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We publish a data set of environmental and biological data collected in 2000 during the ice-free period in high mountain lakes located above the local timberline in the Alps, in Italy, Switzerland and Austria. Environmental data include coordinates, geographical attributes and detailed information on vegetation, bedrock and land use in lake catchments. Chemical analyses of a sample for each lake collected at the lake surface in Summer 2000 are also reported. Biological data include phytoplankton (floating algae and cyanobacteria), zooplankton (floating animals), macroinvertebrates (aquatic organisms visible to the naked eye living in contact with sediments on lake bottom), benthic diatoms. Diatoms, cladocera and chironomids remains and algal and bacterial pigments were also analysed in lake sediments.

Arctic environments may respond very sensitively to ongoing global change, as observed during the past decades for Arctic vegetation. Only little is known about the broad-scale impacts of early and mid 20th-century industrialization and climate change on remote Arctic environments. Palynological analyses of Greenland ice cores may provide invaluable insights into the long-term vegetation, fire, and pollution dynamics in the Arctic region. We present the first palynological record from a Central Greenland ice core (Summit Eurocore ’89, 72°35’N, 37°38’W; the location of Greenland Ice Core Project GRIP) that provides novel high-resolution microfossil data on Arctic environments spanning AD 1730–1989. Our data suggest an expansion of birch woodlands after AD 1850 that was abruptly interrupted at the onset of the 20th century despite favorable climatic conditions. We therefore attribute this Betula woodland decline during the 20th century to anthropogenic activities such as sheep herding and wood collection in the sub-Arctic. First signs of coal burning activities around AD 1900 coincide with the onset of Arctic coal mining. The use of coal and fire activity increased steadily until AD 1989 resulting in microscopic-size pollution of the ice sheet. We conclude that human impact during the 20th century strongly affected (sub)-Arctic environments. Moreover, ecosystems have changed through the spread of adventive plant species (e.g. Ranunculus acris, Rumex) and the destruction of sparse native woodlands. We show for the first time that optical palynology allows paleoecological reconstructions in extremely remote sites >500 km from potential sources, if adequate methods are used.

Specialized and systematic underwater fieldwork at the prehistoric site of Ploča Mičov Grad at Gradište (North Macedonia) on the eastern shore of Lake Ohrid was undertaken in 2018 and 2019. It has substantiated the archeological site's outstanding preservation condition, and furthermore proven the numerous construction timbers’ suitability for dendrochronological analysis. Dendrochronological analysis on archaeological timbers was applied, combined with radiocarbon dating. Bayesian radiocarbon modeling allowed to ‘wiggle match’ the dendrochronological mean curves, i.e. allowed the precise chronological anchoring of ‘floating’ tree-ring sequences. Furthermore, radiocarbon dates of plant remains from the site's main archaeological layer are statistically evaluated. Based on the new findings, the strikingly high density of wooden piles at the site can be attributed to several construction phases of Neolithic (middle of 5th millennium BC) and Bronze Age (2nd millennium BC: 1800, 1400 and 1300 BCE) settlements. Intense settlement activity is furthermore evidenced by a cultural layer of mainly organic material under the lakebed up to 1.7 m in thickness, which accumulated during the Neolithic occupation of the bay in the middle of the 5th millennium BC. The presented research enables precise absolute dating of a series of settlement phases at Ploča Mičov Grad from the Neolithic and the Bronze Age, and hence provides important reference points for an absolute chronological framework for the prehistory of the southwestern Balkans. The investigations underline the potential of future research on waterlogged prehistoric settlements in the region., Journal of Archaeological Science: Reports, 38

A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format. Fil: Kaufman, Darrell. Northern Arizona University.; Estados Unidos Fil: McKay, Nicholas. Northern Arizona University.; Estados Unidos Fil: Routson, Cody. Northern Arizona University.; Estados Unidos Fil: Erb, Michael. Northern Arizona University.; Estados Unidos Fil: Davis, Basil. University Of Lausanne; Suiza Fil: Heiri, Oliver. University Of Basel; Suiza Fil: Jaccard, Samuel. University Of Bern; Suiza Fil: Tierney, Jessica. University of Arizona; Estados Unidos Fil: Dätwyler, Christoph. University Of Bern; Suiza Fil: Axford, Yarrow. Northwestern University; Estados Unidos Fil: Brussel, Thomas. University of Utah; Estados Unidos Fil: Cartapanis, Olivier. University Of Bern; Suiza Fil: Chase, Brian. Universite de Montpellier; Francia Fil: Dawson, Andria. Mount Royal University; Canadá Fil: de Vernal, Anne. Université du Québec a Montreal; Canadá Fil: Engels, Stefan. University of London; Reino Unido Fil: Jonkers, Lukas. University Of Bremen; Alemania Fil: Marsicek, Jeremiah. University of Wisconsin-Madison; Estados Unidos Fil: Moffa Sánchez, Paola. University of Durham; Reino Unido Fil: Morrill, Carrie. University of Colorado; Estados Unidos Fil: Orsi, Anais. Université Paris-Saclay; Francia Fil: Rehfeld, Kira. Heidelberg University; Alemania Fil: Saunders, Krystyna. Australian Nuclear Science And Technology Organisation; Australia Fil: Sommer, Philipp. University Of Lausanne; Suiza Fil: Thomas, Elizabeth. University At Buffalo; Estados Unidos Fil: Tonello, Marcela Sandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Tóth, Mónika. Balaton Limnological Institute; Hungría Fil: Vachula, Richard. Brown University; Estados Unidos Fil: Andreev, Andrei. Alfred Wegener Institut Helmholtz Centre for Polar and Marine Research; Alemania Fil: Bertrand, Sebastien. Ghent University; Bélgica Fil: Massaferro, Julieta. Administración de Parques Nacionales. Parque Nacional "Nahuel Huapi"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format., Measurement(s)climateTechnology Type(s)digital curationFactor Type(s)temporal interval • geographic location • proxy typeSample Characteristic - Environmentclimate systemSample Characteristic - LocationEarth (planet) Machine-accessible metadata file describing the reported data: https://www.ncdc.noaa.gov/paleo/study/27330

