The major climate change recorded during the Early-Middle Pleistocene Transition (1.4–0.4 Ma) is characterized by an increase in the length of climatic cycles from 41 to 100 ka. During this period, the Mediterranean climate underwent aridification associated with a drop in temperatures. This period also corresponds to the arrival of the first hominins in Western Europe. This study aims to establish the climatic framework at the end of the Early Pleistocene between MIS 37-31 (∼ 1.25 to 1.06 Ma). To this end, a multiproxy approach was applied to assemblages of planktonic foraminifera, pollen and clay mineralogy, constituting a multi-method approach to climate reconstruction. Comparisons with other sequences from the Central and Western Mediterranean show major differences between the Iberian Peninsula and southern Italy. Indeed, the MIS 31 appears cooler and dryer in the south of the Iberian Peninsula than in central Mediterranean. Clay mineralogy analysis highlights a sudden change in oceanic and atmospheric circulation in the Alboran Basin around 1140 ka. Climate reconstructions follow climatic cycles, with temperatures that appear to be underestimated compared to temperature reconstructions based on fauna from southern Spain. Precipitation reconstructions, on the other hand, are more consistent, suggesting that the climate and vegetation of this region are more likely to be influenced by variations in precipitation. These new data enhance our understanding of the climate of the South-western Mediterranean at the beginning of the Early-Middle Pleistocene Transition.
The Eocene–Oligocene Transition (EOT dated at ∼ 34 Ma) represents one of the most significant climatic shifts of the Cenozoic, marking the transition from the last warmhouse state to a coolhouse state. This global cooling had major consequences for terrestrial ecosystems and was synchronous with the dispersal of numerous Asian mammalian clades towards western Europe. However, the terrestrial expression of the EOT exhibits strong regional heterogeneity questioning its role in establishing dispersal corridors associated with floral and faunal turnovers. Here, we describe, date, and document the paleoenvironments of a continental sedimentary section from Balkanatolia, a biogeographic province corresponding to the present-day Balkans (NE Mediterranean region) and Anatolia (Türkiye). This region most likely functioned as a critical stepping stone for the dispersal of Asian mammals toward western Europe. Our sedimentary record represents a fluvio-lacustrine system exposed over a ∼ 200 m section located in Büyükteflek (Çiçekdağı/Kırşehir area, Türkiye), dated by magnetostratigraphy to the Priabonian and the lower Rupelian, including the Oi-1 glaciation (∼ 33.65 Ma). Clumped isotope analyses on pedogenic carbonates across our record show evidence for a Late Eocene Warming starting during the middle Priabonian (ca. 37 Ma), followed by a marked cooling event at the Eocene–Oligocene Glacial Maximum (EOGM). Stable isotopic data and sedimentary facies further indicate that this complete interval is associated with a long-term aridification trend, starting during the Late Eocene warming and culminating at the EOT. Our results provide the first quantitative record of late Eocene warming on land, and our temperature estimates for the earliest Oligocene cooling are consistent with other Eurasian clumped-isotope records. These temperature shifts and associated aridification steps may have acted as contributing drivers of the late Eocene decline of Balkanatolian endemic taxa and likely facilitated the westward expansion of Asia-derived mammals ultimately resulting in the colonization of western Europe.
