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The vicinity of the Rozprza archaeological site (central Poland) has been the area of a series of palaeoecological studies tracking the environmental history of the Luciąża River valley up to ca. 13,200 cal. BP. Numerous subfossil palaeomeanders of different sizes have been discovered in the valley floor. Here, we present the first results of multiproxy research on the paleo-oxbow lake fill, one of the oldest in the region. The wide range of palaeoecological analyses resulted in reconstructions of vegetation history, climatic, hydrological and habitat changes. The studied oxbow was an aquatic ecosystem with diverse invertebrate fauna until the end of Younger Dryas when it transformed into a limno-telmatic habitat. The sediment composition indicates active denudation processes and several episodes of turbulent hydrological conditions. Such an increased river activity could have caused flooding, resulting in an allochthonous matter supply to the oxbow lake in Late Vistulian. Environmental changes were strictly related to the regional features of the catchment, the transformation of soils, and the hydrogeological conditions. The chironomid- and pollen-inferred climatic reconstructions indicate periods of high and low continentality. The chironomid record indicates relatively cool summer conditions in the Allerød, especially ca. 13,000 cal. BP, possibly related to the Gerzensee Oscillation. On the other hand, a distinct increase of summer temperatures in Younger Dryas (up to 16 °C) was recorded. Such a situation was also confirmed in some other studies from the region, suggesting that it might be the effect of some specific, local palaeoclimatic conditions. Fundator badań: Fundator badań: Optional.empty

The Warta River val ley was greatly in flu enced by the ice sheet of the Last Gla cial Max i mum (LGM). A small peatland lo cated in the Warta drain age sys tem is here used as a palaeoarchive of cli ma tic and hab i tat changes dur ing the Late Gla cial (Weichselian). The ugi pound sed i ment pro file was in ves ti gated us ing multi-proxy (pol len, Chironomidae, Cladocera and geo chem is try) anal y ses that re corded changes in a fluviogenic sed i men tary de pres sion. Af ter the Poznan Phase (LGM), ugi pound func tioned as an ox bow lake that was cut off from the ac tive river chan nel as a re sult of flu vial ero sion. Since that time, the Warta River has flowed only along the sec tion now oc cu pied by the Jeziorsko Res er voir. Sed i men ta tion of lac us trine de pos its started at the be gin ning of the Late Gla cial. Sum mer tem per a ture re con struc tions in di cate cool Old est and Youn ger Dryas, but no clear cool ing in the Older Dryas. Dur ing the Youn ger Dryas the palaeolake was com pletely oc cu pied by a peatland (fen), which pe ri od i cally dried out dur ing the Ho lo cene. In ves ti ga tion of this site has tracked the re ac tion of the hab i tat to cli ma tic, hy dro log i cal and geomorphological changes through out the Late Weichselian.

To investigate the Lateglacial and early Holocene climatic and environmental dynamics in the Eastern Baltic we analysed chironomid and pollen data from Lieporiai palaeolake, North Lithuania. The first quantitative mean July air temperature reconstruction from Lithuania based on fossil chironomid assemblages was performed using expanded Fennoscandian calibration model. Our study suggests that sedimentation started at about 14 600 cal yrs BP and lasted until the early Holocene. The mean July air temperature for Lateglacial and early Holocene from studied site ranged between 13 °C−16 °C which was ~ 2–4 °C lower than the present. Rapidly after the deglaciation during Bolling (GI-1e) interstadial reconstructed July air temperature reached ~ 15 °C. The marked temperature decrease to 13.2 °C was recorded during the Older Dryas (GS-1d). Temperature reached its highest values (up to 16 °C) during the Allerod (GI-1a). The Younger Dryas (GS-1) was relatively cold with the mean July air temperature ~ 14 °C and this was 3.9 °C colder than the present. The pattern of the Lateglacial temperature changes from Lieporiai Lake shows both similarities and some differences from the other chironomid based regional and European reconstructions. Chironomid inferred palaeoenvironmental changes are in positive correlation with changes in the development of vegetation.

Understanding local patterns and large-scale processes in past climate necessitates a detailed network of temperature reconstructions. In this study, a merged temperature inference model using fossil chironomid (Diptera: Chironomidae) datasets from Finland and Poland was constructed to fill the lack of an applicable training set for East European sites. The developed weighted averaging partial least squares (WA-PLS) inference model showed favorable performance statistics, suggesting that the model can be useful for downcore reconstructions. The combined calibration model includes 212 sites, 142 taxa, and a temperature gradient of 11.3-20.1 degrees C. The 2-component WA-PLS model has a cross-validated coefficient of determination of 0.88 and a root mean squared prediction error of 0.88 degrees C. We tested the new East European temperature transfer function in chironomid stratigraphies from a Finnish high-resolution short-core sediment record and a Polish paleolake (Zabieniec) covering the past similar to 20 000 yr. In the Finnish site, the chironomid-inferred temperatures correlated closely with the observed instrumental temperatures, showing improved accuracy compared to estimates by the original Finnish calibration model. In addition, the long-core reconstruction from the Polish site showed logical results in its general trends compared to existing knowledge on the past regional climate trends; however, it had distinct differences when compared with hemispheric climate oscillations. Hence, based on these findings, the new temperature model will enable more detailed examination of long-term temperature variability in Eastern Europe, and consequently, reliable identification of local and regional climate variability of the past.

Few fossil-based environmental and climate records in northern Europe are dated to Marine Isotope Stage (MIS) 5a around 80 ka BP. We here present multiple environmental and climate proxies obtained froma lake sequence of MIS 5a age in the Sokli basin (northern Finland). Pollen/spores, plant macrofossils, NPPs (e.g. green algae), bryozoa, diatoms and chironomids allowed an exceptionally detailed reconstruction of aquatic and telmatic ecosystem successions related to the development of the Sokli Ice Lake and subsequent infilling of a relatively small and shallow lake confined to the Sokli basin. A regional vegetation development typical for the early half of an interglacial is recorded by the pollen, stomata and plant macrofossil data. Reconstructions of July temperatures based on pollen assemblages suffer from a large contribution of local pollen from the lake’s littoral zone. Summer temperatures reaching present-day values, inferred for the upper part of the lake sequence, however, agree with the establishment of pine-dominated boreal forest indicated by the plant fossil data. Habitat preferences also influence the climate record based onchironomids. Nevertheless, the climate optima of the predominant intermediate- to warm-water chironomid taxa suggest July temperatures exceeding present-day values by up to several degrees, in line with climate inferences from a variety of aquatic and wetland plant indicator species. The disequilibrium between regional vegetation development and warm, insolation-forced summers is also reported for Early Holocene records from northern Fennoscandia. The MIS 5a sequence is the last remaining fossil-bearing deposit in the late Quaternary basin infill at Sokli to be studied using multi-proxy evidence. A unique detailed climate record for MIS5 is now available for formerly glaciated northern Europe. Our studies indicate that interglacial conditions persisted into MIS 5a, in agreement with data for large parts of the European mainland, shortening the Last Glacial by some 50 ka to MIS 4-2. The Swedish Nuclear Fuel and Waste Management Company (SKB) provided funding for this study; furthermore, the Bolin Centre for Climate Research at Stockholm University is acknowledged for funding to the Sokli studies (KFH). JSS acknowledges funding from the Academy of Finland (project 1310649). Wethank Sanna Piilo (University of Helsinki) for the LOI measurements.