The Eurasian (née European) Modern Pollen Database (EMPD) was established in 2013 to provide a public database of high-quality modern pollen surface samples to help support studies of past climate, land cover, and land use using fossil pollen. The EMPD is part of, and complementary to, the European Pollen Database (EPD) which contains data on fossil pollen found in Late Quaternary sedimentary archives throughout the Eurasian region. The EPD is in turn part of the rapidly growing Neotoma database, which is now the primary home for global palaeoecological data. This paper describes version 2 of the EMPD in which the number of samples held in the database has been increased by 60% from 4826 to 8134. Much of the improvement in data coverage has come from northern Asia, and the database has consequently been renamed the Eurasian Modern Pollen Database to reflect this geographical enlargement. The EMPD can be viewed online using a dedicated map-based viewer at https://empd2.github.io and downloaded in a variety of file formats at https: //doi.pangaea.de/10.1594/PANGAEA.909130 (Chevalier et al., 2019)., Swiss National Science Foundation (SNSF) 200021_169598, University of Lausanne

High-resolution sediment chronologies with the best possible time control are essential for comparing palaeoecological studies with independent high-precision climatic, archaeological or historic data in order to disentangle causes and effects of past environmental, ecological and societal change. We present two varved lake sediment sequences from Moossee and Burgäschisee (Swiss Plateau) that have chronologies developed with Bayesian models and radiocarbon (14C) dating of terrestrial plant macrofossils extracted from sediment samples with constant age ranges. We illustrate the potential of high-resolution14C dating for the construction of robust, high-precision sediment chronologies. The mean 2σ age uncertainties were reduced to±19 cal yr for Moossee and to±54 cal yr for Burgäschisee over the entire period of 3000 cal yr, while 2σ uncertainties of only±13 cal yr and±18 cal yr respectively, were achieved for shorter time intervals. These precisions are better than or comparable to those of previous varve studies. Our results imply that a sophisticated subsampling strategy and a careful selection of short-lived and well-defined terrestrial plant remains are crucial to avoid outlying14C ages. A direct linkage between palaeoeological studies with dendrochronologically dated, local archaeological sites as well as a precise comparison with high-resolution climate proxy data have become feasible.

Increased cultural eutrophication since the 20th century, caused by phosphorus (P) enrichment, has become a major problem worldwide. In deep, stratified lakes, eutrophication-induced hypolimnetic anoxia often stimulates the release of labile P from the sediment into the water column. This positive feedback, termed internal P loading, maintains or even accelerates eutrophication. However, most studies on internal P loading have focused on recent times. Little is known about whether such positive feedbacks caused by labile P release from sediments also played a role under natural conditions with little or no human impact. We investigated a high-resolution 15,000-year sediment record of paleoproduction, anoxia, and five sedimentary P fractions from a small, deep lake, Soppensee, on the Swiss Central Plateau. We estimated long-term qualitative internal P loading by comparing the Holocene record of diatom-inferred epilimnetic total P (DI-TP) concentrations with labile P fraction (Fe P) concentrations in sediments under changing trophic state, redox, and lake mixing regimes. Intensified P cycling from sediments into the water column (enhanced internal P loading) apparently occurred as a positive feedback to natural eutrophication with persistent bottom-water anoxia during the early to mid-Holocene (~9000–6000 cal BP). However, this positive feedback was not inferred for other eutrophic phases. Fe-rich layers formed during seasonal mixing of the lake in the late Holocene (~2000–200 cal BP) and magnetite-type minerals produced by magnetotactic bacteria (MTB) internal P loading during anoxic phases in the mid- to late Holocene (~6000–2000 cal BP) appeared to prevent internal P loading. MTB presence resulted in high concentrations of potentially labile Fe P in sediments. Our study demonstrates the potential contribution of internal P loading during long-term natural eutrophication of deep stratified lakes and has wide implications for lake management and restoration. Our results highlight the importance of the coupled geochemical cycles of P and Fe in the long-term trophic state evolution of stratified, ferruginous, low-sulfate-water lakes, conditions that have been reported to serve as analogs for the Archaean Ocean.

Este artículo contiene 16 páginas, 6 figuras, 3 tablas., 1. Pigments in lake surface sediments integrate both benthic and pelagic primary producer composition at the whole‐lake ecosystem level. 2. We gathered a comprehensive set of water chemistry, morphometric, physical and biological lake variables, catchment and climate characteristics, and geographical descriptors. We used multiple regressions to relate whole‐lake algal pigment concentration to environmental conditions and multivariate statistical analyses to assess the factors most associated with photoautotrophic algal and bacterial community composition. The relative influence of environmental factors and spatial distribution was assessed by variance partitioning analysis among three groups of variables: (1) in‐lake factors, (2) external factors, and (3) geographic descriptors. 3. Pigment concentration and community composition were most sensitive to in‐lake factors. Pigment‐inferred abundance of algae, including cyanobacteria, tended to be highest in shallower systems with high nutrient concentrations, independent of the latitudinal temperature or irradiance gradients. Pigment‐inferred community composition was best explained by nutrients and biotic composition (zooplankton and fish communities). Only in maritime temperate lakes did a link with regional location occur due to their low dissolved inorganic nitrogen to soluble reactive phosphorus ratios (1.5 atomic ratio), suggesting nitrogen limitation of phytoplankton growth; accordingly, the sediment pigments revealed cyanobacteria to be the dominant group, although this may also be a consequence of the overall high nutrient levels in these 4. Despite the large climate gradient covered, in‐lake rather than external factors were associated with the patterns observed in pigment concentration (from benthic and pelagic microorganisms) and inferred composition and abundance in these shallow lakes. Our results suggest that pigment assemblages in sediments, which integrate both benthic and pelagic microbial photoautotrophic community and processes, are valuable indicators of changes in shallow (0.75–12 m depth) lake ecosystems., This research was funded by a post‐doctoral Beatriu de Pinós grant from the Departament d'Universitats, Recerca i Societat de la Informació, Generalitat de Catalunya (T.B.). Further support came from The Netherlands Organization for Scientific Research (NWO) grant W84‐549 and WB84‐586, The National Geographic Society grant 7864‐5; in Brazil by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) grants 480122, 490409, 311427; in Uruguay by PEDECIBA, Maestría en Ciencias Ambientales, Donación Aguas de la Costa S.A., and Banco de Seguros del Estado. N.M. was supported by Sistema Nacional de Investigadores. E.J. was supported by the MARS project (Managing Aquatic ecosystems and water Resources under multiple Stress) funded under the 7th EU Framework Programme, Theme 6 (Environment including Climate Change) and AU Centre for Water Technology (watec.au.dk).