The cause of the fundamental reorganisation of the climate system during the Middle Pleistocene Transition (MPT; ∼ 1.25–0.65 million years ago (Ma)), when glacial cycles intensified and lengthened from 41 thousand year (kyr) to quasi-100 kyr periodicity, remains one of the enduring unsolved questions in palaeoclimate science. Increasing attention has focused on the role of the marine carbon cycle, with enhanced carbon storage in the deep sea linked to changes in deep-water temperature and salinity that increase abyssal ocean density stratification. Here we report new high-resolution reconstructions of deep-water temperature and the isotopic composition of seawater (δ18Oseawater), a proxy for ice volume and salinity, from North Atlantic Site U1385, using paired benthic foraminiferal Mg/Ca and oxygen isotope (δ18O) analyses. Together with published records, we present basin-scale and globally distributed compilations of deep-water temperature and δ18Oseawater to assess changes in abyssal ocean stratification for the past 1.5 million years (Myr). Across the MPT, interbasinal gradients suggest North Atlantic deep-water became colder while Pacific deep-water became more saline during glacial periods after ∼ 930 thousand years ago (ka). Deep-ocean δ18Oseawater increased in both the Atlantic and Pacific across the MPT indicating increased continental ice volume. But, the increase was greater in the Pacific than the Atlantic, which we suggest reflects increased salinity of Southern Component Water (SCW). We propose the following sequence of changes during the MPT as a working hypothesis: (1) freshwater input to the marginal seas around Antarctica was reduced beginning at 930 ka by decreased melting of the Antarctic Ice Sheet and/or marine ice shelves and increased sea ice formation in the Southern Ocean; (2) the salinity and density of SCW increased, resulting in enhanced abyssal ocean density stratification and rendering the deep ocean a more effective carbon trap; (3) together with increased export production of organic matter and reduced deep-to-surface water exchange in the Southern Ocean, carbon storage in the deep ocean increased, lowering glacial atmospheric pCO2; (4) lower pCO2 permitted the growth of larger continental ice sheets, which reached a critical size and lengthened the glacial cycles. Our hypothesis supports an important role for abyssal ocean density stratification in the MPT, and requires further testing with additional benthic Mg/Ca-δ18O records, numerical model simulations, and forthcoming atmospheric pCO2 and mean ocean temperature results from the Beyond EPICA–Oldest Ice core from Antarctica.
The Laurentide ice-sheet affected the North Atlantic Ocean during the last glacial period, but its impact on the global atmospheric circulation remains unclear. Here, we use the Australian Earth System Model to investigate the relative roles of Marine Isotope Stage 3 (65 000–25 000 years ago; 65–25 ka) boundary conditions in shaping global climate ∼ 49 ka, a period marked by prominent millennial-scale variability. Our simulations show that Northern Hemisphere (NH) ice sheets were the primary driver of large-scale circulation changes. In particular, NH ice-sheet topography induced a 6 and 4° southward shift of the NH westerlies during boreal winter and summer, respectively, increasing rainfall over Eurasia during summer by 31 % but reducing it in winter. In contrast, orbital forcing and greenhouse gas (GHG) changes did not lead to a significant NH westerly shift, while ice-sheet albedo strengthened the NH westerlies (10 %–14 %) through enhanced cooling (by 3–4 °C) without altering their position in both seasons. NH ice-sheet topography also affected the global atmospheric circulation, leading to an additional 0.9° southward shift of the Intertropical Convergence Zone (ITCZ) and a 1.5° southward displacement of the NH Hadley cell in austral summer, relative to changes simulated due to orbital forcing plus GHG (0.6 and 2° southward shifts for the ITCZ and the NH Hadley cell, respectively), and albedo (0.4 and 0.1°, respectively). The full glacial boundary conditions, including changes in Antarctic ice-sheet topography, also led to a 2° equatorward shift of the Southern Hemisphere (SH) Hadley cell, and a 2.5° equatorward shift of the SH westerlies during austral winter. Orbital forcing plus GHG and albedo primarily modulated the strength of the SH westerlies and tropical atmospheric circulation. These results highlight the role of ice-sheet topography in controlling shifts in the atmospheric circulation and the role of surface albedo in modulating atmospheric circulation intensity through radiative cooling.
The article presents a description of an early-instrumental series of meteorological measurements made in Wrocław (SW Poland) in 1773–1781 and its importance for improving knowledge of climate and climate change in Silesia, Poland, and Central Europe. The series is the third-oldest available for Wrocław and is based on observations made by Johann Ephraim Scheibel on the premises of the Gymnasium that belonged to the Church of St. Elizabeth (central Wrocław). Meteorological observations of air temperature were made three times a day: in the morning immediately after sunrise; in the afternoon between 1 and 2 o'clock; and in the evening 1 or 2 h after sunset and were published in the newspaper Oekonomische Nachrichten der Patriotischen Gesellschaft in Schlesien, issued weekly in Wrocław in the years 1773–1781. The quality of the original sub-daily temperature data was assessed in accordance with WMO recommendations. In addition, mean daily and monthly values were compared and validated against time series from other sites located near Wrocław (Żagań, Jelenia Góra, Prague, Berlin and Warsaw). Air temperatures in Wrocław during the period 1773–1781 were 1.4 and 0.5 °C warmer than in the respective equivalent periods 100 and 200 years later (i.e., 1873–1881 and 1973–1981) but 1.9 °C colder than in the most recent period (2013–2021). The increase in temperature between the study period and the most recent period was greatest in summer (2.7 °C) and winter (2.4 °C) and smallest in autumn (0.8 °C).
