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A chironomid data-set calibrated to July air temperatures, based on 44 lakes in western Norway, is used to reconstruct mean July air temperatures from late-glacial and early-Holocene fossil chironomid assemblages at Kråkenes Lake. The calibration function is based on Weighted Averaging Partial Least Squares regression and has a root mean square error of prediction (RMSEP) of 1.13 °C, a r2 of 0.69, and a maximum bias of 2.66 °C. All these statistics are based on leave-one-out cross-validation. A calibration function based on summer surface-water temperatures has a poorer performance (RMSEP = 2.22 °C, r2 = 0.30, maximum bias = 5.29 °C). The reconstructed July air temperatures at Kråkenes rise to 10.5 °C soon after deglaciation, are about 11.5 °C in the Allerød, decrease to 9.5-10 °C in the Younger Dryas, and rise rapidly within 15 yrs to 11.5 °C at the onset of the Holocene. There is a two-step rise to 13 °C or more in the early-Holocene. The likely over-estimation of Younger Dryas temperatures and under-estimation of early-Holocene temperatures probably result from the limited temperature range represented by the existing calibration set. The data set is currently being expanded to include lakes with warmer air temperatures (> 14 °C) and with colder air temperatures (< 8 °C). [ABSTRACT FROM AUTHOR]

A correction to this paper has been published: https://doi.org/10.1007/s10933-021-00196-8 [ABSTRACT FROM AUTHOR]

Although extensive archeological research works have been conducted in the Serteya region in recent years, the Holocene climate history in the Western Dvina Lakeland in Western Russia is still poorly understood. The Neolithic human occupation of the Serteyka lake–river system responded to climate oscillations, resulting in the development of a pile-dwelling settlement between 5.9 and 4.2 ka cal BP. In this paper, we present the quantitative paleoclimatic reconstructions of the Northgrippian stage (8.2–4.2 ka cal BP) from the Great Serteya Palaeolake Basin. The reconstructions were created based on a multiproxy (Chironomidae, pollen and Cladocera) approach. The mean July air temperature remained at 17–20 °C, which is similar to the present temperature in the Smolensk Upland. The summer temperature revealed only weak oscillations during 5.9 and 4.2 ka cal BP. A more remarkable feature during those events was an increase in continentality, manifested by a lower winter temperature and lower annual precipitation. During the third, intermediate oscillation in 5.0–4.7 ka cal BP, a rise in summer temperature and stronger shifts in continental air masses were recorded. It is still unclear if the above-described climate fluctuations are linked to the North Atlantic Oscillation and can be interpreted as an indication of Bond events because only a few high-resolution paleoclimatic reconstructions from the region have been presented and these reconstructions do not demonstrate explicit oscillations in the period of 5.9 and 4.2 ka cal BP. [ABSTRACT FROM AUTHOR]

The physical effects of climate warming have been well documented, but the biological responses are far less well known, especially at the ecosystem level and at large (intercontinental) scales. Global warming over the next century is generally predicted to reduce food web complexity, but this is rarely tested empirically due to the dearth of studies isolating the effects of temperature on complex natural food webs. To overcome this obstacle, we used 'natural experiments' across 14 streams in Iceland and Russia, with natural warming of up to 20°C above the coldest stream in each high‐latitude region, where anthropogenic warming is predicted to be especially rapid. Using biomass‐weighted stable isotope data, we found that community isotopic divergence (a universal, taxon‐free measure of trophic diversity) was consistently lower in warmer streams. We also found a clear shift towards greater assimilation of autochthonous carbon, which was driven by increasing dominance of herbivores but without a concomitant increase in algal stocks. Overall, our results support the prediction that higher temperatures will simplify high‐latitude freshwater ecosystems and provide the first mechanistic glimpses of how warming alters energy transfer through food webs at intercontinental scales. [ABSTRACT FROM AUTHOR]

Warming can have profound impacts on ecological communities. However, explorations of how differences in biogeography and productivity might reshape the effect of warming have been limited to theoretical or proxy-based approaches: for instance, studies of latitudinal temperature gradients are often conflated with other drivers (e.g., species richness). Here, we overcome these limitations by using local geothermal temperature gradients across multiple high-latitude stream ecosystems. Each suite of streams (6-11 warmed by 1-15°C above ambient) is set within one of five regions (37 streams total); because the heating comes from the bedrock and is not confounded by changes in chemistry, we can isolate the effect of temperature. We found a negative overall relationship between diatom and invertebrate species richness and temperature, but the strength of the relationship varied regionally, declining more strongly in regions with low terrestrial productivity. Total invertebrate biomass increased with temperature in all regions. The latter pattern combined with the former suggests that the increased biomass of tolerant species might compensate for the loss of sensitive species. Our results show that the impact of warming can be dependent on regional conditions, demonstrating that local variation should be included in future climate projections rather than simply assuming universal relationships. The responses of freshwater stream biodiversity and biomass to temperature in Arctic regions varies with biogeography. [ABSTRACT FROM AUTHOR]

