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  • 1. Ampel, Linda
    et al.
    Bigler, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Wohlfarth, Barbara
    Risberg, Jan
    Lotter, André F
    Veres, Daniel
    Modest summer temperature variability during DO cycles in western Europe2010Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, nr 11/12, s. 1322-1327Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Abrupt climatic shifts between cold stadials and warm interstadials, termed Dansgaard-Oeschger (DO) cycles, occurred frequently during the Last Glacial. Their imprint is registered in paleorecords worldwide, but little is known about the actual temperature change both annually and seasonally in different regions. A recent hypothesis based on modelling studies, suggests that DO cycles were characterised by distinct changes in seasonality in the Northern Hemisphere. The largest temperature change between stadial and interstadial phases would have occurred during the winter and spring seasons, whereas the summer seasons would have experienced a rather muted temperature shift. Here we present a temporally high-resolved reconstruction of summer temperatures for eastern France during a sequence of DO cycles between 36 and 18 thousand years before present. The reconstruction is based on fossil diatom assemblages from the paleolake Les Echets and indicates summer temperature changes of ca 0.5–2 °C between stadials and interstadials. This study is the first to reconstruct temperatures with a sufficient time resolution to investigate DO climate variability in continental Europe. It is therefore also the first proxy record that can test and support the hypothesis that temperature changes during DO cycles were modest during the summer season.

  • 2.
    Ehnvall, Betty
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, Umeå, Sweden.
    Ratcliffe, Joshua L.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, Umeå, Sweden.
    Bohlin, Elisabet
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, Umeå, Sweden.
    Nilsson, Mats B.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, Umeå, Sweden.
    Öquist, Mats G.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, Umeå, Sweden.
    Sponseller, Ryan A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Grabs, Thomas
    Department of Earth Sciences, Geocentrum, Uppsala University, Villavägen 16, Uppsala, Sweden.
    Landscape constraints on mire lateral expansion2023Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 302, artikel-id 107961Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Little is known about the long-term expansion of mire ecosystems, despite their importance in the global carbon and hydrogeochemical cycles. It has been firmly established that mires do not expand linearly over time. Despite this, mires are often assumed to have expanded at a constant rate after initiation simply for lack of a better understanding. There has not yet been a serious attempt to determine the rate and drivers of mire expansion at the regional, or larger spatial scales. Here we make use of a natural chronosequence, spanning the Holocene, which is provided by the retreating coastline of Northern Sweden. By studying an isostatic rebound area we can infer mire expansion dynamics by looking at the portion of the landscape where mires become progressively scarce as the land becomes younger. Our results confirms that mires expanded non-linearly across the landscape and that their expansion is related to the availability of suitably wet areas, which, in our case, depends primarily on the hydro-edaphic properties of the landscape. Importantly, we found that mires occupied the wettest locations in the landscape within only one to two thousand years, while it took mires three to four thousand years to expand into slightly drier areas. Our results imply that the lateral expansion of mires, and thus peat accumulation is a non-linear process, occurring at different rates depending, above all else, on the wetness of the landscape.

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  • 3. Farjon, Aljos
    et al.
    Horne, David J.
    Parfitt, Simon A.
    Buckland, Philip I.
    Umeå universitet, Humanistiska fakulteten, Institutionen för idé- och samhällsstudier, Miljöarkeologiska laboratoriet.
    Lewis, Mark D.
    Early Pleistocene conifer macrofossils from Happisburgh, Norfolk, UK, and their environmental implications for early hominin occupation2020Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 232, artikel-id 106115Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Continuing coastal erosion in the vicinity of Happisburgh in north Norfolk has revealed archaeological sites documenting early human presence during at least two episodes in the Early and early Middle Pleistocene. At Happisburgh 3, the oldest archaeological site in northern Europe (approximately 900,000 years old) finds include at least 80 flint artefacts and human footprints associated with abundant, well-preserved organic remains. The deposits consist of gravels and estuarine sands and silts contained within a complex of channels, which accumulated in the estuary of a large river, probably the ancestral River Thames. The environmental remains reflect a slow-flowing tidal river, at the limit of tidal influence, and a grassland valley bordered by conifer-dominated woodland. Analyses of the pollen, wood, cones and leaves have identified a diversity of coniferous taxa, with some unexpected central and southern European elements (Pinus mugo ssp. mugo, Pinus mugo ssp. rotundata and Juniperus thurifera) indicating a type of coniferous woodland no longer present in Europe today. Here we present the conifer finds and their environmental implications. A new multi-proxy consensus palaeoclimate reconstruction, using conifer and beetle mutual climatic ranges, confirms and refines previous indications of a more continental climate than today, with significantly colder winters. These results provide a new perspective for understanding the climate and environment encountered by Early Pleistocene hominins at the northernmost limit of their range.

