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  • 1. Emmanouilidis, Alexandros
    et al.
    Katrantsiotis, Christos
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies, Environmental Archaeology Lab.
    Dotsika, Elissavet
    Kokkalas, Sotirios
    Unkel, Ingmar
    Avramidis, Pavlos
    Holocene paleoclimate variability in the eastern Mediterranean, inferred from the multi-proxy record of Lake Vouliagmeni, Greece2022In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 595, article id 110964Article in journal (Refereed)
    Abstract [en]

    This study presents a Holocene multi-proxy record from Lake Vouliagmeni, eastern Gulf of Corinth, Greece. The lake is subjected to intense climatic and tectonic forces causing stratigraphic variations with laminated sediments frequently interrupted by homogenous sections and event deposits. Lamination couplets consist of aragonite layers alternating with detrital and organic residues formed during periods of seawater intrusion and stratification of the lake water. The discontinuous occurrence of laminated deposits excludes a varve based chronology from being established but highlights the susceptibility of the lake to record environmental and climatic changes. Our synthesis model for regional climatic reconstruction and local environmental changes derives from δ18O and δ13C data from laminated and homogenous sediments studied separately and depending on the dominant carbonate mineral. This is further strengthened by high-resolution geochemical proxies, diatom and sedimentological data. Regional climatic signals from key sites and possible links to the Lake Vouliagmeni record are explored in response to atmospheric circulation patterns. Phases of overall humid conditions are recorded by increased inflow of siliciclastic material to the lake and negative δ18Obulk values. In contrast, periods of marine intrusion and enhanced evaporation are recorded by aragonite precipitation, positive δ18OAr values and laminations. The laminations formed in the lake seem to occur during periods of sea water intrusion into the lake, which led to pycnocline stabilization and stratified lake waters.

  • 2.
    Helmens, Karin
    et al.
    Swedish Museum of Natural History and Värriö Research Station, Institute for Atmospheric and Earth System Research INAR/Physics, University of Helsinki.
    Katrantsiotis, Christos
    Department of Physical Geography, Stockholm University, Sweden.
    Kuosmanen, Niina
    Department of Geosciences and Geography, University of Helsinki.
    Luoto, Tomi
    Ecosystems and Environment Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki.
    Salonen, Sakari
    Department of Geosciences and Geography, University of Helsinki.
    Väliranta, Minna
    Ecosystems and Environment Research Programme, ECRU, Faculty of Biological and Environmental Sciences, University of Helsinki.
    Prolonged interglacial warmth during the Last Glacial in northern Europe2021In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 50, no 2, p. 331-350Article in journal (Refereed)
    Abstract [en]

    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 from a 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 on chironomids. 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 MIS 5 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.

  • 3.
    Katrantsiotis, Christos
    et al.
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies.
    Dahl, Martin
    School of Natural Sciences, Technology and Environmental Studies, Södertörn University, Huddinge, Sweden.
    Palm, Veronica
    School of Historical and Contemporary Studies, Södertörn University, Huddinge, Sweden; Västerviks Museum, Västervik, Sweden.
    Rönnby, Johan
    School of Historical and Contemporary Studies, Södertörn University, Huddinge, Sweden.
    Andrén, Thomas
    School of Historical and Contemporary Studies, Södertörn University, Huddinge, Sweden.
    Andrén, Elinor
    School of Historical and Contemporary Studies, Södertörn University, Huddinge, Sweden.
    Holocene relative sea level changes in the Västervik‐Gamlebyviken region on the southeast coast of Sweden, southern Baltic Sea2023In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 52, no 2, p. 206-222Article in journal (Refereed)
    Abstract [en]

    We reconstruct the Holocene shore displacement of the Västervik-Gamlebyviken area on the southeast coast of Sweden, characterised by a maritime cultural landscape and archaeological significance since the Mesolithic. Sediment cores were retrieved from four lake basins that have been raised above sea level due to the postglacial land uplift and eustatic sea level changes after the melting of the Fennoscandian Ice Sheet. The cores were radiocarbon dated and analysed for loss on ignition and diatoms. The isolation thresholds of the basins were determined using LiDAR data. The results provide evidence for the initiation of the first Littorina Sea transgression in this area at 8.5 thousand calibrated years before present (cal. ka BP). A relative sea level rise by ∼7 m a.s.l. is recorded between 8.0 and 7.5 cal. ka BP with a highstand at ∼22 m a.s.l. between 7.5 and 6.2 cal. ka BP. These phases coincide with the second and third Littorina Sea transgressions, respectively, in the Blekinge area, southern Sweden and are consistent with the final deglaciation of North America. After 6.2 cal. ka BP, the relative sea level dropped below 22 m a.s.l., and remained at ∼20 m a.s.l. until 4.6 cal. ka BP coinciding with the fourth Littorina Sea transgression in Blekinge. From 4.6 to 4.2 cal. ka BP, the shore displacement shows a regression rate of 10 mm a−1 followed by a slowdown with a mean value of 4.6 mm a−1 until 1.6 cal. ka BP, when the relative sea level dropped below 3.3 m a.s.l. The Middle to Late Holocene highstand and other periods of minor sea level transgressions and/or higher salinity between 6.2 and 1.7 cal. ka BP are attributed to a combination of warmer climate and higher inflow of saline waters in the southern Baltic Sea due to stronger westerlies, caused by variations in the North Atlantic atmospheric patterns.

