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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]

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]

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]

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]

Understanding the dynamics that drove past abrupt climate changes, such as the Dansgaard-Oeschger (DO) events, depends on combined proxy evidence from disparate archives. To identify leads, lags and synchronicity between different climate system components, independent and robust chronologies are required. Cryptotephrochronology is a key geochronological tool as cryptotephra horizons can act as isochrons linking disparate and/or distant records. Here, we investigated marine sediment core MD99-2284 from the Norwegian Sea to look for previously identified Greenland ice core cryptotephra horizons and define time-parallel markers between the archives. We explored potential secondary transport and depositional mechanisms that could hamper the isochronous integrity of such horizons. We identified six cryptotephra layers of which four correlate to previously known Greenland ice core horizons. None of those were identified in other marine cores and thus, this study contributes greatly to the North Atlantic tephra framework tripling the original amount of existing isochrons between ca. 25 and 60 ka b2k. The latter allow a synchronization between MD99-2284 and the Greenland ice cores between ca. 32–40 ka b2k, which is, in the North Atlantic, the shortest time-interval during the Last Glacial Period to be constrained by four independent tephra isochrons. These findings provide essential tephra-based evidence for synchronous and rapid oceanic and atmospheric temperature rises during the Greenland Stadial-Interstadial transitions. Furthermore, it enables us to estimate the average peak-duration of interstadial temperature overshoots at approximately 136 years. As such, this well-targeted high-resolution investigation successfully demonstrates the use of cryptotephra for geochronological purposes in the marine realm. • Six distinct cryptotephra deposits are discovered for the first time in marine sediment core MD99-2284. • The existing amount of isochrons between ca. 25 and 60 ka b2k is tripled by four new ones. • Four new tephra isochrons allow for a highly detailed synchronization of disparate palaeo records. • Oceanic and atmospheric temperature changed synchronously over the GS-GI transitions. • The average peak-duration of interstadial temperature overshoots is estimated at ca. 136 years. [ABSTRACT FROM AUTHOR]

The regional patterns and timing of the Younger Dryas cooling in the North Atlantic realm were complex and are mechanistically incompletely understood. To enhance understanding of regional climate patterns, we present molecular biomarker records at subannual to annual resolution by mass spectrometry imaging (MSI) of sediments from the Lake Meerfelder Maar covering the Allerød-Younger Dryas transition. These analyses are supported by conventional extraction-based molecular-isotopic analyses, which both validate the imaging results and constrain the sources of the target compounds. The targeted fatty acid biomarkers serve as a gauge of the response of the local aquatic and terrestrial ecosystem to climate change. Based on the comparison of our data with existing data from Meerfelder Maar, we analyse the short-term environmental evolution in Western Europe during the studied time interval and confirm the previously reported delayed hydrological response to Greenland cooling. However, despite a detected delay of Western European environmental change of ∼135 years, our biomarker data show statistically significant correlation with deuterium excess in Greenland ice core at ∼ annual resolution during this time-transgressive cooling. This suggests a coherent atmospheric forcing across the North Atlantic realm during this transition. We propose that Western European cooling was postponed due to major reorganization of the westerlies that were intermittently forcing warmer and wetter air masses from lower latitudes to Western Europe and thus resulted in delayed cooling relative to Greenland. • Application of MSI to obtain molecular records at ultra-high temporal resolution. • An annually resolved fatty acid data from the Lake Meerfelder Maar covering the Allerød-Younger Dryas transition. • Application of molecular-isotopic analyses to constrain the sources of the target fatty acids. • Confirmation of previously reported delayed hydrological response to Greenland cooling. [ABSTRACT FROM AUTHOR]