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  • 1.
    Andersson, Rina Argelia
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Meyers, Philip
    Department of Earth and Environmental Sciences, The University of Michigan, Ann Arbor, Michigan, U.S.A..
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Johansson, Carina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Organic matter delivery to Quaternary sediments of Amundsen Basin, central Arctic OceanManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Quaternary marine sediments retrieved from the central Arctic Ocean in a 30 cm long core, were analyzed for paleoenvironmental reconstruction. n-Alkane biomarkers combined with elemental analyses that include X-ray fluorescence (XRF) core scanning provide complementary information that suggest important influxes of terrigenous derived organic matter (OM) with depth. Changes in the variability of n-alkane-derived and elemental ratios with depth reflect the complexity of the organic carbon cycle in this region. The distributions and abundances of the long-chain n-alkanes reveal a high content of terrigenous derived components and suggest together with mathematical estimations high deliveries of the terrigenous OM in the past. XRF trace metal analyses suggest less-oxygenated bottom waters that may have allowed for better preservation conditions of OM deeper in the core.

  • 2. Björk, Göran
    et al.
    Anderson, L. G.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Antony, D.
    Eriksson, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Eriksson, P. B.
    Hell, Benjamin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Hjalmarsson, S.
    Janzen, T.
    Jutterström, Sara
    Linders, J.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Marcussen, C.
    Olsson, K. Anders
    Rudels, B.
    Sellén, Emma
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Sölvsten, M.
    Flow of Canadian basin deep water in the Western Eurasian Basin of the Arctic Ocean2010Ingår i: Deep Sea Research Part I: Oceanographic Research Papers, ISSN 0967-0637, E-ISSN 1879-0119, Vol. 57, nr 4, s. 577-586Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The LOMROG 2007 expedition targeted the previously unexplored southern part of the Lomonosov Ridge north of Greenland together with a section from the Morris Jesup Rise to Gakkel Ridge. The oceanographic data show that Canadian Basin Deep Water (CBDW) passes the Lomonosov Ridge in the area of the Intra Basin close to the North Pole and then continues along the ridge towards Greenland and further along its northernmost continental slope. The CBDW is clearly evident as a salinity maximum and oxygen minimum at a depth of about 2000 m. The cross-slope sections at the Amundsen Basin side of the Lomonosov Ridge and further south at the Morris Jesup Rise show a sharp frontal structure higher up in the water column between Makarov Basin water and Amundsen Basin water. The frontal structure continues upward into the Atlantic Water up to a depth of about 300 m. The observed water mass division at levels well above the ridge crest indicates a strong topographic steering of the flow and that different water masses tend to pass the ridge guided by ridge-crossing isobaths at local topographic heights and depressions. A rough scaling analysis shows that the extremely steep and sharply turning bathymetry of the Morris Jesup Rise may force the boundary current to separate and generate deep eddies.

  • 3. Chen, H.-F.
    et al.
    Song, S.-R.
    Lee, T.-Q.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Chi, Z.
    Yong, W.
    A multiproxy lake record from Inner Mongolia displays a late Holocene teleconnection between central Asian and North Atlantic climate2010Ingår i: Quaternary International, ISSN 1040-6182, E-ISSN 1873-4553, Vol. 227, nr 2, s. 170-182Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In order to study how the Holocene Central Asian climate is coupled to the global climate system, a 4.24 m long lake core from western Inner Mongolia in China was studied using a multiproxy approach. Sedimentology and geochemical parameters such as gypsum and dolomite content, presence of lakeshore sand changing to aeolian sand, and changes in paleomagnetic properties bear witness to a trend toward a generally drier climate over the late Holocene. Aridification is linked to the southward retreat of the northern boundary of the Asian summer monsoon, leaving central Asia under the influence of the westerly belt. The weakening of the Asian summer monsoon in turn was caused by an orbitally driven decrease in summer insolation. The weakening summer insolation also likely increased the intensity of the Siberian High pressure system, further promoting aridification of central Asia. On a shorter time scale, the multiproxy record shows the climate to have been relatively dry during the Medieval Warm Period (AD 800–1100) with the ensuing humid environment at the end of this period gradually turning to become extremely dry (AD 1100–1550) at the Little Ice Age Maximum. Switches in the North Atlantic Oscillation caused these changes through a teleconnection in the form of westerlies. These westerlies provided most of central Asia’s moisture after the retreat of the Asian summer monsoon. The central Asian climate therefore corresponds closely with late Holocene European climate changes.

