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  • 1.
    Andrén, Elinor
    et al.
    Stockholm University.
    Andrén, Thomas
    Stockholm University.
    Sohlenius, Gustav
    Swedish University of Agriculture.
    The Holocene history of the southwestern Baltic Sea as reflected in a sediment core from the Bornholm Basin2000In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 29, p. 233-250Article in journal (Refereed)
    Abstract [en]

    A study of changes in siliceous microfossil assemblages and chemical analyses in a well-dated offshore sediment core from the Bornholm Basin, southwestern Baltic Sea, is carried out with the objective of increasing knowledge of the Holocene history of the area. The core covers about 11 300 calendar years from the brackish phase of the Yoldia Sea stage to the present. The first weak marine influence in the Ancylus Lake stage is recorded about 10 100 cal. yr BP (c. 8900 C-14 BP), indicating a complex transition to the Litorina Sea with different phases of brackish-water inflow. The lithology, organic carbon content and C/N and C/S ratios indicate no major changes in the sedimentary environment during the Litorina-Post-Litorina Sea stages. A high productivity event recorded in the Post-Litorina Sea stage around 950 cal. yr BP correlates with the Medieval warm event. A biostratigraphical change indicating a colder climate is recorded in the sediment at about 800 cal. yr BP, which might mark the beginning of the Little Ice Age.

  • 2. Andrén, Thomas
    et al.
    Lindeberg, Greger
    Andrén, Elinor
    Evidence of the final drainage of the Baltic Ice Lake and the brackish phase of the Yoldia Sea in glacial varves from the Baltic Sea2002In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 31, p. 226-238Article in journal (Refereed)
    Abstract [en]

    A clay-varve chronology based on 14 cross-correlated varve graphs from the Baltic Sea and a mean varve thickness curve has been constructed. This chronology is correlated with the Swedish Time Scale and covers the time span 11 530 to 10 250 varve years BP. Two cores have been analysed for grain size, chemistry, content of diatoms and changes in colour by digital colour analysis. The final drainage of the Baltic Ice Lake is dated to c. 10800 varve years BP and registered in the cores analysed as a decrease in the content of clay. This event can be correlated with atmospheric D 14 C content and might have resulted in an increase in these values recorded between 11565 and 11545 years BP. The results of the correlation between the varve chronology from the Baltic Sea, the Greenland GRIP ice core and the atmospheric D 14 C record indicate that c. 760 years are missing in the Swedish Time Scale in the part younger than c. 10 250 varve years BP. A change in colour from a brownish to grey varved glacial clay recorded c. 10 770 varve years BP is found to be the result of oxygen deficiency due to an increase in the rate of sedimentation in the early Preboreal. The first brackish influence is recorded c. 10 540 varve years BP in the northwestern Baltic Sea and some 90 years later in the eastern Gotland Basin.

  • 3. Robertsson, A M
    et al.
    Svedlund, J O
    Andrén, Thomas
    Sundh, M
    Pleistocene stratigraphy in the Dellen region, central Sweden1997In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 26, p. 237-260Article in journal (Refereed)
    Abstract [en]

    The Pleistocene stratigraphy in the Dellen region, central Sweden was studied using field observations made during mapping of Quaternary deposits and fabric analyses in excavated sections. The lithostratigraphy was also studied by seismic refraction measurements, analyses of grain-size distribution and organic carbon content. Biostratigraphical methods applied were pollen and diatom analyses. A general outline of the Pleistocene stratigraphy in the area is presented. Three different till beds are identified, the lowermost suggested to have been deposited during the Saalian glaciation and the other two during the Weichselian glaciation. According to the interpretation of the stratigraphy, it is questioned whether the first Weichselian ice sheer did in fact reach the Dellen area. A clayey sediment sequence at Norra Sannas accumulated during an interglacial, probably the Eemian. Most of the interglacial vegetation succession is reflected in the identified pollen flora. An initial phase with a light-demanding forest of Betula and Pinus was followed by immigration of Alnus, Picea and scattered occurrences of Corylus. A freshwater diatom flora was identified dominated by plankton taxa, e.g. Aulacoseira italica, A. distans and Cyclotella spp. In the lower part of the sequence a brackish-marine flora was registered, representing accumulation in a bay of the Eemian Sea. Fine-grained sediments at the Sundson and Vastansjo sites are interpreted as rebedded Eemiar. sediments according to the pollen flora. An (Early Weichselian) interstadial age is suggested ibr sediments found at Bjuraker. Dating by the C-14- and OSL methods was carried out on the interglacial and interstadial sediments, respectively. The ages range from approximately 19 000 to 92 000 BP. Correlation of interglacial vegetation history with central Finland and other areas is discussed.