  • 4. Hahn, A
    et al.
    Kliem, P
    Ohlendorf, C
    Zolitschka, B
    Rosen, Peter
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Climate induced changes as registered in inorganic and organic sediment components from Laguna Potrok Aike (Argentina) during the past 51 ka2013Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 71, s. 154-166Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Total organic carbon, total inorganic carbon, biogenic silica content and total organic carbon/total nitrogen ratios of the Laguna Potrok Aike lacustrine sediment record are used to reconstruct the environmental history of south-east Patagonia during the past 51 ka in high resolution. High lake level conditions are assumed to have prevailed during the Last Glacial, as sediments are carbonate-free. Increased runoff linked to permafrost and reduced evaporation due to colder temperatures and reduced influence of Southern Hemispheric Westerlies (SHIN) may have caused these high lake levels with lake productivity being low and organic matter mainly of algal or cyanobacterial origin. Aquatic moss growth and diatom blooms occurred synchronously with southern hemispheric glacial warming events such as the Antarctic A-events, the postglacial warming following the LGM and the Younger Dryas chronozone. During these times, a combination of warmer climatic conditions with related thawing permafrost could have increased the allochthonous input of nutrients and in combination with warmer surface waters increased aquatic moss growth and diatom production. The SHW were not observed to affect southern Patagonia during the Last Glacial. The Holocene presents a completely different lacustrine system because (a) permafrost no longer inhibits infiltration nor emits meltwater pulses and (b) the positioning of the SHW over the investigated area gives rise to strong and dry winds. Under these conditions total organic carbon, total organic carbon/total nitrogen ratios and biogenic silica cease to be first order productivity indicators. On the one hand, the biogenic silica is influenced by dissolution of diatoms due to higher salinity and pH of the lake water under evaporative stress characterizing low lake levels. On the other hand, total organic carbon and total organic carbon/total nitrogen profiles are influenced by reworked macrophytes from freshly exposed lake level terraces during lowstands. Total inorganic carbon remains the most reliable proxy for climatic variations during the Holocene as high precipitation of carbonates can be linked to low lake levels and high autochthonous production. The onset of inorganic carbon precipitation has been associated with the southward shift of the SHW over the latitudes of Laguna Potrok Aike. The refined age-depth model of this record suggests that this shift occurred around 9.4 cal. ka BP. (c) 2012 Elsevier Ltd. All rights reserved.

  • 5.
    Katrantsiotis, Christos
    et al.
    Umeå universitet, Humanistiska fakulteten, Institutionen för idé- och samhällsstudier.
    Norström, Elin
    Department of Physical Geography and the Bolin Centre for Climate Research, Stockholm University, 106 91, Stockholm, Sweden.
    Smittenberg, Rienk H.
    Department of Geological Sciences and the Bolin Centre for Climate Research, Stockholm University, 10691, Stockholm, Sweden.
    Salonen, J. Sakari
    Department of Geosciences and Geography, P.O. Box 64, 00014, University of Helsinki, Finland.
    Plikk, Anna
    The Archaeologists, National Historical Museums, SE, 126 53, Hägersten, Sweden.
    Helmens, Karin
    Swedish Museum of Natural History, P.O. Box 50007, 10405, Stockholm, Sweden and Värriö Research Station, Institute for Atmospheric and Earth System Research INAR / Physics, P.O. Box 64, 00014, University of Helsinki, Finland.
    Seasonal variability in temperature trends and atmospheric circulation systems during the Eemian (Last Interglacial) based on n-alkanes hydrogen isotopes from Northern Finland2021Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 273, s. 107250-107250, artikel-id 107250Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Last Interglacial warm period, the Eemian (ca. 130–116 thousand years ago), serves as a reference for projected future climate in a warmer world. However, there is a limited understanding of the seasonal characteristics of interglacial climate dynamics, especially in high latitude regions. In this study, we aim to provide new insights into seasonal trends in temperature and moisture source location, linked to shifts in atmospheric circulation patterns, for northern Fennoscandia during the Eemian. Our study is based on the distribution and stable hydrogen isotope composition (δD) of n-alkanes in a lake sediment sequence from the Sokli paleolake in NE Finland, placed in a multi-proxy framework. The δD values of predominantly macrophyte-derived mid-chain n-alkanes are interpreted to reflect lake water δD variability influenced by winter precipitation δD (δDprec), ice cover duration and deuterium (D)-depleted meltwater. The δD values of terrestrial plant-derived long-chain n-alkanes primarily reflect soil water δD variability modulated by summer δDprec and by the evaporative enrichment of soil and leaf water. The δDprec variability in our study area is mostly attributed to the temperature effect and the moisture source location linked to the relative dominance between D-depleted continental and polar air masses and D-enriched North Atlantic air masses. The biomarker signal further corroborates earlier diatom-based studies and pollen-inferred January and July temperature reconstructions from the same sediment sequence. Three phases of climatic changes can be identified that generally follow the secular variations in seasonal insolation: (i) an early warming trend succeeded by a period of strong seasonality (ii) a mid-optimum phase with gradually decreased seasonality and cooler summers, and (iii) a late climatic instability with a cooling trend. Superimposed on this trend, two abrupt cooling events occur in the early and late Eemian. The Sokli δD variability is generally in good agreement with other North Atlantic and Siberian records, reflecting major changes in the atmospheric circulation patterns during the Eemian as a response to orbital and oceanic forcings.

