North Atlantic Realm Research Articles

Reconstructing Younger Dryas ground temperature and snow thickness from cave deposits

Abstract. The Younger Dryas stadial was characterised by a rapid shift towards cold-climate conditions in the North Atlantic realm during the last deglaciation. While some climate parameters including atmospheric temperature and glacier extent are widely studied, empirical constraints on permafrost temperature and snow thickness are limited. To address this, we present a regional dataset of cryogenic cave carbonates (CCCs) from three caves in Great Britain that formed at temperatures between −2 and 0 °C. Our CCC record indicates that these permafrost temperatures persisted for most of the Younger Dryas. By combining ground temperatures with surface temperatures from high-resolution ground-truthed model simulations, we demonstrate that ground temperatures were approximately 6.6 ± 2.3 °C warmer than the mean annual air temperature. Our results suggest that the observed temperature offset between permafrost and the atmosphere can be explained by an average snow thickness between 0.2 and 0.9 m, which persisted for 233 ± 54 d per year. By identifying modern analogues from climate reanalysis data, we demonstrate that the inferred temperature and snow cover characteristics for the British Isles during the Younger Dryas are best explained by extreme temperature seasonality, comparable to continental parts of today's Arctic Archipelago. Such a climate for the British Isles necessitates a winter sea ice margin at approximately 45° N in the North Atlantic Ocean.

Bioproductivity and vegetation changes documented in Eifel maar lake sediments (western Germany) compared with speleothem growth indicating three warm phases during the last glacial cycle

Understanding supra-regional climate variability such as the changes in the North Atlantic realm is important to identify the drivers of the climate system. In this study maar lake sediments from the Eifel (western Germany) were analysed with a multi-proxy approach and compared to central and western European speleothem growth phases.Corg (chlorins) and the pollen assemblage were analysed from two sediment cores of the Hoher List infilled maar lake. To generate Corg (chlorins) and pollen records covering the entire last 130,000 yr b2k (years before year 2000 CE), the data from this study were stacked with published data from other Eifel maar lake sediment cores (Sirocko et al., 2013, 2021, 2022). The sediment cores from Hoher List infilled maar lake were dated by marker tephra layers giving chronological anchor points and the precise dating of the sediment cores was performed by the tuning of the Corg (chlorins) records to the NGRIP δ18O record (Rasmussen et al., 2014). The speleothems, whose growth phases are compared to the lake sediment proxy records, were compiled from the literature as well as speleothems from Dechencave (western Germany) dated by the 230Th/U-method in this study.The Corg (chlorins) variability shows the bioproductivity in the maar lake, which is related to water temperature and corresponds to the Greenland Interstadials (GIs) in the NGRIP δ18O record indicates its dependence on supra-regional climate variations in the North Atlantic. The pollen record shows three periods of forest with temperate forest species, during the Eemian, early Marine Isotope Stage (MIS) 3, and the Holocene. Speleothem growth in four caves in central and western Europe (Dechencave, Spannagel Cave, Hölloch Cave, Villars Cave) is predominantly sensitive to cold periods with glaciers and/or permafrost conditions above the caves inhibiting speleothem growth. The forested phases and phases of high bioproductivity in the Eifel correspond well with phases of speleothem growth indicating three warm phases in central Europe during the last glacial cycle.

Weakened AMOC related to cooling and atmospheric circulation shifts in the last interglacial Eastern Mediterranean

There is limited understanding of temperature and atmospheric circulation changes that accompany an Atlantic Meridional Overturning Circulation (AMOC) slowdown beyond the North Atlantic realm. A Peqi’in Cave (Israel) speleothem dated to the last interglacial period (LIG), 129–116 thousand years ago (ka), together with a large modern rainfall monitoring dataset, serve as the base for investigating past AMOC slowdown effects on the Eastern Mediterranean. Here, we reconstruct LIG temperatures and rainfall source using organic proxies (TEX86) and fluid inclusion water d-excess. The TEX86 data show a stepwise cooling from 19.8 ± 0.2° (ca. 128–126 ka) to 16.5 ± 0.6 °C (ca. 124–123 ka), while d-excess values decrease abruptly (ca. 126 ka). The d-excess shift suggests that rainfall was derived from more zonal Mediterranean air flow during the weakened AMOC interval. Decreasing rainfall d-excess trends over the last 25 years raise the question whether similar atmospheric circulation changes are also occurring today.

