr, with a maximum amplitude of 1.1‰ at 8175yr. The event is characterized by a rapid onset and a more gradual demise and U–Th data as well as annual lamina counting support a rapid climate change towards cooler conditions within 10–20yr. There is no strong evidence that the 8.2kyr anomaly was superimposed on a pronounced longer-term cooling episode, nor do the new data support two separate cooling events within the 8.2kyr event as reported by other studies. Our record also shows a distinct climate anomaly around 9.1kyr, which lasted 70–110yr and showed a maximum amplitude of 1.0‰, i.e. it had a similar duration and amplitude as the (central) 8.2kyr event. Compared to the 8.2kyr event, the 9.1kyr anomaly shows a more symmetrical structure, but onset and demise still occurred within a few decades only. The different progression of the 8.2 (asymmetrical) and 9.1kyr anomaly (symmetrical) suggests a fundamental difference in the trigger and/or the response of the climate system. Moreover, both stalagmites show evidence of a climate anomaly around 10.0kyr, which was of comparable magnitude to the two subsequent events. Using a well constrained modern calibration between air temperature and δ 18O of precipitation for the study area and cave monitoring data (confirming speleothem deposition in Katerloch reflecting cave air temperature), a maximum cooling by ca 3°C can be inferred at 8.2 and 9.1kyr, which is similar to other estimates, e.g., from Lake Ammersee north of the Alps. The O isotopic composition of meteoric precipitation, however, is a complex tracer of the hydrological cycle and these temperature estimates do not take into account additional effects such as changes in the source area or synoptic shifts. Apart from that, the relative thickness of the seasonally controlled lamina types in the Katerloch stalagmites remains rather constant across the intervals comprising the isotopic anomalies, i.e. the stalagmite petrography argues against major shifts in seasonality during the early Holocene climate excursions. [Copyright &y& Elsevier]

Abstract: This paper is the first to summarize research on fluctuations of local glaciers in Greenland (e.g. ice caps and mountain glaciers independent of the Greenland Ice Sheet) during latest Pleistocene and Holocene time. In contrast to the extensive data available for fluctuations of the Greenland Ice Sheet, surprisingly little data exist to constrain local glacier extents. Much of the available research was conducted prior to wide-spread use of AMS radiocarbon dating and the advent of surface-exposure and luminescence dating. Although there is a paucity of data, generally similar patterns of local glacier fluctuations are observed in all regions of Greenland and likely reflect changes in paleoclimate, which must have influenced at least the margins of the Inland Ice. Absolute-age data for late-glacial and early Holocene advances of local glaciers are reported from only two locations: Disko (island) and the Scoresby Sund region. Subsequent to late-glacial or early Holocene time, most local glaciers were smaller than at present or may have disappeared completely during the Holocene Thermal Maximum. In general, local glacier advances that occurred during Historical time (1200–1940 AD) are the most extensive since late-glacial or early Holocene time. Historical documents and more recent aerial photographs provide useful information about local glacier fluctuations during the last ∼100 yrs. In all but one area (North Greenland), local glaciers are currently receding from Historical extents. [Copyright &y& Elsevier]

Abstract: The opening and closing of ocean gateways affects the global distribution of heat, salt, and moisture, potentially driving climatic change on regional to global scales. Between 65 and 45 million years ago (Ma), during the early Paleogene, exchange between the Arctic and global oceans occurred through two narrow and shallow seaways, the Greenland–Norway seaway and the Turgai Strait. Sediments from the Arctic Ocean suggest that, during this interval, the surface ocean was warm, brackish, and episodically enabled the freshwater fern Azolla to bloom. The precise mechanisms responsible for the development of these conditions in the Paleogene Arctic remain uncertain. Here we show results from an isotope-enabled, atmosphere-ocean general circulation model, which indicate that Northern Hemisphere climate would have been very sensitive to the degree of oceanic exchange through the Arctic seaways. We also present modelled estimates of seawater and calcite δ 18O for the Paleogene. By restricting these seaways, we simulate freshening of the surface Arctic Ocean to ~6 psu and warming of sea-surface temperatures by 2 °C in the North Atlantic and 5–10 °C in the Labrador Sea. Our results may help explain the occurrence of low-salinity tolerant taxa in the Arctic Ocean during the Eocene and provide a mechanism for enhanced warmth in the north western Atlantic. We propose that the formation of a volcanic land-bridge between Greenland and Europe could have caused increased ocean convection and warming of intermediate waters in the Atlantic. If true, this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates and supports a tectonic trigger hypothesis for the Paleocene Eocene Thermal Maximum (PETM). [Copyright &y& Elsevier]