The sediment profile from Lake Gościąż in central Poland comprises a continuous, seasonally resolved and exceptionally well‐preserved archive of the Younger Dryas (YD) climate variation. This provides a unique opportunity for detailed investigation of lake system responses during periods of rapid climate cooling (YD onset) and warming (YD termination). The new varve record of Lake Gościąż presented here spans 1662 years from the late Allerød (AL) to the early Preboreal (PB). Microscopic varve counting provides an independent chronology with a YD duration of 1149+14/–22 years, which confirms previous results of 1140±40 years. We link stable oxygen isotopes and chironomid‐based air temperature reconstructions with the response of various geochemical and varve microfacies proxies especially focusing on the onset and termination of the YD. Cooling at the YD onset lasted ~180 years, which is about a century longer than the terminal warming that was completed in ~70 years. During the AL/YD transition, environmental proxy data lagged the onset of cooling by ~90 years and revealed an increase of lake productivity and internal lake re‐suspension as well as slightly higher detrital sediment input. In contrast, rapid warming and environmental changes during the YD/PB transition occurred simultaneously. However, initial changes such as declining diatom deposition and detrital input occurred already a few centuries before the rapid warming at the YD/PB transition. These environmental changes likely reflect a gradual increase in summer air temperatures already during the YD. Our data indicate complex and differing environmental responses to the major climate changes related to the YD, which involve different proxy sensitivities and threshold processes., National Science Centre, Virtual Institute of Integrated Climate and Landscape Evolution Analysis (ICLEA)

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

Soft-sediment deformation structures are preserved in clastic-biogenic varves of the Lake Nurmijarvi sequence from central-southern Finland. Deformation structures include centimeter-scale folding and faulting structures and larger convolute bedding, which are separated from the overlying undisturbed varved section by a turbidite dated at 7400 cal BP. The soft-sediment deformation provides evidence for postglacial seismic activity ca. 3500 years after the deglaciation of the study area. By screening the sizes of potential source faults for the event, the maximum earthquake moment magnitudes associated with the deformation structures were constrained to MW ≈ 5.1–6.9 with realistic 40% rupture scenarios, or up to MW ≈ 5.1–7.7 if more conservative scenarios are considered. The results of the study thus indicate a relatively high-magnitude postglacial seismic event in southern Finland, which adds to the evidence that the postglacial seismic activity was not just restricted to northern Fennoscandia, but was a more widespread phenomenon. The age of the Lake Nurmijarvi seismic event further demonstrates that high-magnitude seismic activity was not restricted to a relatively short period after deglaciation, but the period of high-magnitude postglacial seismic activity was much longer than previously thought. By assessing the orientations of faults that are presently active and using available focal mechanism data, our results suggest that strike-slip faulting may be a more important mechanism for the generation of both present-day and postglacial earthquakes in southern Finland than reverse faulting, which should further be accounted for in the assessment of long-term seismic hazards.

Detailed studies on fossil remains of plants or animals in glacial lake sediments are rare. As a result, environmental conditions right at the moment of deglaciation of the large N-Hemisphere ice-sheets remain largely unknown. Here we study three deglacial phases of the Fennoscandian Ice Sheet as a unique, repeated element in a long sediment record preserved at Sokli in northern Finland. We summarize extensive multi-proxy data (diatoms, phytoliths, chironomids, pollen, spores, non-pollen palynomorphs, macrofossils, lithology, loss-on-ignition, C/N) obtained on glacial lake sediments dated to the early Holocene (ca. 10 kyr BP), early MIS 3 (ca. 50 kyr BP) and early MIS 5a (ca. 80 kyr BP). In contrast to the common view of an unproductive ice-marginal environment, our study reconstructs rich ecosystems both in the glacial lake and along the shores with forest on recently deglaciated land. Higher than present-day summer temperatures are reconstructed based on a large variety of aquatic taxa. Rich biota developed due to the insolation-induced postglacial warming and high nutrient levels, the latter resulting from erosion of fresh bedrock and sediment, leaching of surface soils, decay of plant material under shallow water conditions, and sudden decreases in lake volume. Aquatic communities responded quickly to deglaciation and warm summers and reflect boreal conditions, in contrast to the terrestrial ecosystem which responded with some delay probably due to time required for slow soil formation processes. Birch forest is reconstructed upon deglaciation of the large LGM ice-sheet and shrub tundra following the probably faster melting smaller MIS 4 and MIS 5b ice-sheets. Our study shows that glacial lake sediments can provide valuable palaeo-environmental data, that aquatic biota and terrestrial vegetation rapidly accommodated to new environmental conditions during deglaciation, and that glacial lake ecosystems, and the carbon stored in their sediments, should be included in earth system modeling.

The Rozprza stronghold functioned as a seat of a noble family since at least the early14th century AD in the form of the motte-and-bailey residence. The remains of the residence are situated in the central part of mid-Luciąza River valley, on the river terrace remnant adjoining a strongly expanding floodplain. The situation and state of preservation give a unique opportunity to conduct research that explain the construction process, detailed history of the medieval moat and palaeoenvironmental reconstruction of the valley floor. Radiocarbon and dendrochronological dating and analysis of artefacts confirmed 14th century age of the moat. Organic deposits (gyttja, peat and organic mud) of moat fill allowed for a set of multiproxy analyses based on sediment cores. The research results indicate shallow water with brief episodes of in-wash in the first stage (13th-14th c. AD), followed by a transformation into telmatic habitat in the second phase of the moat development from 16th-17th c. AD. The deposition of overbank alluvium took place within the moat ditch system as late as the 18th and/or 19th c. AD. We studied the development of this moat environment in the context of valley floor changes.

Existing paleoclimate data are exceedingly sparse from southern Spitsbergen, a High Arctic region predicted to experience significant environmental changes because of amplified warming. We analyzed biotic and isotopic paleolimnological proxies to reconstruct past climate from a lacustrine sediment core, with a basal age of ∼5500 a BP, in southern Spitsbergen (77°N). We used fossil Chironomidae assemblages to quantitatively reconstruct past mean July air temperatures and stable oxygen isotope values (δ18O) of these fossils to estimate changes in mean annual air temperature. These proxy records are strikingly similar and show that the coldest anomaly since the mid-Holocene occurred between 350 and 50 cal a BP, during the ‘Little Ice Age’, whereas the warmest period in the summer temperature record occurred between 5500–5000 and ∼2000 cal a BP. Our findings indicate that the natural long-term air temperature dynamics in our study area are most likely connected to solar minima and positive feedback mechanisms from sea-surface temperature maxima. The results also highlight that the recent temperature increase is unprecedented in its rate with a ∼2 °C increase in the summer temperatures during the past ∼50 years.

Four biotic proxies (plant macrofossils, pollen, chironomids and diatoms) are employed to quantitatively reconstruct variations in mean July air temperatures ( Tjul) at Lake Loitsana (northern Finland) during the Holocene. The aim is to evaluate the robustness and biases in these temperature reconstructions and to compare the timing of highest Tjul in the individual reconstructions. The reconstructed Tjul values are evaluated in relation to local-scale/site-specific processes associated with the Holocene lake development at Loitsana as these factors have been shown to significantly influence the fossil assemblages found in the Lake Loitsana sediments. While pollen-based temperatures follow the classical trend of gradually increasing early-Holocene Tjul with a mid-Holocene maximum, the aquatic/wetland assemblages reconstruct higher-than-present Tjul already during the early Holocene, that is, at the peak of summer insolation. The relatively low early-Holocene July temperatures recorded by the pollen are the result of site-specific factors possibly combined with a delayed response of the terrestrial ecosystem compared with the aquatic ecosystem. Our study shows that all reconstructions are influenced at least to some extent by local factors. This finding stresses the need to evaluate quantitatively reconstructed climate values against local lake development and highlights the benefit of using multi-proxy data in Holocene climate reconstructions.