First eurhinodelphinid dolphin from the Paratethys reveals a new family of specialised echolocators

ABSTRACT Eurhinodelphinids are a family of extremely long-snouted dolphins that once was widespread across the North Atlantic realm, but so far has not been recorded from the epicontinental Paratethys Sea. Here, we describe a new specimen of Xiphiacetus cristatus, including the cranium, left ear bones and a partial mandible, from the Middle Miocene (Badenian) of Austria. Our new fossil is the first record of this species outside the North Atlantic proper, and the first unequivocal record of eurhinodelphinids from the Paratethys. Its presence suggests a local invasion via the Mediterranean, and corroborates the persistence of an active marine gateway between the Mediterranean and the Central Paratethys throughout the Middle Miocene. Measurements of the bony labyrinth reveal that X. cristatus likely employed narrow-band high-frequency echolocation, making eurhinodelphinids only the second extinct odontocete family with this trait. Marked non-orthogonality of the semicircular canals suggests that X. cristatus was unsuited to rapid head movements, and thus more likely a benthic forager than a snap feeder.

Jet transitions caused multiple abrupt droughts in the Asian summer monsoon margin during Holocene times

The Asian Summer Monsoon (ASM) margin is vulnerable to climate change and a distinct boundary of population and archeological sites exists along the margin. Although lots of studies have been undertaken along the margin, the Holocene history of climate variation is highly debated; for example, whether the climatic optimum occurred in the early Holocene or middle Holocene. In addition, moisture variations on millennial to centennial timescales remain unclear. In this study, we reconstruct moisture variation at the modern junction of the ASM and the Westerlies based on a well-dated (13.3–0.5 ka) loess section in northwest China. On an orbital timescale, moisture variations generally follow changes in insolation with the longest and most intense humid period from 11.3 ka to 8.7 ka, supporting the concept of an early Holocene climatic optimum in the ASM margin. On millennial to centennial timescales, four sequences of long-term gradual wetting and subsequent abrupt drought are noted, i.e., thousands of years were required to reach a favorable environment in the ASM margin, while in only a few hundred years of drought would occur subsequently. Terminations of humid periods correspond to the occurrences of cold events in the North Atlantic realm, indicating an important role for the Atlantic Meridional Overturning Circulation (AMOC) on millennial to centennial timescales. We suggest solar insolation and the AMOC as the dominant factors on orbital timescale and millennial to centennial timescales, respectively. Both factors modulate moisture variations in the ASM margin by influencing the interplay between the ASM and the Westerlies.

Precise timing of MIS 7 substages from the Austrian Alps

Abstract. Investigating the precise timing of regional-scale climate changes during glacial terminations and the interglacial periods that follow is key to unraveling the mechanisms behind these global climate shifts. Here, we present a high-precision time series of climate changes in the Austrian Alps that coincide with the later portion of Termination III (TIII), the entire penultimate interglacial (Marine Isotope Stage (MIS) 7), Termination IIIa (TIIIa), and the penultimate glacial inception (MIS 7–6 transition). Using state-of-the-art mass spectrometry techniques, we have constructed a uranium-series chronology with relative age uncertainties averaging 1.7 ‰ (2σ) for our study period (247 to 191 thousand years before present, ka). Results reveal the onset of warming in the Austrian Alps associated with TIII at 242.5 ± 0.2 ka and the duration of MIS 7e warming between 241.8 and 236.7 (±0.6) ka. An abrupt shift towards higher δ18O values at 216.8 ka marks the onset of regional warming associated with TIIIa. Two periods of high δ18O values (greater than −10 ‰ Vienna Pee Dee Belemnite (VPDB)) between 215.9–213.3 and 204.3–197.5 (±0.4) ka coincide with interglacial substages MIS 7c and 7a, respectively. Multiple fluorescent inclusions suggest a partial retreat of the local Alpine glacier during peak obliquity forcings at 214.3 ± 0.4 ka. Two newly collected stalagmites from Spannagel Cave (SPA146 and 183) provide high-resolution replications of the latter portion of the MIS 7a-to-6e transition. The resulting multi-stalagmite record reveals important chronological constraints on climate shifts in the Austrian Alps associated with MIS 7 while offering new insight into the timing of millennial-scale changes in the North Atlantic realm leading up to TIII and TIIIa.