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Chironomids preserved in a sediment core from Lago di Origlio (416 m a.s.l.), a lake in the foreland of the Southern Swiss Alps, allowed quantitative reconstruction of Late Glacial and Early Holocene summer temperatures using a combined Swiss–Norwegian temperature inference model based on chironomid assemblages from 274 lakes. We reconstruct July air temperatures of ca. 10 °C between 17 300 and 16 000 cal yr BP, a rather abrupt warming to ca. 12.0 °C at ca. 16 500–16 000 cal yr BP, and a strong temperature increase at the transition to the Bølling/Allerød interstadial with average temperatures of about 14 °C. During the Younger Dryas and earliest Holocene similar temperatures are reconstructed as for the interstadial. The rather abrupt warming at 16 500–16 000 cal yr BP is consistent with sea-surface temperature as well as speleothem records, which indicate a warming after the end of Heinrich event 1 (sensu stricto) and before the Bølling/Allerød interstadial in southern Europe and the Mediterranean Sea. Pollen records from Origlio and other sites in southern Switzerland and northern Italy indicate an early reforestation of the lowlands 2000–1500 yr prior to the large-scale afforestation of Central Europe at the onset of the Bølling/Allerød period at ca. 14 700–14 600 cal yr BP. Our results suggest that these early afforestation processes in the formerly glaciated areas of northern Italy and southern Switzerland have been promoted by increasing temperatures.

Carpinus betulus L. is a mesic, usually considered late-successional tree widely distributed in Europe, but almost absent from Iberia, where it is generally assumed that disappeared during the coldest stages of the Wurm. High-resolution pollen analyses were carried out in 14C dated sediments from a drowned estuary (ria) and a small mountain lake. Carpinus pollen identification was confirmed by comparative light and scanning electron microscopy. Hornbeam dynamics are interpreted using palaeoclimatic reconstructions based on independent proxies (diatoms, chironomids and dinocysts). Our results support that hornbeam declined between ca. 60,000 and ca. 9,000 cal yr bp, when multiproxy evidence suggests a major regional relative sea-level rise. Moreover, chironomid-inferred July temperatures show an increase of more than 6 °C between 15,600 and 10,500 cal yr bp, while freshwater aquatics and diatoms indicate a general tendency towards increasing precipitation and a more oceanic climate. Carpinus survived during the Wurm in a variety of habitats in coastal valleys in NW Iberia which had adequate climatic and edaphic conditions. Such habitats might be comparable to the oak-ash, ravine, and hardwood floodplain forests currently existing in other regions of Europe. Large areas of these coastal ecosystems disappeared at the onset of the Holocene, when the sea-level rose. Later hornbeam was apparently unable to compete and expand further inland. Therefore, the sea-level rise combined with the climatically-induced Holocene tree succession and the increasing human impact during the Mid and Late Holocene led to hornbeam progressively becoming a marginal tree in the area.

Gerhard Lang, one of the great German botanists and palaeoecologists of the 20th century, died on the 19th June 2016 in Biberach, southern Germany. He will be greatly missed by his friends and colleagues, not only for his vast expertise in botany, ecology, biogeography, and vegetation history, but also for his integrity, kindness, and humour. For many of his students and post-doctoral fellows he was not only an excellent teacher and mentor, but also an important role model.

Understanding past methane dynamics in arcticwetlands and lakes is crucial for estimating future methane release. Methane fluxes from lake ecosystems have increasingly been studied, yet only few reconstructions of past methane emissions from lakes are available. In this study,we develop an approach to assess changes in methane availability in lakes based on δ13c of chitinous invertebrate remains and apply this to a sediment record from a Siberian thermokarst lake. Diffusive methane fluxes from the surface of ten newly sampled Siberian lakes and seven previously studied Swedish lakes were compared to taxon-specific δ13c values of invertebrate remains from lake surface sediments to investigate whether these invertebrates assimilated 13C-depleted carbon typical for methane. Remains of chironomid larvae of the tribe Orthocladiinae that, in the study lakes, mainly assimilate plant-derived carbon had higher δ13c than other invertebrate groups. δ13c of other invertebrates such as several chironomid groups (Chironomus, Chironomini, Tanytarsini, and Tanypodinae), cladocerans (Daphnia), and ostracods were generally lower. δ13c of Chironomini and Daphnia, and to a lesser extent Tanytarsini was variable in the lakes and lower at sites with higher diffusive methane fluxes. δ13c of Chironomini, Tanytarsini, and Daphnia were correlated significantly with diffusive methane flux in the combined Siberian and Swedish dataset (r1=-0.72, p = 0.001, r = 0.53, p = 0.03, and r1\4;0.81, p < 0.001, respectively), suggesting that δ13c in these invertebrates was affected by methane availability. In a second step, we measured δ13c of invertebrate remains from a sediment record of Lake S1, a shallow thermokarst lake in northeast Siberia. In this record, covering the past ca 1000 years, δ13c of taxa most sensitive to methane availability (Chironomini, Tanytarsini, and Daphnia) was lowest in sediments deposited from ca AD 1250 to ca AD 1500, and after AD 1970, coinciding with warmer climate as indicated by an independent local temperature record. As a consequence the offset in δ13c between methane-sensitive taxa and bulk organic matterwas higher in these sections than in other parts of the core. In contrast, δ13c of other invertebrate taxa did not show this trend. Our results suggest higher methane availability in the study lake during warmer periods and that thermokarst lakes can respond dynamically in their methane output to changing environmental conditions.

High-resolution quantitative temperature records from continents covering glacial to interglacial transitions are scarce but important for understanding the climate system. We present the first decadal resolution record of continental temperatures in Central Europe during the last deglaciation (similar to 14,60010,600cal. yrB.P.) based on the organic geochemical palaeothermometer TEX86. The TEX86-inferred temperature record from Lake Lucerne (Vierwaldstattersee, Switzerland) reveals typical oscillations during the Late Glacial Interstadial, followed by an abrupt cooling of 2 degrees C at the onset of Younger Dryas and a rapid warming of 4 degrees C at the onset of the Holocene, within less than 350years. The remarkable resemblance with the Greenland and regional stable oxygen isotope records suggests that temperature changes in continental Europe were dominated by large-scale reorganizations in the northern hemispheric climate system.