  • 4. Dowdeswell, J. A.
    et al.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Hogan, K. A.
    O'Regan, Matt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Backman, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Evans, J.
    Hell, Benjamin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Marcussen, C.
    Noormets, R.
    O'Cofaigh, C.
    Sellén, Emma
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Sölvsten, M.
    High-resolution geophysical observations of the Yermak Plateau and northern Svalbard margin: Implications for ice-sheet grounding and deep-keeled icebergs2010Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, nr 25-26, s. 3518-3531Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-resolution geophysical evidence on the seafloor morphology and acoustic stratigraphy of the Yermak Plateau and northern Svalbard margin between 79°20′ and 81°30′N and 5° and 22°E is presented. Geophysical datasets are derived from swath bathymetry and sub-bottom acoustic profiling and are combined with existing cores to derive chronological control. Seafloor landforms, in the form of ice-produced lineations, iceberg ploughmarks of various dimensions (including features over 80 m deep and down to about 1000 m), and a moat indicating strong currents are found. The shallow stratigraphy of the Yermak Plateau shows three acoustic units: the first with well-developed stratification produced by hemipelagic sedimentation, often draped over a strong and undulating internal reflector; a second with an undulating upper surface and little acoustic penetration, indicative of the action of ice; a third unit of an acoustically transparent facies, resulting from debris flows. Core chronology suggests a MIS 6 age for the undulating seafloor above about 580 m. There are several possible explanations, including: (a) the flow of a major grounded ice sheet across the plateau crest from Svalbard (least likely given the consolidation state of the underlying sediments); (b) the more transient encroachment of relatively thin ice from Svalbard; or (c) the drift across the plateau of an ice-shelf remnant or megaberg from the Arctic Basin. The latter is our favoured explanation given the evidence currently at our disposal.