Constraining two climate field reconstruction methodologies over the North Atlantic realm using pseudo-proxy experiments

This study presents pseudo-proxy experiments to quantify the reconstruction skill of two climate field reconstruction methodologies for a marine proxy network subject to age uncertainties. The BARCAST methodology (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) is tested for sea surface temperature (SST) reconstruction for the first time over the northern North Atlantic region, and compared with a classic analogue reconstruction methodology. The reconstruction experiments are performed at annual and decadal resolution. We implement chronological uncertainties inherent to marine proxies as a novelty, using a simulated age-model ensemble covering the past millennium. Our experiments comprise different scenarios for the input data network, with the noise levels added to the target variable extending from ideal to realistic. Results show that both methodologies are able to reconstruct the Summer mean SST skillfully when the proxy network is considered absolutely dated, but the skill of the analogue method is superior to BARCAST. Only the analogue method provides skillful correlations with the true target variable in the case of a realistic noisy and age-uncertain proxy network. The spatiotemporal properties of the input target data are partly contrasting with the BARCAST model formulations, resulting in an inferior reconstruction ensemble that is similar to a white-noise stochastic process in time. The analogue method is also successful in reconstructing decadal temperatures, while BARCAST fails. The results contribute to constraining uncertainties in CFR for ocean dynamics which are highly important for climate across the globe.

Benthic foraminiferal faunas associated with cold‐water coral environments in the North Atlantic realm

AbstractSurface benthic foraminiferal assemblages associated with cold‐water coral mounds and reefs from the Irish margin and Norwegian shelf (North‐east Atlantic) are for the first time compared quantitatively. Results indicate that the considered sites share a common assemblage, dominated by elevated epibenthic and distinct infaunal species. This surface assemblage is typical of environments that are subject to strong bottom‐water turbulence with enhanced food availability. It provides a benchmark for comparison with fossil benthic foraminiferal assemblages from past cold‐water coral environments. Similar to macrofaunal and megafaunal communities, surface benthic foraminiferal diversity is higher on reefs and mounds than in surrounding off‐mound/off‐reef sediments. Benthic foraminiferal diversity is highest within the living coral macrohabitat, possibly as a result of enhanced availability and variety of food sources, and ecological niche separation. Indeed, living coral generally thrives on the summits or flanks of reefs and mounds where food availability is most important. The second part discusses the use of fossil benthic foraminiferal assemblages as palaeoceanographic proxies from past cold‐water coral environments. The overview of previous observations demonstrates that benthic foraminifera are valuable tools to reconstruct past bottom‐water oxygenation, bottom‐water currents and surface productivity, all of which are key environmental variables controlling cold‐water coral growth. Moreover, the advantages of a detailed investigation of benthic foraminiferal assemblages within cold‐water coral environments are compared to other palaeoceanographic proxies. This study highlights that benthic foraminiferal assemblages are an often overlooked proxy within cold‐water coral environments, despite yielding valuable information.

