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  • 1.
    Andrén, Elinor
    et al.
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Andrén, Thomas
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Syrefria bottnar - orsakade av klimat, människa eller både och?2014In: Havsutsikt, ISSN 1104-0513, no 2, p. 12-14Article in journal (Other (popular science, discussion, etc.))
  • 2.
    Andrén, Elinor
    et al.
    Stockholm University.
    Andrén, Thomas
    Stockholm University.
    Kunzendorf, Helmar
    Risø National Laboratory.
    Holocene history of the Baltic Sea as a background for assessing records of human impact in the sediments of the Gotland Basin2000In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 10, p. 687-702Article in journal (Refereed)
    Abstract [en]

    Sediment cores from the Gotland Basin were studied for their siliceous microfossil assemblages and organic carbon content to compare recent environmental changes in the Baltic Sea with its natural long-term history. Age models were constructed using Pb-210, Cs-137 and corrected and calibrated C-14 dates. The transgression that marks the onset of the Ancylus Lake stage is recorded in the sediments as a small increase in organic carbon coinciding with a peak in diatom abundance and increased diatom diversity. A minor occurrence of brackish-freshwater diatoms is recorded in the Ancylus Lake c. 9950-9750 cal. yr BP (c. 8900-8800 C-14 yr BP), correlating with the onset of the Initial Litorina Sea in the Bornholm Basin. A high-productivity event is recorded in the end of the Post-Litorina Sea and corresponds to the Mediaeval warm event. An alteration in the diatom assemblage contemporaneous with a decrease in organic carbon, interpreted as representing a deterioration in the climate, correlates with the start of the ‘Little Ice Age’ about 850-700 cal. yr BP. A change dated to ad 1950-1960 is probably an effect of increased nutrient availability in the open Baltic Sea. This effect of eutrophication was probably caused by increased discharge of nutrients deriving from fertilizers, as the responding diatom species partly indicate a cold climate rather than a warm one, as would have been expected if this had been only a response to the warmer climate documented during the last 100 years or so.

  • 3.
    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.

  • 4. Andrén, Thomas
    Ancylussjön – fortfarande ett mysterium2003In: HavsUtsikt, ISSN 1104-0513, no 3, p. 8-9Article in journal (Other (popular science, discussion, etc.))
  • 5.
    Andrén, Thomas
    Södertörn University, School of Life Sciences, Environmental science. Södertörn University, School of Life Sciences, Geography.
    Baltic Sea Basin, since the latest deglaciation2012In: Encyclopedia of Lakes and Reservoirs / [ed] Lars Bengtsson, Reginald W. Herschy, Rhodes W. Fairbridge, Dordrecht: Springer Science+Business Media B.V., 2012, p. 95-102Chapter in book (Refereed)
  • 6. Andrén, Thomas
    Baltic Sea Science Congress 2001 - Preface2005In: Quaternary International, ISSN 1040-6182, E-ISSN 1873-4553, Vol. 130, no 1Article in journal (Refereed)
  • 7. Andrén, Thomas
    Baltiska Issjön – eller hur det hela började2003In: HavsUtsikt, ISSN 1104-0513, no 1, p. 4-5Article in journal (Other (popular science, discussion, etc.))
  • 8. Andrén, Thomas
    Littorinahavet – en salt historia2004In: HavsUtsikt, ISSN 1104-0513, no 1, p. 8-9Article in journal (Other (popular science, discussion, etc.))
  • 9. Andrén, Thomas
    Quaternary International: "Baltic Sea Science Congress 2001".2005Collection (editor) (Other academic)
  • 10. Andrén, Thomas
    Yoldiahavet – en viktig parentes2003In: HavsUtsikt, ISSN 1104-0513, no 2, p. 2-3Article in journal (Other (popular science, discussion, etc.))
  • 11.
    Andrén, Thomas
    et al.
    Stockholm University.
    Andrén, Elinor
    Södertörn University, School of Life Sciences.
    Berglund, Björn E.
    Lund University.
    Yu, Shi-Yong
    University of Minnesota.
    New insights on the Yoldia Sea low stand in the Blekinge archipelago, southern Baltic Sea2007In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 129, no 4, p. 277-285Article in journal (Refereed)
    Abstract [en]

    One sediment core from the Jarnavik bay in Blekinge archipelago has been investigated for its content of pollen and diatoms and its chemical properties. Two levels were also dated by radiocarbon. Based on the results the sediment sequence analysed has been divided into three environmental units largely corresponding to the lithology of the sequence. A lowermost unit consisting of weakly varved and homogeneous clay was deposited during the end of the brackish phase of the Yoldia Sea at a moderate water depth. On top of this unit a gyttja-clay unit was deposited. The onset of the deposition of this unit has been dated to c. 11 100 cal. yrs. BP. An increasing organic production and increased terrestrial influence is recorded in the chemical data and a very shallow water depth is indicated in the pollen and diatom flora. These results point to conditions in a bay probably isolated from the Yoldia Sea. A local tentative shore displacement curve have been constructed and it is proposed that this unit represents the low stand at c. -18 m during the Yoldia Sea stage in this part of the Baltic Sea basin. The uppermost unit consists of homogeneous clay with a low content of organic carbon. An increasing water depth is indicated by the composition of both pollen and diatoms. The diatom flora also displays an increase in freshwater species. This environmental change was probably the result of a transgression in the beginning of the Ancylus Lake stage.