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  • 5.
    Dowdeswell, Julian A.
    et al.
    University of Cambridge.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Hogan, K.A.
    O'Regan, Matthew
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Antony, D
    Backman, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Darby, Dennis
    Old Dominion University.
    Eriksson, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Evans, J
    Hell, Benjamin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Marcussen, Christian
    GEUS.
    Noormets, R.
    UNIS.
    Polyak, Leonid
    Ohio State University.
    Sellén, Emma
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Sölvsten, Morten
    Geophysical and geological observations from the Yermak Plateau and northern Svalbard margin: Implications for ice-sheet grounding and deep-keeled icebergs2009Ingår i: Third Conference on Arctic Palaeoclimate and its Extremes- beyond the frontier, Copenhagen: The Natural History Museum and University of Copenhagen , 2009, s. 22-22Konferensbidrag (Övrigt vetenskapligt)
  • 6.
    Immonen, Ninna
    et al.
    University of Oulu.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Köykkä, Juha
    University of Oulu.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Poikolainen, Jonna
    Strand, Kari
    Mineralogy of the late Pleistocene deposits in the Arctic Ocean Basin: Evidence for sediment sources, pathways and rapid deglaciation events2012Ingår i: / [ed] Ninna Immonen, Martin Jakobsson, Juha Pekka Lunkka, Kari Strand, 2012, s. 55-55Konferensbidrag (Övrigt vetenskapligt)
  • 7.
    Jakobsson, Martin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Darby, Dennis
    Polyak, Leonid
    Eriksson, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Hanslik, Daniela
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Hell, Benjamin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Karasti, Markus
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Sellén, Emma
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Sjöö, Carin
    Wallin, Åsa
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Lomonosov Ridge off Greenland (LOMROG) 2007: Coring and high-resolution geophysical mapping2008Rapport (Övrigt vetenskapligt)
  • 8.
    Jakobsson, Martin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Mayer, L.A.
    Scientific Party, LOMROG
    Scientific Party, Healy
    Sellén, Emma
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Hanslik, Daniela
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Eriksson, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Wallin, Åsa
    Glaciogenic bedforms on the Chukchi Borderland, Morris Jesup Rise and Yermak Plateau: three prolongations of the Arctic Ocean continental margin2008Ingår i: EOS Transactions, American Geophysical Union, v. 89(53): Fall Meet. Suppl.,, 2008, s. Abstract C14A-05Konferensbidrag (Övrigt vetenskapligt)
  • 9.
    Jakobsson, Martin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Nilsson, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    O'Regan, Matt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Backman, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Dowdeswell, J. A.
    Mayer, L.
    Polyak, L.
    Colleoni, Florence
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Anderson, L. G.
    Björk, G.
    Darby, D.
    Eriksson, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Hanslik, Daniela
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Hell, Benjamin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Marcussen, C.
    Sellén, Emma
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Wallin, T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    An Arctic Ocean ice shelf during MIS 6 constrained by new geophysical and geological data2010Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, nr 25-26, s. 3505-3517Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The hypothesis of floating ice shelves covering the Arctic Ocean during glacial periods was developed in the 1970s. In its most extreme form, this theory involved a 1000 m thick continuous ice shelf covering the Arctic Ocean during Quaternary glacial maxima including the Last Glacial Maximum (LGM). While recent observations clearly demonstrate deep ice grounding events in the central Arctic Ocean, the ice shelf hypothesis has been difficult to evaluate due to a lack of information from key areas with severe sea ice conditions. Here we present new data from previously inaccessible, unmapped areas that constrain the spatial extent and timing of marine ice sheets during past glacials. These data include multibeam swath bathymetry and subbottom profiles portraying glaciogenic features on the Chukchi Borderland, southern Lomonosov Ridge north of Greenland, Morris Jesup Rise, and Yermak Plateau. Sediment cores from the mapped areas provide age constraints on the glaciogenic features. Combining these new geophysical and geological data with earlier results suggests that an especially extensive marine ice sheet complex, including an ice shelf, existed in the Amerasian Arctic Ocean during Marine Isotope Stage (MIS) 6. From a conceptual oceanographic model we speculate that the cold halocline of the Polar Surface Water may have extended to deeper water depths during MIS 6 inhibiting the warm Atlantic water from reaching the Amerasian Arctic Ocean and, thus, creating favorable conditions for ice shelf development. The hypothesis of a continuous 1000 m thick ice shelf is rejected because our mapping results show that several areas in the central Arctic Ocean substantially shallower than 1000 m water depth are free from glacial influence on the seafloor.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 10.
    Jakobsson, Martin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Scientific Party, LOMROG
    Sellén, Emma
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Hanslik, Daniela
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Eriksson, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Wallin, Åsa
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Lomonosov Ridge off Greenland 2007 (LOMROG): Geophysical mapping and coring for the Arctic glacial and sea ice history2007Ingår i: First Conference on Arctic Palaeoclimate and its Extremes (APEX): The Royal Swedish Academy of Sciences, 2007, s. March 28-29Konferensbidrag (Övrigt vetenskapligt)
  • 11.
    Kylander, Malin M
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Lind, Ewa M
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Wastegård, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Recommendations for using XRF core scanning as a tool in tephrochronology2012Ingår i: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 22, nr 3, s. 371-375Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    X-ray fluorescence (XRF) core scanning is a relatively new arrangement of a classic analytical technique which allows for non-destructive, in situ XRF analysis of sediment cores from submillimetre resolution upwards. In this contribution we explore the use of XRF core scanning for tephrochronology based on the analysis of three gyttja-rich sediment cores from the Faroe Islands. Using a combination of optical and radiographic images, analytical parameters and elemental profiles (Si, K, Ca, Ti, Mn, Fe, Sr and Zr), higher concentration basaltic tephra layers (>1000 shards/cm3) were positively identified. The XRF core scanning did not capture the lower concentration (<850 shards/cm3) rhyolitic layers found in the core. The elemental data generated for the detected tephra layers using XRF core scanning was not comparable to individual shard analysis by electron microprobe. We recommend using XRF core scanning for tephra screening in order to localize depths for high-resolution subsampling and to avoid depths where sediment mixing has caused tailing/mixing of the tephra signal. At the studied site the basaltic Saksunarvatn ash as well as a tephra belonging to the Askja-S/10 ka eruption were identified.