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  • 6.
    Kullman, Leif
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Early postglacial appearance of tree species in northern Scandinavia: review and perspective2008Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 27, nr 27-28, s. 2467-2472Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper reviews megafossil evidence for the first postglacial records of different tree species in northern Scandinavia. Betula pubescens coll. appeared at the Arctic coast of northern Norway by 16. 900 yr BR In addition, Betula Pubescens (14, 000 yr BP), Pinus sylvestris (11, 700 yr BP) and Picea abies (11, 000 yr BP) existed on early ice- free mountain peaks (nunataks) at different locations in the Scandes during the Lateglacial. Larix sibirica, currently not native to Fennoscandia, and several thermophilous broadleaved tree species were recorded in the earliest part of the Holocene. The conventional interpretation of pollen and macrofossil records from peat and sediment stratigraphies do not consider the Occurrence of the species mentioned above that early at these northern and high altitude sites. This very rapid arrival after the local deglaciation implies that the traditional model of far distant glacial refugial areas for tree species has to be challenged. The Current results are more compatible with a situation involving scattered "cryptic" refugia quite close to margin of the ice sheet at its full-glacial extension. This fits a more general pattern currently emerging on different continents. In general, "cryptic" refugia should be considered in connection with modelling extinction risks related to modern and possible future "climatic crises".

  • 7. Kylander, Malin E.
    et al.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Cortizas, Antonio Martinez
    Gallagher, Kerry
    Morth, Carl-Magnus
    Rauch, Sebastien
    A novel geochemical approach to paleorecords of dust deposition and effective humidity: 8500 years of peat accumulation at Store Mosse (the "Great Bog"), Sweden2013Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 69, s. 69-82Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Both bog surface wetness and atmospheric dust deposition are intricately linked to changes in the hydrological cycle and pairing these types of records at the same site provides complementary information. Here a peat core from Store Mosse in southern Sweden covering the last 8500 years was used to make a high-resolution paleoclimate reconstruction based on a combination of bog development, colourimetric humification and inorganic geochemistry data. The coupling of Principal Component Analysis with changepoint modelling allowed for precise linking of changes in bog surface wetness and dust deposition records. A long-term trend towards warm (and possibly wet) conditions starts ca 8150 cal yr BP and culminates with the most pronounced conditions from 6900 to 6600 cal yr BP. The most significant arid period at Store Mosse occurred between 6500 and 5600 cal yr BP during which dust deposition was significantly higher. Wetter conditions dominate from 5500 to 4980 cal yr BP as the transition from the Hypsithermal and into the Neoglacial is made. After a shift to drier conditions, humification enters a more stable period that lasts from 4525 until 3200 cal yr BP. It is during this time that the first possible anthropogenic dust signals occur at ca 4200 cal yr BP. From 3200 cal yr BP to present humification generally shows a long-term decline moving towards wetter conditions. The main exceptions are during the transition from the Neoglacial to Roman Warm Period which is registered as a significantly wetter period and two dry periods recorded 2365 to 2155 cal yr BP and 1275-1105 cal yr BP. In general, the observed changes agree well with regional records of effective humidity and temperature. The high temporal resolution of the Store Mosse record reveals that palaeoclimatic change over the last 8500 years in southern Sweden has had a complex and variable structure. (c) 2013 Elsevier Ltd. All rights reserved.