Pollen records are among the highest-resolution spatial and temporal proxies for reconstructing past vegetation dynamics, environmental changes and climate variability. Over the past decade, a large variety of methods based on different ecological or mathematical concepts has been used to reconstruct paleoclimatic conditions from pollen assemblages. However, the accuracy of these climate reconstructions strongly depends on the choice of the modern calibration dataset, the taxonomic resolution, and/or the modelling assumptions. The lack of a univocal response still limits the application of pollen-based climate reconstructions to assess key climate changes over multiple time periods especially during the Last Glacial Maximum (LGM, ∼ 23–19 ka BP). Here, we present a multi-method approach, including the Modern Analogue Technique (MAT), the Weighted Averaging Partial Least Squares regression (WA-PLS) and the probability density function-based Climate REconstruction SofTware (CREST), to reconstruct European climates during the LGM. The quality and performance of our climate reconstructions show strong heterogeneity when based on large calibration datasets encompassing wide climatic and vegetation gradients, making local sampling for climate reconstructions difficult. Instead of sampling the global calibration dataset, we test the effect of the latest biomization and megabiomization methods (local calibrations based on megabiomization approaches) on climate reconstructions by introducing a new biome-based approach. Unlike previous studies, we use the weighted mean of climate variables from all megabiome scores rather than only considering the dominant (i.e., highest score) megabiome. This significantly reduces some of the statistical noise of climate reconstructions, drastically minimizing threshold and non-linear effects associated with megabiome classification changes. With these methodological advancements and our multi-method comparison, we evaluate the uncertainties (RMSEP) of the paleoclimate reconstructions for the LGM in Europe. Across climate reconstruction methods (MAT, WA-PLS and CREST methods), European LGM annual temperatures from the biomization method were on average 6.4±2.0 °C (mean SD) colder than today, consistent with megabiomization results (6.8±2.2 °C colder). Winter temperature (mean temperature of the coldest month, MTCO) results exhibit substantial spatial variability across Europe. Local calibration techniques significantly reduce uncertainties in LGM MTCO reconstructions, but they remain highly sensitive to the choice of calibration datasets.
The article includes an overview of the current state of knowledge regarding climate in Poland (Central Europe) in the 16th century and its changes. For this purpose, we utilised all previously published reconstructions and five new quantitative reconstructions incorporating dendrochronological data and documentary evidence. New dendrochronological data were used to reconstruct the mean winter or late winter-early spring temperatures, while documentary evidence enabled the reconstruction of mean winter (DJF) and summer (JJA) temperatures. The climate of Poland in the 16th century, as reconstructed from documentary evidence, was colder than it is today (1991-2020), particularly in winter (by 3.6 degrees C). In summer, it was only 0.7 degrees C colder than today. Compared to the average for the entire 20th century, however, the summer average in the 16th century was 0.3 degrees C warmer, whereas the winter average was 2.5 degrees C colder. In both dendrochronological reconstructions of the temperature of south-eastern Poland, the temperatures in the 16th century were generally lower than those recorded today (1951-2000), particularly in the case of the reconstruction based on the fir chronology (December-March). Anomalies, however, both positive and negative, were usually of less than one standard deviation from the long-term mean. On the other hand, in northern Poland, the February-March temperatures in the 16th century were, on average, comparable to those of the present. Most available temperature reconstructions for Poland reveal cooling over the last few decades of the 16th century, particularly during the winter half-year. The climate in the 16th century was more continental than it is today.
Understanding Pliocene (5.33-2.58 Ma) climate evolution is critical to establishing the conditions that enabled large ice sheets to form in the Arctic region during the intensification of Northern Hemisphere Glaciation (iNHG) around 2.72 Ma. The causes of iNHG remain unclear, with hypotheses ranging from tectonic changes to CO2 reductions. An anomalous, pre-iNHG cooling signal was recorded in a previously published alkenone-based sea surface temperature (SST) record from Ocean Drilling Program (ODP) Site 1090, located in the southeastern Atlantic Ocean. This record has been used to posit that late Pliocene cooling of the already-glaciated Southern Hemisphere could have driven planetwide cooling and the intensification of Northern Hemisphere Glaciation. Here, we expand the SST record of Site 1090 using the same proxy but with higher resolution and improved laboratory protocols. Our revisited record substantially revises conclusions based on prior work. We find that SST at ODP Site 1090 follows similar cooling trends to those found of equatorial and high latitude Northern Hemisphere sites, suggesting that a global forcing, such as a reduction in atmospheric CO2, prompted iNHG, as opposed to an early cooling of the Southern Hemisphere.