  • 12.
    Andrén, Thomas
    et al.
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Andrén, Elinor
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Zhang, Rui
    Xiamen University, China.
    Baltic Sea Basin Paleoenvironment: paleoenvironmental evolution of the Baltic Sea Basin through the last glacial cycle2014Report (Other academic)
  • 13.
    Andrén, Thomas
    et al.
    Södertörn University, School of Life Sciences, Environmental science.
    Barker Jørgensen, Bo
    Aarhus University, Denmark.
    Cotterill, Carlo
    British Geological Survey, UK.
    Morgan, Sally
    University of Leicester, UK.
    IODP Expedition 347:Paleoenvironmental evolution of the Baltic Sea Basin through the last glacial cycle2012In: ECORD Newsletter, ISSN 2264-1556, no 19, p. 14-15, 23Article in journal (Other academic)
  • 14. Andrén, Thomas
    et al.
    Björck, J
    Johnsen, S
    Correlation of Swedish glacial varves with the Greenland (GRIP) oxygen isotope record1999In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 14, no 4, p. 361-371Article in journal (Refereed)
    Abstract [en]

    A mean varve thickness curve has been constructed for a part of the Swedish varve chronology from the northwestern Baltic proper. The mean varve thickness curve has been correlated with the delta(18)O record from the GRIP ice-core using the Younger Dryas-Preboreal climate shift. This climate shift was defined by pollen analyses. The Scandinavian ice-sheet responded to a warming at the end of the Younger Dryas, ca. 10 995 to 10 700 clay-varve yr BP. Warming is recorded as a sequence of increasing mean varve thickness and ice-rafted debris suggesting intense calving of the ice front. The Younger Dryas-Preboreal climatic shift is dated to ca. 10 650 clay-varve yr BP, about 40 yr after the final drainage of the Baltic Ice Lake. Both the pollen spectra and a drastic increase in varve thickness reflect this climatic shift. A climate deterioration, correlated with the Preboreal oscillation, is dated to ca. 10 440 to 10 320 clay-varve yr BP and coincides with the brackish water phase of the Yoldia Sea stage. The ages of the climatic oscillations at the Younger Dryas-Preboreal transition show an 875 yr discrepancy compared with the GRIP record, suggesting a large error in the Swedish varve chronology in the part younger than ca. 10 300 clay-varve yr BP.

  • 15.
    Andrén, Thomas
    et al.
    Södertörn University, School of Life Sciences, Environmental science. Södertörn University, School of Life Sciences, Geography.
    Björck, S
    Andrén, Elinor
    Södertörn University, School of Life Sciences, Environmental science. Södertörn University, School of Life Sciences, Geography.
    Conley, D J
    Lambeck, K
    Zillén, L
    The development of the Baltic Sea basin during the last 130 000 years2011In: The Baltic Sea Basin / [ed] Jan Harff, Svante Björck, Peer Hoth, Springer Berlin/Heidelberg, 2011, p. 75-97Chapter in book (Other academic)
  • 16. Andrén, Thomas
    et al.
    Brunnberg, L
    Miller, U
    PROCEEDINGS FROM THE BALTIC-ICE-LAKE-YOLDIA-SEA-SYMPOSIUM, MARCH 1993: PREFACE1995In: Quaternary International, ISSN 1040-6182, E-ISSN 1873-4553, Vol. 27, p. 3-3Article in journal (Other academic)
  • 17.
    Andrén, Thomas
    et al.
    Södertörn University, School of Life Sciences, Environmental science.
    Jørgensen, B. B.
    Aarhus Universit, Denmark.
    Cotterill, C.
    British Geological Survey, UK.
    Baltic Sea Basin Paleoenvironment: paleoenvironmental evolution of the Baltic Sea Basin through the last glacial cycle2012Report (Other academic)
  • 18.
    Andrén, Thomas
    et al.
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Jørgensen, Bo Barker
    Cotterill, Carol
    Green, Sophie
    IODP expedition 347: Baltic Sea basin paleoenvironment and biosphere2015In: Scientific Drilling, ISSN 1816-8957, E-ISSN 1816-3459, Vol. 20, p. 1-12Article in journal (Refereed)
    Abstract [en]

    The Integrated Ocean Drilling Program (IODP) expedition 347 cored sediments from different settings of the Baltic Sea covering the last glacial–interglacial cycle. The main aim was to study the geological development of the Baltic Sea in relation to the extreme climate variability of the region with changing ice cover and major shifts in temperature, salinity, and biological communities. Using the Greatship Manisha as a European Consortium for Ocean Research Drilling (ECORD) mission-specific platform, we recovered 1.6 km of core from nine sites of which four were additionally cored for microbiology. The sites covered the gateway to the North Sea and Atlantic Ocean, several sub-basins in the southern Baltic Sea, a deep basin in the central Baltic Sea, and a river estuary in the north.

     

    The waxing and waning of the Scandinavian ice sheet has profoundly affected the Baltic Sea sediments. During theWeichselian, progressing glaciers reshaped the submarine landscape and displaced sedimentary deposits from earlier Quaternary time. As the glaciers retreated they left a complex pattern of till, sand, and lacustrine clay, which in the basins has since been covered by a thick deposit of Holocene, organic-rich clay. Due to the stratified water column of the brackish Baltic Sea and the recurrent and widespread anoxia, the deeper basins harbor laminated sediments that provide a unique opportunity for high-resolution chronological studies.

     

    The Baltic Sea is a eutrophic intra-continental sea that is strongly impacted by terrestrial runoff and nutrient fluxes. The Holocene deposits are recorded today to be up to 50m deep and geochemically affected by diagenetic alterations driven by organic matter degradation. Many of the cored sequences were highly supersaturated with respect to methane, which caused strong degassing upon core recovery. The depth distributions of conservative sea water ions still reflected the transition at the end of the last glaciation from fresh-water clays to Holocene brackish mud. High-resolution sampling and analyses of interstitial water chemistry revealed the intensive mineralization and zonation of the predominant biogeochemical processes. Quantification of microbial cells in the sediments yielded some of the highest cell densities yet recorded by scientific drilling.

  • 19.
    Andrén, Thomas
    et al.
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Jørgensen, Bo Barker
    Cotterill, Carol
    Green, Sophie
    Andrén, Elinor
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Baltic Sea Basin Paleoenvironment: Expedition 347 of the mission-specific drilling platform  from and to Kiel, Germany Sites M0059–M0067  12 September–1 November 20132015Report (Other academic)
  • 20. 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.