To provide insights into the long-term evolution of aquatic ecosystems without human interference, we hereevaluate a decadal- to centennial-scale-resolution diatom record spanning about 12 ka of the Holsteinian inter-glacial (Marine Isotope Stage 11c). Using a partially varved sediment core from the Dethlingen palaeolake(northern Germany), which has previously been studied for palynological and microfacies signals, we documentthe co-evolution of the aquatic and surrounding terrestrial environment. The diatom record is dominated by thegenera Stephanodiscus, Aulacoseira, Ulnaria and Fragilaria. Based on the diatom assemblages and physicalsediment properties, the evolution of the Dethlingen palaeolake can be subdivided into three major phases.During the oldest phase (lasting ~1900 varve years), the lake was ~10–15 m deep and characterized by anoxicbottom-water conditions and a high nutrient content. The following ~5600 years exhibited water depths >20 m,maximum diatom and Pediastrum productivity, and a peak in allochtonous nutrient input. During this phase,water-column mixing became more vigorous, resulting in a breakdown of anoxia. The youngest lake phase(~4000–5000 years) was characterized by decreasing water depth, turbulent water conditions and decreasednutrient loading. Based on our palaeolimnological data, we conclude that the evolution of the Dethlingenpalaeolake during the Holsteinian interglacial responded closely to (i) changes within the catchment area (asdocumented by vegetation and sedimentation) related to the transition from closed forests growing on nutrient-rich soils (mesocratic forest phase) to open forests developing on poor soils (oligocratic forest phase), and(ii) short-term climate variability as reflected in centennial-scale climate perturbations.

One of the key factors in understanding past climate change is the development of robust age models that have sufficient chronological precision for comparing different palaeoclimate archives, while retaining accuracy. Recent developments in Bayesian age modelling are applied here to the Swiss varve lake, Soppensee. We develop revised age models for this sequence using the available stratigraphic information to constrain the calibrated radiocarbon ages. We begin by using stratigraphical order as the only constraint and then sequentially increase the information incorporated into the model, using relative varve age, sample depth, and varying depositional models. Within this Bayesian framework, we develop internally robust models that significantly improve the dating precision and are applicable to both varved and non-varved sequences. We then compare the model output to wider chronological information, such as the age of the Laacher See Tephra in order to test the model accuracy. The results of this exercise suggest that these methods can be used to build very reliable improved age models in a variety of records.

The tephrostratigraphy of Soppensee, Switzerland, is presented here for the first time, with new geochemical data for four tephra layers, derived from three volcanic centres. The best available age estimates for the Laacher See Tephra and Vedde Ash layers are incorporated into a revision of the radiocarbon-based Bayesian age-model for the last glacial to interglacial transition at Soppensee, which is used to explore synchronicity of climatic events between Europe and the North Atlantic. Local temperature changes, recorded by biotic and abiotic proxies in Soppensee, appear to shift in phase with the oxygen isotope signal in Greenland at the onset of the Younger Dryas; however with the clarity of improved precision, an apparent offset that likely results from a dating artefact, is seen between records at the termination of the stadial event. From a methodological standpoint, the results clearly show that only by establishing detailed and independent chronological frameworks can abrupt climatic variability be compared between different regions with sufficiently high temporal precision to addresses the notion of hemispheric climatic synchronicity at the centennial scale in the Late Quaternary. Continuing to develop such approaches is therefore essential in order to understand how far in time and space the climate has behaved in such a way.

The effects of eutrophication on short term changes in the microbial community were investigated using high resolution lipid biomarker and trace metal data for sediments from the eutrophic Lake Rotsee (Switzerland). The lake has been strongly influenced by sewage input since the 1850s and is an ideal site for studying an anthropogenically altered ecosystem. Historical remediation measures have had direct implications for productivity and microbial biota, leading to community composition changes and abundance shifts. The higher sewage and nutrient input resulted in a productivity increase, which led predominantly to a radiation in diatoms, primary producers and methanogens between about 1918 and 1921, but also affected all microorganism groups and macrophytes between about 1958 and 1972. Bacterial biomass increased in 1933, which may have been related to the construction of a mechanical sewage treatment plant. Biomarkers also allowed tracing of fossil organic matter/biodegraded oil contamination in the lake. Stephanodiscus parvus, Cyclotella radiosa and Asterionella formosa were the dominant sources of specific diatom biomarkers. Since the 1850s, the cell density of methanogenic Archaea (Methanosaeta spp.) ranged within ca. 0.5–1.8 × 109 cells g−1 dry sediment and the average lipid content of Rotsee Archaea was ca. 2.2 fg iGDGTs cell−1. An altered BIT index (BITCH), indicating changes in terrestrial organic matter supply to the lake, is proposed.

To gain insights into the mechanisms of abrupt climate change within interglacials, we have examined the characteristics and spatial extent of a prominent, climatically induced vegetation setback during the Holsteinian interglacial (Marine Isotope Stage 11c). Based on analyses of pollen and varves of lake sediments from Dethlingen (northern Germany), this climatic oscillation, here termed the “Older Holsteinian Oscillation” (OHO), lasted 220 years. It can be subdivided into a 90-year-long decline of temperate tree taxa associated with an expansion of Pinus and herbs, and a 130-year-long recovery phase marked by the expansion of Betula and Alnus, and the subsequent recovery of temperate trees. The climate-induced nature of the OHO is corroborated by changes in diatom assemblages and δ18O measured on biogenic silica indicating an impact on the aquatic ecosystem of the Dethlingen paleolake. The OHO is widely documented in pollen records from Europe north of 50° latitude and is characterized by boreal climate conditions with cold winters from the British Isles to Poland, with a gradient of decreasing temperature and moisture availability, and increased continentality towards eastern Europe. This pattern points to a weakened influence of the westerlies and/or a stronger influence of the Siberian High. A comparison of the OHO with the 8.2 ka event of the Holocene reveals close similarities regarding the imprint on terrestrial ecosystems and the interglacial boundary conditions. Hence, in analogy to the 8.2 ka event, a transient, meltwater-induced slowdown of the North Atlantic Deep Water formation appears as a plausible trigger mechanism for the OHO. If correct, meltwater release into the North Atlantic may be a more common agent of abrupt climate change during interglacials than previously thought. We conclude that meltwater-induced climate setbacks during interglacials preferentially occurred when low rates of summer insolation increase during the preceding terminations facilitated the persistence of large-scale continental ice-sheets well into the interglacials.