  • 8.
    Kylander, Malin E.
    et al.
    Department of Geological Sciences, Stockholm University, Stockholm, Sweden; Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.
    Martínez-Cortizas, Antonio
    Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden; CRETUS, EcoPast (GI-1553), Universidade de Santiago de Compostela, Santiago de Compostela, Spain.
    Sjöström, Jenny K.
    Department of Geological Sciences, Stockholm University, Stockholm, Sweden; Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.
    Gåling, Jenny
    Department of Geological Sciences, Stockholm University, Stockholm, Sweden; Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.
    Gyllencreutz, Richard
    Department of Geological Sciences, Stockholm University, Stockholm, Sweden; Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Alexanderson, Helena
    Department of Geology, Lund University, Lund, Sweden; Department of Geosciences, The Arctic University of Norway, Tromsø, Norway.
    Schenk, Frederik
    Department of Geological Sciences, Stockholm University, Stockholm, Sweden; Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.
    Reinardy, Benedict T.I.
    Department of Sustainable Development, Environmental Science and Engineering (SEED), KTH the Royal Institute of Technology, Stockholm, Sweden.
    Chandler, Benjamin M.P.
    School of Geography, University of Nottingham, Nottingham, United Kingdom.
    Gallagher, Kerry
    University of Rennes, CNRS, Géosciences Rennes, Rennes, France.
    Storm chasing: Tracking Holocene storminess in southern Sweden using mineral proxies from inland and coastal peat bogs2023Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 299, artikel-id 107854Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Severe extratropical winter storms are a recurrent feature of the European climate and cause widespread socioeconomic losses. Due to insufficient long-term data, it remains unclear whether storminess has shown a notable response to changes in external forcing over the past millennia, which impacts our ability to project future storminess in a changing climate. Reconstructing past storm variability is essential to improving our understanding of storms on these longer, missing timescales. Peat sequences from coastal ombrotrophic bogs are increasingly used for this purpose, where greater quantities of coarser grained beach sand are deposited by strong winds during storm events. Moving inland however, storm intensity decreases, as does sand availability, muting potential paleostorm signals in bogs. We circumvent these issues by taking the innovative approach of using mid-infrared (MIR) spectral data, supported by elemental information, from the inorganic fraction of Store Mosse Dune South (SMDS), a 5000-year-old sequence from a large peatland located in southern Sweden. We infer past changes in mineral composition and thereby, the grain size of the deposited material. The record is dominated by quartz, whose coarse nature was confirmed through analyses of potential local source sediments. This was supported by further mineralogical and elemental proxies of atmospheric input. Comparison of SMDS with within-bog and regionally relevant records showed that there is a difference in proxy and site response to what should be similar timing in shifts in storminess over the ∼100 km transect considered. We suggest the construction of regional storm stacks, built here by applying changepoint modelling to four transect sites jointly. This modelling approach has the effect of reinforcing signals in common while reducing the influence of random noise. The resulting Southern Sweden-Storm Stack dates stormier periods to 4495–4290, 3880–3790, 2885–2855, 2300–2005, 1175–1065 and 715-425 cal yr BP. By comparing with a newly constructed Western Scotland-Storm Stack and proximal dune records, we argue that regional storm stacks allow us to better compare past storminess over wider areas, gauge storm track movements and by extension, increase our understanding of the drivers of storminess on centennial to millennial timescales.

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  • 9.
    Larocque, I.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Halla, R.I.
    Holocene temperature estimates and chironomid community composition in the Abisko Valley, northern Sweden2004Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 23, nr 23-24, s. 2453-2465Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multi-proxy paleoenvironmental reconstructions are useful to determine the various factors affecting the biological communities of a lake, but to assess if changes in community composition of one indicator organism accurately reconstructs climatic changes through time, it may be more useful to compare temperature reconstructions using the same indicator in several lakes. Here, we compare reconstructions of mean July air temperature using chironomid-based transfer functions from Holocene records at three nearby lakes in the Abisko Valley of northern Sweden to assess if chironomids can be used as indicators of regional temperature changes. The three study lakes experience the same regional climatic conditions, but are located along gradients of elevation (348–999 m a.s.l), temperature (8.1–12°C) and terrestrial vegetation (coniferous to alpine). Chironomid-temperature reconstructions from the three sites indicate a general pattern of temperature decrease (1.5–2.4°C) during the Holocene, consistent with decreases observed from analyses of other proxies in this area, and from other alpine regions in Europe and North America. Similarities between these reconstructions suggest that chironomids can adequately record general patterns of temperature changes through the Holocene, although effects of site-specific factors such as variations in lake water pH can cause deviations in inferred temperature among sites during some periods.

  • 10. Leng, Melanie J.
    et al.
    Wagner, Bernd
    Boehm, Anne
    Panagiotopoulos, Konstantinos
    Vane, Christopher H.
    Snelling, Andrea
    Haidon, Cheryl
    Woodley, Ewan
    Vogel, Hendrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Zanchetta, Gianni
    Baneschi, Ilaria
    Understanding past climatic and hydrological variability in the Mediterranean from Lake Prespa sediment isotope and geochemical record over the last glacial cycle2013Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 66, s. 123-136Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Here we present stable isotope and geochemical data from Lake Prespa (Macedonia/Albania border) over the Last Glacial cycle (Marine Isotope Stages 5-1) and discuss past lake hydrology and climate (TIC, oxygen and carbon isotopes), as well as responses to climate of terrestrial and aquatic vegetation (TOC, Rock Eval pyrolysis, carbon isotopes, pollen). The Lake Prespa sediments broadly fall into 5 zones based on their sedimentology, geochemistry, palynology and the existing chronology. The Glacial sediments suggest low supply of carbon to the lake, but high summer productivity; intermittent siderite layers suggest that although the lake was likely to have mixed regularly leading to enhanced oxidation of organic matter, there must have been within sediment reducing conditions and methanogenesis. MIS 5 and 1 sediments suggest much more productivity, higher rates of organic material preservation possibly due to more limited mixing with longer periods of oxygen-depleted bottom waters. We also calculated lakewater delta O-18 from siderite (authigenic/Glacial) and calcite (endogenic/Holocene) and show much lower lakewater delta O-18 values in the Glacial when compared to the Holocene, suggesting the lake was less evaporative in the Glacial, probably as a consequence of cooler summers and longer winter ice cover. In the Holocene the oxygen isotope data suggests general humidity, with just 2 marked arid phases, features observed in other Eastern and Central Mediterranean lakes. (C) 2012 Elsevier Ltd. All rights reserved.