  • 21.
    Andrén, Thomas
    et al.
    Södertörn University, School of Life Sciences, Environmental science. Södertörn University, School of Life Sciences, Geography.
    Rytkönen, Paulina
    Södertörn University, School of Life Sciences, Culinary arts and meal science.
    Vinlandet Sverige - konsumtionen, produktionen och framtida förutsättningar2011In: Ymer, ISSN 0044-0477, p. 121-146Article in journal (Other academic)
  • 22. Andrén, Thomas
    et al.
    Sohlenius, Gustav
    Late Quaternary development of the north-western Baltic Proper: Results from the clay-varve investigation1995In: Quaternary International, ISSN 1040-6182, E-ISSN 1873-4553, Vol. 27, p. 5-10Article in journal (Refereed)
    Abstract [en]

    Within the project "Late Quaternary development of the north-western Baltic Proper" a total of 36 piston core samples have been collected. The results presented in this study are based on analyses of 7 cores with emphasis on the late glacial part of the sequence. The varved glacial clay sequences have been analyzed for calcareous micro-fossils and mineral magnetic properties as well as measurements of clay-varves. The results from these analyses indicate that there is a close correlation between the occurrence of brackish water ostracods and foraminifera and a distinct change in the mineral magnetic parameters. The lithological composition of the clay-varves also differs in this sequence. The duration of this marine phase of the Yoldia Sea stage is 60 to 120 clay-varve years. It is concluded that correlations between the cores can be made using fossil assemblages and mineral magnetic parameters. It has not yet been possible, however, to make any reliable clay-varve connections.

  • 23. Bianchi, Thomas S
    et al.
    Engelhaupt, Erika
    Westman, Per
    Andrén, Thomas
    Rolff, Carl
    Elmgren, Ragnar
    Cyanobacterial blooms in the Baltic Sea: Natural or human-induced?2000In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 45, no 3, p. 716-726Article in journal (Refereed)
    Abstract [en]

    Massive summer blooms of nitrogen-fixing cyanobacteria have been documented in the Baltic Sea since the 19th century, but are reported to have increased in frequency, biomass, and duration in recent decades-presumably in response to the well-documented anthropogenic eutrophication of the Baltic. Here, we present an 8,000-yr record of fossil cyanobacterial pigments, diatom microfossil assemblages, and delta(15)N variations in sediment cores from the Baltic proper. This record indicates that nitrogen-living cyanobacterial blooms are nearly as old as the present brackish water phase of the Baltic Sea, starting as far back as ca. 7000 B.P.-soon after the former freshwater Ancylus Lake turned into the brackish Litorina Sea. Demonstration of cyanobacterial blooms in the Baltic prior to the greatly increased anthropogenic nutrient inputs of the 20th century is important for setting realistic goals when trying to reduce the magnitude of present brooms. Our results suggest that the presently predominating nitrogen (N) limitation of phytoplankton in the Baltic Sea proper is not man-induced, but a natural phenomenon, which has endured for some 7,000 yr. These cyanobacterial blooms were possibly initiated by increased availability of phosphorus (P)-from inflow of P-rich seawater and increased P release from sediments-during periods of deep-water anoxia, caused by the establishment of salinity stratification. Efforts to restore the Baltic proper to a more oligotrophic and natural condition should take into account that nitrogen-fixing cyanobacterial blooms are a characteristic, natural feature of this sea.

  • 24. Bindler, Richard
    et al.
    Renberg, Ingemar
    Rydberg, Johan
    Andrén, Thomas
    Södertörn University, School of Life Sciences, Geography. Södertörn University, School of Life Sciences, Environmental science.
    Widespread waterborne pollution in central Swedish lakes and the Baltic Sea from pre-industrial mining and metallurgy2009In: Environmental Pollution, ISSN 0269-7491, E-ISSN 1873-6424, Vol. 157, p. 2132-2141Article in journal (Refereed)
    Abstract [en]

    Metal pollution is viewed as a modern problem that began in the 19th century and accelerated through the 20th century; however, in many parts of the globe this view is wrong. Here, we studied past waterborne metal pollution in lake sediments from the Bergslagen region in central Sweden, one of many historically important mining regions in Europe. With a focus on lead (including isotopes), we trace mining impacts from a local scale, through a 120-km-long river system draining into Malaren - Sweden’s third largest lake, and finally also the Baltic Sea. Comparison of sediment and peat records shows that pollution from Swedish mining was largely waterborne and that atmospheric deposition was dominated by long-range transport from other regions. Swedish ore lead is detectable from the 10th century, but the greatest impact occurred during the 16th-18th centuries with improvements occurring over recent centuries, i.e., historical pollution > modern industrial pollution.

  • 25. Björck, Jonas
    et al.
    Andrén, Thomas
    Wastegård, Stefan
    Possnert, Göran
    Schoning, Kristian
    An event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden: results from investigations of varved clay and terrestrial sequences2002In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 21, no 12/13, p. 1489-1501Article in journal (Refereed)
    Abstract [en]

    This paper presents an event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden. The event stratigraphy for eastern middle Sweden comprises ten events and covers the time-span from ca 12,900 to 10,200 cal yr BP. The local event stratigraphy has been linked to the GRIP isotopic event stratigraphy by different correlations. The onset of the Younger Dryas is dated to 12,650 cal yr BP. This cold event lasted for ca 1125 cal yr in the area. The Vedde Ash (ca 12,000 cal yr BP) has been recorded in two terrestrial sequences, which makes it possible to exactly link the event stratigraphy to the GRIP ice-core and to marine cores in the North Atlantic region. The final drainage of the Baltic Ice Lake has been dated to ca 11,560 cal yr BP, which predates the Younger Dryas/Preboreal climatic boundary with ca 35 yr. An early Holocene cold event has been detected both in terrestrial and varved clay sequences at ca 11,305-11,185 cal yr BP. This cold event coincides almost exactly with a brackish water phase in the Baltic Sea. A previously unrecorded early Holocene tephra horizon has been found in lacustrine sediments at ca 10,200 cal yr BP.