Benthic foraminifera show distinct temporal and spatial distribution patterns in the Central Arctic Ocean (CAO) demonstrating their potential to provide robust age constraints and to address paleoceanographic change in the Pleistocene. Several benthic foraminifera bioevents have been previously reported from the Pleistocene that are critically evaluated here by studying three sediment cores from the Mendeleev and Lomonosov ridges and analysing published data sets. Based on these data bioevents are defined by using absolute abundances of species in the >63 µm grain-size fraction, whereas relative abundances are considered not reliable because taphonomic processes such as disintegration and/or dissolution overprint the original assemblage composition. Bioevents are correlated to lithological horizons, and linked to marine isotope stages (MIS) based on available independent stratigraphic data. Three calcareous bioevents can be defined in the Middle Pleistocene: (1) the highest common occurrence of Bolivina arctica (∼MIS 9), (2) the lowest common occurrence of Oridorsalis umbonatus (∼MIS 7), and (3) the acme of Bulimina aculeata (∼MIS 7) in water depths of less than ∼2000 m. The lowest common occurrence of Oridorsalis umbonatus is coeval with the base of the acme of Bulimina aculeata at shallow sites. Since the number of radiometric and biostratigraphic ages is limited, the proposed correlation of bioevents to marine isotope stages should be considered provisional. Further benthic foraminifera bioevents may be useful for stratigraphic correlation on a regional to supra-regional scale but require evaluation of previous taxonomic identifications and additional sediment core studies. The extinct agglutinated species Haplophragmoides obscurus disappeared at the Lomonosov Ridge in the Middle Pleistocene but the complex taxonomy and the few data on the occurrence in Arctic sediment cores currently prohibits the application as biostratigraphic marker. The assemblage turnover from agglutinated to calcareous benthic foraminifera occurred close to the first downcore change of normal to reverse magnetic polarity at the Lomonosov Ridge and Morris Jesup Rise and might be a synchronous event in the eastern Arctic Ocean in middle Pleistocene sediments older than MIS 11. However, this fundamental change in assemblage composition is time-transgressive across the Arctic Ocean because it occurred in the Amerasian Basin in the Early Pleistocene. The bioevents in the CAO are caused by a complex interplay of various biological processes. Apart from B. arctica and H. obscurus that likely evolved in the Arctic Ocean, B. aculeata and O. umbonatus must have invaded the Arctic Ocean from subpolar latitudes. Since an unrestricted exchange of intermediate to deep-water masses with subpolar latitudes is only facilitated through the Fram Strait and the Barents Sea, these intermediate to deep-water species had to be transported as juvenile specimens (propagules) by Atlantic Water to CAO sites during time periods favourable for their propagation. The maximum reachable location for settlement within the Arctic Ocean depended on the species, the local environmental conditions, and the strength of Atlantic Water advection. Environmental conditions, in particular the availability of food, played then a major role for the successful colonization at a particular site, not only for the invading species but also for the species endemic to the CAO (H. obscurus, B. arctica). These sites must have faced a high (H. obscurus, B. arctica, O. umbonatus) or significantly higher particulate organic carbon export to the sea floor than today (B. aculeata). Such environmental conditions must have occurred basin-wide to trigger the synchronous and coincident changes in assemblage compositions. Moreover, external forcing may have triggered environmental change. A massive discharge of detrital dolomite-rich ice-rafted debris might have induced the abrupt collapse of a Bolivina arctica dominated fauna and imminent disappearance of Haplophragmoides obscurus. The most conspicuous change in the environment is expressed in the turnover from a predominance of agglutinated to calcareous benthic foraminifera which was either caused by a fundamental change in food supply and its quality or by corrosive bottom waters. In general, due to selective dissolution of thin-shelled epifaunal taxa, assemblages are enriched in robust epifaunal and/or infaunal calcareous species, or may consist only of an agglutinated taphocoenosis.