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  • 4.
    Katrantsiotis, Christos
    et al.
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies.
    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 Finland2021In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 273, p. 107250-107250, article id 107250Article in journal (Refereed)
    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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  • 5. Norström, Elin
    et al.
    West, Johannes
    Kouli, Katerina
    Katrantsiotis, Christos
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies.
    Hättestrand, Martina
    Smittenberg, Rienk
    Evaluation of anhydrosugars as a molecular proxy for paleofire activity: A case study on a Holocene sediment core from Agios Floros, Peloponnese, Greece2021In: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 153Article in journal (Refereed)
    Abstract [en]

    The anhydrosugars levoglucosan, mannosan and galactosan have been regarded a suitable molecular indicator of natural biomass combustion. Here we evaluate the summed anhydrosugars (SAS) as paleofire indicator in a 6000 year-long fossil core from Agios Floros fen, Peloponnese, Greece, by analyzing charcoal fragments in parallel throughout the sediment sequence. Modern surface soil samples from the same region were analysed for presence of SAS, confirming the biomarker as an indicator of recent fire activity. The highest SAS concentrations in the fossil core were found in sections representing periods of wet conditions both on local and regional scale, and regionally widespread arboreal vegetation. Low or absence of SAS in the fossil core is associated with periods of dryness, regional dominance of non-arboreal vegetation and a fen rather than lake ecosystem at the site. Micro-charcoal fragments were generally more abundant under these conditions. This suggests that SAS yield and deposition may vary with fuel availability and fire behavior which in turn is affected by climate, local moisture and vegetation type. Forest fires result in more SAS compared to grass fires. SAS yield is also favored by low-temperature fires sustained under wet climate conditions. Preservation of SAS is likely to be compromised in the only seasonally wet fen ecosystem under the dry and warm Mediterranean climate conditions. The moist and shallow conditions in the wetland during hot summer months are probably promoting oxidation and biodegradation of the labile SAS molecules compared to the more robust charcoal fragments. Thus, a multiproxy approach - using several proxies, both for fire, hydroclimate and vegetation change - is preferred when aiming to reconstruct past biomass burning from wetland ecosystems in a Mediterranean environment. The micro-charcoal record from Agios Floros reveals significant fire activity between 4400-2800 cal yr BP. This partly overlaps the Bronze Age period, associated with intense human environmental interaction and climate change in this area of Peloponnese, Greece.

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  • 6.
    Vignola, Cristiano
    et al.
    Palaeo-Science and History (PS&H) Independent Research Group, Max Planck Institute for the Science of Human History, Jena, Germany and Department of Environmental Biology, Sapienza University of Rome, Rome, Italy.
    Hättestrand, Martina
    Department of Physical Geography, Stockholm University, Stockholm, Sweden.
    Bonnier, Anton
    Department of Archaeology and Ancient History, Uppsala University, Uppsala, Sweden.
    Finné, Martin
    Department of Archaeology and Ancient History, Uppsala University, Uppsala, Sweden and Department of Social and Economic Geography, Uppsala University, Uppsala, Sweden.
    Izdebski, Adam
    Palaeo-Science and History (PS&H) Independent Research Group, Max Planck Institute for the Science of Human History, Jena, Germany and Institute of History, Jagiellonian University in Krakow, Krakow, Poland.
    Katrantsiotis, Christos
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies, Environmental Archaeology Lab. Department of Physical Geography, Stockholm University, Sweden.
    Kouli, Katerina
    Palaeo-Science and History (PS&H) Independent Research Group, Max Planck Institute for the Science of Human History, Jena, Germany and Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, Athens, Greece.
    Liakopoulos, Georgios C.
    Palaeo-Science and History (PS&H) Independent Research Group, Max Planck Institute for the Science of Human History, Jena, Germany.
    Norström, Elin
    Department of Physical Geography, Stockholm University, Stockholm, Sweden and Department of Geological Sciences, Stockholm University, Stockholm, Sweden.
    Papadaki, Maria
    Palaeo-Science and History (PS&H) Independent Research Group, Max Planck Institute for the Science of Human History, Jena, Germany.
    Strandberg, Nichola A.
    Department of Physical Geography, Stockholm University, Stockholm, Sweden and School of Geography and Environmental Science, University of Southampton, Southampton, United Kingdom.
    Weiberg, Erika
    Department of Archaeology and Ancient History, Uppsala University, Uppsala, Sweden.
    Masi, Alessia
    Palaeo-Science and History (PS&H) Independent Research Group, Max Planck Institute for the Science of Human History, Jena, Germany and Department of Environmental Biology, Sapienza University of Rome, Rome, Italy.
    Mid-late Holocene vegetation history of the Argive Plain (Peloponnese, Greece) as inferred from a pollen record from ancient Lake Lerna2022In: PLOS ONE, E-ISSN 1932-6203, Vol. 17, no 7, article id e0271548Article in journal (Refereed)
    Abstract [en]