A high-resolution paleolimnological study from Lake Brazi, a small mountain lake in the Southern Carpathian Mountains, Romania, shows distinct diatom responses to late glacial and early Holocene climate change between ca. 15,750 and 10,000 cal year BP. Loss-on-ignition, titanium, sulphur, phosphorus, biogenic silica content, and diatom assemblage composition were used as proxies for past environmental changes. Total epilimnetic phosphorus (TP) concentrations and lakewater pH were reconstructed quantitatively using diatom-TP and pH transfer functions. The most remarkable changes in the aquatic ecosystem were found at ca. 12,870 and 10,400 cal year BP. Whereas the onset of the Younger Dryas (YD) climatic reversal was conspicuous in our record, the beginning of the Holocene was not well marked. Two diatom assemblage zones characterize the YD in Lake Brazi, suggesting a bipartite division of this climatic oscillation. The diatom responses to the YD cooling were (1) a shift from Staurosira venter to Stauroforma exiguiformis dominance; (2) a decrease in overall diatom diversity; (3) a decrease in lake productivity, inferred from DI-TP, organic matter, and biogenic silica content; and (4) a lowering of the DI-pH. Compositional change of the diatom assemblages suggested a sudden shift towards more acidic lake conditions at 12,870 cal year BP, which is interpreted as a response to prolonged ice cover and thus shorter growing seasons and/or enhanced outwash of humic acids from the catchment. Taking into account the chironomid-based inference of only moderate July mean temperature decrease (

This paper summarises the results of tephrochronological investigations into a suite of central and southern European records, which include: Rotmeer, southern Germany; Soppensee and Rotsee, central Swiss Plateau; Lago di Lavarone and Lago Piccolo di Avigliana, Italian southern Alpine foreland. These sites provide records of palaeoenvironmental changes for the Last Glacial to Interglacial Transition (LGIT) at the boundary between North Atlantic and Mediterranean climatic influences. Chemical characterisation of glass shards in volcanic ash layers indicates that multiple volcanic sources have contributed to the central European tephra record. Amongst other volcanic markers, the Laacher See Tephra, originating from the Eifel region of Germany c. 12.9 ± 0.1 ka, and the Vedde Ash from Iceland c. 12.1 ± 0.1 ka, are found co-located within the sediments of Rotmeer, Soppensee, Rotsee and Lago Piccolo di Avigliana. These key horizons, which bracket the onset of the Younger Dryas stadial, provide precise calendrically-dated tie points around which a detailed picture of the timing of local and regional environmental transitions can be constructed. Using the co-located tephra layers the re-colonisation of Northern Italian catchment areas by Quercus is shown to occur just prior to the deposition of the Laacher See Tephra layer, whereas to the North of the Alps Quercus and other thermophilous trees do not reappear until several centuries after the deposition of the Vedde Ash. Furthermore, the discovery of the Vedde Ash in Lago Piccolo di Avigliana and Lago di Lavarone is indicative of atmospheric transport of polar air into southern Europe during the Younger Dryas stadial, matching evidence proposed for such transport of polar air during the Last Glacial Maximum (LGM).

Quantitative July temperature reconstructions using fossil chironomid and pollen data have been carried out with a high temporal resolution for the Termination 1a and the late-glacial Interstadial (ca 15 000–13 000 cal years BP) on a sediment core from Gerzensee (Switzerland). The biota-based July temperature reconstructions show a rapid warming of 4–5 °C (pollen) and 2–3 °C (chironomids) at Termination 1a (i.e. the onset of the late-glacial Interstadial, ca 14 650 cal. BP). These temperature changes go parallel with a shift of more than 3‰ in a high-resolution stable oxygen isotope record measured on bulk carbonates from the same core, also indicating a substantial and rapid warming. Pollen-inferred July temperatures follow the shape of the oxygen-isotope record with a generally decreasing trend of ca 2 °C throughout the Interstadial, showing even minor cold oscillations of 0.5–1 °C in July temperature recorded in many central European sites (e.g. Aegelsee and Gerzensee Oscillations) and the Greenland ice cores (e.g. GI-1d and GI-1b). Chironomid-inferred summer temperatures, however, show a gradual increase of ca 2–3 °C throughout the Interstadial, interrupted by some cold oscillations (e.g. GI-1b) of 0.5–1 °C. The reconstructions based on both proxies are in agreement with comparable studies in the Jura Mountains and the Alps. Given the close correlation between the oxygen isotope record and the pollen-inferred temperatures, the discrepancies between the two biota-specific July temperature inferences could be explained by the higher sensitivity of vegetation to changes in seasonality and precipitation, whereas aquatic organisms such as chironomids are more responsive to summer season conditions.

The INTIMATE protocol for the correlation of marine ice core and terrestrial records is here updated, reflecting recent developments in palaeoclimate research. Originally focussed on Last Glacial to Interglacial Transition (LGIT: 22,000–11,500 years B.P.), the INTIMATE group has now extended its study period back to 60,000 years. As a first step, the INTIMATE event stratigraphy has now been extended to include 8000–48,000 b2k based on a combined NGRIP and GRIP isotope profile against a GICC05 chronology and key tephra horizons from Iceland and continental European volcanic sources. In this lead article of this INTIMATE special issue we introduce some of the recent achievements of the INTIMATE community and discuss the challenges associated with extending the INTIMATE approach back in time, focussing in particular on the chronological problems inherent in comparing different proxy records. The INTIMATE approach has thus far been limited predominantly to the North Atlantic and Australasian regions and we also discuss the potential to extend the INTIMATE protocol beyond these regions.

The Vedde Ash is the most important volcanic event marker layer for the correlation of Late Quaternary palaeoenvironmental archives in Europe and the North Atlantic. First defined from its type site localities near Alesund, Western Norway, the Vedde Ash has now been traced across much of northern and central Europe, into northwest Russia, within North Atlantic marine sediments and into the Greenland ice cores. The Vedde Ash is thought to derive from an eruption of the Katla volcano in Iceland that occurred midway through the Younger Dryas/Greenland Stadial 1 (GS-1), ∼12.1 ka BP. Visible and cryptotephra deposits of the Vedde Ash have been found in numerous stratified sites with robust chronologies, which allow its age to be constrained and its dispersal to be mapped. The eruption must have been highly explosive, however few proximal outcrops have been confirmed and this crucial ash layer remains almost exclusively distally-described and characterised using major element glass compositions. The widespread distribution, stratigraphic associations and consistent major element glass chemistry have led the Quaternary tephrochronological community to see the Vedde Ash as a robust and unique chronological marker layer for the Last Glacial to Interglacial Transition (∼10–18 ka BP). Here we present new glass analyses of the Vedde Ash from multiple sites around the dispersal area, using a full suite of compositional analysis, including for the first time, single-grain trace element data. These data demonstrate the strong compositional coherence of Vedde Ash deposits. However, comparison with major, minor, and trace element compositional data from several other distally-described Icelandic tephras reveals that both before and after the Younger Dryas chronozone, there were eruptions that generated widespread tephra layers that have comparable glass shard compositions to the Vedde Ash. This implies that these numerous events not only hail from the same volcanic system, but that the melts share similar crystallisation trends and mixing patterns prior to eruption. It seems therefore that composition alone is insufficient for the correlation of some widespread tephra layers: good stratigraphic information and/or robust dating control are also essential.

