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  • 1
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    Evaluating sedimentary DNA for tracing changes in cyanobacteria dynamics from sediments spanning the last 350 years of Lake Tiefer See, NE Germany (2021)
    Springer Netherlands
    Details
    Publication Date: 2023-08-25
    Description: Since the beginning of the Anthropocene, lacustrine biodiversity has been influenced by climate change and human activities. These factors advance the spread of harmful cyanobacteria in lakes around the world, which affects water quality and impairs the aquatic food chain. In this study, we assessed changes in cyanobacterial community dynamics via sedimentary DNA (sedaDNA) from well-dated lake sediments of Lake Tiefer See, which is part of the Klocksin Lake Chain spanning the last 350 years. Our diversity and community analysis revealed that cyanobacterial communities form clusters according to the presence or absence of varves. Based on distance-based redundancy and variation partitioning analyses (dbRDA and VPA) we identified that intensified lake circulation inferred from vegetation openness reconstructions, δ13C data (a proxy for varve preservation) and total nitrogen content were abiotic factors that significantly explained the variation in the reconstructed cyanobacterial community from Lake Tiefer See sediments. Operational taxonomic units (OTUs) assigned to Microcystis sp. and Aphanizomenon sp. were identified as potential eutrophication-driven taxa of growing importance since circa common era (ca. CE) 1920 till present. This result is corroborated by a cyanobacteria lipid biomarker analysis. Furthermore, we suggest that stronger lake circulation as indicated by non-varved sediments favoured the deposition of the non-photosynthetic cyanobacteria sister clade Sericytochromatia, whereas lake bottom anoxia as indicated by subrecent- and recent varves favoured the Melainabacteria in sediments. Our findings highlight the potential of high-resolution amplicon sequencing in investigating the dynamics of past cyanobacterial communities in lake sediments and show that lake circulation, anoxic conditions, and human-induced eutrophication are main factors explaining variations in the cyanobacteria community in Lake Tiefer See during the last 350 years.
    Description: Virtual Institute of Integrated Climate and Landscape Evolution Analyses -ICLEA-
    Description: Leibniz-Gemeinschaft http://dx.doi.org/10.13039/501100001664
    Description: Helmholtz-Gemeinschaft (DE)
    Description: Deutsche Bundesstiftung Umwelt http://dx.doi.org/10.13039/100007636
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:577.6 ; Late Holocene ; Methylheptadecanes ; Varves ; Anthropocene ; Sericytochromatia ; Melainabacteria
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 2
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    Atmosphere-ocean changes in the Pacific Southern Ocean over the past 1 Million years and implications for global climate (2017)
    SCAR
    In:  EPIC3Past Antarctic Ice Sheet Dynamics (PAIS) Conference, Trieste, 2017-09-10-2017-09-15SCAR
    Details
    Publication Date: 2018-08-10
    Description: Atmosphere-ocean interactions play an important role for understanding processes and feedbacks in the Southern Ocean (SO) and are relevant for changes in Antarctic ice-sheets and atmospheric CO2 concentrations. The most important atmospheric forcing at high and mid-latitudes of the Southern Hemisphere is the westerly wind belt (SWW), which strongly affects the strength and extension of the Antarctic Circumpolar Current (ACC), upwelling of deep-water masses, and controls the back-flow of intermediate waters to the tropics. In order to address orbital and millennial-scale changes of the SWW and the ACC, we present sediment proxy records from the Pacific SO including the Chilean Margin and the Drake Passage. The Drake Passage (DP) represents the most important oceanic gateway along the ACC. Based on grain-size and geochemical properties of sediment records from the southernmost continental margin of South America, we reconstruct changes in DP throughflow dynamics over the past 65,000 years. In combination with published sediment records from the Scotia Sea and preliminary sediment records from the central Drake Passage (Polarstern cruise PS97, 2016), we argue for a considerable total reduction of DP transport and reveal an up to ~40% decrease in flow speed along the northernmost ACC pathway entering the DP during glacial times. Superimposed on this long-term decrease are high-amplitude millennial-scale variations, which parallel Southern Ocean and Antarctic temperature patterns. The glacial intervals of strong weakening of the ACC entering the DP imply a reduced Pacific-Atlantic exchange via the DP (“cold-water route”). The reduced Drake Passage glacial throughflow was accompanied by a pronounced northward extension of the Antarctic cold-water sphere in the Southeast Pacific sector and stronger export of northern ACC water into the South Pacific gyre. These oceanographic changes are consistent with reduced SWW within the modern maximum wind strength zone over the subantarctic ACC and reduced wind forcing due to extended sea-ice further south. Despite this reduction in winds in the core of the westerlies, we observe 3-fold higher dust deposition during glacial periods in Past Antarctic Ice Sheet Dynamics (PAIS) Conference September 10-15th 2017, Trieste - Italy the Pacific Southern Ocean (SO). This observation may be explained by a combination of factors including more expanded arid dust source areas in Australia and a northward extent or enhancement of the SWW over Southeast Australia during glacials that would plausibly increase the dust uptake and export into the Pacific SO. Such scenario would imply stronger SWW at the present northernmost margin of the wind belt coeval with weaker core westerlies in the south and reduced ACC strength, including Drake Passage throughflow during glacials. We conclude that changes in DP throughflow play a critical role for the global meridional overturning circulation and interbasin exchange in the Southern Ocean, most likely regulated by variations in the westerly wind field and changes in Antarctic sea-ice extent. Keywords: Pelagic Southern Ocean, Antarctic Circumpolar Current, Southern Westerlies, Teleconnections.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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  • 3
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    Reduced Drake Passage through flow during the last glacial and millennial-scale variability (2014)
    SCAR
    In:  EPIC3XXXIII Biennial Meetings, 2014 Open Science Conference, Auckland, New Zealand, 2014-08-25-2014-08-28SCAR
    Details
    Publication Date: 2018-08-10
    Description: The Antarctic Circumpolar Current (ACC) plays an essential role in the thermohaline circulation and global climate. Today, a large volume of ACC water passes through the Drake Passage, the major geographic constrain for the circumpolar flow. Here we present the first millennial-scale proxy records of Holocene and last glacial variations of the Drake Passage throughflow. Our study reports geochemical, paleomagnetic, and grain-size data from a sediment core retrieved from the upper continental slope off southernmost Chile. The site is located beneath the strong Cape Horn Current that transports northern ACC water towards the Drake Passage. Our data reveal large amplitude changes in current intensity proxy records suggesting pronounced variations in surface and sub-surface flow. We interpret these changes in terms of strongly reduced contributions of northern ACC water to the Drake Passage throughflow during the glacial in general and particularly during millennial-scale cold phases as known from e.g. Antarctic ice-cores. At the same time, advection of northern ACC water into the Humboldt current system was likely enhanced. These results support climate models showing largely reduced volume transport through the Drake Passage during the last glacial maximum and an increasing throughflow during the last deglaciation that affected the strengthening of the Atlantic Meridional Overturning Circulation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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    PAPER (OA)
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