A new delphinid from the lower Pliocene of the North Sea and the early radiations of true dolphins

Abstract. With a remarkable exception for the Mediterranean, the worldwide Pliocene record of true dolphins (Cetacea, Odontoceti, Delphinidae) remains scarce, in stark contrast with the large number of extant species testifying to the evolutionary success of this family. Based on a fragmentary skull discovered in lower Pliocene deposits (Zanclean, 5 to 4.4 Ma) of the Kattendijk Formation in the Antwerp harbour (Belgium, southern margin of the North Sea basin), we describe here a new delphinid species, Pliodelphis doelensis gen. et sp. nov. This small dolphin with cranial dimensions in the range of the short-beaked common dolphin Delphinus delphis can be distinguished from other extinct and extant delphinids by a combination of cranial features including the maxilla being significantly narrower than the premaxilla at a short distance anterior to the antorbital notch in dorsal view, the maximum opening of the mesorostral groove being located at the level of the antorbital notches, a transversely wide and anteroposteriorly long dorsal exposure of the presphenoid anterior to the bony nares, and all dorsal infraorbital foramina being located posterior to the premaxillary foramina. P. doelensis constitutes the first member of the family described from the early Pliocene of the North Sea basin and, for the whole North Atlantic realm, only the third outside the Mediterranean. This new record contributes thus to our understanding of the poorly known Pliocene radiation(s) of true dolphins.

EURHINODELPHINIDS FROM THE EARLY MIOCENE OF PERU: FIRST UNAMBIGUOUS RECORDS OF THESE HYPER-LONGIROSTRINE DOLPHINS OUTSIDE THE NORTH ATLANTIC REALM

Among the many hyper-longirostrine dolphins (Odontoceti) from the Miocene, members of the family Eurhinodelphinidae bear two highly distinctive cranial features: a long and edentulous premaxillary portion of the rostrum and a mandible that is significantly shorter than the rostrum. Until now, unambiguously attributed members of this clade were only recorded from early to middle Miocene deposits of the North Atlantic realm (east coast U.S.A., North Sea Basin, and Mediterranean). In this work we describe and compare two partial skulls of longirostrine dolphins from late early Miocene (Burdigalian, 19.25-18 Ma) marine deposits of the Chilcatay Formation, in the East Pisco Basin (southern coast of Peru), preserving rostral and mandibular material, as well as ear bones. Based on these specimens we report diagnostic remains attributable to this family for the first time for the whole Southern Hemisphere and the whole Pacific Ocean. This major expansion of eurhinodelphinids' palaeogeographic distribution contrasts with their proposed shallow-water, coastal environments; it suggests a new dispersal route for members of the family across the Central American Seaway; and it further highlights the similarities between the odontocete faunas of the southeastern Pacific and North Atlantic realm during the Miocene. Better-preserved eurhinodelphinid specimens from the odontocete-rich Chilcatay Formation will allow for a more detailed comparison with North Atlantic members of the family.

Stable isotopes in cave ice suggest summer temperatures in east-central Europe are linked to Atlantic Multidecadal Oscillation variability

Abstract. The climate of east-central Europe (ECE) is the result of a combination of influences originating in the wider North Atlantic realm, the Mediterranean Sea, and the western Asian and Siberian regions. Previous studies have shown that the complex interplay between the large-scale atmospheric patterns across the region results in strongly dissimilar summer and winter conditions on timescales ranging from decades to millennia. To put these into a wider context, long-term climate reconstructions are required, but, largely due to historical reasons, these are lacking in ECE. We address these issues by presenting a high-resolution, radiocarbon-dated record of summer temperature variations during the last millennium in ECE, based on stable isotope analysis of a 4.84 m long ice core extracted from Focul Viu Ice Cave (Western Carpathians, Romania). Comparisons with both instrumental and proxy-based data indicate that the stable isotope composition of cave ice records the changes in summer air temperature and has a similar temporal evolution to that of the Atlantic Multidecadal Oscillation on decadal to multidecadal timescales, suggesting that changes in the North Atlantic are transferred, likely via atmospheric processes towards the wider Northern Hemisphere. On centennial timescales, the data show little summer temperature differences between the Medieval Warm Period (MWP) and the Little Ice Age (LIA) in eastern Europe. These findings are contrary to those that show a marked contrast between the two periods in terms of both winter and annual air temperatures, suggesting that cooling during the LIA was primarily the result of wintertime climatic changes.