  • 4.
    Stepanova, A.
    et al.
    Texas A&M University, College Station, USA.
    Obrochta, S.
    Akita University, Akita, Japan.
    Quintana Krupinski, N. B.
    Lund University.
    Hyttinen, O.
    University of Helsinki, Helsinki, Finland.
    Kotilainen, A.
    Geological Survey of Finland, Marine Geology, Espoo, Finland.
    Andrén, Thomas
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Late Weichselian to Holocene history of the Baltic Sea as reflected in ostracod assemblages2019In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 48, no 3, p. 761-778Article in journal (Refereed)
    Abstract [en]

    The study presents the first description and analysis of ostracod records from three sites cored in different parts of the Baltic Sea during the IODP Expedition 347, Baltic Sea Paleoenvironment. Our data present the first high-resolution ostracod records from the Late Weichselian and Holocene sediments collected across the Baltic Sea Basin. Using published data on modern ostracod species ecology of the Baltic Sea, we were able to provide ostracod-based palaeoreconstructions of the history of the region. The stratigraphical framework for the sites is based on radiocarbon-based age models. The three studied sites reveal different ostracod assemblage successions that reflect environmental changes in the study area. Site M0060, located in the Kattegat area, contains the oldest ostracod assemblages that document a marine environment with very high sedimentation rates during the most recent deglaciation. Between ~13 000 and 7500 cal. a BP a modern-like near-shore environment developed. Site M0059 in the southwestern Baltic Sea, Little Belt area, contains assemblages reflecting the transition from a freshwater lake to the brackish Littorina Sea between ~7500 and 7300 cal. a BP. Site M0063 is the deepest location in the central Baltic, Landsort Deep, and yielded very limited ostracod data, but comparison with our organic carbon data allowed us to distinguish the Yoldia Sea, Ancylus Lake and Littorina Sea intervals. The ostracod record correlates well with the organic carbon record with alternation between periods of hypoxia and periods of low oxygen that still supported ostracods.

  • 5.
    Warnock, Jonathan
    et al.
    Indiana University of Pennsylvania, Indiana, United States.
    Andrén, Elinor
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Juggins, Steve
    Newcastle University, Newcastle upon Tyne, United Kingdom.
    Lewis, Jonathan
    Loughborough University, Loughborough, United Kingdom.
    Ryves, David B.
    Loughborough University, Loughborough, United Kingdom.
    Andrén, Thomas
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Weckström, Kaarina
    University of Helsinki, Helsinki, Finland.
    A high‐resolution diatom‐based Middle and Late Holocene environmental history of the Little Belt region, Baltic Sea2020In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, no 1, p. 1-16Article in journal (Refereed)
    Abstract [en]

    The large‐scale shifts in the salinity of the Baltic Sea over the Holocene are well understood and have been comprehensively documented using sedimentary proxy records. More recent work has focused on understanding how past salinity fluctuations have affected other ecological parameters (e.g. primary productivity, nutrient content) of the Baltic basin, and salinity changes over key events and over short time scales are still not well understood. The International Ocean Drilling Program Expedition 347 cored the Baltic basin in order to collect basin‐wide environmental records through a glacial–interglacial cycle. Site M0059 is located in the Little Belt between the Baltic Sea and the Atlantic Ocean. A composite splice section from Site M0059 was analysed at a decadal resolution to study changes in salinity, nutrient conditions and other surface water column parameters based on changes in diatom assemblages and on quantitative diatom‐based salinity inferences. A mesotrophic slightly brackish assemblage is seen in the lowermost analysed depths, corresponding to 7800–7500 cal. a BP. An increase in salinity and nutrient content of the water column leads into a meso‐eutrophic brackish phase. The observed salinity increase is rapid, lasting from 7500 to 7150 cal. a BP. Subsequently, the Little Belt becomes oligotrophic and is dominated by tychopelagic diatoms from c. 7100 to c. 3900 cal. a BP. This interval contains some of the highest salinities observed followed by diatom assemblages similar to those of the Northern Atlantic Ocean, composed primarily of cosmopolitan open ocean marine diatoms. A return to tychopelagic productivity is seen from 3850 to 980 cal. a BP. Anthropogenic eutrophication is detected in the last 300 years of the record, which intensifies in the uppermost sediments. These results represent the first decadally resolved record in the region and provide new insight into the transition to a brackish basin and subsequent ecological development.