It is believed that the atmospheric circulation on Snowball Earth produced a net ablation zone exposing bare sea ice. Under sufficiently low temperatures, salt begins to precipitate out of sea ice, forming a lag deposit of crystals with high albedo as the ice sublimates. This could have resulted in a salt-albedo feedback that has not previously been included in modeling studies of Snowball Earth. We implement a salt-albedo feedback in a simple climate model and show that, once initiated, this mechanism could have intensified global cooling in the initial phase of Snowball Earth. Our results suggest that salt precipitation may have played a role in shaping the early climate of Snowball Earth.
Riukojietna, a small, low-altitude, low-gradient plateau ice cap in northern Sweden, has been retreating rapidly over at least the last century. Its low surface gradient implies that it should be quite sensitive to, and therefore a potentially valuable indicator of, climate change since regional deglaciation at 9.8 ka. Here, we assess its former extent and activity by combining cosmogenic nuclide measurements in bedrock (in situ 14C, 10Be, and 26Al) that constrain ice-free and ice-buried conditions with indirect evidence of glacial activity from proglacial lake sediment records, complemented by historical ice thickness reconstructions. These data are the basis for subsequent forward modeling of measured cosmogenic nuclide concentrations to constrain the Holocene history of Riukojietna. The ice cap has an outlet glacier tongue that drains to the northeast, with a bouldery moraine deposit further down valley constraining its extent at the end of the Little Ice Age (LIA, ca. 1910 CE). Five cosmogenic nuclide samples were collected: two from bedrock on the plateau adjacent to the ice cap, two from a bedrock knob protruding from the outlet glacier tongue (exposed in 2011), and one from an outcrop embedded within the LIA moraine at the outlet of the most proximal of a series of four proglacial lakes. The latter sample yielded concentrations of 14C, 10Be, and 26Al consistent with continuous exposure since 8.1 ± 0.1 ka (weighted mean). Nuclide measurements in the other four samples indicate complex exposure/burial histories. Lake cores from Pajep Luoktejaure, the third of the four down-valley proglacial lakes, indicate up to three periods of glacigenic sediment deposition > 8.1 ka, from 5.4–5.0 ka, and after 1.8 ka, with intervening gyttja that indicates minimal or no glacial influence, with radiocarbon age constraints from bulk sediment and plant macrofossils. We perform a forward modeling exercise to determine whether the cosmogenic-nuclide concentrations in the recently exposed bedrock samples are consistent with the glacial history inferred from the lake sediment record and the deglaciation age of 9.8 ka. Riukojietna persisted during the Holocene Thermal Maximum (ca. 8–5 ka), in contrast to earlier suggestions that Scandinavian glaciers vanished during the Holocene, as a result of an inferred increase in precipitation due to atmospheric circulation changes. The glacier has been in a retracted state similar or smaller than today during the late Holocene, as climate grew colder and drier. This approach combining short- and long-lived cosmogenic nuclides with lake sediments can thus provide new constraints on high-latitude Holocene glacial and paleoclimate history.
Marine anoxia has been implicated as a key environmental driver of the end-Permian mass extinction (EPME) and the subsequent prolonged recovery. However, the spatial and temporal extent of oxygen limitation during the EPME interval remains contentious. Here, we present iron speciation, pyrite framboid and molybdenum–uranium (Mo–U) covariation data from two palaeogeographically distinct settings: the Tethyan Chibi section (South China) and the Panthalassian Ursula Creek section (Western Canada) to evaluate redox dynamics across the Permian-Triassic transition. Our data suggest that bottom waters were predominantly dysoxic during the late Changhsingian at both sites. Later, the prevalence of small pyrite framboids, elevated Mo and U enrichment factors (MoEF and UEF), and high MoEF / UEF ratios near the EPME horizon implicate seafloor anoxia as a key trigger for marine extinctions in the Ursula Creek section. In the post-extinction Early Triassic, iron speciation and MoEF–UEF covariation data reveal a shift to persistently ferruginous conditions in both locations. A global compilation of iron speciation data indicates redox variation between ferruginous and euxinic conditions in epicontinental seas during the Permian-Triassic crisis, with ferruginous conditions expanding significantly in the earliest Triassic. The expansion of a ferruginous seafloor would have limited phosphorus bioavailability, suppressing primary productivity in the immediate aftermath of the EPME, thereby contributing to the slow recovery.