Is High Topography Around the North Atlantic Supported From the Upper Mantle?

AbstractThe traveltime residuals of 393 receiver sites with more than 21,000 P wave and 9,700 S wave arrivals are used to investigate the upper‐mantle P and S wave velocity structure down to the depth of 500 km beneath the regions of high topography of the North Atlantic Caledonian crust. In east Greenland, we observe high‐velocity anomalies beneath high topography. In northern Norway and Sweden, a stable thick lithosphere beneath both the high topography and the Baltic shield exists. Only southern Norway exhibits a weak correlation between high topography and low‐velocity anomalies of P and S waves. Consequently, the correlation of topography versus average relative traveltime residuals in four regions of proposed Cenozoic epeirogenic uplift reveals positive correlation only in southern Norway and negative or absence of correlation in other regions. These results show that high topography does not correlate with the inferred velocity structure of the upper mantle in the North Atlantic realm. Consequently, our findings weaken the hypothesis of dynamic topography and epeirogenic uplift of the Atlantic margins during the Late Cenozoic.

Impact of Eurasian Ice Sheet and North Atlantic Climate Dynamics on Black Sea Temperature Variability During the Penultimate Glacial (MIS 6, 130–184 ka BP)

AbstractUnderstanding hemisphere‐wide millennial‐scale temperature variability during past glacials in response to ice sheet dynamics and orbital forcing is one of the key targets for Quaternary climate research. While an inland propagation of abrupt temperature changes into Eurasia from the North Atlantic realm during the last glacial (Weichselian) receives increasingly broad support, much less is known regarding the penultimate glacial (Saalian) temperature variability, especially from a continental interior perspective. Here, we present a TEX86‐derived lake surface temperature (LST) record from the former Black Sea “Lake” covering nearly the entire Marine Isotope Stage (MIS) 6. While orbital‐scale LST cooling likely relates to meltwater discharge from the retreating Eurasian Ice Sheet during insolation maxima, millennial‐scale LST variability suggests interstadial warming in phase with Greenland and northern Mediterranean Sea temperature records during the first half of MIS 6. Although summer insolation reached an interglacial‐like level during this period, we propose that the reduced extent of the Eurasian Ice Sheet associated with northward shifted atmospheric fronts was ultimately responsible for the inland propagation of Dansgaard‐Oeschger‐like temperature variability. During the second half of MIS 6, temperature patterns across the North Atlantic‐Eurasian corridor were more variable and less comparable with each other, likely because of the larger continental ice sheet weakening northern hemisphere atmospheric teleconnections. Temperature records across the North Atlantic‐Eurasian realm suggest a weaker atmospheric teleconnection during MIS 6 compared to MIS 3, likely related to a stronger imprint of the Eurasian Ice Sheet on the continental and regional climate.

A mid-Cretaceous petroleum source-rock in the North Atlantic region? Implications of the Nanok-1 fully cored borehole, Hold with Hope, northeast Greenland