SUMMARY 1. Methanogenic carbon can be incorporated by methane-oxidising bacteria, leading to a 13 C-depleted stable carbon isotopic composition (d 13 C) of chironomids that feed on these microorganisms. This has been shown for the chironomid tribe Chironomini, but very little information is available about the d 13 C of other abundant chironomid groups and the relationship between chironomid d 13 C and methane production in lakes. 2. Methane flux was measured at the water surface of seven lakes in Sweden. Furthermore, fluxes from the sediments to the water column were measured in transects in two of the lakes. Methane fluxes were then compared with d 13 C of chitinous chironomid remains isolated from the lake surface sediments. Several different chironomid groups were examined (Chironomini, Orthocladiinae, Tanypodinae and Tanytarsini). 3. Remains of Orthocladiinae in the seven study lakes had the highest d 13 C values ()31.3 to )27.0&), most likely reflecting d 13 C of algae and other plant-derived organic matter. Remains of Chironomini and Tanypodinae had lower d 13 C values ()33.2 to )27.6& and )33.6 to )28.0&, respectively). A significant negative correlation was observed between methane fluxes at the lake surface and d 13 C of Chironomini (r = )0.90, P = 0.006). Methane release from the sediments was also negatively correlated with d 13 C of Chironomini (r = )0.67, P = 0.025) in the transect samples obtained from two of the lakes. The remains of other chironomid taxa were only weakly or not correlated with methane fluxes measured in our study lakes (P > 0.05). 4. Selective incorporation of methane-derived carbon can explain the observed correlations between methane fluxes and d 13 C values of Chironomini. Remains of this group might therefore have the potential to provide information about past changes in methane availability in lakes using sediment records. However, differences in productivity, algal d 13 C composition and the importance of allochthonous organic matter input between the studied lakes may also have influenced Chironomini d 13 C. More detailed studies with a higher number of analysed samples and detailed measurement of d 13 C of different ecosystem components (e.g. methane, dissolved inorganic carbon) will be necessary to further resolve the relative contribution of different carbon sources to d 13 C of chironomid remains.

A 274-lake calibration data-set for chironomid-based temperature reconstruction is presented which is based on the taxonomic amalgamation of a 117-lake data-set from Switzerland and a 157-lake data-set from Norway and Svalbard. Taxonomic consistency of the two data-sets was ensured by joint microscope sessions by the two involved analysts, re-identifying chironomid assemblages in the Swiss data-set to reach an identical taxonomic resolution as in the Norwegian data, and by double-checking selected samples of the Norwegian calibration data-set. The combined Swiss-Norwegian calibration data-set contains information on the distribution of 154 chironomid taxa over a July air temperature range of 3.5–18.4 °C, a pH range of 4.7–8.8, and an altitudinal range of 5–2815 m asl from lakes in temperate, subarctic, arctic, and alpine environments. Inference models developed based on this data-set using weighted averaging-partial least squares (WA-PLS) regression outperformed inference models based on maximum likelihood regression. After outlier deletion WA-PLS regression predicted July air temperature with a bootstrapped (cross-validated) root mean squared error of prediction (RMSEP) of 1.40 °C. Inference models developed from the separate regional data-sets have an RMSEP of 1.16 and 1.43 °C for the Norwegian and the Swiss calibration data-set, respectively. The WA-PLS inference model based on the Norwegian data-set adequately predicted July air temperature based on chironomid assemblages in the Swiss data-set (RMSEP 2.05 °C; r 2 0.74). In contrast, the WA-PLS model based on the Swiss chironomid assemblages performed poorly in inferring July air temperatures based on the Norwegian chironomid assemblages (RMSEP 2.70 °C; r 2 0.39). We attribute this discrepancy to the large proportion of chironomid taxa in Norwegian samples not represented in the Swiss data-set, the larger range of both pH and lake types included in the Norwegian calibration data-set, and the lack of some chironomid taxa with an arctic and boreal distribution in the Swiss data-set. The WA-PLS inference model based on the combined Swiss-Norwegian calibration data-set is the largest taxonomically consistent chironomid-based inference model available to date and outperforms other existing models if the r 2 and RMSEP relative to the overall temperature gradient are examined. We demonstrate that the combined model can reconstruct a larger range of temperatures when applied to fossil assemblages than models based on the Norwegian or Swiss calibration data-sets only. The combined data-set includes the majority of chironomid taxa expected in late Pleistocene and Holocene sediments of lakes from Northern, Eastern, and Central Europe as well as from southern European mountain lakes. The newly developed WA-PLS inference model is therefore well suited for developing continental-scale reconstructions of late Quaternary temperature change based on chironomid records from different parts of Europe.

An understanding of modern relationships between the stable oxygen isotope composition (δ18O) of lake water and aquatic invertebrates is essential for the interpretation of paleoclimate records based on δ18O of organic remains of these organisms. We analyzed δ18O of lake water and invertebrate remains, including head capsules of chironomid larvae and resting eggs (ephippia) of planktonic Cladocera, in surface sediments from 31 large, deep, and stratified lakes along a latitudinal transect through Europe. The δ18O values measured for both lake water and aquatic invertebrate remains were compared to estimated δ18O in precipitation. A strong linear relationship between mean annual air temperature and δ18O of precipitation was observed along the north–south transect (r = 0.97), whereas the relationship between precipitation δ18O and lake-water δ18O was weaker (r = 0.80). A strong positive correlation was observed between δ18O in lake water and aquatic invertebrates (r = 0.95 and 0.94 for chironomids and cladocerans, respectively). Although slopes of linear regressions between lake-water δ18O and δ18O of both aquatic invertebrate groups are similar, a systematic offset between the absolute δ18O values of chironomids and cladocerans was observed; chironomids were on average 2.4‰ heavier than Cladocera. We attribute this offset to differences in ecology, metabolism, and/or behavior between benthic chironomid larvae and planktonic Cladocera. δ18O records based on subfossil chironomid and cladoceran remains have the potential to quantitatively characterize past lake-water δ18O and, indirectly, past climatic changes.