The North African desert margin is considered one of the most sensitive areas to future climate changes, yet the periodicities, coupling mechanisms and external forcing of Holocene environmental variability remain poorly understood. To investigate millennial- to centennial-scale periodicities in Holocene climatic variability and geomorphological processes, we use a Holocene sediment record from Lake Sidi Ali in the semiarid to sub-humid Middle Atlas with a robust 210Pb / 137Cs and pollen-concentrates-based 14C chronology. We use a high-resolution core scanning-XRF record, in order to distinguish between lake-internal (e.g., chemical precipitation) and lake-external (e.g., detrital input) processes. Redfit and Wavelet time series analyses reveal distinct periodicities of millennial to centennial scale. By a correlation analysis of extracted, highly significant, frequency analysis spectra, three XRF-based “Redfit Proxy Groups” (RPGs) which potentially reflect different hydroclimatic forcing mechanisms were derived. Subsequently, we integrated environmental and climatic proxies from the same core (Cedrus pollen abundance, magnetic susceptibility, δ18O and δ13C values of ostracod shells, grain-size endmembers and total organic carbon) and used their wavelet domain to improve the interpretation. Finally, we identified two main periodicity regimes that affected, on the one hand, the hydrological regime and, on the other hand, the lake productivity and catchment erosion dynamics. For RPG 1 (Ca, Sr, Ca/Ti, Sr/Ti), we identified 2 and 1 kyr periodicities, which we interpret as precipitation/evaporation related proxies in the context of North Atlantic and solar forcing. For RPG 2 (Fe, Ti, K, Si/Ti), we observe 3.5 and 1.5 kyr periodicities, which we interpret as driven by lake productivity or detrital input. Overall, our results show that Holocene environmental variability at Lake Sidi Ali was structured by two partly decoupled regimes: hydroclimatic variability linked to precipitation/evaporation changes and catchment-related variability linked to erosion, productivity and terrestrial sediment supply.
Abstract. Density of seawater is a critical property that controls ocean dynamics. Previous works suggest the use of the δ18O calcite of foraminifera as a potential proxy for paleodensity. However, potential quantitative reconstructions were limited to the tropical and subtropical surface ocean and without an explicit estimate of the uncertainty in calibration model parameters. We developed the use of the δ18Oc of planktonic foraminifera as a surface paleodensity proxy using Bayesian regression models calibrated to annual surface density. Predictive performance of the models improves when we account for inter-species specific differences. We investigate the additional uncertainties that could be introduced by potential evolution of the δ18Oc-density relationship with time – from the last glacial maximum (LGM) to the preindustrial (PI) – through the combination of past isotope enabled climate model simulations and a foraminiferal growth module. We demonstrate that additional uncertainties are weak globally, except for the Nordic Seas region. We applied our Bayesian regression model to LGM and Late Holocene (LH) δ18Oc foraminifera databases to reconstruct annual surface density during these periods. We observe stronger LGM density value changes at low latitudes compared to mid latitudes. These results will be used to evaluate numerical climate models in their ability to simulate ocean surface density during the extreme climatic period of the LGM. The new calibration has great potential to reconstruct the past temporal evolution of ocean surface density over the Quaternary. Under climates outside the Quaternary period and in ocean basins characterized by anti-estuary circulation, like the current Mediterranean Sea and Red Sea, our calibration could provide density estimates with larger uncertainty, a point that requires further investigations.