  • 26. Björck, S.
    et al.
    Andrén, Thomas
    Södertörn University College, School of Life Sciences.
    Jensen, J. B.
    An attempt to resolve the partly conflicting data and ideas on the Ancylus - Littorina transition2008In: Proceedings of the workshop "Relative sea level changes - from subsiding to uplifting coasts" / [ed] Szymon Uścinowicz, Joanna Zachowicz, 2008, p. 21-26Conference paper (Other academic)
  • 27.
    Hardisty, Dalton S.
    et al.
    University of California-Riverside, Riverside California, USA .
    Riedinger, Natascha
    Oklahoma State University, Stillwater, Oklahoma, USA .
    Planavsky, Noah J.
    Yale University, New Haven, Connecticut, USA.
    Asael, Dan
    Yale University, New Haven, Connecticut, USA.
    Andrén, Thomas
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Jorgensen, Bo B.
    Aarhus University, Aarhus C, Denmark .
    Lyons, Timothy W.
    University of California-Riverside, Riverside California, USA .
    A Holocene History Of Dynamic Water Column Redox Conditions In The Landsort Deep, Baltic Sea2016In: American Journal of Science, ISSN 0002-9599, E-ISSN 1945-452X, Vol. 316, no 8, p. 713-745Article in journal (Refereed)
    Abstract [en]

    The modern Baltic Sea is the world's largest anthropogenically forced anoxic basin. Using integrated geochemical records collected during Integrated Ocean Drilling Program (IODP) Expedition 347 from the deepest and one of the most reducing sub-basins in the Baltic Sea, Landsort Deep, we explore the degree and frequency of natural anoxia through the Baltic Holocene. A marked decrease in carbon-to-sulfur ratios (C/S) from the cores indicate the transition from the Baltic Ice Lake to the current brackish sea, which occurred about 8.5 kyrs B.P. Following this, laminations throughout sediments recording brackish deposition suggest sustained anoxia or extreme low oxygen, while high molybdenum (Mo) concentrations of >100 ppm and iron (Fe) geochemistry suggest water column sulfide accumulation, or euxinia, that persisted beyond seasonal timescales during deposition of two distinct sapropel units. Sedimentary Mo isotope values range from +1.11 to -0.50 permil, which are distinctly fractionated from modern Baltic seawater (+2.26 to -2.67 parts per thousand) and thus indicate that each of the sapropels experienced only weak and/or oscillatory euxinia-in contrast to the more stable euxinic conditions of more restricted basins. A shift in delta Mo-98 starting above the lower sapropel to a distinctly more negative range suggests particularly weak and oscillatory euxinia, with an enhanced contribution of manganese (Mn) redox cycling to Mo deposition relative to the lower portion of the profile. This conclusion is supported by extreme sedimentary Mn enrichments of up to 15 weight percent. We interpret the combined data to indicate episodic but major Baltic inflow events of saline and oxygenated North Sea water into the anoxic Landsort Deep that limited the concentrations and residence time of water column sulfide and caused episodic oxide deposition. Considering the temporal overlap between the most reducing conditions and periods of redox instability, we hypothesize that major Baltic inflows, as is observed today, lead to short-term instability while simultaneously supporting longer-term Baltic anoxia by strengthening the halocline. Ultimately, our results indicate that periods more reducing than the modern Baltic Sea have occurred naturally over the Holocene, but the characteristic dynamic saline inputs have historically prevented the relatively more widespread and stable anoxia observed in other classic restricted basins and will likely continue to do so.

  • 28.
    Hyttinen, O.
    et al.
    University of Helsinki, Helsinki, Finland.
    Kotilainen, A. T.
    Geological Survey of Finland (GTK), Espoo, Finland.
    Virtasalo, J. J.
    Geological Survey of Finland (GTK), Espoo, Finland.
    Kekäläinen, P.
    University of Helsinki, Helsinki, Finland / WSP Finland Oy, Helsinki, Finland.
    Snowball, I.
    Uppsala universitet.
    Obrochta, S.
    Akita University, Akita City, Japan.
    Andrén, Thomas
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Holocene stratigraphy of the Ångermanälven River estuary, Bothnian Sea2017In: Geo-Marine Letters, ISSN 0276-0460, E-ISSN 1432-1157, Vol. 37, no 3, p. 273-288Article in journal (Refereed)
    Abstract [en]

    This study explores the Holocene depositional succession at the IODP Expedition 347 sites M0061 and M0062 in the vicinity of the Ångermanälven River estuary in the Bothnian Sea sector of the Baltic Sea in northern Scandinavia. Site M0061 is located in a coastal offshore setting (87.9 m water depth), whereas site M0062 is fully estuarine (69.3 m water depth). The dataset comprises acoustic profiles and sediment cores collected in 2007 and late 2013 respectively. Three acoustic units (AUs) were recognized. Lowermost AU1 is interpreted as a poorly to discontinuous stratified glaciofluvial deposit, AU2 as a stratified conformable drape of glaciolacustrine origin, and AU3 as a poorly stratified to stratified mud drift. A strong truncating reflector separates AU2 and AU3. Three lithological units (LUs) were defined in the sediment cores. LU1 consists of glaciofluvial sand and silt gradating into LU2, which consists of glaciolacustrine varves. A sharp contact interpreted as a major unconformity separates LU2 from the overlying LU3 (brackish-water mud). In the basal part of LU3, one debrite (site M0061) or two debrites (site M0062) were recognized. Information yielded from sediment physical properties (magnetic susceptibility, natural gamma ray, dry bulk density), geochemistry (total carbon, total organic carbon, total inorganic carbon and nitrogen), and grain size support the LU division. The depositional succession was formally subdivided into two alloformations: the Utansjö Alloformation and overlying Hemsön Alloformation; the Utansjö Alloformation was further subdivided into two lithostratigraphic formations: the Storfjärden and Åbordsön formations. The Storfjärden (sandy outwash) and Åbordsön (glaciolacustrine rhythmite) formations represent a glacial retreat systems tract, which started at ca. 10.6 kyr BP. Their deposition was mainly controlled by meltwater from the retreating ice margin, glacio-isostatic land uplift and the regressive (glacial) lake level. The Hemsön Alloformation (organic-rich brackish-water mud) represents a period of forced regression, starting possibly at ca. 9.5 kyr BP. At about 7 kyr BP, brackish water reached the study area as a result of the mid-Holocene marine flooding of the Baltic Sea Basin, but the rapid land uplift soon surpassed the associated (Littorina) transgression. Changed near-bottom current patterns, caused by the establishment of a permanent halocline, and the reduced sediment consistency caused by increased organic deposition resulted in a sharp and erosional base of the brackish-water mud. Estuarine processes and salinity stratification at site M0062 started to play a more important role. This study applies a combined allostratigraphic and lithostratigraphic approach over the conventional Baltic Sea stages. This approach makes it more straightforward to study this Baltic Sea deglaciation–postglacial sequence and compare it to other formerly glaciated shallow sea estuaries.