To unravel the short-term climate variability during Marine Isotope Stage (MIS) 11, which represents a close analogue to the Holocene with regard to orbital boundary conditions, we performed microfacies and time series analyses on a ~3200-yr-long record of annually laminated Holsteinian lake sediments from Dethlingen, northern Germany. These biogenic varves comprise two sub-layers: a light sub-layer, which is controlled by spring/summer diatom blooms, and a dark sub-layer consisting mainly of amorphous organic matter and fragmented diatom frustules deposited during autumn/winter. Time series analyses were performed on the thickness of the light and dark sub-layers. Signals exceeding the 95% and 99% confidence levels occur at periods that are near-identical to those known from modern instrumental data and Holocene palaeoclimatic records. Spectral peaks at periods of 90, 25, and 10.5 yr are likely associated with the 88-, 22- and 11-yr solar cycles, respectively. This variability is mainly expressed in the light sub-layer spectra, suggesting solar influence on the palaeoproductivity of the lake. Significant signals at periods between 3 and 5 yr and at ∼6 yr are strongest expressed in the dark sub-layer spectra and may reflect an influence of the El Niño-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) during autumn/winter. Our results suggest that solar forcing and ENSO/NAO-like variability influenced central European climate during MIS 11 similarly to the present interglacial, thus demonstrating the comparability of the two interglacial periods at sub-decadal to decadal timescales.

A pollen-inferred vegetation shift, from pioneer birch-pine woodland to mixed pine-summergreen oak forests, in the southern Alpine forelands, is commonly attributed to a centennial-scale warming that occurred between the Gerzensee Oscillation (GO) and the Younger Dryas. Two microtephra layers bracketing the Younger Dryas onset (the Laacher See Tephra and the Vedde Ash) improve the chronology at Lago Piccolo di Avigliana (northern Italy) and allowed accurate correlation with Central European records where the GO is clearly detected. We used pollen percentages, pollen accumulation rates (PARs) and plant macrofossils to assess the population dynamics of Quercus, and leaf-cuticle analysis for a better taxonomic identification of Quercus. Our results indicate that the species that was locally present was probably Quercus robur. PARs suggest that the population expansion started as early as the Bolling and followed an exponential increase through time. We attribute this gradual shift to increasing summer temperatures and longer growing seasons which contrast with a gradually decreasing temperature trend as recorded in Greenland ice cores and in Central Europe. Breaks or set-backs in the PAR record may indicate the biotic response to minor Lateglacial cooling events of different life-history stages in the Quercus population. Copyright # 2011 John Wiley & Sons, Ltd.

Earlier spring onset and the associated extension of the growing season in high latitudes belong to the most obvious consequences of global warming. The natural dynamics of growing-season properties during past climate shifts however, are extremely difficult to reconstruct since temperature reconstructions are hardly ever seasonally resolved and the applied proxies such as chirinomid or pollen analysis are mainly sensitive to summer temperatures. Here we apply a newly developed leaf cuticle-based proxy to reconstruct growing degree-days (GDD) in a quantitative way and to estimate changes in the timing of spring onset over the last deglaciation. Cuticle analyses of fossil birch leaves preserved in lake sediments from southern Germany reveal extremely low GDD values during the Late Pleniglacial, which are rapidly increasing at the onset of the Bolling/Allerod interstadial. While temperature and GDDs show a simultaneous warming during deglaciation, a GDD decline precedes lowering of summer temperatures during the Older Dryas cooling. Later bud-burst dates support the hypothesis of a shortening the growing season during this cool pulse.

Sacrower See is a eutrophic lake with annually laminated sediments extending back to A.D. 1868. Analysis of annual layers revealed multi-decadal periods of distinct diatom assemblages at A.D. 1868–1875, 1876–1940, 1941–1978, and 1979–2000. Detrended correspondence analysis performed on individual seasonal sediment layers showed decadal-scale patterns of turnover in the diatom flora. The spring–summer layers showed higher sample scores until the early 1960s, after which the differences with the autumn–winter layers became smaller. Rates-of-change analysis revealed that the seasonal variability in diatom assemblages was higher than the annual changes. Summer diatom rates of change over the period A.D. 1894–1960 was on average higher than for winter, whereas between the 1960s and 1970s the winter rates of change became higher than the summer ones. Redundancy Analyses showed that seasonal temperatures and wind strength were significant explanatory variables for diatom assemblages in both annual and seasonal layers. These results suggest that meteorological changes indirectly affected diatom assemblages via the mixing regime of the lake. A comparison of the diatom rates of change with the amplitude of inter-annual climate change shows a statistically significant correlation for the spring-summer layers in the period of A.D. 1963–2000, showing that the sensitivity of diatom assemblages to meteorological changes has varied over the past century, with a stronger effect on diatoms registered during the past 40 years.

Summary 1. The distributions of subfossil remains of chironomid larvae in 28 large, deep and stratified lakes in Europe were examined in surface sediments along a latitudinal transect ranging from northern Sweden to southern Italy. 2. Canonical correspondence analysis (CCA) showed that summer surface water and July air temperature, as well as total phosphorus (TP) concentrations, hypolimnetic oxygen availability and conductivity were statistically significant (P

We explored whether the stable oxygen isotope composition (δ18O) of fossil chironomid remains can be used to reconstruct past variations in lake water δ18O from Lateglacial and early Holocene sediments from Rotsee (Switzerland). A sediment core from the former littoral zone of the lake was examined since it contained both high concentrations of chironomid remains and abundant authigenic carbonates and therefore allowed a direct comparison of chironomid δ18O with values measured on bulk carbonates. Since carbonate particles adhering to chironomid remains potentially affect 18O measurements we tested two methods to chemically remove residual carbonates. Trials with isotopically heavy and light acid solutions indicated that treatment with hydrochloric acid promoted oxygen exchange between chironomid remains and the water used during pretreatment. In contrast, a buffered 2 M ammonium chloride (NH4Cl) solution did not seem to affect chironomid δ18O to a significant extent. Fossil chironomid δ18O was analyzed for the Rotsee record both using standard palaeoecological methods and after pretreatment with NH4Cl. Samples prepared using standard techniques showed a poor correlation with δ18O of bulk carbonate (r2 = 0.14) suggesting that carbonate contamination of the chironomid samples obscured the chironomid δ18O signature. Samples pretreated with NH4Cl correlated well with bulk carbonate δ18O (r2 = 0.67) and successfully tracked the well-known Lateglacial changes in δ18O. Chironomid δ18O indicated depleted lake water δ18O during the Oldest Dryas period, the Aegelsee and Gerzensee Oscillations, and the Younger Dryas, whereas enriched δ18O values were associated with sediments deposited during the Lateglacial interstadial and the early Holocene. Differences in the amplitude of variations in bulk carbonate and chironomid δ18O are attributed to differential temperature effects on oxygen isotope fractionation during the formation of carbonates and chironomid head capsules or seasonal changes of lake water δ18O, potentially affecting δ18O of these two substances to a different extent. Our results indicate that chironomid δ18O can successfully reconstruct centennial to millennial-scale changes in lake water δ18O and that the method can be applied to carbonate-rich records provided that care is taken to eliminate carbonate contamination from the samples.