  • 11. Rosqvist, Gunhild C
    et al.
    Leng, Melanie J.
    Goslar, Tomasz
    Sloane, Hilary J.
    Bigler, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Cunningham, Laura
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Dadal, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bergman, Jonas
    Berntsson, Annika
    Jonsson, Christina
    Wastegard, Stefan
    Shifts in precipitation during the last millennium in northern Scandinavia from lacustrine isotope records2013Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 66, s. 22-34Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Here we present delta P-18(diatom) data from two high-latitude lakes; one has short residence time and a water isotopic composition (delta O-18(lake)) that fluctuate due to seasonal variations in precipitation and temperature, and the other has delta O-18(lake) that is influenced by longer lake water residence times and evaporation. The delta O-18(diatom) records reveal common responses to precipitation forcing over the past millennium. Relatively wet summers are inferred from delta O-18(diatom) between 1000 and 1080 AD, 1300 and 1440 AD, and during the early 19th century, coincided with periods of high cloud cover inferred from tree-ring carbon isotopes, and other data for high Arctic Oscillation index. While relatively dry summers with increasing influence of winter snow are indicated between 1600 and 1750 AD. The co-response between carbon isotopes in trees and oxygen isotopes in diatoms strengthens the relationship between cloud cover and precipitation and the hypothesis that these changes were the result of significant regional shifts in atmospheric circulation. (C) 2012 Elsevier Ltd. All rights reserved.

  • 12.
    Voldstad, Linn H.
    et al.
    The University Centre in Svalbard (UNIS), Longyearbyen, Norway; Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Ås, Norway.
    Alsos, Inger G.
    The Arctic University Museum of Norway, UiT The Arctic University of Norway, Tromsø, Norway.
    Farnsworth, Wesley R.
    The University Centre in Svalbard (UNIS), Longyearbyen, Norway; Department of Geosciences, UiT The Arctic University of Norway, Tromsø, Norway; NordVulk, Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, Askja, Reykjavik, Iceland.
    Heintzman, Peter D.
    The Arctic University Museum of Norway, UiT The Arctic University of Norway, Tromsø, Norway.
    Håkansson, Lena
    The University Centre in Svalbard (UNIS), Longyearbyen, Norway.
    Kjellman, Sofia E.
    Department of Geosciences, UiT The Arctic University of Norway, Tromsø, Norway.
    Rouillard, Alexandra
    Department of Geosciences, UiT The Arctic University of Norway, Tromsø, Norway; Centre for GeoGenetics, University of Copenhagen, Copenhagen K., Denmark.
    Schomacker, Anders
    Department of Geosciences, UiT The Arctic University of Norway, Tromsø, Norway.
    Eidesen, Pernille B.
    The University Centre in Svalbard (UNIS), Longyearbyen, Norway.
    A complete Holocene lake sediment ancient DNA record reveals long-standing high Arctic plant diversity hotspot in northern Svalbard2020Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 234, artikel-id 106207Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Arctic hotspots, local areas of high biodiversity, are potential key sites for conservation of Arctic biodiversity. However, there is a need for improved understanding of their long-term resilience. The Arctic hotspot of Ringhorndalen has the highest registered diversity of vascular plants in the Svalbard archipelago, including several remarkable and isolated plant populations located far north of their normal distribution range. Here we analyze a lake sediment core from Ringhorndalen for sedimentary ancient DNA (sedaDNA) and geochemical proxies to detect changes in local vegetation and climate. Half of the plant taxa appeared already before 10,600 cal. yr BP, indicating rapid colonization as the ice retreated. Thermophilous species had a reoccurring presence throughout the Holocene record, but stronger signal in the early than Late Holocene period. Thus, thermophilous Arctic plant species had broader distribution ranges during the Early Holocene thermal maximum c. 10,000 cal. yr BP than today. Most of these thermophilous species are currently not recorded in the catchment area of the studied lake, but occur locally in favourable areas further into the valley. For example, Empetrum nigrum was found in >40% of the sedaDNA samples, whereas its current distribution in Ringhorndalen is highly restricted and outside the catchment area of the lake. Our findings support the hypothesis of isolated relict populations in Ringhorndalen. The findings are also consistent with main Holocene climatic shifts in Svalbard identified by previous studies and indicate an early warm and species-rich postglacial period until c. 6500 cal. yr BP, followed by fluctuating cool and warm periods throughout the later Holocene. 