The major climate events of the Common Era (CE) have global imprints but significant variations in their timing and magnitude have been suggested. For reliable assessments of the past climate patterns and their applications for evaluations of the ongoing changes, spatially comprehensive network of high-fidelity paleorecords are necessary. In this study, we reconstruct summer air temperatures of the past 2000 years from northern Lapland (Utsjoki, Finland). We use fossil Chironomidae (Diptera) assemblages from sediments of a remote subarctic lake (Loažžejavri) and the transfer function approach for quantitative temperature reconstruction. The results indicate that the Chironomidae fauna were responding to air temperature and the core assemblages had good modern analogues in the calibration set allowing reliable paleoclimate reconstruction. In our reconstruction, a warm period between ∼900 and 1300 CE is synchronous with the globally defined extent of the Medieval Climate Anomaly (MCA), though beginning considerably later than previously reconstructed for eastern Scandinavia. The MCA was also relatively mild, as the temperatures were only 0.5 °C higher than the record average. Similar to eastern Scandinavia, a cold period corresponding to the Little Ice Age (LIA) was longer that typically observed in hemispheric reconstructions beginning already at ∼1400 CE and lasting very close to modern times. We also found confirming evidence that the LIA was interrupted by a short-lived warmer period dividing it into two separate cold events in the region. Based on our results, the present is warmer than during any time of the MCA displaying how rapid and severe the ongoing climate change is.

The uppermost 50 cm of sediments from the 23 m deep lacustrine basin of Nurmijarvi, a lake in south-central Finland, are composed of the clastic-biogenic type of varves. We use multiple dating methods to render a sediment chronology that is as precise and accurate as possible for future paleoenvironmental research on this high-fidelity sedimentary archive. The 250-year-long varve chronology contains a chronological error of ±2%, as estimated based on repeated varve counts. The varve-based chronology was verified with the vertical distribution of 137Cs by comparing variations in the paleomagnetic relative declination of the surface sediments with instrumental observations and a calculated representation of declination features in Finland. A comparison of the sediment cesium content using two gamma counters, different sediment pretreatments, and normalization of the 137Cs concentration with masses and accumulation rates of different sediment components revealed that the AD 1986 fallout peak from the Chernobyl accident is the dominant feature in the studied sediments, regardless of the sample pretreatment or normalizing procedure. The vertical distribution of the AD 1986 peak in sediments with clastic-biogenic varves is fairly narrow, thus providing an accurate age-depth marker for the recent deposits. However, the Nurmijarvi section also reveals a ca. 10-year-long period of catchment-to-basin 137Cs mobilization and redeposition after the AD 1986 fallout, as well as significant downwards diffusion of the Chernobyl-derived cesium in the sediment. This study highlights the ways in which the quality of surface sediment chronology needs to be considered and secured prior to comparisons between paleoproxy records and instrumental observations.

The oxygen isotope composition of chironomid head capsules in a sediment core spanning the past 5500 years from Lake Svartvatnet in southern Spitsbergen was used to reconstruct the oxygen isotope composition of lake water (δ18Olw) and local precipitation. The δ18Olw values display shifts from the baseline variability consistent with the timing of recognized historical climatic episodes, such as the Roman Warm Period, the Dark Ages Cold Period and the ‘Little Ice Age’. The highest values of the record, ca. 3‰ above modern δ18Olw values, occur at ca. 1900–1800 cal. yr BP. Three negative excursions increasing in intensity toward the present, at 3400–3200, 1250–1100, and 350–50 cal. yr BP, are tentatively linked to roughly synchronous episodes of increased glacier activity and general cold spells around the northern North Atlantic. Their manifestation in the Svartvatnet δ18Olw record not only testify to the sensitivity and potential of high Arctic lacustrine δ18Ochir records in tracking terrestrial climate evolution but also highlight nonlinear dynamics within the northern North Atlantic hydroclimatic system. The ‘Little Ice Age’ period at 350–50 cal. yr BP displays a remarkable 8–9‰ drop in δ18Olw values, construed to predominantly represent significantly decreased winter temperatures during a period of increased seasonal differences and extended sea ice cover inducing changes in moisture source regions.

This paper provides a high-resolution temperature reconstruction for the last Millennium from Lake Atnsjøen, SE Norway (61°52′31″N, 10°10′37″E). The sedimentary record reveals strong influence of the large-scale global climate patterns on the local climate in southern part of Eastern Norway. We reconstructed mean July air temperature using Chironomidae-based transfer function and fossil Chironomidae assemblages. The reconstruction was supported by a selection of climate-sensitive geochemical and paleoecological sedimentary proxies of terrestrial and aquatic origin, including Cladocera, pollen and macrofossils. Presented results revealed that summer temperatures were 1–2 °C warmer than the mean Millennial temperatures during the 11th, 13th, 15th and 20th centuries and 1–2 °C lower during the 12th, 14th, 17th–18th centuries. A persistent cold period, the Little Ice Age (LIA), occurred between 1550 and 1800 CE, was interrupted by a short warming at 1650 CE. The recognized regional climate fluctuations during the last Millennium affected the lake and its catchment, of which the strongest impact was caused by the LIA cooling. During the LIA the catchment vegetation was impacted by climate deterioration and the lake productivity reached its lowest level during the last Millennium. The current temperature reconstruction is in agreement with a previous continental scale temperature reconstruction for Europe. From obtained results it emerges that during the LIA the climate of western Scandinavia has been dictated by the atmospheric patterns originating from the North Atlantic. peerReviewed

The Wietrzychowice Cultural Park protects one of the last preserved megalithic barrows of the Funnel Beaker Culture people at the Kuyavia Lakeland (Central Poland). Archaeological excavations of the lake palaeolittoral zone were conducted on the nearby Karania Lake shore. Numerous Mesolithic and Neolithic remains were excavated including: flint artefacts, potsherds, arrowheads, and mammal bones with traces of human processing. The SM9G2 core from the miey site covers gyttias and peats with the Holocene history of Karania Lake. The age-depth model is based on 3 AMS and 3 LSC radiocarbon dates as well as cultural remains. The bottom section of the core (275-190cm b.g.l.) includes the record of the early to mid-Holocene layers that fall on the Mesolithic and Neolithic in the region. The multi-proxy study (geochemistry, plant macrofossils, pollen, Mollusca, Cladocera and Chironomidae analyses) were conducted on the Mesolithic-Neolithic section of the core. Additionally, Chironomidae subfossil analysis was conducted on the SM1 core from another part of the Karania Lake shore zone, documenting the mid-Holocene age of the lake littoral shore development.

The fast sedimentation rate of Rozprza palaeo-oxbow deposits gives a chance for tracking environmental changes in the end of the Late Vistulian very thoroughly. The range of palaeoecological analyses were done, resulting in reconstructions of vegetation history, climate and habitat changes. The chironomid-inferred summer temperatures indicate the short cooling in the late Allerd, confirmed by the plant macrofossils. It may correspond to Gerzensee oscillation, recorded mainly from western Europe. The studied oxbow was a truly aquatic ecosystem until the end of Younger Dryas, with diverse invertebrate fauna. The second phase of the oxbow-lake was characterised by its systematic overgrowing and, finally, mire development with overbank deposition in the Holocene. The wide range of used proxies provided a reliable picture of the Late Glacial oxbow evolution in Central Poland.