The Late-Quaternary climate of Beringia remains unresolved despite the region's role in modulating glacial-interglacial climate and as the likely conduit for human dispersal into the Americas. Here, we investigate Beringian temperature change using an ∼32,000-year lacustrine record of leaf wax hydrogen isotope ratios (δ2H wax) from Arctic Alaska. Based on Monte Carlo iterations accounting for multiple sources of uncertainty, the reconstructed summertime temperatures were ∼3 °C colder (range: −8 to +3 °C) during the Last Glacial Maximum (LGM; 21-25 ka) than the pre-industrial era (PI; 2–0.1 ka). This ice-age summer cooling is substantially smaller than in other parts of the Arctic, reflecting altered atmospheric circulation and increased continentality which weakened glacial cooling in the region. Deglacial warming was punctuated by abrupt events that are largely synchronous with events seen in Greenland ice cores that originate in the North Atlantic but which are also controlled locally, such as by the opening of the Bering Strait between 13.4 and 11 ka. Our reconstruction, together with climate modeling experiments, indicates that Beringia responds more strongly to North Atlantic freshwater forcing under modern-day, open-Bering Strait conditions than under glacial conditions. Furthermore, a 2 °C increase (Monte Carlo range: −1 to +5 °C) over the anthropogenic era reverses a 6 °C decline (Monte Carlo range: −10 to 0 °C) through the Holocene, indicating that recent warming in Arctic Alaska has not surpassed peak Holocene summer warmth. • Alaska's climate history is evaluated using leaf wax hydrogen isotope ratios in a 32,000 year-long lacustrine record. • The record reveals mild ice-age cooling, abrupt deglacial climate events, strong Holocene cooling, and recent warming. • Proxy-model comparison highlights the importance of the Bering Strait opening as a control of Beringian climate. [ABSTRACT FROM AUTHOR]

The century-long 8.2 ka cold event interrupted early Holocene boreal warmth and may have halted retreat of Greenland ice-sheet margins during the last deglaciation. Here, we synthesize new and existing glacial geological data to assess the behavior of the southwest Greenland ice sheet during the 8.2 ka cold event. In southwest Greenland near the town of Kangerlussuaq, existing and new 10Be surface exposure ages demonstrate that deposition of the Keglen moraines ended at 8.0 ± 0.1 ka (n = 10, 1 outlier), with prior studies arguing that these moraines represented an ice-margin stillstand in response to the 8.2 ka cold event. However, new 10Be ages show that the southwest Greenland ice-sheet margin retreated from the Umîvît moraines, which lie 5–10 km outboard of the Keglen moraines, at 8.2 ± 0.2 ka (n = 11). Accordingly, we suggest that the southwest Greenland ice-sheet margin in the Kangerlussuaq region retreated 5–10 km during the 8.2 ka cold event. Farther south and inland from Nuuk, new 10Be boulder-on-bedrock ages adjacent to the modern ice-sheet margin demonstrate that the ice-margin was retreating with no moraine deposition at 8.2 ± 0.1 ka (n = 4, 1 outlier), with this retreat continuing up to at least ∼7.5 ka according to an existing threshold lake record. Therefore, we propose that the southwest Greenland ice-sheet margin underwent continued retreat during the 8.2 ka cold event in response to elevated early Holocene boreal summer insolation that overwhelmed the impacts from century-scale cooling. Caution should be used in assuming climatic causation for moraine deposition based on temporal correlation. • New 10Be ages in SW Greenland show ice retreat during the 8.2 ka cold event. • Elevated shortwave radiation may have offset the impacts of 8.2 ka cooling. • Moraine-age correlation with a cold period is not necessarily causation. [ABSTRACT FROM AUTHOR]