  • 12.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    A ~500 ky sedimentary record of late Quaternary climatic variability from the southern South China Sea2007Ingår i: 17th SASQUA Congress, April 10-13, Howick, South Africa, 2007Konferensbidrag (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    The position of the South China Sea between the world’s largest land mass and the largest ocean, bridging different climate zones, makes it very susceptible to climatic variations. The summer and winter monsoons, sea level/global ice volume, and insolation exert a strong control on seasonal winds, precipitation and run-off patterns, and the character of land vegetation. Thus, the sediments in the basin provide not only exquisite Quaternary paleoceanographic records, but also records of surrounding continental climate changes. A growing amount of evidence suggests that the tropics play an important role in the global climate system through their influence on the global heat and moisture budgets, as convincingly demonstrated by the El Niño-Southern Oscillation phenomenon.

    Here we present records from MIS 1-12 from the southeastern South China Sea (MD972142). The results show a clear glacial-interglacial eccentricity signal in most measured parameters, while some parameters display the presence of obliquity and precession cyclicity superimposed on the longer cycles. In particular, differences in the isotopic composition of the two planktic foraminifers G. ruber and N. dutertrei show a very clear precessional pattern, indicating that the surface layers of the South China Sea are very sensitive to changes in the monsoon system, ITCZ, and possibly variations in El Niño frequency and intensity.

  • 13.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Ethological analysis of the trace fossil Zoophycos: Hints from the Arctic Ocean2012Ingår i: Lethaia: an international journal of palaeontology and stratigraphy, ISSN 0024-1164, E-ISSN 1502-3931, Vol. 45, nr 2, s. 290-298Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The distribution of the trace fossil Zoophycos in Quaternary marine sediments from the Arctic Ocean was studied in twelve piston and gravity cores retrieved during the Swedish icebreaker expeditions YMER80, Arctic Ocean-96 and LOMROG I & II. The sampled cores span an area from the Makarov Basin to the Fram Strait. Zoophycos was only found in two cores taken at more than 2 km water depth on the slope of the Lomonosov Ridge, but was absent in cores obtained at shallower depth, confirming earlier observations of the trace maker’s bathymetric preferences. The two cores containing Zoophycos are characterized by quiet sedimentation and slightly enhanced food flux compared with the general Arctic. The occurrence of Zoophycos in these cores in a setting that is characterized by extreme seasonal variations in food flux due to the total ice coverage during winters and high primary productivity during the long summer days, is interpreted to be a cache-behaviour response to pulsed flux of food to the benthic realm. □Arctic Ocean, ethology, Quaternary, spreiten, trace fossils, Zoophycos.