Aim: To investigate if connectivity and zebra mussel (Dreissena polymorpha) occurrence can mitigate effects of eutrophication in a lowland lake landscape. Location: Upper Lough Erne, Northern Ireland, UK. Methods: Data on environment, macrophytes and invertebrates were assembled for three basins of a large central lake and its satellite floodplain lakes via field surveys and palaeolimnological analyses. Space–time interaction analyses of palaeoecological data were compared pre‐1950 and post‐1950. Multivariate analyses examined how connectivity, environment and zebra mussels influenced contemporary lake communities, and explain their divergence from historical communities in the past. Results: Pre‐1950, we found high community variation across sites and low within‐lake variation in macrophytes, but progressive eutrophication accentuated within‐lake community variation after 1950. Partitioning analysis showed larger effects of connectivity than nutrient enrichment on contemporary macrophyte composition, while local effects structured invertebrate communities. Three clusters of lakes were revealed according to variation in macrophyte composition, isolation from the central lake and nutrient enrichment: Group 1– the central lake and six nearby lakes were meso‐eutrophic (TP = 66.7 ± 47.6 μg/L; TN = 0.79 ± 0.41 mg/L) and had the highest zebra mussel abundances and organismal biodiversity; Group 2– Eight eutrophic (TP = 112±36.6 μg/L; TN = 1.25 ± 0.5 mg/L) and connected lakes; Group 3– Seven isolated and hypertrophic (TP = 163.2 ± 101.5 μg/L; TN = 1.55 ± 0.3 mg/L) lakes. Pre‐1950 palaeolimnological data for macrophytes and invertebrates for 5 lakes and a basin in the central lake most resembled extant lake communities of Group 1. However, palaeo‐records revealed that macrophytes and invertebrates subsequently converged towards those of Groups 2 and 3. Main conclusions: Our study reveals that the central "mother" lake acts as a hub for preserving biodiversity via shared hydrological connectivity with satellite lakes and high zebra mussel abundances. These may buffer the impoverishing effects of eutrophication and sustain unexpectedly high biodiversity in the short term. Such protective buffering, however, cannot be relied upon indefinitely to conserve biodiversity. [ABSTRACT FROM AUTHOR]

A terrestrial (lacustrine and fluvial) palaeoclimate record from Hoxne (Suffolk, UK) shows two temperate phases separated by a cold episode, correlated with MIS 11 subdivisions corresponding to isotopic events 11.3 (Hoxnian interglacial period), 11.24 (Stratum C cold interval), and 11.23 (warm interval with evidence of human presence). A robust, reproducible multiproxy consensus approach validates and combines quantitative palaeotemperature reconstructions from three invertebrate groups (beetles, chironomids, and ostracods) and plant indicator taxa with qualitative implications of molluscs and small vertebrates. Compared with the present, interglacial mean monthly air temperatures were similar or up to 4.0°C higher in summer, but similar or as much as 3.0°C lower in winter; the Stratum C cold interval, following prolonged nondeposition or erosion of the lake bed, experienced summers 2.5°C cooler and winters between 5°C and 10°C cooler than at present. Possible reworking of fossils into Stratum C from underlying interglacial assemblages is taken into account. Oxygen and carbon isotopes from ostracod shells indicate evaporatively enriched lake water during Stratum C deposition. Comparative evaluation shows that proxy-based palaeoclimate reconstruction methods are best tested against each other and, if validated, can be used to generate more refined and robust results through multiproxy consensus. [ABSTRACT FROM AUTHOR]

A multi-proxy reconstruction of water depth, temperature and precipitation inferred from Cladocera, Chironomidae and pollen assemblages has been obtained from Świerczyna paleo-oxbow (central Poland) during the Younger Dryas (YD) and Early Holocene. Results suggest that the YD was relatively cold and comprised two main phases. The first (ca. 12,500–12,000 cal. yrs BP) is characterized by a continental climatic regime and a decrease in winter temperatures and precipitation but an increase in spring/summer precipitation. The second phase (ca. 12,000–11,500 cal. yrs BP) was more mild with a variable continental climate, an increase in summer and winter temperature, a lengthening of the growing season and increased annual precipitation. The reconstructed water level generally follows changes in spring and summer precipitation and length of growing season. The frequency and timing of hydroclimatic oscillations at Świerczyna show strong similarities to records from other sites in Europe. This confirms that oxbows and valley mire ecosystems respond to rapid climate change during the YD and Early Holocene. This study therefore brings new insights into the effects of climate changes on river environments, especially during the YD. We also discuss the limitations of water depth, temperature and precipitation reconstructions inferred from the studied biotic assemblages. [ABSTRACT FROM AUTHOR]

West and East Siberian data sets and 55 new sites were merged based on the high taxonomic similarity, and the strong relationship between mean July air temperature and the distribution of chironomid taxa in both data sets compared with other environmental parameters. Multivariate statistical analysis of chironomid and environmental data from the combined data set consisting of 268 lakes, located in northern Russia, suggests that mean July air temperature explains the greatest amount of variance in chironomid distribution compared with other measured variables (latitude, longitude, altitude, water depth, lake surface area, pH, conductivity, mean January air temperature, mean July air temperature, and continentality). We established two robust inference models to reconstruct mean summer air temperatures from subfossil chironomids based on ecological and geographical approaches. The North Russian 2-component WA-PLS model (RMSEP Jack = 1.35 °C, r Jack 2 = 0.87) can be recommended for application in palaeoclimatic studies in northern Russia. Based on distinctive chironomid fauna and climatic regimes of Kamchatka the Far East 2-component WAPLS model (RMSEP Jack = 1.3 °C, r Jack 2 = 0.81) has potentially better applicability in Kamchatka. [ABSTRACT FROM AUTHOR]

Terrestrial records of past climatic conditions, such as lake sediments and speleothems, provide data of great importance for understanding environmental changes. However, unlike marine and ice core records, terrestrial palaeodata are often not available in databases or in a format that is easily accessible to the non-specialist. As a consequence, many excellent terrestrial records are unknown to the broader palaeoclimate community and are not included in compilations, comparisons, or modelling exercises. Here we present a compilation of Western European terrestrial palaeo-records covering, entirely or partially, the 60–8-ka INTIMATE time period. The compilation contains 56 natural archives, including lake records, speleothems, ice cores, and terrestrial proxies in marine records. The compilation is limited to include records of high temporal resolution and/or records that provide climate proxies or quantitative reconstructions of environmental parameters, such as temperature or precipitation, and that are of relevance and interest to a broader community. We briefly review the different types of terrestrial archives, their respective proxies, their interpretation and their application for palaeoclimatic reconstructions. We also discuss the importance of independent chronologies and the issue of record synchronization. The aim of this exercise is to provide the wider palaeo-community with a consistent compilation of high-quality terrestrial records, to facilitate model-data comparisons, and to identify key areas of interest for future investigations. We use the compilation to investigate Western European latitudinal climate gradients during the deglacial period and, despite of poorly constrained chronologies for the older records, we summarize the main results obtained from NW and SW European terrestrial records before the LGM. [ABSTRACT FROM AUTHOR]