  • 6.
    Warnock, J.P.
    et al.
    University of Pennsylvania, Indiana, PA, USA.
    Bauersachs, T.
    Christian-Albrechts-University, Kiel, Germany.
    Kotthoff, U.
    University of Hamburg, Hamburg, Germany.
    Brandt, H.-T.
    University of Hamburg, Hamburg, Germany.
    Andrén, Elinor
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Holocene environmental history of the Ångermanälven Estuary, northern Baltic Sea2018In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 47, no 2, p. 593-608Article in journal (Refereed)
    Abstract [en]

    The Baltic Sea has experienced a complex geological history, with notable swings in salinity driven by changes to its connection with the Atlantic and glacio-isostatic rebound. Sediments obtained during International Ocean Drilling Program Expedition 347 allow the study of the effects of these changes on the ecology of the Baltic in high resolution through the Holocene in areas where continuous records had not always been available. Sites M0061 and M0062, drilled in the Ångermanälven Estuary (northern Baltic Sea), contain records of Holocene-aged sediments and microfossils. Here we present detailed records of palaeoecological and palaeoenvironmental changes to the Ångermanälven Estuary inferred from diatom, palynomorph and organic-geochemical data. Based on diatom assemblages, the record is divided into four zones that comprise the Ancylus Lake, Littorina Sea, Post-Littorina Sea and Recent Baltic Sea stages. The Ancylus Lake phase is initially characterized as oligotrophic, with the majority of primary productivity in the upper water column. This transition to a eutrophic state continues into the Initial Littorina Sea stage. The Initial Littorina Sea stage contains the most marine phase recorded here, as well as low surface water temperatures. These conditions end before the Littorina Sea stage, which is marked by a return to oligotrophic conditions and warmer waters of the Holocene Thermal Maximum. Glacio-isostatic rebound leads to a shallowing of the water column, allowing for increased benthic primary productivity and stratification of the water column. The Medieval Climate Anomaly is also identified within Post-Littorina Sea sediments. Modern Baltic sediments and evidence of human-induced eutrophication are seen. Human influence upon the Baltic Sea begins c. 1700 cal. a BP and becomes more intense c. 215 cal. a BP.

     

  • 7.
    Yu, Shi-Yong
    et al.
    Lund University.
    Andrén, Elinor
    Uppsala University.
    Barnekow, Lena
    Lund University.
    Berglund, Björn E
    Lund University.
    Sandgren, Per
    Lund University.
    Holocene palaeoecology and shoreline displacement on the Biskopsmåla Peninsula, southeastern Sweden2003In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 32, p. 578-589Article in journal (Refereed)
    Abstract [en]

    High-resolution palaeoecological proxies of pollen, macrofossils and diatoms from an isolation lake provide a long-term record of the Holocene landscape history and shoreline displacement on the Biskopsmala Peninsula in central Blekinge, SE Sweden. During the Preboreal/Boreal transition, the peninsula was sparsely vegetated by woodlands, along with lateglacial dwarf shrub/steppe communities. The lake basin was isolated from the shallow Yoldia Sea during this time. The regional climate improved from 10 700 cal. BP, evident as progressive expansion of Pinus -dominated mixed forest with deciduous trees. The lake basin was probably connected with the Ancylus Lake during the period 10 700-10 100 cal. BP. Subsequently the basin became isolated again, corresponding to the Early Littorina Sea phase. Replacement of freshwater diatoms by those with brackish-water affinity at 8100 cal. BP indicates the initial transgression of the Littorina Sea in this basin. But not until 7500 cal. BP were brackish conditions fully established. Peaks of brackish-marine diatoms and dinoflagellates during 7500-7000 cal. BP indicate increased saltwater inflow to the Baltic Sea in response to global meltwater pulse 3. However, interactive changes in seagrass and stonewort macrofossil concentrations suggest that three minor transgressions during 5900-5300, 5000-4700 and 4400-4000 cal. BP occurred locally, associated with centennial-scale variations in regional wind pattern or coastal storminess. By 3000 cal. BP, the lake basin was finally isolated from the Baltic, and thereafter the landscape on the peninsula became gradually more influenced by human activities.

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