Abstract. Associated with ongoing global warming, prolonged periods of negative mass balance affect even Alpine glaciers in high summit regions, which are also prime candidates for paleoclimate-related ice core studies. This greatly complicates the already challenging task of establishing an age-depth relationship where now both, the age at depth and at the surface is an unknown. Radiometric ice dating methods are an important key to tackle this challenge. This study presents a comprehensive age-depth profile of the summit glacier of Weißseespitze (WSS, 3500 m a.s.l.) in the Austrian Alps, utilizing a combination of radiometric dating methods – 39Ar and 14C. Ice cores from drilling campaigns conducted in 2019, 2023, and 2024 were analyzed to overcome challenges posed by extensive ice loss and surface melting that limit traditional dating techniques. All 39Ar samples were measured using atom trap trace analysis (ATTA). Surface mass balance (SMB) data since 2019 were used to align core depths across years, and all samples were referenced to height above bedrock to standardize comparisons. Age modeling using least squares fitting and Monte Carlo sampling was performed for three glaciological models: Nye, Raymond, and a two-parameter (2p) model to test their applicability. The 2p model provided the best fit (χred2 = 0.4), closely matching the data and providing a continuous age-depth scale. The model yielded a mean accumulation rate of 0.53 m w.e. a−1 (1σ range: 0.38–0.63 m w.e. a−1) and a thinning parameter p = 0.92 (1σ: 0.81–0.97), the former agreeing with current accumulation estimates. The results show that the surface ice dates back approximately 400 a, emphasizing the extent of recent ice loss. Apart from this, the continuous age-depth relation shows no sign of prolonged periods of mass loss at WSS within the 6000 a glaciation history prior to today. This work underscores the utility of 39Ar dating in alpine glaciology, enabling precise reconstruction of age-depth relationships even under advanced glacial retreat and enhancing our understanding of Holocene climate history in the Eastern Alps.
The North Atlantic Oscillation (NAO) is a major source of atmospheric variability in the Northern Hemisphere, affecting temperature, precipitation, and storm tracks across North America and Eurasia. Understanding NAO variability on multidecadal to centennial timescales requires paleo-reconstructions, but previously published reconstructions disagree on the magnitude of low-frequency NAO variability over the last millennium. Paleoclimate proxies for the oxygen and hydrogen isotope composition of meteoric waters have thus far been under-utilized in published NAO reconstructions. Here, we investigate multidecadal variability in the reconstructed NAO over the last millennium using 94 high-resolution NAO-sensitive records from the Iso2k database, a collection of globally distributed water isotope-based paleoclimate proxies. We find significant multidecadal to centennial scale variability, which we also highlight in other independent reconstructions of the NAO. Critically, however, the strength of the low-frequency signal has not been consistent throughout the last millennium. Isotope-enabled model simulations did not reproduce the low-frequency signal in the NAO reconstructions and thus it may be necessary to account for low-frequency variability when projecting the impacts of the NAO on temperature and precipitation under future climate scenarios.
The mid-Miocene (15.98 to 13.82 Ma) was characterized by substantially warmer temperatures than today and atmospheric CO2 concentrations comparable to near-future projections. Climate models have generally struggled to reproduce proxy-based reconstructions from this interval, particularly at high latitudes where model temperatures are consistently lower than observations. Here, we present new mid-Miocene simulations using a previously unpublished geography and evaluate the climate's sensitivity to several key components: paleogeography (including land-sea distribution, topography and ice sheets), atmospheric CO2 concentration, atmospheric model choice, and solar forcing. Our baseline mid-Miocene climate yields a global mean surface temperature (GMST) of 19.8 degrees C. In mid-Miocene sensitivity experiments of two and four times pre-industrial CO2 concentrations, consistent with estimates for the mid-Miocene, GMST varies by up to 3.2 degrees C between simulations. Removal of the Antarctic ice-sheet leads to expected local warming of around 25 degrees C at the maximum height of the ice sheet, but nevertheless records an overall global cooling of 1.3 degrees C. Solar forcing and subtle changes of land-sea mask each impact GMST by around 0.2 degrees C. The choice of atmospheric model substantially affects the simulated mid-Miocene climate through modified feedback mechanisms. We estimate an equilibrium climate sensitivity (ECS) of 2.9 degrees C (2.5-3.3 degrees C, 95 % prediction interval) for the mid-Miocene, similar to modern-based estimates from our model (2.8 degrees C, 2.2-3.4 degrees C, 95 % prediction interval), indicating the potential for the Miocene to contribute to constraining ECS. Global precipitation is tightly coupled to GMST across all our simulations. As with previous studies, all our simulations, regardless of specific configuration, underestimate high-latitude proxy-reconstructed temperatures. This highlights the need to improve our understanding on polar amplification and on the limitations affecting the proxy record.