During the last deglaciation, North Atlantic climate abruptly warmed at the Bølling (∼14.7 ka), cooled into the Younger Dryas (∼12.9 ka) and abruptly warmed again into the Holocene (∼11.7 ka). While these events are defined by Greenland ice cores, there is still considerable uncertainty on Greenland ice-sheet margin responses to abrupt climate change. To refine the ice sheet's deglacial history, we present new cosmogenic nuclide surface exposure ages from boulders on bedrock at five sites in southernmost Greenland fjords located midway between the coast and inland ice margin. We find ice-sheet thinning below three local topographic highs at 12.7 ± 0.3 ka (n = 3), 13.1 ± 0.4 ka (n = 1, 2 outliers), and 12.3 ± 0.2 ka (n = 3), with up-fjord retreat at 12.5 ± 0.3 ka (n = 3) and 12.7 ± 0.2 ka (n = 4) based on two sites just above the mid-fjord marine limit. These mid-fjord 10Be ages therefore show southernmost Greenland ice-sheet thinning and retreat during the Younger Dryas. We hypothesize that this thinning and retreat was a response to ocean warming prior to the Holocene and/or summer shortwave radiative forcing during the Younger Dryas due to peak boreal summer insolation. Our results also support a previously hypothesized winter bias in proxy records of Younger Dryas atmospheric cooling, since a large summer cooling during the Younger Dryas could have counteracted the effects of ocean warming and direct radiative forcing, inhibiting ice-sheet retreat. • Southernmost Greenland ice-sheet margin thinned during the Younger Dryas. • Southernmost Greenland ice-sheet margin retreated during the Younger Dryas. • Greenland ice retreat was likely driven by summer insolation and ocean warming. [ABSTRACT FROM AUTHOR]

Abstract: The scientific knowledge of the Greenland and Antarctic ice sheets, and the subsequently derived Earth history, has been greatly increased during the past 50 years. Much of the new information was obtained from various studies made on a relatively small number of deep (300–400 m) and several very deep (some over 3000 m) ice cores, recovered from the inland regions of both ice sheets, by different national and international research teams. The beginning, development, and progress of deep polar ice core drillings and core studies is reviewed from the incipient pit study made by Ernst Sorge in 1930, through the trying efforts of three separate international core drilling projects mounted around 1950. The paper continues with a broad overview of the early role and achievements made by two related US Army Corps of Engineers research laboratories: the Snow, Ice and Permafrost Research Establishment (SIPRE), and the Cold Regions Research and Engineering Laboratory (CRREL), from the early-1950''s to the late-1980''s. International partnerships of CRREL with the University of Copenhagen, Denmark (1966), and the University of Bern, Switzerland (1962), established the foundation of polar ice core science. [Copyright &y& Elsevier]

Abstract: We present here a time series of Pb and Sr isotopes in Greenland ice over the last glacial cycle. The data were obtained by analysing the dust contained in small (less than 10 g) aliquots of sections of the GRIP (European Greenland ice core project) ice core. The concentrations of Pb, Ba and Sr vary by large factors of 70, 140 and 75 respectively over this time period and show a significant correlation with δ 18O, used as a proxy for temperature. Elemental ratios of Pb, Ba and Sr indicate the provenance of dust is mainly crustal with possible volcanic influences but the contribution from seawater is negligible. The Pb and Sr isotopic ratios change over time and form two distinct groups above and below a temperature corresponding to a δ 18O value of ∼ −39‰. While changing elemental concentrations may be explained by changes in wind strengths, the variation in isotopic composition appears to reflect climate induced changes in the source areas of dust deposited in the snow in Greenland. Available source data suggest that dust may originate from the Gobi Desert in central Asia in cooler periods and from glacial sediments adjacent to Greenland in warmer periods. [Copyright &y& Elsevier]

Abstract: Many studies have documented the existence of millennial-scale variability in the Earth system during the last glacial period. An increasing number of studies document the occurrence of similar millennial variability during glacial periods previous to the last one. Here we use the simplest possible thermal-bipolar seesaw model to consider this variability for the last four glacial periods. We invert this model and use the high-pass filtered Vostok stable isotope records to make a first, tentative, attempt to estimate high-latitude N. Hemisphere temperature variability over the last four glacial periods, beyond the reach of Greenland ice-core records. The model result is compared against the Vostok methane record, which shows rapid variations in parallel to Greenland temperature records during the last glacial period. A further comparison is carried out against the planktonic oxygen isotope of north Atlantic core ODP 980. There is agreement between the records on the existence of similar millennial-scale variability during the last three glacial periods with very similar characteristics to the variability during the last glacial cycle. [Copyright &y& Elsevier]