Erroneous information considering Chironomidae and Chaoboridae accumulation was given in Figure 4 published in Luoto et al. (2017).

The Last Interglacial (Eemian, MIS 5e) can be considered a test-bed for climate dynamics under a warmer-than-present climate. In this study we present a chironomid record from the high latitude Sokli site (N Finland), where a long continuous sediment sequence from the last interglacial has been preserved from glacial erosion. The chironomid-analysis shows a diverse fauna, with dominance of warm-water indicators and shifts in assemblage composition that can be attributed to temperature, lake depth, productivity and habitat availability. Quantitative mean July paleotemperature estimates based on the chironomid data indicate overall mean July air temperatures up to 1 degrees C warmer than present. Two cooling events can be discerned, the Tunturi event, dated to about 127.5kaBP, in the lower part of the sequence, and the Varrio event, dated to about 119kaBP, associated with the beginning of a cooling trend in the upper part of the record. Warm conditions already at the onset of the interglacial contrast with a recent chironomid-based last interglacial temperature reconstruction from Denmark, which suggests a late onset of Eemian warming. The relatively small increase in inferred temperatures compared to present day temperatures at Sokli differs from other high latitude Eemian sites, and likely reflects the influence of the Atlantic Meridional Overturning Circulation in maintaining already elevated temperatures in Fennoscandia during interglacials.

A lake sediment record from the north-eastern European Russian Arctic was examined using palaeolimnological methods, including subfossil chironomid and diatom analysis. The objective of this study is to disentangle environmental history of the lake and climate variability during the past 2000 years. The sediment profile was divided into two main sections following changes in the lithology, separating the limno-telmatic phase between ~2000 and 1200 cal. yr BP and the lacustrine phase between ~1200 cal. yr BP and the present. Owing to the large proportion of semi-terrestrial chironomids and poor modern analogues, a reliable chironomid-based temperature reconstruction for the limno-telmatic phase was not possible. However, the lacustrine phase showed gradually cooling climate conditions from ~1200 cal. yr BP until ~700 cal. yr BP. The increase in stream chironomids within this sediment section indicates that this period may also have had increased precipitation that caused the adjacent river to overflow, subsequently transporting chironomids to the lacustrine basin. After a short-lived warm phase at ~700 cal. yr BP, the climate again cooled, and a progressive climate warming trend was evident from the most recent sediment samples, where the biological assemblages seem to have experienced an eutrophication-like response to climate warming. The temperature reconstruction showed more similarities with the climate development in the Siberian side of the Urals than with northern Europe. This study provides a characteristic archive of arctic lake ontogeny and a valuable temperature record from a remote climate-sensitive area of northern Russia.

Despite the biologically damaging impacts of solar ultraviolet radiation (UV) in nature, little is known about its natural variability, forcing mechanisms, and long-term effects on ecosystems and organisms. Arctic zooplankton, for example the aquatic keystone genus Daphnia (Crustacea, Cladocera) responds to biologically damaging UV by utilizing photoprotective strategies, including pigmentation. We examined the preservation and content of UV-screening pigments in fossil Daphnia remains (ephippia) in two arctic lake sediment cores from Cornwallis Island (Lake R1), Canada, and Spitsbergen (Lake Fugledammen), Svalbard. The aims were to document changes in the degree of UV-protective pigmentation throughout the past centuries, elucidate the adaptive responses of zooplankton to long-term variations in UV exposure, and estimate the potential of fossil zooplankton pigments in reconstructing aquatic UV regimes. The spectroscopic absorbance measurements of fossil Daphnia ephippia under UV (280–400 nm) and visible light (400–700 nm) spectral ranges indicated that melanin (absorbance maxima at UV wavebands 280–350 nm) and carotenoids (absorbance maxima at 400–450 nm) pigments were preserved in the ephippia in both sediment cores. Downcore measurements of the most important UV-protective pigment melanin (absorbance measured at 305 and 340 nm) showed marked long-term variations in the degree of melanisation. These variations likely represented long-term trends in aquatic UV exposure and were positively related with solar radiation intensity. The corresponding trends in melanisation and solar activity were disrupted at the turn of the 20th century in R1, but remained as strong in Fugledammen. The reversed trends in the R1 core were simultaneous with a significant aquatic community reorganization taking place in the lake, suggesting that recent environmental changes, likely related to climate warming had a local effect on pigmentation strategies. This time horizon is also concurrent with previously recorded major ecological shifts in circumpolar lakes when human induced changes in ecological processes of sensitive arctic ecosystems started to occur. The current centennial record of UV-induced melanisation of sedimentary Daphnia ephippia presents unique reference material for assessing UV impacts in arctic aquatic ecosystems before human influence and during the 20th century climate change and provides potential for assessing past aquatic UV regimes.

The developmental history, from the Oldest Dryas to the Late Holocene, of a paleolake and mire located in a river valley in Central Poland was studied using high-resolution records of pollen, macrofossils, Cladocera, sedimentology, and geochemistry from a 14 C dated sediment core. We inferred temperature and water level dynamics using cladocerans and palynological and geochemical methods were employed to investigate natural fluvial activity, particularly for these elements that are difficult to find through sedimentological methods. Our research demonstrates how climate fluctuation in the Late Glacial and Holocene periods influenced the development of a paleolake and mire in a small river valley and shows the importance of long-term research to establish hydroclimatic conditions in biogenic sediments. We propose that water level fluctuations were important in modifying biotic assemblages. The results of our multiproxy analysis clearly suggest that the main driver of changes in aquatic and terrestrial ecosystems, as well as in geomorphological processes in the valley, was climate: reconstructed temperatures generally follow the known trends, showing an increase at the beginning of the Bolling, Allerod, and Holocene and a decrease at the beginning of the Oldest and Younger Dryas. Similarly, periods of water level increase are synchronous with climatic changes. However, the local environmental forces were a significant factors affecting biotic diversity in the studied time span. Fish predation, macrophyte structure, pH, and calcium content partly influence the results of the cladoceran-based water depth reconstruction in particular. Interestingly, the cladoceran-inferred summer temperature reconstruction for Pawlowa appear realistic. Although the temperature trends can be considered reliable, our results indicate the important role of local factors which control the species composition of the subfossil assemblages.

We use a range of environmental variables to explore the possible drivers influencing the biota, especially the composition of aquatic invertebrates, during the Younger Dryas (YD) and Early Holocene (EH) in different river valley sites: a well-developed meandering river and the confluence zone of headwater streams. Using pollen, macrofossil, cladoceran, and chironomid as well as geochemical and lithological data as proxies for environmental factors (i.e., water depth and temperature), we attempt to show that these different sites display similar hydroclimatic signals (especially floods). The geochemical records in the studied valley are correlated with environmental factors, such as the evolution of the vegetation, the intensification phase of slope processes, and fluvial activities. Cladocerans and chironomids potentially play important roles in the recognition of flood episodes in the study sites, and any shift in their diversity and, especially, the co-occurrence of planktonic, sediment-associated cladocerans with rheophilic chironomids could be valuable indicators of floods and flow episodes. The variable changes in water levels at the sites reconstructed by the cladoceran-based water-depth model were positively associated with changes in lithophilic elements (K, Na, Al, Mg, and Ti), SiO2(biog + ter) and Fe/Mn, and our estimates of the paleohydraulic parameters for the study sites are generally consistent with changes in the composition of aquatic invertebrates. The recorded YD floods appear to be synchronous, regardless of the size and the different geological and geomorphological settings of each part of the river catchment. Our investigation demonstrates that flood magnitude increases in the downstream direction along the valley. The common increases in the water level at all study sites from the Grabia River valley are significant from 12,400 to 12,200 and from 11,900 to 11,800 cal BP and are comparable with those from elsewhere in Poland and Europe.