Abrupt climatic shifts between cold stadials and warm interstadials, termed Dansgaard-Oeschger (DO) cycles, occurred frequently during the Last Glacial. Their imprint is registered in paleorecords ...

Relative species abundances are the most frequently applied data type used for modern or paleolimnological diatom studies. In contrast, plant ecologists save time by commonly using ordinal scale data (class data), where the abundance of a species is estimated using dominance classes, instead of relative abundance data. This study compares the performance of models based on ordinal diatom species class data (class 1: sporadic (0-1%) up to class 6: dominant (60%)) with similar model types based on relative abundance data for different regional training sets and sediment cores. First, relative diatom abundances were converted into ordinal classes. Species response to total phosphorous (TP) was modelled using both types of data - relative abundance and ordinal class data. Secondly, TP was reconstructed for six sediment cores from North-East Germany, Switzerland, and Denmark using WA and WA-PLS based on both types of data. Thirdly, 20 lake sediment surface samples with known relative diatom abundances and known water TP concentrations were recounted using an ordinal data scale to create an independent test set. No significant differences were found between relative abundance and class data for (1) explained species variance, (2) reconstructed TP values, and (3) inferred TP values of the 20 recounted samples. This approach demonstrates that past TP concentrations may also be reliably reconstructed using class data instead of relative diatom abundances. Thus, by using class data lake managers may not only obtain more long-term records past water quality, but this approach is also quicker and therefore more cost effective. Moreover, the findings of this study may also advance the use of automatic diatom identification with digital image recognition, as we demonstrate that not every damaged diatom valve needs to be identified.

The resolution achievable for chironomid identifications has increased in recent years because of significant improvements in taxonomic literature. However, high taxonomic resolution requires more training for analysts. Furthermore, with greater taxonomic resolution, misidentifications and the number of rare, poorly represented taxa in chironomid calibration datasets may increase. We assessed the effects of various levels of taxonomic resolution on the performance of chironomid-based temperature inference models (transfer functions) and temperature reconstruction. A calibration dataset consisting of chironomid assemblage and temperature data from 100 lakes was examined at four levels of taxonomic detail. The coarsest taxonomic resolution primarily represented identifications to genus or suprageneric level. At the highest level of taxonomic resolution, identification to genus level was possible for 37% of taxa, and identification below genus was possible for 60% of taxa. Transfer functions were obtained using Weighted Averaging (WA) and Weighted Averaging-Partial Least Squares (WA-PLS) regression. Cross-validated performance statistics, such as the root mean square error of prediction (RMSEP) and the coefficient of determination (r2) between inferred and observed values improved considerably from the lowest taxonomic resolution level (WA: RMSEP 1.91°C, r2 0.78; WA-PLS: RMSEP 1.59°C, r2 0.86) to the highest taxonomic resolution level (WA: RMSEP 1.66°C, r2 0.84; WA-PLS: RMSEP 1.41°C, r2 0.89). Reconstructed July air temperatures during the Lateglacial period based on fossil chironomid assemblages from Hijkermeer (The Netherlands) were similar for all levels of taxonomic resolution, except the coarsest level. At the coarsest taxonomic level, reconstruction failed to infer one of the known Lateglacial cold episodes in the record. Also, the difference in reconstructed values based on lowest and highest taxonomic resolutions exceeded sample-specific estimated standard errors of prediction in several instances. Our results suggest that chironomid-based transfer functions at the highest taxonomic resolution outperform models based on lower-resolution calibration data. However, transfer functions of intermediate taxonomic resolution produced results very similar to models based on high-resolution taxonomic data. In studies that include analysts with different levels of expertise, inference models based on intermediate taxonomic resolution, therefore, might provide an alternative to transfer functions of maximum taxonomic detail in order to ensure taxonomic consistency between calibration datasets and down-core records produced by different analysts.

We aim to quantify the changes in regional vegetation cover on the Swiss Plateau during the past two millennia with the recently developed REVEALS model. We used pollen data from four large lakes (≥520 ha), namely (1) Baldeggersee, Hallwilersee, and Greifensee on the Swiss Plateau and from (2) Zugersee at the Swiss Plateau–Alps transition. Also, we used pollen productivity estimates (PPEs) that are available for 13 taxa in this region. First, we estimated present-day vegetation and land-cover composition on the Swiss Plateau. The REVEALS result is much more similar to the observed composition than the pollen percentages from modern surface sediment samples, thus confirming the robustness of the REVEALS approach for the Swiss Plateau. We then reconstructed regional vegetation composition in 200-year intervals over the past two millennia. In both investigated regions the REVEALS results showed a strong anthropogenic impact on vegetation: the results suggest that the landscape was much more open (20–80%) throughout the past 2000 years than pollen percentages (10–50%) suggest. Our model results provide quantitative and more realistic estimates of the regional vegetation and land-cover changes that are relevant for assessing regional vegetation-climate feedbacks. However, PPEs for more plant taxa as well as further assessment of PPEs, particularly for Cerealia, are needed. Also, the model-inferred quantitative vegetation changes reflect the regional differences in agricultural and other human activities during the Roman Time, the Migration Period, the early and late Middle Ages, and since the onset of Modern Times.

A series of surface sediments from 82 lakes of variable water depth and size was analyzed for glycerol dialkyl glycerol tetraethers (GDGTs) in order to investigate the potential of the MBT/CBT (methylation ratio/cyclization ratio of branched tetraethers) as a continental palaeothermometer in lacustrine environments. Branched GDGTs dominated in most sediments, as indicated by the high branched vs. isoprenoid tetraether (BIT) values. We observed that CBT and MBT varied substantially. Mean annual air temperature (MAAT reconstructed) and pH values were calculated using the CBT and MBT values and the calibration from the global soil data set. The MBT/CBT inferred temperatures were considerably lower than measured values. Nevertheless, there was a significant correlation between MAAT reconstructed and MAAT observed on site, although there was still considerable scatter (r(2) 0.47). Lacustrine sediments integrate organic remains of organisms in a lake and its drainage basin, thereby offering a unique opportunity for calibrating MBT and CBT, as small scale variability is averaged out. Since the source of the branched GDGTs in the lake sediments is ambiguous, it is not clear whether only temperature and pH in the catchment area are the driving factors. Therefore, even in lake sediments with high concentrations of branched GDGTs the straightforward application of MBT/CBT as palaeoproxies may be difficult given the uncertainties regarding their source and origin.