  • 29.
    Jakobsson, Martin
    et al.
    Stockholm University.
    Andrén, Thomas
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Gyllencreutz, Richard
    Stockholm University.
    Noormets, Riko
    UNIS Univ Ctr Svalbard, Longyearbyen, Svalbard.
    Sturkell, Erik
    University of Gothenburg.
    In memoriam of Tom Flodén: obituary2017In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 139, no 3, p. 241-242Article in journal (Other academic)
  • 30. Jakobsson, Martin
    et al.
    Björck, Svante
    Alm, Göran
    Andrén, Thomas
    Stockholms universitet.
    Lindeberg, Greger
    Svensson, Nils-Olof
    Reconstructing the Younger Dryas ice dammed lake in the Baltic Basin: Bathymetry, area and volume2007In: Global and Planetary Change, ISSN 0921-8181, E-ISSN 1872-6364, Vol. 57, no 3/4, p. 355-370Article in journal (Refereed)
    Abstract [en]

    A digital 3D-reconstruction of the Baltic Ice Lake’s (BIL) configuration during the termination of the Younger Dryas cold phase (ca. 11700 cal. yr BP) was compiled using a combined bathymetric-topographic Digital Terrain Model (DTM), Scandinavian ice sheet limits, Baltic Sea Holocene bottom sediment thickness information, and a paleoshoreline database maintained at the Lund University. The bathymetric-topographic DTM, assembled from publicly available data sets, has a resolution of 500 X 500 m on Lambert Azimuthal Equal Area projection allowing area and volume calculations of the BIL to be made with an unprecedented accuracy. When the damming Scandinavian ice sheet margin eventually retreated north of Mount Billingen, the high point in terrain of Southern central Sweden bordering to lower terrain further to the north, the BIL was catastrophically drained resulting in a 25 m drop of the lake level. With our digital reconstruction, we estimate that approximately 7800 km(3) of water drained during this event and that the ice dammed lake area was reduced by ca. 18%. Building on previous results suggesting drainage over 1 to 2 years, our lake volume calculations imply that the freshwater flux to the contemporaneous sea in the west was between about 0.12 and 0.25 Sv. The BIL reconstruction provides new detailed information on the paleogeography in the area of southern Scandinavia, both before and after the drainage event, with implications for interpretations of geological records concerning the post-glacial environmental development.

  • 31.
    Kotthoff, U.
    et al.
    University of Hamburg.
    Groeneveld, J.
    University of Bremen.
    Ash, J.L.
    UCLA.
    Fanget, A.-S.
    Aarhus University, Université de Perpignan.
    Krupinski, N.Q.
    Lund University.
    Peyron, O.
    University of Montpellier.
    Stepanova, A.
    Texas A&M University.
    Warnock, J.
    Indiana University of Pennsylvania.
    Van Helmond, N. A. G. M.
    Utrecht University.
    Passey, B.H.
    University of Michigan.
    Clausen, O.R.
    Aarhus University.
    Bennike, O.
    Geological Survey of Denmark and Greenland.
    Andrén, Elinor
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Granoszewski, W.
    Polish Geological Institute-National Research Institute Krakow.
    Andrén, Thomas
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Filipsson, H.L.
    Lund University.
    Seidenkrantz, M.-S.
    Aarhus University.
    Slomp, C.P.
    Utrecht University.
    Bauersachs, T.
    Christian-Albrechts-Universität.
    Reconstructing Holocene temperature and salinity variations in the western Baltic Sea region: a multi-proxy comparison from the Little Belt (IODP Expedition 347, Site M0059)2017In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, p. 5607-5632Article in journal (Refereed)
    Abstract [en]

    Sediment records recovered from the Baltic Sea during Integrated Ocean Drilling Program Expedition 347 provide a unique opportunity to study paleoenvironmental and climate change in central and northern Europe. Such studies contribute to a better understanding of how environmental parameters change in continental shelf seas and enclosed basins. Here we present a multi-proxy-based reconstruction of paleotemperature (both marine and terrestrial), paleosalinity, and paleoecosystem changes from the Little Belt (Site M0059) over the past  ∼  8000 years and evaluate the applicability of inorganic- and organic-based proxies in this particular setting. All salinity proxies (diatoms, aquatic palynomorphs, ostracods, diol index) show that lacustrine conditions occurred in the Little Belt until  ∼  7400 cal yr BP. A connection to the Kattegat at this time can thus be excluded, but a direct connection to the Baltic Proper may have existed. The transition to the brackish–marine conditions of the Littorina Sea stage (more saline and warmer) occurred within  ∼  200 years when the connection to the Kattegat became established after  ∼  7400 cal yr BP. The different salinity proxies used here generally show similar trends in relative changes in salinity, but often do not allow quantitative estimates of salinity. The reconstruction of water temperatures is associated with particularly large uncertainties and variations in absolute values by up to 8 °C for bottom waters and up to 16 °C for surface waters. Concerning the reconstruction of temperature using foraminiferal Mg  /  Ca ratios, contamination by authigenic coatings in the deeper intervals may have led to an overestimation of temperatures. Differences in results based on the lipid paleothermometers (long chain diol index and TEXL86) can partly be explained by the application of modern-day proxy calibrations to intervals that experienced significant changes in depositional settings: in the case of our study, the change from freshwater to marine conditions. Our study shows that particular caution has to be taken when applying and interpreting proxies in coastal environments and marginal seas, where water mass conditions can experience more rapid and larger changes than in open ocean settings. Approaches using a multitude of independent proxies may thus allow a more robust paleoenvironmental assessment.