We investigated a Holocene (since ∼10 500 cal yr BP) sediment core from a high-altitude, UV-sensitive tundra lake in northwestern Finnish Lapland to disentangle long-term dynamics in underwater UV exposure, lake-catchment coupling processes, and aquatic community development under changing climate. We analyzed biogeochemical and paleobiological proxies indicative of catchment impact, lake production and water transparency, including inferences of lake-water total organic carbon (TOC), sediment chlorophyll-a and UV-induced cladoceran (Crustacea) melanin (ABSUV), cladoceran communities, and elemental and isotopic fingerprints of sediment organic matter (OM). The results depicted a general climate-mediated ontogeny of early, mid- and late Holocene limnological regimes. The rapid postglacial temperature increase and the regionally early Holocene temperature maximum initiated lacustrine changes with rapid community turnovers, increasing benthic-dominated autochthonous production and high UV exposure due to low input of terrestrial OM (TOC ∼1–2 mg L−1) from the deglaciated catchment. The mid-Holocene regime was characterized by a general stabilization of the catchment and a benthic-dominated aquatic community that became gradually more productive under the warm and dry climate conditions. Superimposed on late Holocene climate cooling and increasing effective moisture, TOC increased to the highest Holocene values (>3 mg L−1), which was associated with abundant aquatic macrophytes and a phytophilous Acroperus harpae dominated cladoceran community around 4500–3000 cal yr BP. Over the past three millennia, TOC declined to low modern values (∼2 mg L−1) and UV-resistant Alonopsis elongata became the dominant taxon indicating a regime of increased underwater UV exposure. ABSUV was consistently higher around ∼1500–1000 cal yr BP after the late Holocene TOC decline, suggesting a photoprotective response to the new UV regime, possibly through a reduction of available UV refugia among aquatic macrophytes. While ABSUV did not show a straightforward relationship with TOC or solar forcing over the Holocene, the cladoceran community shift suggested a clear limno-ecological response to altering TOC and underwater UV regimes.

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

Arctic freshwater basins are diversity hotspots and sentinels of climate change, but their long-term variability and the environmental variables controlling them are not well defined. We examined four available lake sediment sequences from High Arctic Svalbard for their subfossil Chironomidae communities, biodiversity and functional traits and assessed the influence of climatic and limnological variability on the long-term ecological dynamics. Our results indicated that collector-filterers had an important role in the oligotrophic sites, whereas collector-gatherers dominated the nutrient-enriched sites with significant bird guano inputs. In the oligotrophic sites, benthic production, taxon richness and taxonomic and functional diversity were highest during the early Holocene, when temperatures showed a rapid increase. An increase in subfossil abundance and diversity metrics was also found in recent samples of the oligotrophic sites, but not in the bird-impacted sites, where the trends were decreasing. When partitioning out the environmental forcing on chironomid communities, the influence of climate was significant in all the sites, whereas in-lake production (organic matter) was significant in two of the sites and catchment erosion (magnetic susceptibility) had only minor influence. The findings suggest that major changes in Arctic chironomid assemblages were driven by climate warming with increasing diversity in oligotrophic sites, but deteriorating ecological functions in environmentally stressed sites. We found that although taxonomic and functional diversity were always coupled, taxonomical and functional turnovers were coupled only in the oligotrophic sites suggesting that the ecological functions operated by chironomids in these low-productivity sites may not be as resilient to future environmental change.

Long-term fluctuations in lake-water optical properties were examined using a Holocene sediment sequence and multi-proxy palaeolimnological approach in Lake Einstaken, Nordaustlandet, Svalbard. UV-absorbance of sedimentary cladoceran remains provided information on underwater UV exposure and changes in lake-catchment coupling processes were inferred from sediment geochemistry. In addition, aquatic community succession was used as an indicator for lake-water bio-optical properties and a Holocene record of sun activity (sunspots) was utilized to evaluate long-term solar forcing. The results indicated that the UV-absorbance of cladoceran remains was highest (i.e. maximum UV-induced pigmentation) for a short period during the early Holocene and for several millennia during the mid-Holocene. Sun activity was high during these time intervals, probably impacting the UV intensities, but it is probable that the amount of UV-attenuating compounds (e.g. dissolved organic carbon (DOC)) also significantly affected the underwater UV environment and were low during high UV exposure. Benthic autotrophic communities also responded to the millennial changes in lake-water optical properties. UV-resistant Nostoc cyanobacterial colonies were established during the mid-Holocene, indicative of high underwater UV intensities, and Fontinalis mosses thrived during the early Holocene, indicating a highly transparent water column. The results further suggested that underwater UV exposure decreased during the late Holocene, which is probably attributable to increased DOC and decreased solar forcing. Owing to the location of Lake Einstaken and its catchment in the periglacial barren landscape of the polar desert, the fluctuations of bio-optical lake-water properties were apparently forced by postglacial environmental processes and Holocene climate development. These factors controlled sea shoreline proximity, water discharge, ice-cover duration and littoral-benthic primary production and further affected the underwater UV environment. Although the role of solar forcing cannot be underestimated, the current record emphasizes the role of climate-mediated lake-catchment interactions in impacting bio-optical properties and UV exposure of high arctic aquatic systems.

Multiple regional chironomid-climate calibration datasets are available to reconstruct quantitatively July air temperatures from fossil chironomid assemblages. We examined the relationship between July air temperature and the 40 most common chironomid taxa in three independent Eurasian calibration (training) sets. The estimated temperature optimum of each chironomid taxon is systematically lower (by ~1-2 °C) in a Norwegian calibration set compared to Finnish and Russian calibration sets. This result might partly be explained by the fact that the Norwegian calibration set extends further at the cold end of the temperature gradient. A difference in continentality between the Russian sites and the European sites might also contribute to this pattern. The number of taxa that show a statistically significant unimodal response to temperature is higher in the Norwegian calibration set (34 out of 40 taxa) compared to the modern Finnish (11 of 37 taxa; 3 common taxa absent) and the Russian calibration set (20 of 40 taxa), probably due to the longer temperature gradient incorporated in the Norwegian calibration set. We applied all three calibration sets to fossil chironomid assemblages from the high-latitude study site of Sokli (northeast Finland), a site with a unique series of lacustrine deposits covering (amongst others) the Holocene, part of early MIS 3 (at ~53 ka) and MIS 5d-c (at ~110-95 ka) and with independent proxy-records for comparison. In the early Holocene and during MIS 5c, the chironomid-based temperature inferences from all three inference models had similar values. Temperature reconstructions based on the Norwegian calibration set are 2-4 °C lower for the late Holocene, early MIS 3 and MIS 5d than the inferred temperatures based on the other calibration sets. Although the lakes included in the Finnish calibration set are located closest to the site of Sokli, evaluation tests and a comparison with independent proxy data suggests that the Norwegian calibration set provides the most suitable analogues for reconstruction purposes for most of the fossil assemblages. Our results imply that when choosing a calibration set for quantitative climate reconstructions on glacial timescales, regional proximity of the fossil site may not be a sufficient basis, and the length of the temperature gradient of the calibration dataset and factors such as the continentality gradient covered by the calibration set must also be considered.

