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  • 1. Björck, S
    et al.
    Bennike, O
    Rosen, P
    Andresen, C S
    Bohncke, S
    Kaas, E
    Conley, D
    Anomalously mild Younger Dryas summer conditions in southern Greenland2002In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 30, no 5, p. 427-430Article in journal (Refereed)
    Abstract [en]

    The first late-glacial lake sediments found in Greenland were analyzed with respect to a variety of environmental variables. The analyzed sequence covers the time span between 14400 and 10500 calendar yr B.P., and the data imply that the conditions in southernmost Greenland during the Younger Dryas stadial, 12800-11550 calendar yr B.P., were characterized by an arid climate with cold winters and mild summers, preceded by humid conditions with cooler summers. Climate models imply that such an anomaly may be explained by local climatic phenomenon caused by high insolation and Fohn effects. It shows that regional and local variations of Younger Dryas summer conditions in the North Atlantic region may have been larger than previously found from proxy data and modeling experiments.

  • 2. Jakobsson, M
    et al.
    Lovlie, R
    Al-Hanbali, H
    Arnold, E
    Backman, J
    Morth, M
    Manganese and color cycles in Arctic Ocean sediments constrain Pleistocene chronology2000In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 28, no 1, p. 23-26Article in journal (Refereed)
    Abstract [en]

    Sequential variations in manganese (Mn) content and color of deepsea sediments retrieved from the Lomonosov Ridge (87 degrees N) in the central Arctic Ocean apparently mimic low-latitude delta(18)O glacial-interglacial cyclicity, thereby providing stratigraphic information that together with biostratigraphic data permit the construction of a detailed chronological model. Correlation of this Mn and color chronology to established apparent Brunhes-age estimates of geomagnetic excursions reveals a remarkable fit between these two independently derived time scales. The Mn and color cycles probably provide paleoenvironmental information about material fluxes in the Arctic Ocean over the past 1 m.y. We suggest that the primary source for the observed manganese variations in our sediment core is northern Siberia, which has extensive peat bogs and boreal forests. These Siberian source areas could operate in an off and on mode tuned to Pleistocene glacial and interglacial periods. Contrasts in ventilation of Arctic Ocean waters during interglacial-glacial cycles probably could also enhance the observed Mn and color variability.

  • 3.
    Jakobsson, Martin
    et al.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Anderson, John B.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Nitsche, Frank O.
    Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY 10964 USA..
    Dowdeswell, Julian A.
    Univ Cambridge, Scott Polar Res Inst, Cambridge CB2 1ER, England..
    Gyllencreutz, Richard
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Kirchner, Nina
    Stockholm Univ, Dept Phys Geog & Quaternary, S-10691 Stockholm, Sweden..
    Mohammad, Rezwan
    O'Regan, Matthew
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Alley, Richard B.
    Penn State Univ, Dept Geosci, University Pk, PA 16802 USA..
    Anandakrishnan, Sridhar
    Penn State Univ, Dept Geosci, University Pk, PA 16802 USA..
    Eriksson, Bjorn
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Kirshner, Alexandra
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Fernandez, Rodrigo
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Stolldorf, Travis
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Minzoni, Rebecca
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Majewski, Wojciech
    Polish Acad Sci, Inst Paleobiol, PL-00818 Warsaw, Poland..
    Geological record of ice shelf break-up and grounding line retreat, Pine Island Bay, West Antarctica2011In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 39, no 7, p. 691-694Article in journal (Refereed)
    Abstract [en]

    The catastrophic break-ups of the floating Larsen A and B ice shelves (Antarctica) in 1995 and 2002 and associated acceleration of glaciers that flowed into these ice shelves were among the most dramatic glaciological events observed in historical time. This raises a question about the larger West Antarctic ice shelves. Do these shelves, with their much greater glacial discharge, have a history of collapse? Here we describe features from the seafloor in Pine Island Bay, West Antarctica, which we interpret as having been formed during a massive ice shelf break-up and associated grounding line retreat. This evidence exists in the form of seafloor landforms that we argue were produced daily as a consequence of tidally influenced motion of mega-icebergs maintained upright in an iceberg armada produced from the disintegrating ice shelf and retreating grounding line. The break-up occurred prior to ca. 12 ka and was likely a response to rapid sea-level rise or ocean warming at that time.

  • 4.
    O'Regan, Matt
    et al.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Backman, Jan
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Fornaciari, Eliana
    Jakobsson, Martin
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    West, Gabriel
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Calcareous nannofossils anchor chronologies for Arctic Ocean sediments back to 500 ka2020In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 48, no 11, p. 1115-1119Article in journal (Refereed)
    Abstract [en]

    Poor age control in Pleistocene sediments of the central Arctic Ocean generates considerable uncertainty in paleoceanographic reconstructions. This problem is rooted in the perplexing magnetic polarity patterns recorded in Arctic marine sediments and the paucity of microfossils capable of providing calibrated biostratigraphic biohorizons or continuous oxygen isotope stratigraphies. Here, we document the occurrence of two key species of calcareous nannofossils in a single marine sediment core from the central Arctic Ocean that provide robust, globally calibrated age constraints for sediments younger than 500 ka. The key species are the coccolithophores Pseudoemiliania lacunosa, which went extinct during marine isotope stage (MIS) 12 (478-424 ka), and Emiliania huxleyi, which evolved during MIS 8 (300-243 ka). This is the first time that P lacunosa has been described in sediments of the central Arctic Ocean. The sedimentary horizons containing these age-diagnostic species can be traced, through lithostratigraphic correlation, across more than 450 km of the inner Arctic Ocean. They provide the first unequivocal support for proposed Pleistocene chronologies of sediment from this sector of the Arctic, and they constitute a foundation for developing and testing other geochronological tools for dating Arctic marine sediments.

  • 5. O’Regan, Matt
    et al.
    Forwick, Matthias
    Jakobsson, Martin
    Moran, Kathryn
    Mosher, David
    Seafloor cratering and sediment remolding at sites of fluid escape2015In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 43, no 10, p. 895-898Article in journal (Refereed)
    Abstract [en]

    Episodic fluid escape from marine sediments results from overpressure development and pressure release, and can occur slowly through geologic time or catastrophically. Morphological features in regions of fluid seepage include doming, mud volcanism, cratering, and pockmark formation. Vertical sediment mobilization and surface erosion are considered the principal mechanisms for these topographic changes. However, the impact of mobilization on the geotechnical properties of sediments has not been explicitly considered. Here we develop a one-dimensional numerical subsidence model that incorporates the well-established behavior of remolded fine-grained cohesive sediments. We use this to show that if subsurface overpressure results in the mobilization of sediments, large settlements (20%-35% reduction in volume) can occur when overpressure dissipates. This presents a novel mechanism to explain changes in seafloor and subsurface topography in areas of fluid escape, while highlighting an important interplay between subsurface fluid flow and the geotechnical properties of fine-grained cohesive sediments.

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