Lipid biomarker (brGDGT)- and pollen-based reconstruction of temperature change during the Middle to Late Holocene transition in the Carpathians

To reconstruct changes in vegetation, temperature, and sediment geochemistry through the last 6.5 cal ka BP, in the Subcarpathian belt of the Eastern Carpathians (Romania), pollen, branched glycerol dialkyl glycerol tetraethers (brGDGTs) and X-ray fluorescence analyses have been integrated. Pollen and brGDGTs (a bacterial lipid biomarker proxy) are used as paleothermometers for reconstructing the mean annual air temperature (MAAT) and mean temperature above freezing (MAF), respectively. Both proxies show roughly consistent records. The highest MAAT and MAF occurs during the oldest part of the record (from 6.5 to 4.2 cal ka BP), and the Middle to the Late Holocene shift is marked by a prominent decrease in temperature between 5.4 and 4.2 cal ka BP, coinciding with Bond event 4 and 3. This transition is coeval with a decrease in summer insolation, shift from consistent NAO-conditions to a predominance of NAO+ phase and coincides with the beginning of the Neoglacial cooling in northern latitudes. The warm bias in the MAF reconstruction during the Late Holocene is explained as a change in the lipid provenance or in the composition of the brGDGT producers after 4.2 cal ka BP.Peer reviewe

Ecosystem shift of a mountain lake under climate and human pressure : A move out from the safe operating space

A multiproxy approach including chironomid, diatom, pollen and geochemical analyses was applied on short gravitational cores retrieved from an alpine lake (Lacul Balea) in the Southern Carpathians (Romania) to unveil how this lake responded to natural and anthropogenic forcing over the past 500 years.On the basis of chironomid and diatom assemblage changes, and supported by sediment chemical data and historical information, we distinguished two main phases in lake evolution. Before 1926 the lake was dominated by chironomids belonging to Micropsectra insignilobus-type and benthic diatoms suggesting well-oxygenated oligotrophic environment with only small-scale disturbance. We considered this state as the lake's safe operational space. After 1926 significant changes occurred: Tanytarsus lugens-type and T. mendax-type chironomids took over dominance and collector filterers increased until 1970 pointing to an increase in available nutrients. The diatom community showed the most pronounced change between 1950 and 1992 when planktonic diatoms increased. The highest trophic level was reconstructed between 1970 and 1992, while the indicator species of increasing nutrient availability, Asterionella formosa spread from 1982 and decreased rapidly at 1992. Statistical analyses evidenced that the main driver of the diatom community change was atmospheric reactive nitrogen (Nr) fertilization that drastically moved the community towards planktonic diatom dominance from 1950. The transformation of the chironomid community was primarily driven by summer mean temperature increase that also changed the dominant feeding guild from collector gatherers to collector falterers. Our results overall suggest that the speed of ecosystem reorganisation showed an unprecedented increase over the last 100 years; biological systems in many cases underwent threshold type changes, while several system components displayed non-hysteretic change between alternating community composition. We conclude that Lake Balea is outside of its safe operating space today. The main trigger of changes since 1926 was climate change and human impact acting synergically. (C) 2020 The Authors. Published by Elsevier B.V.Peer reviewe

The Reading Palaeofire Database : an expanded global resource to document changes in fire regimes from sedimentary charcoal records

Sedimentary charcoal records are widely used to reconstruct regional changes in fire regimes through time in the geological past. Existing global compilations are not geographically comprehensive and do not provide consistent metadata for all sites. Furthermore, the age models provided for these records are not harmonised and many are based on older calibrations of the radiocarbon ages. These issues limit the use of existing compilations for research into past fire regimes. Here, we present an expanded database of charcoal records, accompanied by new age models based on recalibration of radiocarbon ages using IntCal20 and Bayesian age-modelling software. We document the structure and contents of the database, the construction of the age models, and the quality control measures applied. We also record the expansion of geographical coverage relative to previous charcoal compilations and the expansion of metadata that can be used to inform analyses. This first version of the Reading Palaeofire Database contains 1676 records (entities) from 1480 sites worldwide. The database (RPDv1b - Harrison et al., 2021) is available at https://doi.org/10.17864/1947.000345.Peer reviewe

The Reading Palaeofire Database: an expanded global resource to document changes in fire regimes from sedimentary charcoal records