Paleoclimate reconstructions based on biological proxies present methodological challenges, especially during non-analog conditions, such as the early Holocene. Here, two chironomid-based training sets from Finland were amalgamated to create a more accurate transfer function of summer air temperature. The aim was to reconstruct Holocene paleoclimate in northernmost Lapland, in an area that has been either too warm or too cold for reliable reconstructions using the original calibration models. The results showed that the combined calibration model had improved performance statistics. The temperature trends inferred from the downcore chironomid record using the original and combined models were very similar. However, there were major changes in their absolute values with the combined model showing greatly improved accuracy. The chironomid-based temperature reconstruction showed significant correlation with the previous pollen-based reconstructions from northwestern Finnish Lapland. However, differences were observed in the temperature trends of the early Holocene, when the chironomid-inferred temperatures rapidly increased, but the pollen-based reconstructions lagged behind suggesting that a cool climate continued for much longer. However, similar to the chironomid record, new plant macrofossil evidence from northwestern Finland also showed warmer-than-present early Holocene temperatures. Therefore, we conclude that the early Holocene was probably warm in northern Lapland.

This study presents a detailed analysis of geochemical and biotic proxies in a lake sediment profile to assess the effects of local and regional environmental drivers on the Holocene development of Lake Loitsana, situated in the northern boreal forest of NE Finland. Multi-proxy studies, in particular those that include a detailed plant macrofossil record, from the part of the northern boreal zone of Fennoscandia which has not been affected by treeline fluctuations, are scarce and few of these records date back to the earliest part of the Holocene. A 9-m sediment sequence of gyttja overlying silts representing the last c. 10,700 cal year, allowed for a high-resolution study with emphasis on the early to mid-Holocene lake history. The lacustrine sediments were studied using lithology, loss-on-ignition and C/N ratios, micro- and macro-fossils of aquatic and wetland taxa, diatoms, chironomids and accelerator mass spectrometry 14C dating on terrestrial plant macrofossils. Our study shows that the local development at Loitsana was complex and included a distinct glacial lake phase and subsequent drainage, a history of fluvial input affected by nearby wetland expansion, and lake infilling in an eventual esker-fed shallow lake. Enhanced trophic conditions, due to morphometric eutrophication, are recorded as Glacial Lake Sokli drained and open water conditions became restricted to a relatively small Lake Loitsana depression. pH appears to have been stable throughout the Holocene with a well-buffered lake due to the local carbonatite bedrock (Sokli Carbonatite Massif). The fossil assemblage changes are best explained by a complex mixture of drivers, including water-body conditions (i.e. depth, turbidity and turbulence), rate of sediment input, and the general infilling of the lake, highlighting the need to carefully evaluate the possible influence of such local factors as palaeoenvironmental conditions are reconstructed based on aquatic proxies.

Lake levels can act as valuable proxy sources for long-term effective precipitation dynamics. In this study, lake-level fluctuations were reconstructed from the Little Ice Age (LIA) until the present using a multiproxy paleolimnological approach from Lake Moaralm (Moaralmsee) in the Niedere Tauern Alps, Austria. Quantitative lake level reconstruction techniques were applied to the sediment core data using intralake (Moaralmsee) calibration models based on fossil Chironomidae and Cladocera assemblages, and supplementary models based on oribatid mites and loss-on-ignition were used. The results showed that the inferred lake-level trends were strongly correlated among one another and also with the observed precipitation record from an adjacent weather station since 1860 AD. Periods of low lake level were reconstructed for ca. 1600-1650 AD and 1700-1900 AD, while high lake level periods occurred from ca. 1650-1700 AD and from ca. 1900 AD to the present. These results were in good agreement with previous records on lake level and precipitation patterns in the European Alps, though with some spatiotemporal differences. Our records of long-term patterns of effective moisture, combined with the previously established temperature variability since the 17th century, suggested that a period of high effective moisture occurred between ca. 1650 and 1700 AD during the LIA, after which moisture levels decreased. High temperatures during the last century were accompanied by increasing moisture, and the lake levels are now at a 400-yr maximum. This study provides a new proxy for spatiotemporal moisture patterns that is invaluable for improved understanding of synoptic climate variability for periods prior to the observational records.

Zoological remains were examined from the sediments of the Pingualuit Crater Lake, Nunavik, Canada. Our objective was to describe past climate events in the area of delayed deglaciation in northernmost Ungava Peninsula. Our record covers 3 separate sections of deglacial and postglacial invertebrate dynamics interrupted by laminated proglacial sediments and a basin-scale erosive slumping event. The abundance of animal remains in the ultra-oligotrophic and extremely deep arctic lake was low, but distinct faunal assemblages were found among the intervals, results implying that they were environmentally heterogeneous. The lowermost fine-grained interval (before 6850 calibrated years before present (cal BP)), revealed that Cladocera Chydorus sphaericus-type and Bosmina (Eubosmina) longispina-type were common in the lake, whereas Chironomidae were relatively rare. The dominance of B. longispina-type showed that planktonic communities were successful at the time, probably indicating more favorable climatic conditions than today soon after the last deglaciation (,7000 cal BP). In the middle interval (between ,6850 and 5750 cal BP), chironomids became more common and were dominated by Heterotrissocladius subpilosus-type and Protanypus, taxa that are characteristic of oligotrophic lakes. The extirpation ofB. longispina-type suggests that planktonic invertebrate communities were not successful, probably because of predation by Arctic char. The presence of the chironomid Oliveridia tricornis-type during the late Holocene (between ,4200 and 600 cal BP) suggested general climate cooling. Our paleoclimatic conclusions on the regional environmental history suggest a stationary ice front in the initial stages of the Holocene, favorable climatic conditions in the mid- Holocene and a general late-Holocene cooling. Our records also indicate a subtle increase in nutrient availability throughout the Holocene. The paleoecological record from Pingualuit Crater Lake is valuable in describing the faunal history and biotic resilience in this environmentally extreme lake, which presently contains one of the world's softest and most transparent waters.

Future climate warming is expected to alter atmospheric moisture balance and therefore paleoclimatic archives of past moisture and hydrological patterns may provide understanding of the magnitude, speed, and ecosystem responses to the regionally altered climatic regimes. The present study aimed at disentangling millennial variation in hydroclimatic parameters, including summer effective moisture (lake levels) and ice-free season by using sedimentary cladoceran fossils. We used a site-specific cladoceran-based inference model to reconstruct lake level fluctuations in a 1500-yr sediment record from Lake Pieni-Kauro, eastern Finland in the context of previously established paleoclimatic data of summer temperature and precipitation. In addition, we applied cladoceran planktonic/littoral ratio, mean body size, and abundance of fossil ephippia as supplementary proxies for paleoclimatic interpretations. The results showed that lake level was lower during the pre- and early Medieval Climate Anomaly (MCA, around 500-1000 AD) than at present and started to rise toward the culmination during the Little Ice Age (LIA, around 1600–1700 AD) when the lake level was higher than at present. Pelagic cladoceran body size was larger and abundance of ephippia increased during the LIA suggesting significant reduction in the length of the ice-free season and lower water temperatures. Comparison of the lake level reconstruction with the previous paleoclimatic data suggested that effective moisture has had a long-term negative relationship with temperature and positive relationship with summer precipitation in eastern Finland. The results indicated that the pre- and early MCA was warm and dry (long ice-free season, low summer effective moisture) and the culmination of the LIA was cool and moist (reduced ice-free season, increased summer effective moisture). Unraveling the seasonality of the multicentury hydroclimatic patterns in eastern Finland may offer important insights in linking the large-scale atmospheric circulation patterns to seasonal climate events.