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  • 13. Wennrich, Volker
    et al.
    Andreev, Andrei A.
    Tarasov, Pavel E.
    Fedorov, Grigory
    Zhao, Wenwei
    Gebhardt, Catalina A.
    Meyer-Jacob, Carsten
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Snyder, Jeffrey A.
    Nowaczyk, Norbert R.
    Schwamborn, Georg
    Chapligin, Bernhard
    Anderson, Patricia M.
    Lozhkin, Anatoly V.
    Minyuk, Pavel S.
    Koeberl, Christian
    Melles, Martin
    Impact processes, permafrost dynamics, and climate and environmental variability in the terrestrial Arctic as inferred from the unique 3.6 Myr record of Lake El'gygytgyn, Far East Russia - A review2016Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 147, s. 221-244Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lake El'gygytgyn in Far East Russia is a 3.6 Myr old impact crater lake. Located in an area that has never been affected by Cenozoic glaciations nor desiccation, the unique sediment record of the lake represents the longest continuous sediment archive of the terrestrial Arctic. The surrounding crater is the only impact structure on Earth developed in mostly acid volcanic rocks. Recent studies on the impactite, permafrost, and sediment sequences recovered within the framework of the ICDP "El'gygytgyn Drilling Project" and multiple pre-site surveys yielded new insight into the bedrock origin and cratering processes as well as permafrost dynamics and the climate and environmental history of the terrestrial Arctic back to the mid-Pliocene. Results from the impact rock section recovered during the deep drilling clearly confirm the impact genesis of the El'gygytgyn crater, but indicate an only very reduced fallback impactite sequence without larger coherent melt bodies. Isotope and element data of impact melt samples indicate a F-type asteroid of mixed composition or an ordinary chondrite as the likely impactor. The impact event caused a long-lasting hydrothermal activity in the crater that is assumed to have persisted for c. 300 kyr. Geochemical and microbial analyses of the permafrost core indicate a subaquatic formation of the lower part during lake-level highstand, but a subaerial genesis of the upper part after a lake-level drop after the Allerod. The isotope signal and ion compositions of ground ice is overprinted by several thaw freeze cycles due to variations in the talik underneath the lake. Modeling results suggest a modern permafrost thickness in the crater of c. 340 m, and further confirm a pervasive character of the talik below Lake El'gygytgyn. The lake sediment sequences shed new leight into the Pliocene and Pleistocene climate and environmental evolution of the Arctic. During the mid-Pliocene, significantly warmer and wetter climatic conditions in western Beringia than today enabled dense boreal forests to grow around Lake Ergygytgyn and, in combination with a higher nutrient flux into the lake, promoted primary production. The exceptional warmth during the mid-Pliocene is in accordance with other marine and terrestrial records from the Arctic and indicates a period of enhanced "Arctic amplification". The favourable conditions during the mid-Pliocene were repeatedly interrupted by climate deteriorations, e.g., during Marine Isotope Stage (MIS) M2, when pollen data and sediment proxies indicate a major cooling and the onset of local permafrost around the lake. A gradual vegetation change after c. 3.0 Ma points to the onset of a long-term cooling trend during the Late Pliocene that culminated in major temperature drops, first during MIS G6, and later during MIS 104. These cold events coincide with the onset of an intensified Northern Hemisphere (NH) glaciation and the largest extent of the Cordilleran Ice Sheet, respectively. After the Pliocene/Pleistocene transition, local vegetation and primary production in Lake El'gygtygyn experienced a major change from relatively uniform conditions to a high-amplitude glacial-to-interglacial cyclicity that fluctuated on a dominant 41 kyr obliquity band, but changed to a 100 kyr eccentricity dominance during the Middle Pleistocene transition (MPT) at c. 1.2-0.6 Ma. Periods of exceptional warming in the Pleistocene record of Lake El'gygytgyn with dense boreal forests around and peaks of primary production in the lake are assigned to so-called "super-interglacial" periods. The occurrence of these super-interglacials well corresponds to collapses of the West Antarctic Ice Sheet (WAIS) recorded in ice-free periods in the ANDRILL core, which suggests strong intrahemispheric teleconnections presumably driven by changes in the thermocline ocean circulation.