  • 14.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Chen, H. -F
    Yang, T. -N
    Kylander, Malin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Yu, E. -F
    Hsu, Y. -W
    Lee, T. -Q
    Song, S. -R
    Jarvis, S.
    Normalizing XRF-scanner data: A cautionary note on the interpretation of high-resolution records from organic-rich lakes2011Ingår i: Journal of Asian Earth Sciences, ISSN 1367-9120, E-ISSN 1878-5786, Vol. 40, nr 6, s. 1250-1256Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    X-ray fluorescence (XRF) scanning of unlithified, untreated sediment cores is becoming an increasingly common method used to obtain paleoproxy data from lake records. XRF-scanning is fast and delivers high-resolution records of relative variations in the elemental composition of the sediment. However, lake sediments display extreme variations in their organic matter content, which can vary from just a few percent to well over 50%. As XRF scanners are largely insensitive to organic material in the sediment, increasing levels of organic material effectively dilute those components that can be measured, such as the lithogenic material (the closed-sum effect). Consequently, in sediments with large variations in organic material, the measured variations in an element will to a large extent mirror the changes in organic material. It is therefore necessary to normalize the elements in the lithogenic component of the sediment against a conservative element to allow changes in the input of the elements to be addressed. In this study we show that Al, which is the lightest element that can be measured using the Wax XRF-scanner, can be used to effectively normalize the elements of the lithogenic fraction of the sediment against variations in organic content. We also show that care must be taken when choosing resolution and exposure time to ensure optimal output from the measurements.

  • 15.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Mörth, Carl Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Backman, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Arctic Ocean manganese contents and sediment color cycles2008Ingår i: Polar Research, Vol. 27, s. 105-113Artikel i tidskrift (Refereegranskat)
  • 16.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Mörth, Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Backman, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Arctic Ocean manganese contents and sediment colour cycles2008Ingår i: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 27, nr 2, s. 105-113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cyclical variations in colour and Mn content in sediments from the central Arctic Ocean have been interpreted to represent climatically controlled changes in the input of Mn from the Siberian hinterland and/or variations in the intermediate and deep water ventilation of the Arctic basins, although a diagenetic origin has not been excluded. A reinvestigation of core 96/12-1pc using an Itrax XRF core scanner confirms that these colour cycles are indeed controlled by variations in Mn content, although changes in the source region of the sediment may override the Mn-colour signal in certain intervals. The prominent Mn cycles show no correspondence to any of the other measured elements. This decoupling of the Mn and the bulk chemistry of the sediment is taken to indicate that the cycles observed are caused by variations in water column ventilation and riverine input rather than variations in sediment source or diagenesis. We therefore conclude that the Mn cycles do represent warm phases with increased ventilation and/or riverine input, and that they therefore could be used for chronostratigraphic correlation between cores from the central Arctic Ocean where traditional isotope stratigraphy is difficult or impossible to establish due to the lack of calcareous microfossils.

  • 17.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Mörth, Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Backman, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Arctic Ocean Mn contents and Sediment Colour Cycles2008Konferensbidrag (Övrigt vetenskapligt)
  • 18.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi. Marin geovetenskap.
    Konstantinou, Konstantinos
    Steinke, Stephan
    Bias in foraminiferal multispecies reconstructions of paleohydrographic conditions caused by foraminiferal abundance variations and bioturbational mixing: A model approach2008Ingår i: Marine GeologyArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    A simple box model was applied to study the combined effect of bioturbation and foraminiferal abundance variations using synthetic isotope records constructed from the Greenland oxygen isotope record (GISP2). Apart from the well known general smoothing of the signal, the attenuation of peak heights, and the up- or downwards shift of the proxy records at intervals of changing abundance, the modeling results draw attention to two effects of special importance to climatic reconstructions based on the comparison of proxy signals from two or more planktonic foraminifer species. First, the bioturbational mixing of tests out of abundance maxima and into over- and underlying sediment can lead to the introduction of stratigraphic shifts between different species when species with opposing abundance patterns are used. This shifting of the signals can easily result in apparent increases or decreases in the isotopic gradients between different species, especially at intervals of rapidly changing climate conditions. Second, in intervals with rapidly changing environmental conditions, such as Dansgaard-Oeschger cycles, where species with different preferences often show opposing abundance patterns, the mixing of foraminifer tests out of their respective abundance maxima can result in a general, but artificial, offset between the two species. This offset then may disappear during intervals of slower variability. These artifacts have the potential of seriously biasing any paleoceanographic and paleoclimatic reconstructions based on multispecies analysis where the studied species show opposing abundance patterns. It is therefore highly recommended that species with as low abundance variations as possible, or at least with similar abundance variations, are used whenever multispecies reconstructions are attempted.