Climate-change projections suggest altered precipitation, temperature, and hydrological patterns for the near future. To better understand these future changes, long-term evidence from paleoarchives is necessary to determine the natural variability and climate relations in surficial hydrology. In this study, we aim to demonstrate that distribution of sedimentary mouthparts (mandibles) of aquatic mayfly (Ephemeroptera) and caddisfly (Trichoptera) larvae are dependent on stream conditions and this relationship can be used in paleohydrological studies to reconstruct past changes in stream flow. The results from a river–lake continuum in eastern Finland showed that the surface sediment accumulation of mayfly and caddisfly mandibles was strongly related to stream flow with highest abundances found from the riverine sediments. A sediment core taken from the deep basin of the lake revealed mandible accumulation patterns that correlated with a previous independent paleohydrological reconstruction. We interpret that the primary forcer for mandible deposition to lake sediments is spring floods caused by snow melt, and hence the mandible accumulation, represents amount of winter precipitation. Subsequently, the results indicated strong stream flow and wet winters during the Medieval Climate Anomaly (MCA) and weaker stream flow and dry winters during and after the Little Ice Age (LIA). This wintertime reconstruction contrasts the general summertime trends of dry MCA and wet LIA. The present results confirm the usability of mayfly and caddisfly mandibles in paleohydrological studies and provide evidence for past hydrological dynamics that can be valuable when addressing the potential magnitude of future changes.

The sedimentary environment, sediment characteristics and age-depth models of sediment sequences from Arctic lakes Revvatnet and Svartvatnet, located near the Polish Polar Station in Hornsund, southern Svalbard (77°N), were studied with a view to establishing a basis for paleolimnological climate and environmental reconstructions. The results indicate that catchment-to-lake hydroclimatic processes probably affect the transportation, distribution and accumulation of sediments in different parts of lakes Revvatnet and Svartvatnet. Locations with continuous and essentially stable sedimentary environments were found in both lakes between water depths of 9 and 26 m. We used several different dating techniques, including 137Cs, 210Pb, AMS 14C, and paleomagnetic dating, to provide accurate and secured sediment chronologies. Arecovered sequence from the northern basin of Revvatnet spans more than one thousand years long with laminated stratigraphy in the upper part of the sediment. Based on AMS 14C dates, it is possible to suppose that Revvatnet basin was not occupied by a valley glacier during the Little Ice Age. The dates were supported by 137Cs chronologies, but not confirmed with other independent dating methods that extent beyond the last 50 years. A sedimentary sequence from the northern basin of Svartvatnet provides a potential archive for the study of climate and environmental change for the last ca. 5000 years. Based on the stratigraphy and a Bayesian age-depth model of AMS14C and paleosecular variation (PSV) dates, the recovered sediment sections represent a continuous and stable sedimentation for the latter half of the Holocene.

Climate dynamics during the past ca. 700 years in southern Finland were reconstructed using fossil midge (Diptera:Nematocera) assemblages aiming to estimate quantitatively the temperature change that has occurred from the Little Ice Age to the present. Midge stratigraphies of two sediment cores from eastern and southern Finland were chosen to be examined for temperature inferences utilizing the modern analogue technique. The new midge-based temperature inference model had a coefficient of determination of 0.901 and a prediction error of 0.498 °C, showing improvement over the previous Finnish models. The combined curve of the inferred temperatures derived from both of the cores showed a decrease towards ca. 1700 AD, when temperatures were approximately 1 °C cooler than the past 700 years average and almost 2 °C colder than present. The temperatures began to increase in southern Finland from 1800 AD and in eastern Finland from 1900 AD onwards. The highest temperatures were reached at the top of the core, representing the present climate warming. Although there was slight overestimation in the recent inferred values, the reconstructed trends were in close correspondence with the previous proxy-based, historical, and measured data that suggests that the reconstruction was realistic and reliable.

A sediment core from Lake Arapisto, Finland, was examined for fossil diatom assemblages to reconstruct changes in Holocene nutrient availability. Our aim was to investigate the long-term relationship between lake trophic status and climate by comparing the diatom-based phosphorus reconstruction with paleoclimatic proxies. Our results showed that the cold early Holocene was characterized by elevated nutrient conditions concurrent with newly exposed fertile ground. As the climate rapidly warmed and ice sheet further retreated, the catchment vegetation developed, which resulted in decreased nutrient flux into the lake. The Holocene Thermal Maximum (HTM), between ~ 8000 and 4000 cal yr BP, was characterized by oligotrophic conditions, which may have been caused by low effective precipitation and stable watershed vegetation. After the HTM, the lake became more productive. There was no particular increase in the trophic state that could be connected to more recent human influence. Although lake productivity has been shown to be affected by temperature, our record indicated that the nutrient dynamics were driven by complex interactions between changes in temperature, precipitation, catchment, and in-lake processes. Understanding of long-term nutrient dynamics and the associated processes can help in resolving relationships between lake productivity and climate during past and present climate changes.

Luoto, T.P., Nevalainen, L., Kubischta, F., Kultti, S., Knudsen, K.L. and Salonen, V.‐P., 2011: Late Quaternary ecological turnover in high arctic Lake Einstaken, Nordaustlandet, Svalbard (80° N). Geografiska Annaler: Series A, Physical Geography, 93, 337–354. DOI:10.1111/j.1468‐0459.2011.00435.xAbstractMultiproxy palaeolimnological analyses of a sediment core record from Lake Einstaken, Nordaustlandet, give insight into long‐term ecological and environmental dynamics in the High Arctic Svalbard during the last c. 13-000 cal yr bp. Fossil remains of foraminifera, chironomidae, cladocera and diatoms (Bacillariophyta) revealed several distinct ecological turnovers during the late Quaternary. The foraminiferal assemblages in a marine interval in the lower part of the core indicated one distinct faunal turnover and two subsequent minor changes. The foraminiferal assemblages reflected high‐arctic, shallow‐water conditions in an area of changing salinity conditions. A development of gradually more restricted ma...

Luoto, T. P. & Sarmaja-Korjonen, K. 2011: Midge-inferred Holocene effective moisture fluctuations in a subarctic lake, northern Lapland. Boreas, 10.1111/j.1502-3885.2011.00217.x. ISSN 0300-9483. We examined fossil midge (Diptera: Chironomidae) assemblages from Lake Varddoaijavri, northern Finland to track Holocene effective moisture variability. Application of a midge-based water-depth calibration model showed that the early Holocene was characterized by a high water level compared with the Holocene average, but the inferred values decreased at c. 8000 cal. a BP and increased again towards c. 6000 cal. a BP. The inferred water level decreased at c. 5500 cal. a BP, but increased again towards c. 4000 cal. a BP. Between 4000 and 3000 cal. a BP the lake experienced two rapid events of lower water level. A relatively high water level detected at c. 3000 cal. a BP was followed by a lowering towards c. 2000 cal. a BP. The time period from c. 2000 cal. a BP onwards was characterized by a general rise in lake level towards the present. Overall, the present reconstruction shows a close correspondence in its trends to previous lake-level records in the region. Two common core taxa, Paratanytarsus and Corynocera ambigua, did not correlate significantly with water depth in the calibration data, creating a potential error source for the present lake-level reconstruction. However, statistical analysis showed a clear community response to long-term lake-level changes, and therefore the major trends in Holocene effective moisture patterns were revealed. The present palaeoclimatic information can also serve as valuable background data when assessing the effects of the present climate change.