The Cenomanian–Turonian transition includes the youngest of the two so-called Cretaceous Oceanic Anoxic Events, sometimes also referred to as the “Bonarelli Event”. This is an interval of global deposition of organic-rich oceanic deposits, including some of the most prolific petroleum source rocks of the World. However, in the greater North Atlantic realm, little direct evidence of notable volumes of rich Cenomanian–Turonian petroleum source rocks exists. As part of a major study of the Cretaceous succession in northeast Greenland between 2009 and 2012, a fully cored borehole (Nanok-1) on eastern Hold with Hope was drilled to penetrate a poorly or non-exposed stratigraphic succession including the Cenomanian–Turonian transition. The Nanok-1 penetrated 160.5 m of Cenomanian to Campanian clastic deposits and terminated at a TD of 168.35 m in an igneous intrusion. Although none of the deposits penetrated qualify as a petroleum source rock, a downwards increasing trend in petroleum source potential starting at c. 100m hint at the existence of such rocks at levels deeper than the TD of the well. The downwards increasing trend in petroleum generation potential is curtailed by maturation from c. 140m, but assuming the trend would have prevailed, were it not for the intrusion, the presence of at least a marginal source rock would be expected at the level of the sill and deeper. The presumed existence of petroleum source rocks below the TD of the borehole is supported by the presence of marked oil staining in sandstones (i.e. migrated petroleum) at shallower levels of the drilled succession. The hopane and sterane distributions and stable carbon isotopic compositions and age-specific nordiacholestane ratios of the oil stains are compatible with an origin from the Cretaceous succession, while the Jurassic can be ruled out. The oil stains recorded were probably generated from a marine shale source rock of Cretaceous age, containing a significant proportion of terrigenous organic matter. The possible presence of at least one marginal petroleum source rock in the mid-Cretaceous succession at the Nanok-1 location has implications for the exploration potential of the conjugate margin. Hence, comparison of sediment accumulation histories of the Møre and Vøring basins and northeast Greenland suggests that the presumed source rock was deposited before the accommodation space at the Nanok-1 location was exhausted. Thus, coeval sediment starvation and deposition of more condensed and richer petroleum source rocks may have prevailed in the offshore basins to the east during the mid-late Cenomanian. This potential source rock will thus be slightly older than Cenomanian–Turonian source rocks that are important worldwide.

Freshwater pearl mussels from northern Sweden serve as long-term, high-resolution stream water isotope recorders

Abstract. The stable isotope composition of lacustrine sediments is routinely used to infer Late Holocene changes in precipitation over Scandinavia and, ultimately, atmospheric circulation dynamics in the North Atlantic realm. However, such archives only provide a low temporal resolution (ca. 15 years), precluding the ability to identify changes on inter-annual and quasi-decadal timescales. Here, we present a new, high-resolution reconstruction using shells of freshwater pearl mussels, Margaritifera margaritifera, from three streams in northern Sweden. We present seasonally to annually resolved, calendar-aligned stable oxygen and carbon isotope data from 10 specimens, covering the time interval from 1819 to 1998. The bivalves studied formed their shells near equilibrium with the oxygen isotope signature of ambient water and, thus, reflect hydrological processes in the catchment as well as changes, albeit damped, in the isotope signature of local atmospheric precipitation. The shell oxygen isotopes were significantly correlated with the North Atlantic Oscillation index (up to 56 % explained variability), suggesting that the moisture that winter precipitation formed from originated predominantly in the North Atlantic during NAO+ years but in the Arctic during NAO− years. The isotope signature of winter precipitation was attenuated in the stream water, and this damping effect was eventually recorded by the shells. Shell stable carbon isotope values did not show consistent ontogenetic trends, but rather oscillated around an average that ranged from ca. −12.00 to −13.00 ‰ among the streams studied. Results of this study contribute to an improved understanding of climate dynamics in Scandinavia and the North Atlantic sector and can help to constrain eco-hydrological changes in riverine ecosystems. Moreover, long isotope records of precipitation and streamflow are pivotal to improve our understanding and modeling of hydrological, ecological, biogeochemical and atmospheric processes. Our new approach offers a much higher temporal resolution and superior dating control than data from existing archives.

Subalternity across the Indian Ocean: the Sidis of Gujarat

Abstract In Gujarat, as in other states of India, the Sidis illustrate the long-term African existence in India, which was dominantly analyzed through Eurocentric categories substantiated either by the semantics of slavery or, more recently, by the paradigm of the African diaspora in the world. Both were mainly produced in and for the North Atlantic realm. This article aims at identifying the intersection between the two margins of the Indian Ocean grounded on an ethnohistory of the Sidis of Gir, in Saurashtra. As an anthropologist, it is at the level of contemporary Indian society within the dialectic and dialogic framework of relationships between the Sidis and the other groups that I observed them, being aware of the discontinuities existing within this category on the one hand and, on the other, of a common idiom through which the Sidis communicate their “Africanness.”