The development of quantitative temperature reconstructions in regions of paleoclimate interest is an important step for providing reliable temperature estimates in that region. Fossil chironomid assemblages have been studied in Patagonia showing great promise for reconstructing paleotemperatures; however there is still a lack of robust temperature inference models in that area. To contribute to the understanding of climate change, a transfer function using chironomids preserved in 46 lakes in Chile and Argentina was developed. The best performing model to infer the mean air temperature of the warmest month was a 3-component WA-PLS model with a coefficient of correlation (r2 jack) of 0.56, a root mean square error of prediction (RMSEP) of 1.69°C and a maximum bias of 2.07°C. This model was applied to the chironomids preserved in the sediment of the Huelmo mire (41°31′ S, 73°00′ W), in the lake district of northwestern Patagonia. The reconstruction showed several cold spells (one at 13,200 to 13,000calyrBP and a cooling trend between 12,600 and 11,500calyrBP) associated with the Younger Dryas and/or Huelmo–Mascardi Cold Reversal (HMCR). Our findings support climate models proposing fast acting inter-hemispheric coupling mechanisms including the recently proposed bipolar atmospheric and/or bipolar ocean teleconnections rather than a bipolar see-saw model. [ABSTRACT FROM AUTHOR]

Abstract: A multi-proxy palaeoecological study of the lateglacial and early Holocene sediments of Jansvatnet, Hammerfest, northernmost Norway (70°39′ N) showed that cold and arid conditions prevailed in both the lateglacial interstadial and the Younger Dryas. Terrestrial proxies are macrofossils and pollen. Aquatic proxies are plant and invertebrate macrofossils, pollen, diatoms, and chironomids. Mean July temperatures were reconstructed using pollen and chironomid calibration functions and ecological knowledge of the fossil flora and fauna. Lake-water pH was reconstructed using a diatom pH-calibration function. Above sterile basal deglacial silts, biotic activity was detected around 14600 years ago in the interstadial (chronologically equivalent to the Bølling-Allerød in the Greenland Ice-Core Chronology). Catchment vegetation resembled polar desert and ultra-cold stenothermic chironomids lived in the lake. However, diatom assemblages were diverse and dynamic. In the Younger Dryas stadial, conditions deteriorated. In the early Younger Dryas chironomid-inferred air temperatures (CI-Tjul) fell about 1 °C. Pollen-inferred temperatures (PI-Tjul) did not fall and the terrestrial vegetation hardly changed because of the extreme aridity. The lake water was turbid from suspended clay which diminished aquatic life. Later in the Younger Dryas (ca 12400 cal yr BP) reconstructed mean July temperatures fell by a further 3 °C and were close to the minimum to support life, at around 3–4 °C. However, decreased turbidity allowed moss growth on the lake bottom that provided habitats for invertebrates and diatoms. In the last 200 years of the Younger Dryas temperatures increased by 2–3 °C and terrestrial and aquatic organisms responded quickly. At the start of the Holocene a rapid increase of more than 3 °C in PI-Tjul to 9.5 °C initiated the replacement of sparse arctic tundra by low-arctic dwarf-shrub heath. Simultaneously, a further 2 °C increase in CI-Tjul to 10–11 °C reflected a regime shift in the lake. Aquatic macrophytes rapidly replaced the moss carpet, diatom assemblages stabilised and diatom plankton developed, and cold stenotherm chironomids were replaced by cool-temperate taxa. Productivity increased as CI-Tjul reached a steady maximum of around 12 °C and PI-Tjul reached 10.5 °C at about 10000 cal yr BP. At this time, tree-birch arrived and woodland developed over the catchment. Birch could have immigrated from the south up the west coast or from the east along the Barents Sea coast. Acidophilous aquatic taxa increased as diatom-inferred pH gradually decreased from 7.3 to 6.6. After ca 9380 cal yr BP, the density and extent of birch woodland decreased and species of exposed rocky areas increased, reflecting increased windiness, precipitation, and possibly a small decrease in July temperatures. Birch now formed the arctic tree-line at Jansvatnet. The lateglacial climatic pattern at Jansvatnet resembles patterns detected elsewhere in northern Norway and Svalbard and in marine records from the Norwegian and Barents Seas but contrasts with patterns in southern Norway. [Copyright &y& Elsevier]

Abstract: Late glacial and early Holocene summer temperatures were reconstructed based on fossil chironomid assemblages at Lake Brazi (Retezat Mountains) with a joint Norwegian–Swiss transfer function, providing an important addition to the late glacial quantitative climate reconstructions from Europe. The pattern of the late glacial temperature changes in Lake Brazi show both similarities and some differences from the NGRIP δ 18O record and other European chironomid-based reconstructions. Our reconstruction indicates that at Lake Brazi (1740ma.s.l.) summer air temperature increased by ~2.8°C at the Oldest Dryas/Bølling transition (GS-2/GI-1) and reached 8.1–8.7°C during the late glacial interstade. The onset of the Younger Dryas (GS-1) was characterized by a weak (<1°C) decrease in chironomid-inferred temperatures. Similarly, at the GS-1/Holocene transition no major changes in summer temperature were recorded. In the early Holocene, summer temperature increased in two steps and reached ~12.0–13.3°C during the Preboreal. Two short-term cold events were detected during the early Holocene between 11,480–11,390 and 10,350–10,190calyr BP. The first cooling coincides with the Preboreal oscillation and shows a weak (0.7°C) temperature decrease, while the second is characterized by 1°C cooling. Both cold events coincide with cooling events in the Greenland ice core records and other European temperature reconstructions. [Copyright &y& Elsevier]