The usability of subfossil Cladocera assemblages in reconstructing long-term changes in lake level was examined by testing the relationship between Cladocera-based planktonic/littoral (P/L) ratio and water-level inference model in a surface-sediment dataset and in a 2000-yr sediment record in Finland. The relationships between measured and inferred water levels and P/L ratios were significant in the dataset, implying that littoral taxa are primarily deposited in shallow littoral areas, while planktonic cladocerans accumulate abundantly mainly in deepwater locations. The 2000-yr water-level reconstructions based on the water-level inference model and P/L ratio corresponded closely with each other and with a previously available midge-inferred water-level reconstruction from the same core, showing a period of lower water level around AD 300–1000 and suggesting that the methods are valid for paleolimnological and -climatological use.

Effective moisture and temperature dynamics during the late glacial and Holocene were reconstructed from fossil midge (Diptera: Nematocera) assemblages in Lake Hirvijarvi, southern Finland. Quantitative inferences were performed using midge-based transfer functions for water depth and mean July air temperature. The aim was to identify major trends in Holocene climate development. The results were generally consistent with patterns found in previous investigations from nearby regions and indicated some distinct differences in palaeoclimate between southern and northern Finland. The results indicate that the region was characterised by a very cold Late Pleistocene, cool and moist but drying early Holocene, warm and moist mid Holocene and cool and moist late Holocene. A progressive trend of increasing lake levels from the early Holocene towards the present was evident. The results of this study provide implications for regional differences in effective moisture between southern and northern Finland during the Holocene. Copyright © 2010 John Wiley & Sons, Ltd.

Lake Mallusjarvi in the cultural landscape of Mallusjoki, southern Finland, suffers from algal blooms during summers and oxygen depletions during winters due to increased nutrient input resulting from extensive agricultural activities in the catchment. In this study, a sediment profile from the lake was studied using fossil midge (Diptera: Nematocera) analysis and a hypolimnetic oxygen transfer function was applied to establish baseline conditions of hypolimnetic oxygen. In addition, physical properties of the sediment were determined. The inferred late winter hypolimnetic oxygen content was elevated in the beginning of the sediment sequence, but decreased dramatically at ca. 200 cal BP, as the inferred values indicated frequently anoxic condition coinciding with increased agricultural use in the catchment. The results indicated that dramatic changes have occurred in the taxon composition. The high-oxygen Stempellina–Ablabesmyia monilis-type community first changed to moderate-oxygen Procladius–Stempellinella community, and finally to low-oxygen Microchironomus tener–Chironomus plumosus-type community, following the eutrophication process. These changes in macrobenthic faunal assemblages reproduced considerably higher inferred hypolimnetic oxygen reference condition values for hypolimnetic oxygen, compared to the present status.

Hydrological changes and air temperature variability are reconstructed from the sediments of Lake Pieni-Kauro, eastern Finland during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) using transfer functions derived from midge (Insecta: Nematocera)-based calibration models. The reconstructions are compared with a regional tree-ring chronology and sediment physical properties are determined to track depositional changes. An objective of the study is to examine the long-term relationship between the North Atlantic Oscillation (NAO) and climate (temperature, precipitation). Our results show that the MCA was characterized by warm and dry summer conditions, which were accompanied by changes in the sediment magnetic susceptibility values most likely representing major forest fires during the tree-ring indicated MCA megadrought. However, the midge-based stream flow reconstruction shows increased values during the MCA, thus implying enhanced spring floods after snowy winters. During the LIA, the tree-ring data indicate that a generally wetter climate prevailed during summers, but the stream flow reconstruction indicates less snowy winters. In the terms of long-term climatology, the present results show support to the concept that the NAO has a positive correlation between winter precipitation and annual temperature and a negative correlation between summer precipitation in eastern Finland. Thus, the results may serve as important background data for global change assessments.

Midge (Insecta: Diptera: Nematocera) assemblages were examined in surface sediment samples from Lake Pieni-Kauro and the Saavanjoki River, eastern Finland, using their sedimentary remains. The aim was first to identify the forcing factors behind midge distribution within an aquatic ecosystem and second to develop new midge-based calibration models for the reconstruction of past environmental conditions, with a special focus on paleohydrology. The third objective was to apply the models to a midge stratigraphy. The effect of sampling-point selection in paleolimnological studies and its possible influence on chironomid-inferred temperature reconstructions was also assessed. The species assemblages in Lake Pieni-Kauro showed high levels of heterogeneity within the surface sediment samples, signifying that the assemblages predominantly incorporate locally dwelling fauna, instead of integrating remains from a larger area. Stream flow and water depth were the most important factors explaining the midge distribu...

In the present study I utilize subfossil chironomid and chaoborid distributions in surface sediments of 68 shallow lakes. The aim is to develop a calibration model for past water-level reconstructions by applying weighted averaging-partial least squares (WA-PLS) techniques and to evaluate its potential applications and limitations. This study considers water depth at sampling sites, rather than maximum lake depth. The best of the water depth models developed uses three components and has a cross-validated coefficient of determination ( r 2 jack ) of 0.68 and root-mean-squared error of prediction (RMSEP) of 0.78 m. The model performance is tested on the sediment sequence of a previously studied lake from southern Finland that is known to have experienced past fluctuations in its water level. The water levels inferred are compared with results of chironomid-inferred air temperature reconstruction to ease separation of the effects of the variables. The reconstruction shows consistent results similar to those of previously published cladoceran planktonic:littoral ratios (P:Ls) from the same lake. However, the results indicate that factors other than depth and temperature, such as pollution, may possibly distort the inference results. The results suggest that in applying the midge-based water depth calibration model, it would be advantageous to use it together with an inference model for temperature and preferably in a multiproxy content where changes in water chemistry may be detected. The model can be useful in studies on past effective moisture variability that is closely related to climatic changes.

The aim of this study was to assess the value of phantom midge Chaoborus (Diptera: Chaoboridae) larvae as a palaeoenvironmental proxy in northern Europe. The presence of Chaoborus was examined in 80 small shallow lakes across Finland (60–70°N), based on their subfossil mandibles preserved in lake sediments. Chaoborus flavicans was present in 33 lakes, but was the most abundant midge taxon in only one of the lakes. Chaoborus crystallinus/obscurripes mandibles were present in two lakes. Statistical analyses showed that the distribution of Chaoborus was significantly correlated with lake depth and mean July air temperature. Chaoborus was absent in the northern study lakes, whereas the results indicated that C. flavicans was frequently found in small shallow lakes in southern Finland. Chaoborus flavicans was particularly abundant in fish-free, macrophyte-rich, dystrophic lakes, but absent in oligotrophic clear-water lakes having fish. The results of this study indicate that the subfossil mandibles of Chaoborus can provide valuable information in multiproxy palaeolimnological studies, especially when investigating past changes in water level and temperature in small shallow lakes in northern Europe.