  • 32.
    Mhatre, Snehit S
    et al.
    Aarhus University, Aarhus, Denmark / University of Southern Denmark, Odense, Denmark.
    Kaufmann, Stefan
    Aarhus University, Aarhus, Denmark.
    Marshall, Ian P G
    Aarhus University, Aarhus, Denmark.
    Obrochta, Stephen
    Akita University, Akita City, Japan.
    Andrén, Thomas
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Jørgensen, Bo Barker
    Aarhus University, Aarhus, Denmark.
    Lomstein, Bente Aa
    Aarhus University, Aarhus, Denmark.
    Microbial biomass turnover times and clues to cellular protein repair in energy-limited deep Baltic Sea sediments2019In: FEMS Microbiology Ecology, ISSN 0168-6496, E-ISSN 1574-6941, Vol. 95, no 6, article id fiz068Article in journal (Refereed)
    Abstract [en]

    The discovery of active microbial life deeply buried beneath the seafloor has opened important questions: how do microorganisms cope with extreme energy limitation, what is their metabolic activity, and how do they repair damages to essential biomolecules? We used a D:L-amino acid model to calculate microbial biomass turnover times. We used a metagenome and metatranscriptome analysis to investigate the distribution of the gene that encodes Protein-L-iso aspartate(D-aspartate) O-methyltransferase (PCMT), an enzyme which recognizes damaged L-isoapartyl and D-aspartyl residues in proteins and catalyzes their repair. Sediment was retrieved during the Integrated Ocean Drilling Program (IODP) Expedition 347 from Landsort Deep and the Little Belt in the Baltic Sea. The study covers the period from the Baltic Ice Lake ca. 13 000 years ago to the present. Our results provide new knowledge on microbial biomass turnover times and protein repair in relation to different regimes of organic matter input. For the first time, we show that the PCMT gene was widely distributed and expressed among phylogenetically diverse groups of microorganisms. Our findings suggest that microbial communities are capable of repairing D-amino acids within proteins using energy obtained from the degradation of a mixture of labile compounds in microbial necromass and more recalcitrant organic matter.

  • 33.
    Norbäck Ivarsson, Lena
    et al.
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science. Södertörn University, Centre for Baltic and East European Studies (CBEES), Baltic & East European Graduate School (BEEGS).
    Andrén, Thomas
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Moros, Matthias
    Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany.
    Andersen, Thorbjörn Joest
    University of Copenhagen, Copenhagen, Denmark.
    Lönn, Mikael
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Mathematics Teaching. University of Gävle.
    Andrén, Elinor
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Baltic Sea Coastal Eutrophication in a Thousand Year Perspective2019In: Frontiers in Environmental Science, ISSN 2296-665X, Vol. 7, article id 88Article in journal (Refereed)
    Abstract [en]

    Sediment cores from three sites along the east-coast of Sweden, north-western Baltic Proper, have been studied with respect to lithologies, geochemistry and diatom assemblages to trace and date early human impact with emphasis on nutrient discharge. The three sites Bråviken, Himmerfjärden and Ådfjärden, have been impacted to various degree during the last millennia by multiple stressors like excessive nutrient discharge and hazardous substances, leading to coastal hypoxia, eutrophication and pollution. These stressors are mainly caused by drivers in the drainage area as increased human population, changed land use and point sources as industries and a sewage treatment plant. Even though their detailed history differs, the results show similar general patterns for all three sites. We find no evidence in our data from the coastal zone supporting the hypothesis that the extensive areal distribution of hypoxia in the open Baltic Sea during the Medieval Climate Anomaly was caused by human impact. Timing of the onset of man-made eutrophication, as identified from d15N and changes in diatom composition, differs between the three sites, reflecting the site specific geography and local environmental histories of these areas. The onset of eutrophication dates to 1800 CE in Bråviken and Himmerfjärden areas, and to 1900 CE in the less urban area of Ådfjärden. We conclude that the recorded environmental changes during the last centuries are unique in a thousand year perspective.

  • 34.
    Obrochta, S. P.
    et al.
    Akita University Akita, Japan.
    Andrén, Thomas
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Fazekas, S. Z.
    Akita University Akita, Japan.
    Lougheed, B. C.
    Uppsala University.
    Snowball, I.
    Uppsala University.
    Yokoyama, Y.
    University of Tokyo, Chiba, Japan.
    Miyairi, Y.
    University of Tokyo, Chiba, Japan.
    Kondo, R.
    Kogakkan University, Mie, Japan.
    Kotilainen, A. T.
    Marine Geology, Espoo, Finland.
    Hyttinen, O.
    University of Helsinki, Helsinki, Finland.
    Fehr, A
    RWTH Aachen University, Aachen, Germany.
    The undatables: Quantifying uncertainty in a highly expanded Late Glacial-Holocene sediment sequence recovered from the deepest Baltic Sea basin—IODP Site M00632017In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 18, no 3, p. 858-871Article in journal (Refereed)
    Abstract [en]

    Laminated, organic-rich silts and clays with high dissolved gas content characterize sediments at IODP Site M0063 in the Landsort Deep, which at 459 m is the deepest basin in the Baltic Sea. Cores recovered from Hole M0063A experienced significant expansion as gas was released during the recovery process, resulting in high sediment loss. Therefore, during operations at subsequent holes, penetration was reduced to 2 m per 3.3 m core, permitting expansion into 1.3 m of initially empty liner. Fully filled liners were recovered from Holes B through E, indicating that the length of recovered intervals exceeded the penetrated distance by a factor of >1.5. A typical down-core logarithmic trend in gamma density profiles, with anomalously low-density values within the upper ∼1 m of each core, suggests that expansion primarily occurred in this upper interval. Thus, we suggest that a simple linear correction is inappropriate. This interpretation is supported by anisotropy of magnetic susceptibility data that indicate vertical stretching in the upper ∼1.5 m of expanded cores. Based on the mean gamma density profiles of cores from Holes M0063C and D, we obtain an expansion function that is used to adjust the depth of each core to conform to its known penetration. The variance in these profiles allows for quantification of uncertainty in the adjusted depth scale. Using a number of bulk 14C dates, we explore how the presence of multiple carbon source pathways leads to poorly constrained radiocarbon reservoir age variability that significantly affects age and sedimentation rate calculations.