Abstract: A c. 18kacal BP long sediment record from Laguna Khomer Kocha Upper (4153m asl), Bolivia, shows that fire regime, governed by climatic variation, has long been a transformative agent in the eastern Andes. Before c. 14.5kacal BP, warming and relatively moist conditions free from fire, facilitated the expansion of high Andean Polylepis woodland. Fire onset at c. 14.5.kacal BP, quickly transformed the local vegetation and the woodlands became restricted to areas protected from fire. A major increase in burning, c. 10.1–6.4kacal BP removed Polylepis woodland locally and this coincided with a region-wide Holocene dry event (HDE) which caused falling lake levels and allowed fire intensification. A decline in burning at c. 6.4kacal BP and an increase in marsh–woodland (Alnus) marked the termination of the HDE and a return to wetter conditions. As well as recording the environmental history of local vegetation dynamics, long-distance pollen transport provides evidence of changes in the Yungas montane forests, highlighting their sensitivity to climate and burning regimes. Simultaneous adjustments in both Andean and Yungas montane taxa suggest that vegetation dynamics in the two environments are linked to a common climatic driver. There is no evidence to indicate that human activity had any impact on the local landscape. [Copyright &y& Elsevier]

Plant-plant interactions are known to vary with changing environmental conditions; however, we have little empirical knowledge of the impact of abrupt environmental changes on millennial scale plant-plant interaction outcomes for long-lived plant species. Here, we used palaeoecological data (13-7.6 k years ) and a novel statistical modelling approach to determine the impact of multiple environmental drivers on predicted tree-grass population interaction outcomes from our study site in eastern England. Changes from high to low herbivore density shortly preceded changes to low fire levels and a shift to warmer summers. These transitions occurred during a period of increasing nitrogen (N) availability. Shortly thereafter, there was a shift in landscape dominance from grasses to oaks and then a change to decreasing N availability. Model predictions of tree-grass interaction outcomes varied over time with respect to all environmental changes. During the time of high disturbances and cool summers, grasses were predicted to out-compete oaks. After climate warming and the loss of regular disturbances, the predicted outcome was stable coexistence. However, changes in the N cycle corresponded with different predicted outcomes: unstable competition under increasing N availability and facilitation of oaks by grasses when N availability was declining. Akaike Information Criterion weights indicate that climate warming and fewer fires were consistent with the best-fitting model of oak-grass interactions for the entire time series (i.e. competitive exclusion to stable coexistence). However, reconciling the conflicting model predictions with the observed population dynamics suggests that a temporary period of unstable competition preceded the predicted shift to stable coexistence. This dynamic behaviour is consistent with known patterns of shifts between alternative stable states. Synthesis. We show that abrupt changes in environmental conditions over time lead to similarly abrupt changes in tree-grass interaction outcomes, which were shown to vary in contrasting directions with respect to resource versus non-resource variables. The approach described here allows plant ecologists to test hypotheses of plant-plant interactions over successional time scales for long-lived species and thus can lead to new knowledge about the structural role of these interactions in community dynamics. [ABSTRACT FROM AUTHOR]

Temperature and the oxygen isotopic composition (δ18O) of meteoric water are both important palaeoclimatic variables, but separating their influences on proxies such as the δ18O of lake carbonates is often problematic. The large temperature variations that are known to have occurred in the northern mid-latitudes during the Late Glacial make this interval an excellent test for a novel approach that combines oxygen-isotope analyses of chironomid larval head capsules with co-occurring endogenic carbonate. We apply this approach to a Late Glacial lake sediment sequence from Hawes Water (NW England). Oxygen-isotope values in chironomid head capsules show marked variations during the Late Glacial that are similar to the oxygen isotope record from endogenic carbonate. However, summer temperature reconstructions based on the paired isotope values and fractionation between chironomids and calcite yield values between −20 and −4 °C, which are unrealistic and far lower than reconstructions based on chironomid assemblages at the same site. The composition of a limited number of samples of fossil chironomid larval head capsules determined using Pyrolysis gas-chromatography mass spectrometry indicates the presence of aliphatic geopolymers, suggesting that diagenetic alteration of the head capsules has systematically biased the isotope-derived temperature estimates. However, a similar trend in the isotope records of the two sources suggests that a palaeoclimate signal is still preserved. • δ18O from late glacial lacustrine chironomids and carbonate show similar trends. • Carbonate-water & chironomid-water fractionations combined to reconstruct temperature. • Temperatures reconstructed from carbonate and chironomid δ18O are implausibly low. • Implausible reconstructed temperatures explained by diagenetic alteration of chitin. [ABSTRACT FROM AUTHOR]

Fens have been forming in the river valleys of central Poland since the Bølling and went through a transformation from fully aquatic to semiterrestrial habitats during the Younger Dryas/Holocene transition. This drove plant and invertebrate communities and left a distinct pattern in chemical sediment composition, which is why river valley peatlands are sensitive palaeo-archives of climatic, hydrological and edaphic changes. Here we reconstruct the Late Weichselian history of the Bęczkowice fen in the upper Luciąża River valley using geochemical, pollen, Cladocera and Chironomidae proxies. Pollen-based age estimation indicates that the analysed peat sequence dates from the Bølling to Early Holocene. The layers 190-170 cm and 125-105 cm of the studied core were reworked by fluvial processes. Chironomidae and Cladocera communities indicate mostly limnetic conditions during the Allerød and early Younger Dryas. Peatland pools were supplied mostly by Luciąża River floods, but also by groundwater. Since the onset of the Holocene, the water level has dropped, eliminating aquatic midges and water fleas, and supporting taxa typical of astatic waters and wet soil. [ABSTRACT FROM AUTHOR]

Chironomids are a useful group for investigating body size responses to warming due to their high local abundance and sensitivity to environmental change. We collected specimens of six species of chironomids every 2 weeks over a 2-year period (2017–2018) from mesocosm experiments using five ponds at ambient temperature and five ponds at 4°C higher than ambient temperature. We investigated (1) wing length responses to temperature within species and between sexes using a regression analysis, (2) interspecific body size responses to test whether the body size of species influences sensitivity to warming, and (3) the correlation between emergence date and wing length. We found a significantly shorter wing length with increasing temperature in both sexes of Procladius crassinervis and Tanytarsus nemorosus, in males of Polypedilum sordens, but no significant relationship in the other three species studied. The average body size of a species affects the magnitude of the temperature-size responses in both sexes, with larger species shrinking disproportionately more with increasing temperature. There was a significant decline in wing length with emergence date across most species studied (excluding Polypedilum nubeculosum and P. sordens), indicating that individuals emerging later in the season tend to be smaller. [ABSTRACT FROM AUTHOR]