Abstract: It is commonly assumed that elevated, passive continental margins have remained uplifted since the time of rifting. In many areas, e.g. Scandinavia, the timing and extent of uplift movements are difficult to determine because the uplifted area consists almost exclusively of ancient metamorphic rocks. However, the preserved Mesozoic–Cenozoic sedimentary and volcanic record of West Greenland makes this a key area for studying the uplift of passive continental margins. We have combined apatite fission-track analysis data with landform analysis to investigate the development of West Greenland landscapes across areas with substantially different geology. We show that the present-day mountains of West Greenland (65–71°N) are the end result of three Cenozoic phases of uplift and erosion. The first phase that began between 36 and 30 Ma led to the formation of a planation surface during the Oligocene–Miocene. This surface was offset by reactivated faults, resulting in megablocks that were tilted and uplifted to present-day altitudes of up to 2 km in two phases that began between 11 and 10 and between 7 and 2 Ma. These late Neogene uplift phases postdate rifting by c. 50 million years and sea-floor spreading west of Greenland by c. 30 million years, while the first of these phases predates onset of glaciation in Greenland by c. 3 million years. The similarity in morphology between West Greenland and other rifted continental margins suggests that uplift of rift flanks to present-day elevations may often post-date rifting significantly. The regional nature of the uplift movements along passive margins and their considerable distance from active plate boundaries suggest that the causal mechanisms must be located in the deep crust or the upper mantle where the thickness of the crust and lithosphere changes substantially over a short distance. [Copyright &y& Elsevier]

Abstract: Two new cores from Disko Bugt, a large marine embayment in West Greenland, are used to assess the deglacial chronology and palaeoceanography of the area during the early Holocene. Deglaciation of the main part of Disko Bugt is directly dated for the first time to a minimum of ca 10.2kacal. BP. By this time the Jakobshavn Isbrae ice stream had retreated to the eastern margins of Disko Bugt. Initial deglaciation took place before the relatively warm West Greenland Current (WGC) was initiated. A strengthening in the WGC is identified from ca 9.2kacal. BP accompanied by retreat of the ice stream to a shallow bank immediately west of the present day Jakobshavn Isfjord. While in this position the calving and melting ice stream produced large volumes of sediment and meltwater. The large volumes of meltwater prevented the relatively warm waters of the WGC reaching the eastern margins of Disko Bugt. The ice stream remained grounded on this bank for over a thousand years until ca 7.9kacal. BP when reduced sedimentation rates and an increase in boreal fauna point to its retreat inside the present day fjord system. [Copyright &y& Elsevier]

Leads, lags, or synchronies in climatic events among different regions are key to understanding mechanisms of climate change, as they provide insights into the causal linkages among components of the climate system. The well-studied transition from the Lateglacial to early Holocene (ca. 16–10 ka) contains several abrupt climatic shifts, making this period ideal for assessing the spatio-temporal structure of climate change. However, comparisons of timings of past climatic events among regions often remain hypothetical because site-specific age scales are not necessarily synchronised to each other. Here we present new pollen data (n = 510) and mean annual temperature reconstruction from the annually laminated sediments of Lake Suigetsu, Japan. Suigetsu's 14C dataset is an integral component of the IntCal20 radiocarbon calibration model, in which the absolute age scale is established to the highest standard. Its exceptionally high-precision chronology, along with recent advances in cosmogenic isotope studies of ice cores, enables temporally coherent comparisons among Suigetsu, Greenland, and other key proxy records across regions. We show that the onsets of the Lateglacial cold reversal (equivalent to GS-1/Younger Dryas) and the Holocene were synchronous between East Asia and the North Atlantic, whereas the Lateglacial interstadial (equivalent to GI-1/Bølling-Allerød) started ca. two centuries earlier in East Asia than in the North Atlantic. Bimodal migration (or 'jump') of the westerly jet between north and south of the Tibetan plateau and Himalayas may have operated as a threshold system responsible for the abruptness of the change in East and South (and possibly also West) Asia. That threshold in Asia and another major threshold in the North Atlantic, associated with switching on/off of the Atlantic meridional overturning circulation (AMOC), were crossed at different times, producing a multi-centennial asynchrony of abrupt changes, as well as a disparity of climatic modes among regions during the transitional phases. Such disparity may have disturbed zonal circulation and generated unstable climate during transitions. The intervening periods with stable climate, on the other hand, coincided with the beginnings of sedentary life and agriculture, implying that these new lifestyles and technologies were not rational unless climate was stable and thus, to a certain extent, predictable. [Display omitted] • The Lateglacial cold reversals in Lake Suigetsu (Japan) and NGRIP were synchronous. • The Lateglacial interstadial in Lake Suigetsu began earlier than in Greenland. • 'Postglacial' in Asia started already at ca. 15.0 kyr BP. • S–N migration of the westerly jet generated abrupt deglacial warming in Asia. • Climatic stability was the key for humans to commence agriculture. [ABSTRACT FROM AUTHOR]