  • 35. 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.

  • 36. Sohlenius, Gustav
    et al.
    Emeis, Kay C
    Andrén, Elinor
    Andrén, Thomas
    Kohly, Alexander
    Development of anoxia during the Holocene fresh-brackish water transition in the Baltic Sea2001In: Marine Geology, ISSN 0025-3227, E-ISSN 1872-6151, Vol. 177, p. 221-242Article in journal (Refereed)
    Abstract [en]

    One of the most pronounced environmental changes during the Holocene Baltic Sea history was the transition from the freshwater Ancylus Lake to the brackish water Litorina Sea. The establishment of brackish conditions during this transition (the A/L) was caused by an interplay of sea level rise and subsidence of sills in the Danish Straits. The northward progression of salt water influence caused the gradual and transgressive development of a halocline which obstructed vertical water circulation in the deep depositional basins. It caused changes in surface water properties (mirrored by diatom flora and productivity levels), in redox conditions of bottom waters, in organic carbon preservation of sediments, and in nutrient cycling. In seven cores from the Arkona, Bornholm and Gotland Basins, the A/L transition was WC dated and studied in high-resolution samples for minor and major element composition. The earliest marine inflows were small and can only be detected by sedimentary properties in the southern Baltic. Further north the salinity increase was gradual and retarded; only when the connection through the Danish Straits was well established the entire Baltic proper became brackish with a stratified water column. This development took altogether 2000 C-14 yr (c. 9000-7000 BP). Diatom analyses indicate a fast increase in salinity c. 7000 C-14 yr BP, which coincides with a transgressive phase in the straits, In the Gotland Basin, deposition of laminated sediments and periodically euxinic conditions were established first at the deepest bottoms, and rose to shallower water depth as the basin was gradually filled with dense brackish water. The laminated sequences have high organic carbon contents, which is attributed to better preservation under anoxic conditions. Litorina sediments from the Arkona and Bornholm Basins are bioturbated even though conditions became more reducing also in these sediments during the A/L transition. The development of reducing conditions during the A/L transition probably caused Pre-mobilization from the sediments and a decrease in the rates of denitrification. Both factors increased primary productivity. A comparison between isochronous sediments from different basins shows that certain elements (Mo, Cu, V and Cd) are enriched sediments deposited during predominantly anoxic conditions.

  • 37.
    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.

  • 38.
    van Helmond, Niels A.G.M.
    et al.
    Utrecht University, Utrecht, Netherlands.
    Quintana Krupinski, Nadine B.
    Lund University.
    Lougheed, Bryan C.
    Uppsala University.
    Obrochta, Stephen P.
    Akita University, Akita, Japan.
    Andrén, Thomas
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Slomp, Caroline P.
    Utrecht University, Utrecht, Netherlands.
    Seasonal hypoxia was a natural feature of the coastal zone in the Little Belt, Denmark, during the past 8 ka2017In: Marine Geology, ISSN 0025-3227, E-ISSN 1872-6151, Vol. 387, p. 45-57Article in journal (Refereed)
    Abstract [en]

    The extent of the hypoxic area in the Baltic Sea has rapidly expanded over the past century. Two previous phases of widespread hypoxia, coinciding with the Holocene Thermal Maximum (HTM; 8–4 ka before present; BP) and the Medieval Climate Anomaly (MCA; 2–0.8 ka BP), have been identified. Relatively little is known about bottom water redox conditions in the coastal zone of the Baltic Sea during the Holocene, however. Here we studied the geochemical composition of a sediment sequence from a currently seasonally hypoxic site in the Danish coastal zone, the Little Belt, retrieved during Integrated Ocean Drilling Program Expedition 347 (Site M0059). The base of the studied sediment sequence consists of clays low in organic carbon (Corg), molybdenum (Mo) and iron sulfides (Fe-sulfides), and rich in iron oxides (Fe-oxides), indicative of a well-oxygenated, oligotrophic (glacial) meltwater lake. An erosional unconformity separates the glacial lake sediments from sediments that are rich in Corg. The absence of Mo, in combination with high Corg/S values, indicates that these sediments were deposited in a highly productive, well-oxygenated freshwater lake. The transition to modern brackish/marine conditions was very rapid, and subsequent continuous sequestration of Mo in the sediment and high ratios of reactive iron (FeHR) over total Fe (FeTOT) suggest (seasonal) hypoxia occurred over the last ~ 8 ka. Maxima in sediment Corg, Mo and FeHR/FeTOT ratios during the HTM and MCA suggest that the hypoxia intensified. Our results demonstrate that the Little Belt is naturally susceptible to the development of seasonal hypoxia. While periods of climatic warming led to increased deoxygenation of bottom waters, high nutrient availability in combination with density stratification were likely the main drivers of hypoxia in this part of the coastal zone of the Baltic Sea during the Holocene.

  • 39.
    van Wirdum, Falkje
    et al.
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies.
    Andrén, Elinor
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Wienholz, D.
    University of Hamburg, Hamburg, Germany.
    Kotthoff, U.
    University of Hamburg, Hamburg, Germany.
    Moros, M.
    Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany.
    Fanget, A. -S
    University of Perpignan, Perpignan, France.
    Seidenkrantz, M. -S
    Aarhus University, Aarhus, Denmark.
    Andrén, Thomas
    Södertörn University, School of Natural Sciences, Technology and Environmental Studies, Environmental Science.
    Middle to late holocene variations in salinity and primary productivity in the central Baltic Sea: A multiproxy study from the landsort deep2019In: Frontiers in Marine Science, E-ISSN 2296-7745, Vol. 6, article id 51Article in journal (Refereed)
    Abstract [en]