1. Body size is highly correlated with physiological traits, fitness, and trophic interactions. These traits are subject to change if there are widespread reductions of body size with warming temperatures, which is suggested as one of the 'universal' ecological responses to climate change. However, general patterns of body size response to temperature in insects have not yet emerged. 2. To address this knowledge gap, we paired the wing length (as a proxy for body size) of 5331 museum specimens of 14 species of British Odonata with historical temperature data. Three sets of analyses were performed: (i) a regression analysis to test for a relationship between wing length and mean seasonal temperature within species and subsequent comparisons across species and suborders; (ii) an investigation of whether the body size of species has an effect on sensitivity to warming temperature; and (iii) a linear‐mixed effects model to investigate factors that potentially affect temperature–size response. 3. The regression analysis indicated that wing length is negatively correlated with mean seasonal temperatures for Zygoptera, whereas Anisoptera showed no significant correlation with temperature. 4. There is a significant decline in wing length of all Zygoptera (but not Anisoptera) with collection date, suggesting that individuals emerging later in the season are smaller. 5. Life‐cycle type was not important for predicting wing length–temperature responses, whereas sex, species, and suborder were indicated as important factors affecting the magnitude of temperature–size responses in Odonata. 6. Overall, wing lengths of Zygoptera are more sensitive to temperature and collection date than Anisoptera. [ABSTRACT FROM AUTHOR]

Abstract In this study, we focus on the environmental changes recorded in the San River valley (Stubno–Nakło site, south-eastern Poland) at the beginning of the Holocene. This multi-proxy study for the first time in the region of the northern foreland of the Western Carpathians included quantitative thermal reconstruction based on Chironomidae and high-stratigraphic resolution of 14C AMS dating. We hypothesised that (i) climate events during the Early Holocene contributed to ecosystem turnovers via stimulating disturbances related to the river's fluvial activity and (ii) woodland and oxbow lake ecosystems became more resilient to flood disturbances along with the advance of forest succession on the floodplain. The results revealed that the response of ecosystems on the Early Holocene warming was strongly linked with the decrease in fluvial activity of the river. The reconstruction of the mean July temperature based on Chironomidae revealed the exceptionally high rate of warming during the period of ca. 11,490–11,460 cal. BP (at least 1 °C per decade) up to values > 2 °C than modern ones. During this period, the lake trophy and productivity started to increase with a simultaneous spread of Betula woodlands on the alluvial plain. The "Preboreal oscillation" cooling was dated at ca. 11,450–11,250 cal. BP. At that time, an increased climate instability led to a higher rate of extremal events such as flood at ca. 11,400–11,330 cal. BP, which probably led to the disruption of the Betula population. The development of riparian woodlands, initiated by the expansion of Ulmus from ca. 11,100 cal. BP, and further spread of Quercus and Fraxinus excelsior on the alluvial plain and lower river terraces increased plant transpiration and therefore limited the river runoff and its fluvial activity. This, together with the expansion of reed belt communities, probably limited the impact of floods on the oxbow lake. However, ca. 10,010–9880 cal. BP traces of higher fluvial activity, but of lower impact, were recorded. Highlights • The Early Holocene valley ecosystem changes in south-eastern Poland. • The ecosystems' response to climate changes was linked with the river activity. • High rate of warming (up to values > 2 °C than nowadays) ca. 11,490–11,460 cal. BP. • The potential influence of floods on Chironomidae populations in the oxbow lake. • Fluvial activity during the Preboreal oscillation was detrimental for Betula stands. [ABSTRACT FROM AUTHOR]

This article presents the first multi-proxy study of palaeoecosystem changes during the Late Weichselian and Early Holocene in western Ukraine. The site is a former oxbow lake situated in the Dniester River valley (western Ukraine). We hypothesised that this area may have been one of the nuclei for the Holocene expansion of elm ( Ulmus ), a primary arboreal taxon in riparian woodlands, in the Central and Eastern European lowlands. Our study was undertaken on a profile encompassing the period ca. 12,900–9880 cal. BP. We applied selected palaeobotanical, palaeozoological and geochemical analyses. During the Younger Dryas the area was dominated by well-developed Pinus sylvestris - Betula woodlands. Drier habitats were overgrown by Juniperus shrublands and steppe communities. Patches of tundra with Betula nana were also present. Ulmus started to spread on the lower river terraces before ca. 11,840 cal. BP i.e., during the late Younger Dryas, which suggests this area as a nucleus for its Holocene expansion. A chironomid-based reconstructed mean July temperature (MJT) of 15–17 °C is suggested during the Younger Dryas. The main Ulmus expansion started ca. 11,160 cal. BP and its optimum in local woodlands lasted until ca. 10,340 cal. BP, when Pinus sylvestris rapidly expanded. The reconstructed MJT varied between 18 and 21 °C during the Ulmus optimum; however, it rapidly declined to 16 °C around ca. 10,800 cal. BP. Fire activity increased before ca. 10,870 cal. BP, concurrent with the climate warming at the Younger Dryas-Holocene transition, but did not affect the population of Ulmus , a taxon intolerant of fires. Wildfires probably affected patches of steppe vegetation and Pinus sylvestris - Betula woodlands occupying higher elevations of the valley and watersheds. However, changes in the fire activity may have stimulated Ulmus retreat at ca. 10,340 cal. BP. [ABSTRACT FROM AUTHOR]