    This study provides a high-resolution reconstruction of the vegetation of the Argive Plain (Peloponnese, Greece) covering 5000 years from the Early Bronze Age onwards. The well dated pollen record from ancient Lake Lerna has been interpreted in the light of archaeological and historical sources, climatic data from the same core and other regional proxies. Our results demonstrate a significant degree of human impact on the environments of the Argive Plain throughout the study period. During the Early Bronze Age evidence of a thermophilous vegetation is seen in the pollen record, representing the mixed deciduous oak woodland of the Peloponnesian uplands. The plain was mainly used for the cultivation of cereals, whereas local fen conditions prevailed at the coring site. Towards the end of this period an increasing water table is recorded and the fen turns into a lake, despite more arid conditions. In the Late Bronze Age, the presence of important palatial centres modified the landscape resulting in decrease of mixed deciduous oak woodland and increase in open land, partly used for grazing. Possibly, the human management produced a permanent hydrological change at Lake Lerna. From the Archaic period onwards the increasing human pressure in association with local drier conditions caused landscape instability, as attested by a dramatic alluvial event recorded in the Pinus curve at the end of the Hellenistic Age. Wet conditions coincided with Roman times and favoured a forest regeneration pattern in the area, at the same time as we see the most intensive olive cultivation in the pollen record. The establishment of an economic landscape primarily based on pastures is recorded in the Byzantine period and continues until modern times. Overgrazing and fires in combination with arid conditions likely caused degradation of the vegetation into garrigue, as seen in the area of the Argive Plain today.

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  • 7.
    Yahiaoui, Nassima
    et al.
    Laboratoire de Paléontologie Stratigraphique et Paléoenvironnements, Université Mohamed Ben Ahmed, El-M’naouer, Oran, Algeria.
    Mansour, Bouhameur
    Laboratoire de Paléontologie Stratigraphique et Paléoenvironnements, Université Mohamed Ben Ahmed, El-M’naouer, Oran, Algeria.
    Katrantsiotis, Christos
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies.
    Risberg, Jan
    Department of Physical Geography, University of Stockholm, Stockholm, Sweden.
    Reimer, Paula J.
    School of Natural and Built Environment, Queen's University, Belfast, United Kingdom.
    Mahboubi, M’hammed
    Laboratoire de Paléontologie Stratigraphique et Paléoenvironnements, Université Mohamed Ben Ahmed, El-M’naouer, Oran, Algeria.
    Early to Middle Holocene hydroclimate changes in the Guern El Louläilet depressions, Algerian Sahara2023In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 69, p. 161-183Article in journal (Refereed)
    Abstract [en]

    Fossil diatoms and litho-stratigraphic changes in the Guern El Louläilet depressions, NW of the Great Western Erg, Algeria, were analysed to infer paleoenvironmental changes in the northern Algerian Sahara during the Early and Middle Holocene. Analysis was based on calcareous diatomite collected from four outcrops within the depressions. The diatom flora consists of brackish and epiphytic taxa, such as Epithemia argus, with percentages of some freshwater and planktonic species, mainly Cyclotella distinguenda. Results provide evidence for two Holocene lacustrine episodes related to the African Humid Period. The first episode (Early to Middle Holocene) was characterized by abrupt development of shallow-water conditions, with extensive littoral zones and evaporative periods that coincided with high salt concentrations in warm, alkaline water (swampy conditions). A second episode (Middle to Late Holocene?), with brackish water and alkaline conditions, coincided with a decline in lake water level that is attributed to drier conditions. Our findings are consistent with those of other studies from the area and demonstrate similar environmental changes occurred after 9300 cal yr BP at sites within the region. The main drivers of the African Humid Period were the northward shift of the Intertropical Convergence Zone (ITCZ) and expansion of summer monsoonal rains. Our study sites were located in the northern Sahara, where variations in the position of the Intertropical Convergence Zone (ITCZ) did not affect rainfall. Early and Middle Holocene climate fluctuations detected in this study may have been caused by intensification of winter precipitation in the south-central Mediterranean and its penetration southward.

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