A precisely dated speleothem isotope record from the Sieben Hengste cave system, Switzerland, reveals a Last Interglacial (LIG) climate optimum centred at 128.1 ± 1.2 ka. The oxygen isotope signal is consistent with a temperature-dominated record and shows a strong correlation with the modelled Greenland δ18O signal. The comparison with speleothems formed during the Last Glacial Maximum (LGM) in the same cave indicates a 4–5‰ difference in δ18O between peak LIG and peak LGM conditions, suggesting peak LIG temperatures being up to 3 °C higher than the Holocene average. Pollen extracted from the stalagmite indicates a vegetation response delayed by up to 3 ka with maximum pollen concentrations recorded at 125 ± 2.2 ka. Our results support a regional vegetation dominated by thermophile tree species including Corylus (hazel), Quercus robur-type (oak), Ulmus (elm), Tilia (lime tree) and Hedera (ivy), consistent with slightly warmer conditions than today. Despite the relatively low pollen concentration, the speleothem-based pollen spectra are consistent with regional pollen assemblage zones from paleolake sediments and provide the first direct paleovegetation evidence of thermophilization during the LIG at high altitudes in the Alps. • A Last Interglacial speleothem underlines the ocean control on the North Alpine climate. • The speleothem δ18O signal reveals a temperature-dominated record. • The Last Interglacial thermal optimum is dated at 128.1 ± 1.2 ka. • A delay is observed between the temperature and local vegetation response. • First palynological evidence of high-altitude thermophilization during the LIG. [ABSTRACT FROM AUTHOR]

The Late Pleistocene to Holocene transition in the Northern Hemisphere was characterized by abrupt millennial-scale climatic changes testified in the Alpine Chain by proxy records derived from glacial landforms and deposits. A detailed reconstruction of the paleo-glaciers during the deposition of the pre-Little Ice Age (LIA) moraines and newly obtained 10Be exposure ages provide information on the timing of a glacier advance in the Gran Paradiso Group (Western Alps, Italy) related to the regional Egesen stadial as a response to the climatic deterioration at around 12.9–11.7 ka (corresponding to the Younger Dryas in northern Europe and to the Greenland stadial 1 in the INTIMATE event stratigraphy). The study area represents a key site to define the behaviour of the Egesen paleo-glaciers, since they are located in a significant climatic area between the moister Maritime Alps and the Northern Alps. The ELA reconstructions and the comparison with other Alpine sectors provide evidence that current relatively drier conditions in the area postdate the LGM and were already present during the Egesen stadial. Our results support a strong positive YD Arctic Oscillation index, which led to drier conditions in southern Europe and caused negative winter precipitation anomalies. • First chronological constraint of the Egesen stadial in the Gran Paradiso. • ELAs during the Egesen stadial among the highest values recorded in the entire Alps. • Seasonal paleoclimatic information at the ELA reconstructed for the Egesen stadial. • Current relatively dry conditions were established at least since the Egesen stadial. [ABSTRACT FROM AUTHOR]