Animals with distinct life stages are often exposed to different temperatures during each stage. Thus, how temperature affects these life stages should be considered for broadly understanding the ecological consequences of climate warming on such species. For example, temperature variation during particular life stages may affect respective change in body size, phenology and geographic range, which have been identified as the 'universal' ecological responses to climate change. While each of these responses has been separately documented across a number of species, it is not known whether each response occurs together within a species. The influence of temperature during particular life stages may help explain each of these ecological responses to climate change., Our goal was to determine if monthly temperature variation during particular life stages of a butterfly species can predict respective changes in body size and phenology. We also refer to the literature to assess if temperature variability during the adult stage influences range change over time., Using historical museum collections paired with monthly temperature records, we show that changes in body size and phenology of the univoltine butterfly, Hesperia comma, are partly dependent upon temporal variation in summer temperatures during key stages of their life cycle. June temperatures, which are likely to affect growth rate of the final larval instar, are important for predicting adult body size (for males only; showing a positive relationship with temperature). July temperatures, which are likely to influence the pupal stage, are important for predicting the timing of adult emergence (showing a negative relationship with temperature). Previous studies show that August temperatures, which act on the adult stage, are linked to range change., Our study highlights the importance of considering temperature variation during each life stage over historic time-scales for understanding intraspecific response to climate change. Range edge studies of ectothermic species that have annual life cycles, long time-series occurrence data, and associated temperature records (ideally at monthly resolutions) could be useful model systems for intraspecific tests of the universal ecological responses to climate change and for exploring interactive effects. [ABSTRACT FROM AUTHOR]

The question of the relative importance of biotic interactions versus abiotic drivers for structuring plant communities is highly debated but largely unresolved. Here, we investigate the relative importance of mean July air temperature, nitrogen (N) availability and direct plant interactions in determining the millennial-scale population dynamics through the Holocene (10 700-5200 cal. years bp) for four temperate tree taxa in the Scottish Highlands., A variety of dynamic population models were fitted to our palaeoecological time-series data to determine the mechanism(s) by which each driver affected the population biomass dynamics of Betula (birch), Pinus (pine), Alnus (alder) and Quercus (oak). Akaike information criterion weights identified the best model(s) for describing the relationship between each population and driver. The relative importance of these drivers was then assessed by the ability of each model to predict the observed population biomass dynamics. We also measured the change in goodness-of-fit of each model over time., We found that models of intra- and interspecific plant interactions described the plant population dynamics better than temperature- or N-dependent population growth models over the 5000-year study period. The best-fitting models were constant over time for pine, alder and oak. However, the plant-N availability and plant-temperature models provided a progressively better fit to the birch data when temperatures rose and N availability declined, suggesting increasing importance of these abiotic factors coincident with changing conditions., Synthesis. Multiple mechanistic models were applied to palaeoecological data to infer the most likely processes driving millennial-scale plant biomass dynamics in a woodland ecosystem. Direct plant interactions provided a better explanation for population biomass dynamics than growing season temperature or N availability over the full study period. The relative importance of all drivers we assessed here varied by species and - in the case of birch - over time in response to warming and reduced N availability. [ABSTRACT FROM AUTHOR]

During an archaeological investigation at Lutomiersk–Koziówki in central Poland, deposits indicative of an old rettery from the 16th–17th century AD were discovered. The artifacts found in the lacustrine deposits, together with historical sources and radiocarbon dates of organic matter, show that the pond at a local mill was present from ca. AD 1525 to at least AD 1620. The high content of Cannabis and Linum subfossil macro- and micro-remains in the sediment indicate that the pond was most probably used as a rettery for hemp and flax fibre production. Pollen analysis revealed strong deforestation of the local landscape at the beginning of the pond history. Despite high pollution caused by plant retting, species-rich chironomid, cladoceran and diatom communities occupied the pond. Our investigations reveal that the rettery was situated on the artificial channel of a local stream. High abundance of yellow flatsedge ( Cyperus flavescens ) fruit remains and coprophile beetle subfossils indicate that pond was also used as a watering place for cattle. Decline in the concentration of aquatic invertebrate subfossils, diatoms, aquatic and cultivated plant macrofossils, reveals rapid abandonment of the rettery in the mid-17th century AD. For some time after the basin was a telmatic ecosystem overgrown by sedges and bulrush. The basin was finally filled by a high-energy overbank deposition not later than in the beginning of 19th century AD. [ABSTRACT FROM AUTHOR]

We reconstruct mean July temperature (Tjul) from three sites on the island of Andøya, northern Norway for the period 15 000–9000 cal yr BP using three biotic proxies. A probabilistic indicator species approach (pdf method) was used for plant macrofossil data from all sites (M-Tjul). Reconstructions based on pollen (P-Tjul) (2 sites) and chironomids C-Tjul) (1 site) were done using weighted averaging and weighted-averaging partial least-squares, respectively. A sediment proxy for catchment glacier development was measured at the main site, Lusvatnet. The July temperature reconstructions from all the sites show a similar development through the deglaciation. An initial July temperature of 4 °C increased to a maximum of 7–8 °C during the Allerød at c.13 200 cal yr BP. There was no marked cooling at the start of the Younger Dryas (YD) chronozone, at Lusvatnet, C-Tjul decreased after 12 700 cal yr BP to a low of 6 °C at about 12 550 cal yr BP before increasing markedly around 12 400 cal yr BP. Conversely, P-Tjul rose slowly through the early YD. Both proxies exceeded the Allerød temperatures for around 300 years before decreasing towards a minimum of 6 °C at c. 12 000 cal yr BP. M-Tjul maintained a mean of c. 8 °C throughout the YD. Different sensitivities of proxies are discussed. Their different responses during the YD at the three sites, along with the glacial evidence, highlight the role of aridity. At c. 11 500 cal yr BP, July temperatures increased rapidly over Andøya to about 10 °C, and then rose gradually to maximum values of 12 °C at c. 9700 cal yr BP. The temperature reconstructions are consistent with the flow of Atlantic water into the Nordic Seas except during the YD, when variability in sea ice may have been more important. During the early Holocene there are some differences between sites, resulting from local site factors such as altitude and exposure, soil development, and catchment instability. [ABSTRACT FROM AUTHOR]