An ~130 kyr Record of Surface Water Temperature and δ18O From the Northern Bay of Bengal: Investigating the Linkage Between Heinrich Events and Weak Monsoon Intervals in Asia

AbstractMillennial‐scale reductions in monsoon precipitation, so‐called Weak Monsoon Intervals (WMIs), have been identified in numerous paleoclimate records across the Afro‐Asian monsoon domain throughout the last glacial‐interglacial cycle. These are considered the regional response to cooling during Heinrich events in the North Atlantic realm and several mechanisms have been suggested to explain this hemisphere‐scale climatic teleconnection. In particular, reductions in Indian Ocean sea surface temperature (SST) have been proposed as the linking element between Heinrich events and WMIs. However, the validity of this relationship has only been demonstrated for the last ~20 kyr, leaving unresolved whether it also holds on longer time scales. Here we present a new paired record of planktonic foraminifera‐based δ18Osw‐ivc and UK'37‐based SST from the northern Bay of Bengal, covering the last ~130 kyr. The δ18Osw‐ivc record clearly reflects orbitally paced changes of Indian Summer Monsoon intensity superimposed by centennial‐ to millennial‐scale WMIs that occurred synchronously to North Atlantic Heinrich events. Comparison with the UK'37‐based SST reconstruction reveals, however, that WMIs in most cases were not paralleled by ocean surface cooling, questioning whether Indian Ocean SST lowering was the linking element between Heinrich events and reductions in monsoon precipitation in Asia also during the last glacial period.

An annually resolved record of Western European vegetation response to Younger Dryas cooling

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.

Response of alpine vegetation to climate changes in the Nanling Mountains during the second half of the Holocene

Studying the response of vegetation to past climate changes may help better predict the potential impacts of future climate changes on the terrestrial ecosystems. Here we present a pollen record that covers the second half of the Holocene from the Nanling Mountains, southern China. Our record reveals six cooling events occurring during 5600−4800, 4400−4100, 3800−3300, 3200−2900, 1600−1400, and 500−380 cal yr BP in this area. These cooling events broadly correspond to the episodic weakening of the Asian summer monsoon and the Bond events in the North Atlantic realm, suggesting a common forcing mechanism. Given that temperature has an important effect on the vertical distribution of alpine vegetation in this area, the projected future warming may lead to a large upward shift of the upper forest line and a threat to the life of alpine tree species on the Nanling Mountains. For example, under the RCP8.5 scenario, mean surface air temperature is projected to increase by 4.9 °C by the end of this century. This magnitude of warming definitely would result in the disappearance of Tsuga chinensis in this area.

North Atlantic influences on climate conditions in East-Central Europe in the late Holocene reflected by flowstone compositions

A stalagmitic flowstone deposit from the Béke Cave (called Nagy-tufa deposit), East-Central Europe is characterized by complex, climate related textural and geochemical records as documented from a drill core (BNT-2 core) covering the period of 4 to 1 ka cal BP. The core location was monitored in an earlier study. Based on monitoring, textural and chemical relationships, it has been hypothesized that the stable carbon isotope signal of the flowstone deposit is a regional humidity record, indicating wet periods 3.8 to 3.4, 3.0 to 2.8 and 2.0 to 1.6 ka cal BP, and a prominent dry period between 2.1 and 2.7 ka cal BP. Furthermore, stable H isotope data of inclusion-hosted water were used to reconstruct the atmospheric temperatures that fit independent regional paleotemperature records, indicating warm conditions around 2.7 ka BP and a relatively cold period between 2.5 and 1.5 ka BP. Comparisons with regional speleothem records and reconstructed North Atlantic Oscillation data indicate that the Late Holocene paleohumidity changes recorded by the BNT-2 stable carbon isotope record can be detected in the entire Western-Central European region with further links to the North Atlantic realm.