We explore Holocene climatic changes recorded by geochemical proxies in a single, well-dated, stalagmite from the northern Zagros Mountains of Iran, a region where stalagmite records have so far only provided short glimpses of Holocene climatic changes. Stalagmite KT-3 from Katalekhor Cave began growing ∼9.5 ka under wet early Holocene conditions coincident with the timing of Sapropel 1. At this time δ18O values were at or below −9.0‰, stalagmite growth diameter was at its maximum, 234U/238U 0 activity values were low and trace element contents indicate flushing of the epikarst. Progressive reduction in winter precipitation amount after 7.0 ka, is recorded by increasing δ18O and 234U/238U 0 activity values and reduction in trace element contents and growth diameter until ∼2.0 ka. These trends follow the reduction in summer insolation and agree with model-simulated changes in total rainfall and rainwater isotopes. Sub-centennial-scale variability is not a feature of the δ18O or trace element records; this suggests a stable winter recharge regime, a feature that might militate against KT-3 δ18O recording changes in the seasonality of rainfall. KT-3 δ13C compositions are enriched relative to lower altitude stalagmites in the Levant, implying low soil CO 2 contribution (thin montane soils). However, a broadly decreasing millennial-scale trend in δ13C suggests that soil carbon contributions increased with time despite the progressive reduction in winter precipitation amount. The δ13C changes probably reflect decreasing summer temperatures and less extreme wintertime coldness, driven by reducing summer- and increasing winter-insolation respectively. These combined effects decreased effective evaporation and improved soil-moisture availability favouring vegetation development during the growth season. The δ13C values also show ∼1.5‰ centennial-scale variability with higher δ13C values between 9.0 and 8.7 ka, 8.3–7.7 ka, 6.5–5.5 ka, 5.4–4.5 ka and ∼4.3–2.0 ka: three of these correspond with Rapid Climate Change (RCC) events based on non-seasalt potassium (K+) in Greenland ice cores. Higher δ13C values indicate poor soil development caused by aridity. The centennial-scale δ13C anomaly (8.3–7.7 ka) is in part overprinted by the ∼160 year-long, 8.2 ka cold/dry event, but culmination ∼7.7 ka corresponds with other records suggesting an intensified Siberian High Pressure system affecting regional climate. The centennial-scale δ13C anomaly between 4.3 and 2.0 ka overlaps the 2.65 to 2.50 ka 'Assyrian megadrought' evident in stalagmite stable isotope records in northern Iraq. The KT-3 record is key in better understanding Holocene climate change in the central Zagros region, representative of montane 'fertile crescent' environments. • New 'fertile crescent' Holocene stalagmite palaeoclimate record from the Zagros Mountains of Iran. • Increasing δ18O (7.0-2.0 ka) indicate reducing winter precipitation amount which follows decrease in summer insolation. • Sub-centennial variability is not a feature of the δ18O or trace element records indicating a stable winter recharge regime. • δ13C compositions indicate thin, montane soils, higher values driven by aridity. • Three centennial-scale periods of higher δ13C (∼ 1.5‰) correspond with Rapid Climate Change events in Greenland ice cores. [ABSTRACT FROM AUTHOR]

Human paleodemographic changes were related to environmental fluctuations for the North American Arctic and boreal region, including Greenland. Using the frequency of archaeological radiocarbon dates as a proxy for population size, past changes in population were estimated and quantitatively examined in relation to reconstructions of temperature and sea ice conditions. This analysis was conducted across three spatial scales in order to better identify potential climate impacts on population size: the entire area, four major cultural-environmental regions and sixteen sub-regions. The timing of initial settlement differed by region, and population size fluctuated through time, but there was nevertheless an overall, accelerating increase in most areas. There was a high correspondence between millennial and centennial-scale climate variability and paleodemographic changes across the region, with population size generally increasing during warmer periods and decreasing during cooling episodes. Late Holocene cooling (neoglaciation) triggered a nearly-synchronous population decline across the entire region at 3.9 ka, a time when significant societal disruptions have been identified around the world, and are here shown in the Arctic. Decreasing temperatures and increased sea ice coverage also influenced large-scale migration patterns of Paleo-Inuit peoples as well as their cultural evolution. The growth of Paleo-Inuit populations after 3 ka during continued climate cooling is consistent with archaeological evidence suggesting Paleo-Inuit technological change enabled adaptations to increased sea ice. • Multi-scale analysis of human-environment interactions discerns local and regional population dynamics. • Climate changes caused increases and decreases in population in the Arctic and Subarctic. • Neoglaciation triggered continental-scale population decline across the north. • Population density underwent long-term growth despite climate-induced regional decreases. [ABSTRACT FROM AUTHOR]