  • 19.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi. Marin geovetenskap.
    Lin, In-Tian
    Wang, Chung-Ho
    Schönfeld, Joachim
    A test of the gardening hypothesis as behavioral explanation for the Zoophycos trace2008Ingår i: Sediment-Organism Interactions: A Multifaceted Ichnology, SEPM, Tulsa , 2008, s. 79–86-Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    The trace fossil Zoophycos has long been considered an archetypical example of a deposit-feeding trace. The important discovery that at least some types of Zoophycos actively introduce surface material into the burrow sparked a new interest in alternative ethological explanations. Recently proposed ethological explanations for the trace fossil Zoophycos include gardening of microorganisms. In the gardening model, organic rich material is collected on the sediment surface and introduced into the burrow as substrate for the cultivation of microorganisms. Because microorganisms are known to fractionate strongly against 13C, especially under low oxic to anoxic conditions, it is argued that any gardening activity in the trace would result in a noticeable shift in d13Corg between spreiten and adjacent host sediment. In order to test this hypothesis, d13Corg of spreiten material and directly adjacent host material was measured in 12 host-spreite couples from three cores from the eastern North Atlantic. The results show d13Corg values ranging from –23.6 to –21.6 ‰ for host sediment and between –23.4 and –21.8 ‰ for Zoophycos material. The difference in the couples is usually only a few tenths of a permil. The minimal difference between Zoophycos and host material suggests that gardening plays an insignificant role. However, the trace material generally displays a significant enrichment in organic carbon compared to surrounding host sediment. Therefore, the gardening hypothesis is rejected in favor of a cache model, where food is squirreled away for poorer times.

  • 20.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Mellqvist, Matteo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Cyclic variations in the ventilation of the central Arctic Ocean recorded by trace fossils2008Konferensbidrag (Övrigt vetenskapligt)
  • 21.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi. Marin geovetenskap.
    Mellqvist, Matteo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi. Marin geovetenskap.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi. Marin geovetenskap.
    Stratigraphic correlation in the Arctic Ocean using Mn Cycles2008Ingår i: IGC, Oslo, 2008Konferensbidrag (Övrigt vetenskapligt)
  • 22.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Mellqvist, Matteo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Strand, Kari
    Tessier, Heather
    Jakobsson, Martin
    A catastrophic flooding event in the Arctic Ocean2009Ingår i: Annual Congress of Chinese Geophical Society and Geological Society of Taiwan, May 2009, 2009Konferensbidrag (Refereegranskat)
  • 23.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Mellqvist, Matteo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Strand, Kari
    Tessier, Heather
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Evidence for a catastrophic flooding of the Arctic Ocean during MIS 42009Ingår i: APEX, Copenhagen, Denmark, March-April 2009, 2009Konferensbidrag (Refereegranskat)
  • 24.
    Löwemark, Ludvig
    et al.
    Stockholms universitet.
    Müller, Anne
    Steinke, Stephan
    Wang, Chung-Ho
    Chen, Min-Te
    Shiau, Liang-Jian
    Kao, Shuh-Ji
    Song, Sheng-Rong
    Lin, Hui-Ling
    Wei, Kuo-Yen
    Glacio-eustatic influence on deep water circulation in the South China Sea over the past 500 kyrs – implications for global biogeochemical cycling2008Ingår i: Western Pacific Geophysics Meeting, American Geophysical Union, Cairns, Australia, July/August 2008, 2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We provide new evidence for the development of a stable estuarine

    circulation characterized by stagnating water bodies, nutrient recycling and increased primary productivity in the South China Sea