    Anthropogenic forcing has led to an increased extent of hypoxic bottom areas in the Baltic Sea during recent decades. The Baltic Sea ecosystem is naturally prone to the development of hypoxic conditions due to its geographical, hydrographical, geological, and climate features. Besides the current spreading of hypoxia, the Baltic Sea has experienced two extensive periods of hypoxic conditions during the Holocene, caused by changing climate conditions during the Holocene Thermal Maximum (HTM; 8–4.8 cal ka BP) and the Medieval Climate Anomaly (MCA; 1–0.7 cal ka BP). We studied the variations in surface and bottom water salinity and primary productivity and their relative importance for the development and termination of hypoxia by using microfossil and geochemical data from a sediment core retrieved from the Landsort Deep during IODP Expedition 347 (Site M0063). Our findings demonstrate that increased salinity was of major importance for the development of hypoxic conditions during the HTM. In contrast, we could not clearly relate the termination of this hypoxic period to salinity changes. The reconstructed high primary productivity associated with the hypoxic period during the MCA is not accompanied by considerable increases in salinity. Our proxies for salinity show a decreasing trend before, during and after the MCA. Therefore, we suggest that this period of hypoxia is primarily driven by increasing temperatures due to the warmer climate. These results highlight the importance of natural climate driven changes in salinity and primary productivity for the development of hypoxia during a warming climate.

  • 40. Wastegård, S
    et al.
    Andrén, Thomas
    Sohlenius, G
    Sandgren, P
    Different phases of the Yoldia Sea in the north-western Baltic Proper1995In: Quaternary International, ISSN 1040-6182, E-ISSN 1873-4553, Vol. 27, p. 121-129Article in journal (Refereed)
    Abstract [en]

    Four sediment cores from the north-western Baltic Proper, covering the time from the Weichselian deglaciation to the present have been studied. Main interest is focused on the Yoldia stage, and especially the duration of the marine phase of this stage. The lithological compositions of the sediments and results of different analyses (magnetic, carbonate, ostracods and foraminifera) have resulted in a subdivision into five stratigraphical units (A-E, from older to younger). Unit A was deposited in a glaciolacustrine environment, probably during the first non-saline phase of the Yoldia stage. The first ingression of saline water is recorded in unit B. Brackish water ostracods and foraminifera occur exclusively in this unit, which represents the only saline phase of the Yoldia stage. This phase lasted for less than 120 clay varve years. Unit C was deposited in fresh water, probably during the last phase of the Yoldia stage and the Ancylus stage. The uppermost units, D and E are of Holocene age and represent different phases of the Litorina and Post-Litorina stages.

  • 41. Wastegård, Stefan
    et al.
    Andrén, Thomas
    Salinity changes in the central Baltic Sea (NW Europe) over the last 10 000 years: a comment on Emeis, Struk, Blanz, Kohly, Voss2005In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 15, no 3, p. 472-474Article in journal (Refereed)
    Abstract [en]

    We question the effort to date the lower part of a core from the Baltic Sea with a combination of tephra layers and stratigraphical markers. No geochemical data is presented for the two tephra layers, believed to be the Saksunarvatn Ash and Vedde Ash. Furthermore, the age used for one of the stratigraphical markers is erroneous. We present two alternative age models, of which the second gives a plausible sediment accumulation rate but excludes the identification of the Vedde Ash.

  • 42. Zillén, Lovisa
    et al.
    Conley, Daniel J.
    Andrén, Thomas
    Södertörn University, School of Life Sciences.
    Andrén, Elinor
    Södertörn University, School of Life Sciences.
    Björck, Svante
    Past occurrences of hypoxia in the Baltic Sea and the role of climate variability, environmental change and human impact2008In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 91, p. 77-92Article in journal (Refereed)
    Abstract [en]

    The hypoxic zone in the Baltic Sea has increased in area about four times since 1960 and widespread oxygen deficiency has severely reduced macro benthic communities below the halocline in the Baltic Proper and the Gulf of Finland, which in turn has affected food chain dynamics, fish habitats and fisheries in the entire Baltic Sea. The cause of increased hypoxia is believed to be enhanced eutrophication through increased anthropogenic input of nutrients, such as nitrogen and phosphorus. However, the spatial variability of hypoxia on long time-scales is poorly known: and so are the driving mechanisms. We review the occurrence of hypoxia in modern time (last c. 50ᅵyears), modern historical time (AD 1950-1800) and during the more distant past (the last c. 10ᅵ000ᅵyears) and explore the role of climate variability, environmental change and human impact. We present a compilation of proxy records of hypoxia (laminated sediments) based on long sediment cores from the Baltic Sea. The cumulated results show that the deeper depressions of the Baltic Sea have experienced intermittent hypoxia during most of the Holocene and that regular laminations started to form c. 8500-7800ᅵcal. yr BP ago, in association with the formation of a permanent halocline at the transition between the Early Littorina Sea and the Littorina Sea s. str. Laminated sediments were deposited during three main periods (i.e. between c. 8000-4000, 2000-800ᅵcal. yr BP and subsequent to AD 1800) which overlap the Holocene Thermal Maximum (c. 9000-5000ᅵcal. yr BP), the Medieval Warm Period (c. AD 750-1200) and the modern historical period (AD 1800 to present) and coincide with intervals of high surface salinity (at least during the Littorina s. str.) and high total organic carbon content. This study implies that there may be a correlation between climate variability in the past and the state of the marine environment, where milder and dryer periods with less freshwater run-off correspond to increased salinities and higher accumulation of organic carbon resulting in amplified hypoxia and enlarged distribution of laminated sediments. We suggest that hydrology changes in the drainage area on long time-scales have, as well as the inflow of saltier North Sea waters, controlled the deep oxic conditions in the Baltic Sea and that such changes have followed the general Holocene climate development in Northwest Europe. Increased hypoxia during the Medieval Warm Period also correlates with large-scale changes in land use that occurred in much of the Baltic Sea watershed during the early-medieval expansion. We suggest that hypoxia during this period in the Baltic Sea was not only caused by climate, but increased human impact was most likely an additional trigger. Large areas of the Baltic Sea have experienced intermittent hypoxic from at least AD 1900 with laminated sediments present in the Gotland Basin in the Baltic Proper since then and up to present time. This period coincides with the industrial revolution in Northwestern Europe which started around AD 1850, when population grew, cutting of drainage ditches intensified, and agricultural and forest industry expanded extensively.

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