Sedimentary charcoal records are widely used to reconstruct regional changes in fire regimes through time in the geological past. Existing global compilations are not geographically comprehensive and do not provide consistent metadata for all sites. Furthermore, the age models provided for these records are not harmonised and many are based on older calibrations of the radiocarbon ages. These issues limit the use of existing compilations for research into past fire regimes. Here, we present an expanded database of charcoal records, accompanied by new age models based on recalibration of radiocarbon ages using IntCal20 and Bayesian age-modelling software. We document the structure and contents of the database, the construction of the age models, and the quality control measures applied. We also record the expansion of geographical coverage relative to previous charcoal compilations and the expansion of metadata that can be used to inform analyses. This first version of the Reading Palaeofire Database contains 1676 records (entities) from 1480 sites worldwide. The database (RPDv1b – Harrison et al., 2021) is available at https://doi.org/10.17864/1947.000345

Neolithic human impact on the landscapes of North-East Hungary inferred from pollen and settlement records

In this article, we discuss the Neolithic and Early Copper Age (ECA) part of two pollen records from the Middle Tisza Floodplain in association with the local archaeological settlement record. We address the hypothesis of Willis and Bennett (2004) that there was little human impact by farmers on the environment of SE Europe until the Bronze Age. Contrary to this hypothesis, our results show that small-scale agriculture and woodland clearance is already attestable in the earliest Neolithic in Eastern Hungary, there are signs of expanding scale of mixed farming in the Middle Neolithic and strong evidence for extensive landscape alterations with enhanced pasturing and mixed farming in the Late Neolithic (LN) and ECA. The main vegetation exploitation techniques in the alluvial plain of Sarló-hát were selective tree felling (mainly Quercus), coppicing (mainly Corylus and Ulmus) and woodland clearance to establish grazing pastures and small-scale crop farming. Comparison with other well-dated pollen diagrams from Eastern Hungary suggested that, in the Early and Middle Neolithic (8000–7000 cal. b.p.), Corylus and Ulmus coppicing were probably frequent, while pastoral activities and associated woodland clearance is distinguished in the LN (7000–6500 cal. b.p.). Our data also suggested a shift to moister summer conditions in the alluvium during the ECA, which may have contributed to a trend towards settlement dispersion and increased reliance on animal husbandry in the NE Hungarian Plain

New measures for quantifying directional changes in presence-absence community data

Variation in community composition and species turnover are different types of beta diversity, expressing nondirectional and directional changes, respectively. While directional changes (e.g. turnover) along geographic gradients can be studied in any direction depending on the hypothesis of interest to researchers, temporal changes can only be meaningfully studied from past to present. Although a wide variety of methods exist for partitioning variation and related community-level phenomena such as similarity, richness difference and nestedness, approaches evaluating species turnover along geographic or temporal gradients, based on an analogous conceptual framework, are rare. We therefore look into the possibilities for examining different aspects of directional changes along a gradient when presence-absence community data are available. Measures of community overlap, as well as species loss and gain from one sampling unit to another along a gradient are combined to define a variety of turnover and nestedness concepts and to derive functions for their quantification. Each concept represents an ecological phenomenon to be indicated (indicandum), whereas measures (indicators) quantify relevant properties of these concepts. The measures use the raw number of species as well as relativized forms in accordance with the well-known Jaccard and Sorensen indices. The main innovation is the development of new measures of directional community change. We demonstrate differences between traditional nondirectional and the new directional measures and use several examples to show that actual communities display directional responses to a particular ecological gradient. The new measures therefore reveal an uncovered aspect of community ecology

A high-resolution Early Holocene-late MIS 3 environmental rock- and palaeomagnetic record from Lake Sf. Ana, Carpathian Mts, Romania

Lacustrine sediments are excellent sources of palaeoenvironmental and palaeoclimatic information because they usually provide continuous and high-resolution records. In centraleastern Europe however lacustrine records that extend beyond the Holocene are rather sparse.Palaeomagnetic records from this region are also insufficiently explored, and usually associated with terrestrial deposits such as loess. In this context, the lacustrine record of Lake Sf. Ana, a volcanic crater lake in the East Carpathians, Romania, provides an important archive for reconstructing past paleomagnetic secular variation in the region from early Holocene to late Marine Isotope Stage (MIS) 3.</p