Abstract: At Koźmin Las, in the Warta River basin, Central Poland, a series of well-preserved tree trunks and in situ stumps, accompanied by organic deposits, all of Alleröd/Younger Dryas age, have been the focus of a multiproxy palaeoecological study using pollen, plant macrofossil, Cladocera and Chironomidae based on absolute radiocarbon dating. This is the first study to use a dendrological approach to Late Weichselian palaeoenvironmental reconstructions in Central Poland. This study reveals a series of short terrestrial events interrupted by flood episodes in response to climate cooling and provides new opportunities for research into the economic adaptation of Late Palaeolithic hunters to changes in the local environment. Evidence from dendrological studies shows that the riparian forest consisted predominantly of pines of a maximum age of about 140 years and an average age of 68 years. A local pine chronology spanning 133 years has been constructed. The forest appears to have been destroyed ca. 12,600 cal BP by deteriorating hydrological conditions or a sudden catastrophic event (strong wind ?) related to climatic change. [Copyright &y& Elsevier]

Abstract: A lacustrine sediment core from Fiddaun, western Ireland was studied to reconstruct summer temperature changes during the Weichselian Lateglacial. This site is located close to the Atlantic Ocean; and so is potentially sensitive to climatic changes associated with changes in ocean circulation. The record, comprising the end of the Weichselian Pleniglacial to the early Holocene, was analysed for fossil chironomids, lithology, and oxygen and carbon isotopes in the sedimentary carbonates. These proxies clearly show rapid warming at the onset of the Lateglacial Interstadial, relatively high summer temperatures during the Interstadial, pronounced cooling during the Younger Dryas, and subsequent warming at the transition to the Holocene. Chironomid-inferred mean July air temperatures for the Interstadial are ~12.5–14.5°C, ~7.5°C for the Younger Dryas, and ~15.0°C for the early Holocene. Furthermore, this research provides evidence for at least two cold events during the Interstadial. These more moderate temperature oscillations can be correlated to Greenland Interstadial events 1b and 1d, on the basis of the age-depth model for the Fiddaun sequence. Based on multiple proxies, the first cold oscillation (GI-1d) was the more severe of the two in Ireland. [Copyright &y& Elsevier]

Abstract: Icelandic and Norwegian chironomid calibration or training sets were merged to investigate whether a larger combined training set would be useful to apply to subfossil chironomid data from Iceland for periods such as the early Holocene, the Holocene Thermal Maximum and the Little Ice Age, when temperatures can be expected to be outside the current temperature range of the Icelandic training set. Following taxonomic harmonisation, the Icelandic and Norwegian data sets were compared before being merged to form a combined Norwegian-Icelandic training set. Analyses showed that it was biologically and statistically valid to merge the two data sets. The resulting combined inference model for mean July air temperature had improved performance statistics (r2 jack = 0.87; RMSEPjack = 1.13) when compared to the best performing Icelandic model (r2 jack = 0.61; RMSEPjack = 0.83), due to the longer environmental gradient covered (Icelandic 6–11 °C; combined 3.5–16 °C), and to the increased number of samples (Icelandic = 53 lakes; combined = 207 lakes) and taxa (Icelandic = 47 taxa; combined = 133 taxa) present within the combined training set. The inference models were applied to an early Holocene chironomid sequence from Vatnamýri, north Iceland, and a 450-year recent record from Myfluguvatn, north-west Iceland, to compare the reconstructions produced. The various inference models produced similar trends and patterns of temperature reconstruction, but the inference model based on the combined training set produced a larger range of reconstructed temperatures than the Icelandic model. It was found that different inference models produced more variation in the reconstruction than when different training sets were used. A comparison of the Myfluguvatn reconstructions with meteorological observations showed that the combined Norwegian–Icelandic inference model produced more reliable results than the Icelandic or Norwegian inference models alone. [Copyright &y& Elsevier]

Abstract: Subfossil Chironomidae assemblages were studied in a sediment sequence from Żabieniec bog in central Poland. The climate history and habitat changes in the palaeo-lake were reconstructed from these assemblages. Currently no chironomid-based climate calibration set is available from Poland and so past mean July air temperatures were inferred from chironomid-climate calibration data-sets from Norway, Russia, and Switzerland. During the Late Weichselian the three calibration functions from these data-sets provided similar temperature inferences but there was some divergence in the reconstructions for the Younger Dryas and Holocene. In the late Pleniglacial, inferred summer air temperature was relatively low (8–12°C) and the lake was oligotrophic. At about 16.5ka BP, temperature rapidly rose to 15°C and assemblage diversity substantially increased. During the interstadial, temperature stayed at this level. In the Younger Dryas, July air temperature was only 1–2°C lower than in the interstadial, as inferred from the Norwegian calibration data-set, whereas the Russian and Swiss calibration functions did not indicate any temperature decrease. From the beginning of the Holocene, taxa typical of meso-eutrophic conditions dominated. There was an increased abundance of phytophilous species and the assemblage composition was also influenced by changes in water-level. Palaeotemperature reconstructions differed in their values. From 8.0 to 8.7ka BP, inferences based on the Swiss and Russian data-sets indicated a cold oscillation while reconstructions based on the Norwegian data-set did not show any temperature decrease. After 2.5ka BP assemblage diversity and head-capsule concentrations decreased. In the last millennium semi-terrestrial taxa dominated, except from Late Medieval to Early Modern times when shallow-water species reappeared. [Copyright &y& Elsevier]