  • 14.
    Wienhues, Giulia
    et al.
    Institute of Geography and Oeschger Center for Climate Change Research, University of Bern, Bern, Switzerland.
    Lami, Andrea
    CNR Water Research Institute (IRSA), Verbania, Italy.
    Bernasconi, Stefano
    Department of Earth Sciences, ETH Zürich, Zurich, Switzerland.
    Jaggi, Madalina
    Department of Earth Sciences, ETH Zürich, Zurich, Switzerland.
    Morlock, Marina A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Institute of Geological Sciences, University of Bern, Bern, Switzerland.
    Vogel, Hendrik
    Institute of Geological Sciences, University of Bern, Bern, Switzerland.
    Cohen, Andrew S.
    Department of Geosciences, University of Arizona, AZ, Tucson, United States.
    Courtney Mustaphi, Colin J.
    Geoecology, Department of Environmental Sciences, University of Basel, Basel, Switzerland; Nelson Mandela African Institution of Science and Technology, P.O. Box 9124, Arusha, Tanzania.
    Heiri, Oliver
    Geoecology, Department of Environmental Sciences, University of Basel, Basel, Switzerland.
    King, Leighton
    Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland; Department of Fish Ecology and Evolution, Swiss Federal Institute for Aquatic Science and Technology (EAWAG), Kastanienbaum, Switzerland.
    Kishe, Mary A.
    Tanzania Fisheries Research Institute, P.O. Box 09750, Dar es Salaam, Tanzania.
    Misra, Pavani
    Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland; Department of Fish Ecology and Evolution, Swiss Federal Institute for Aquatic Science and Technology (EAWAG), Kastanienbaum, Switzerland.
    Muschick, Moritz
    Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland; Department of Fish Ecology and Evolution, Swiss Federal Institute for Aquatic Science and Technology (EAWAG), Kastanienbaum, Switzerland.
    Ngoepe, Nare
    Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland; Department of Fish Ecology and Evolution, Swiss Federal Institute for Aquatic Science and Technology (EAWAG), Kastanienbaum, Switzerland.
    Matthews, Blake
    Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland; Department of Fish Ecology and Evolution, Swiss Federal Institute for Aquatic Science and Technology (EAWAG), Kastanienbaum, Switzerland.
    Seehausen, Ole
    Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland; Department of Fish Ecology and Evolution, Swiss Federal Institute for Aquatic Science and Technology (EAWAG), Kastanienbaum, Switzerland.
    Temoltzin-Loranca, Yunuen
    Institute of Plant Sciences, University of Bern, Bern, Switzerland.
    Tinner, Willy
    Institute of Plant Sciences, University of Bern, Bern, Switzerland.
    Grosjean, Martin
    Institute of Geography and Oeschger Center for Climate Change Research, University of Bern, Bern, Switzerland.
    Latest pleistocene and holocene primary producer communities and hydroclimate in Lake Victoria, Eastern Africa2024Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 330, artikel-id 108599Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Lake Victoria ecosystem is emblematic of the catastrophic effects that human activities, particularly cultural eutrophication, can have on freshwater biodiversity. However, little is known about the long-term spatial and temporal pattern of aquatic primary paleo-production (PPaq) and producer communities in Lake Victoria and how these patterns relate to past climate variability, landscape evolution, lake hydrology, mixing regimes, nutrient cycling, and biodiversity dynamics in the past 17 kyr. We use sediments from four well-dated cores along a transect from offshore to nearshore sites, and exploit XRF element scanning and hyperspectral imaging data, TC, TN, bSi, δ13C and δ15N, and sedimentary pigments to investigate paleolimnological variability and change. Our findings demonstrate that changes in PPaq and algal communities during the past 17 kyr were closely related to hydroclimatic changes, lake mixing, and nutrient availability. During the wetland phase (16.7–14.5 cal ka BP), PPaq levels remained generally low, while chromophytes and chlorophytes dominated the algal community. Following the rapid lake level rise (∼14.2 cal ka BP) during the early African Humid Period (AHP), PPaq levels steadily increased, accompanied by a shift towards cyanobacteria and chromophytes. During the Holocene, our results suggest repeated short-lived arid intervals (∼10.5, ∼9, 7.8–7.2, ∼4, and 3.2–3.0 cal ka BP) and two distinct periods of enhanced lake mixing associated with high PPaq and high diatom productivity: the first one between 11 and 9 cal ka BP, which coincided with the maximum of the AHP (high precipitation, high wind, enhanced mixing), and the second, less pronounced one, between 7 and 4 cal ka BP. Between these two periods (i.e. 9–7 cal ka BP) we observe reduced diatom productivity, relatively low PPaq, and high C/N ratios, suggesting conditions with more stable lake stratification, likely associated with reduced wind strength, and some nutrient limitation (N and P). Finally, the drier conditions around the end of the AHP (ca. 4 cal ka BP) and during the late Holocene were associated with decreasing lake mixing and increasing dominance of cyanobacteria. Given our reconstruction of PPaq over the past 17 kyr, we conclude that the levels in the 20th century are unprecedentedly high, consistent with the massive human-mediated impact on the Lake Victoria ecosystem including biodiversity loss.