Dust deposits in ice cores provide a valuable archive of past atmospheric circulation, offering insights into climate dynamics during key climate transitions such as the last glacial termination. Here, we present a novel high-resolution reconstruction of dust provenance in the EPICA Dome C (EDC) ice core from 33.7 to 2.8 kyr BP, based on Rare Earth Element (REE) patterns. Using a statistical unmixing algorithm on 279 samples, we quantify, for the first time, contributions from key Southern Hemisphere dust sources. During the late Marine Isotope Stage 3 (MIS3), the Last Glacial Maximum (LGM) and Heinrich Stadial 1 (HS1), dust at EDC was dominated by Patagonian sources, ∼ 65 %–75 % of total deposition, with secondary inputs from Australia (∼ 9 %–11 %), Southern Africa (∼ 5 %–9 %), New Zealand (∼ 6 %–14 %), and Puna-Altiplano (∼ 2 %–4 %). After ∼ 14.5 kyr BP, and especially during the Holocene, the dust assemblage shifted toward greater contributions from low-latitude sources including Australia (21 %–28 %), Southern Africa (∼ 8 %–9 %), and the Puna-Altiplano (∼ 8 %–9 %) – while the Patagonian contribution decreased to an average of ∼ 43 %–53 %, New Zealand (∼ 4 %–10 %) – and source compositions became more variable. This transition in dust provenance contribution is supported by our modeled Sr-Nd isotope composition of EDC dust, which also aligns with changes observed in other East Antarctic ice cores. Comparison with the EDML ice core provenance record reveals overall agreement in major sources and timing of the shifts but also highlights regional variations in the secondary contributions, with EDC showing more consistent inputs from Australia and EDML from Southern Africa. The coherence of the provenance shift recorded at EDC and EDML ice cores points to a common large-scale control, in line with the influence of eustatic sea-level rise and postglacial reorganization of fluvial sediment routing and availability in southern South America.
Holocene flood reconstructions from western and southern Norway indicate a non-stationary behaviour through time, with a major regime shift around 4000 years ago. Under the influence of global warming, flood frequency, seasonality, and magnitude are changing worldwide. The full range of natural variability in flood frequency and seasonality remains poorly constrained, underscoring the need for ultra-high-resolution records to place recent changes in a long-term context. This study presents an 8000-year flood record from Lake Vangsvatnet, Western Norway, that combines high-resolution computed tomography (CT) scanning, X-ray fluorescence (XRF), grain-size analysis, and radiocarbon dating to differentiate between seasonal flood deposits (spring snowmelt versus autumn rainfall). The 11 m sediment core reveals distinct flood layers (n = 230), linked to varying hydrological conditions, and validated by historical discharge data (1892-2016 CE). The record shows fluctuating flood frequencies, with peaks at 6000-5300 and 1400 cal yr BP to present. A seasonal shift from rainfall-dominated to snowmelt-dominated floods occurred around 3100 cal yr BP, coinciding with regional cooling. The last 500 years exhibit the highest flood frequency of the entire record. These findings highlight the sensitivity of flood regimes to climatic and, in the most recent centuries, human influence. Under future warming, reduced snowpack may diminish spring floods, while intensified autumn and winter rainfall could increase flood risks.
Quantitative reconstructions of terrestrial climate conditions typically rely on biological proxies such as pollen. Despite their widespread use, these proxies exhibit inherent limitations such as low taxonomic resolution and complex taphonomies. Sedimentary ancient DNA (sedaDNA), particularly plant metabarcoding using chloroplast markers (trnL-gh), has emerged as a promising alternative offering enhanced taxonomic precision and local origin. Here, we present the framework for quantitative reconstruction of summer temperatures from sedaDNA assemblages applying methods that rely on surface samples for calibration (weighted-averaging partial least squares (WA-PLS), modern analogue technique (MAT)) and introducing a framework that combines modern plant occurrences and species distribution modeling (SDM) to derive taxon-specific probability density functions (PDFs) for calibration. Applying these approaches to sedaDNA data from 203 lake sediment-surface samples across Siberia, we obtained highly accurate reconstructions with median biases as low as 0.5 degrees C and a strong correlation with observed temperatures. Our method shows a low reconstruction bias when compared to those from other proxy calibration studies. Applied to a Lake Billyakh sediment core in eastern Siberia, our sedaDNA-based reconstructions using various approaches show similar trends and successfully reproduce regional climate changes over the past 32 000 years, aligning closely with independent pollen-based records. We also reveal that higher taxonomic resolution results in a more precise reconstruction due to narrower tolerance ranges with higher taxonomic resolution. The demonstrated reliability, low bias, and superior taxonomic resolution underscore the significant potential of sedaDNA as a robust and sensitive new terrestrial proxy for quantitative paleoclimatic research.