Abstract: The Cochabamba Basin (Bolivia) is on the ancient road network connecting Andean and lowland areas. Little is known about the longevity of this trade route or how people responded to past environmental changes. The eastern end of the Cochabamba valley system constricts at the Vacas Lake District, constraining the road network and providing an ideal location in which to examine past human–environmental interactions. Multi-proxy analysis of sediment from Lake Challacaba has allowed a c. 4000year environmental history to be reconstructed. Fluctuations in drought tolerant pollen taxa and calcium carbonate indicate two periods of reduced moisture availability (c. 4000–3370 and c. 2190–1020calyr BP) compared to adjacent wetter episodes (c. 3370–2190 and c. 1020calyr BP–present). The moisture fluctuations broadly correlate to El Niño/Southern Oscillation variations reported elsewhere. High charcoal abundance from c. 4000 to 2000yr ago indicates continuous use of the ancient road network. A decline in charcoal and an increase in dung fungus (Sporormiella) c. 1340–1210calyr BP, suggests that cultural changes were a major factor in shaping the modern landscape. Despite undisputable impacts of human populations on the Polylepis woodlands today, we see no evidence of woodland clearance in the Challacaba record. [Copyright &y& Elsevier]

Abstract: There is a strong chance that 20th century warming will cause differences in precipitation distribution, hydrological cycle and effective moisture changes over the globe. Arid central Asia (ACA), a unique dry-land area whose atmospheric circulation is dominated today by the westerlies, is one of the specific regions that are likely to be strongly impacted by global warming. An understanding of past variations in effective moisture in such regions is an important prerequisite for the prediction of future hydrological change. Here we evaluate spatial and temporal patterns of effective moisture variations documented by different proxies from 17 records in ACA, and synthesize a decadal-resolution moisture curve for ACA over the past millennium, using 5 of the 17 records selected on the basis of reliable chronologies and robust proxies. The high- and low-resolution data all show that, over the past millennium, ACA has been characterized by a relatively dry Medieval Warm Period (MWP; the period from ∼1000 to 1350 AD), a wet Little Ice Age (LIA; from ∼1500 to 1850 AD) and increasing moisture during recent decades. As a whole, the LIA in the ACA was not only relatively humid but also had high precipitation. Over the past millennium, the multi-centennial moisture changes in ACA show a generally inverse relationship with the temperature changes in the Northern Hemisphere, China, and western central Asia. The effective moisture history in ACA also shows an out-of-phase relationship with that in monsoon Asia (especially during the LIA). We propose that the humid LIA in ACA, possibly extending to Mediterranean Sea and Western Europe, may have resulted from increased precipitation due to more frequent mid-latitude cyclone activities as a result of the strengthening and equator-ward shift of the westerly jet stream, and the predominantly negative North Atlantic Oscillation conditions, coupled with a decrease in evapotranspiration caused by the cooling at that time. [Copyright &y& Elsevier]

The Last Glacial-Interglacial Transition (ca 16–8 ka BP) in north-west Europe is an important period of climatic change where millennial-scale climatic evolution led to environmental reorganisation. Imprinted upon these long-term changes are a series of short-lived, centennial-scale events that appear to be spatially and temporally complex across Europe. The complexity of environmental change in response to these climatic events is poorly understood because of a paucity of paired investigations that provide evidence of both driver and response variables. We present a high-resolution palynological, charcoal and stable isotopic record alongside chironomid-inferred temperature data from Tirinie, south-east Grampian Highlands, Scotland. The record is stratigraphically and chronologically constrained using tephra and radiocarbon dating. The isotopic and chironomid data reveal centennial-scale climatic deteriorations at ca 14.0; 13.2 and 11.4 cal ka BP. In response to these cooling events, vegetation became more open, fire frequency increased and landscape erosion was common. The reconstruction of both climate and environment reveals asynchrony in the phasing of annual and summer temperature variability, vegetation change and fire for each climatic event. Whilst responses appear strongest following the convergence of annual and summer temperature variability across all events, the ca 13.2 ka BP event reveals a two-stage environmental and fire response to climatic change, and the ca 11.4 ka BP event exhibits environmental change in the absence of summer temperature variability. The data further suggests that fire is an integral component of abrupt climatic change in this part of north-west Europe. • Multi-proxy study using palynology, charcoal, stable isotopes, chironomids. • Annual and summer temperature variability drive environmental responses over abrupt climatic events. • Hydrology is an unknown component driving vegetation change. • Climatic variability and environmental responses are asynchronous across climatic events during the LGIT. • Fire is an agent of landscape change within abrupt climatic events during the LGIT. [ABSTRACT FROM AUTHOR]

Understanding the effects of climate change on ecosystem structure and stability is challenging, especially in high latitude regions that are predicted to experience the largest increases in ambient temperature. Global warming is likely to be a key driver of ecosystem change in freshwater lakes. Increased temperature can positively or negatively affect lake community composition through the loss of cold-adapted taxa and the arrival of temperate or eurytopic taxa. Here, we analyse the likely effects of temperature-induced changes in taxonomic richness and compositional turnover of environmentally-sensitive chironomids (Diptera: Chironomidae) across three regions - northern North America, Norway, and Russia - using existing datasets. Structural parameters (beta diversity, compositional disorder, and network skewness) were applied to model-simulated and empirical chironomid datasets across a large spatial temperature gradient. The analyses of empirical datasets showed changes in community structure across temperature gradients, suggesting varying states of ecosystem stability or instability. The comparison with null models enabled assessment as to whether these stresses agreed with expected patterns due to covarying summer temperature conditions or whether they deviated from expectations suggesting additional stress on the ecosystems. For all three regions, lakes in the mid-temperature range showed most evidence of relative ecosystem stability, with greater beta diversity, compositional disorder, and skewness, unanticipated by the modelled simulations. This is most likely due to more diverse habitats across the ecotone boundaries and additional factors that can influence ecosystem structures. Thus, we show that structural changes typical for ecosystem stability can be detected through changes in community structure across temperature gradients. This is important for understanding how lakes may change under current and future climate change. • Change in ecosystem stability is explored through lake community structure. • Arctic (coldest) lake communities indicate signs of temperature stress. • Structural metrics indicate least stress in mid-temperature range lakes. • Impacts on subarctic (warmest) lake communities are likely caused by local stresses. [ABSTRACT FROM AUTHOR]