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  • 15.
    Yan, Dongna
    et al.
    State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Shaanxi, Xi'an, China.
    Han, Yongming
    State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Shaanxi, Xi'an, China; National Observation and Research Station of Regional Ecological Environment Change and Comprehensive Management in the Guanzhong Plain, Shaanxi, Xi'an, China.
    An, Zhisheng
    State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Shaanxi, Xi'an, China.
    Lei, Dewen
    State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Shaanxi, Xi'an, China; University of Chinese Academy of Sciences, Beijing, China.
    Zhao, Xue
    State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Shaanxi, Xi'an, China.
    Zhao, Haiyan
    State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Shaanxi, Xi'an, China; Xi'an Institute for Innovative Earth Environment Research, Xi'an, China.
    Liu, Jinzhao
    State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Shaanxi, Xi'an, China.
    Capo, Eric
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Anthropogenic drivers accelerate the changes of lake microbial eukaryotic communities over the past 160 years2024Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 327, artikel-id 108535Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Human impacts on Earth's atmosphere, hydrosphere, litosphere and biosphere are so significant as to naming a new geological epoch, the Anthropocene. Lakes and their biota are highly sensitive to environmental changes. Among aquatic organisms, microbial eukaryotes play fundamental roles associated with lake ecosystem functioning, food webs, nutrient cycling, and pollutant degradation. However, the response of lake microbial eukaryotic community during the Anthropocene to changes in environmental conditions remain poorly understood. Here, we applied a 18S metabarcoding approach to sedimentary DNA to reconstruct the temporal dynamics of microbial eukaryotic community over the past 160 years. We investigated the influence of environmental conditions and of biotic interactions on the microbial eukaryotes in Sihailongwan Maar Lake, one of the candidate sites of Global boundary Stratotype Section and Point (GSSP) for demarcation of the Anthropocene. Microbial eukaryotes were dominated by dinoflagellates, chlorophytes, ciliates, pirsoniales, rotifers, ochrophytes, apicomplexans and cercozoans that were divided into four functional groups that are photoautotrophs, mixotrophs, consumers and parasites. The predominance of phototrophs and their strong associations with organisms from other trophic levels, confirmed their crucial roles in nutrient cycling, energy flows and ecosystem services in freshwater ecosystems. Abrupt changes in the 1950s in microbial eukaryotic diversity and composition were consistent with changes observed in the pollutants emissions i.e., heavy metals, combustion indices (spheroidal carbonaceous particles, polycyclic aromatic hydrocarbon, Soot F14C), radioactivity indicators (239,240Pu, 129I/127I), nutrients (total organic carbon, total nitrogen, phosphorus), and temperature. Statistical analysis revealed that anthropogenic drivers controlled the temporal dynamic of microbial eukaryotic community. Our findings provide additional biostratigraphy evidence of the impact of environmental change on this lake biota, which further supports the value of this system to characterize the Anthropocene.

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  • 16.
    Zale, Rolf
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Huang, Y. -T
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bigler, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Wood, J. R.
    Dalén, L.
    Wang, Xiao-Ru
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Segerström, U.
    Klaminder, Jonatan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Growth of plants on the Late Weichselian ice-sheet during Greenland interstadial-1?2018Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 185, s. 222-229Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Unglaciated forelands and summits protruding from ice-sheets are commonly portrayed as areas where plants first establish at the end of glacial cycles. But is this prevailing view of ice-free refugia too simplistic? Here, we present findings suggesting that surface debris supported plant communities far beyond the rim of the Late Weichselian Ice-sheet during Greenland interstadial 1 (GI-1 or Bolling-Altered interstadial). We base our interpretations upon findings from terrigenous sediments largely resembling 'plant-trash' deposits in North America (known to form as vegetation established on stagnant ice became buried along with glacial debris during the deglaciation). In our studied deposit, we found macrofossils (N = 10) overlapping with the deglaciation period of the area (9.5-10 cal kyr BP) as well as samples (N = 2) with ages ranging between 12.9 and 13.3 cal kyr BP. The latter ages indicate growth of at least graminoids during the GI-1 interstadial when the site was near the geographic center of the degrading ice-sheet. We suggest that exposure of englacial material during GI-1 created patches of supraglacial debris capable of supporting vascular plants three millennia before deglaciation. The composition and resilience of this early plant community remain uncertain. Yet, the younger group of macrofossils, in combination with pollen and ancient DNA analyses of inclusions, imply that shrubs (Salix sp., Betula sp. and Ericaceae sp) and even tree species (Larix) were present in the debris during the final deglaciation stage. 

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