    during glacial intervals caused by the closure of the shallow and

    narrow straits connecting the South China Sea in the south and west. Our main evidence comes from records of Mn concentrations and Mn/Al ratios in two sedimentary cores from the northern and southeastern South China Sea covering the last 500 ky. Concentrations and Mn/Al ratios of the redox sensitive element Mn show clear glacial-interglacial cycles with maxima during interglacial periods and minima during glacial periods. These cycles indicate ventilation cycles of the bottom water connected to the glacial-interglacial changes in sea level. In contrast, total organic carbon (TOC) concentrations display an opposite pattern with pronounced maxima during glacial times, especially in the southern part of the basin. The variations in TOC can be ascribed to two factors. Firstly to variations in primary productivity controlled by variations in the

    intensity of the winter monsoon. Secondly to the degree of preservation of TOC controlled by variations in ventilation, ultimately controlled by sea level. Variations in TOC consequently

    represent a superimposition of sea level influenced preservation

    control and primarily winter monsoon driven variations in primary

    productivity intensity. The decrease in Mn correspond to times when sea level dropped below 40-50 m. Larger amplitude of the variations in TOC and Mn in the southern part of the basin compared to the northern sites suggest that oxygen depletion and nutrient recycling was stronger in the parts of the basin situated the furthest from the only remaining opening to the open Pacific, the Luzon strait.

  • 25.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi. Marin geovetenskap.
    Müller, Anne
    Steinke, Stephan
    Wang, Chung-Ho
    Chen, Min-Te
    Shiau, Liang-Jian
    Kao, Shuh-Ji
    Song, Sheng-Rong
    Lin, Hui-Ling
    Wei, Kuo-Yen
    New evidence of a glacioeustatic influence on deep water circulation, bottom water ventilation and primary productivity in the South China Sea2008Ingår i: 5th Asia Oceania Geoscience Society Annual Conference 2008, Busan, Korea, June 2008, 2008Konferensbidrag (Övrigt vetenskapligt)
  • 26.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Nara, Masakazu
    Morphological variability of the trace fossil Schaubcylindrichnus coronus as a response to environmental forcing2013Ingår i: PALAEONTOLIA ELECTRONICA, ISSN 1935-3952, Vol. 16, nr 1, s. 5A-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Schaubcylindrichnus is an important trace fossil used in the characterization of offshore and shoreface depositional environments. Our understanding of this trace has followed a winding path including the introduction of several new ichnospecies and the subsequent recent synonymization into one ichnospecies. Likewise, our understanding of the ethological interpretation of the trace fossil has evolved from gregarious head-down deposit feeders to filter feeders, until it recently was shown that the tracemaker probably was a funnel feeder. Although several ichnospecies were recently synonymized into one ichnospecies, Schaubcylindrichnus coronus, variability in the number of tubes per sheaf and abundance of nested tubes, i.e., tubes that break up older tubes, were observed between different settings. These differences were studied in close detail at Miocene outcrops in Japan and Taiwan where the trace fossil occurs copiously and therefore allows the intraspecific morphological variability to be addressed. Around 2000 specimens from Japan and Taiwan were studied. The results show a distinct tendency for higher tube numbers in the offshore facies where sediments are characterized by higher silt/mud content, suggesting that S. coronus with higher tube numbers were constructed in a calm environment allowing longer dwelling periods. The increased abundance of nested tubes in settings characterized by thin sand layers indicate that the nested tubes are a reparation response to erosional events destroying the feeding funnels at the sediment-water interface. Consequently, tube number per sheaf and abundance of nested tubes may be used to further characterize the depositional environment in shoreface to offshore facies.

  • 27.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Nara, Masakazu
    Morphology, ethology and taxonomy of the ichnogenus Schaubcylindrichnus: Notes for clarification2010Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 297, nr 1, s. 184-187Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two recent publications dealing with the trace fossil Schaubcylindrichnus (Frey and Howard, 1981) in Cenozoic outcrops have been published independently in the same year (Löwemark and Hong, 2006; Nara, 2006). The two studies came to similar conclusions regarding morphology, somewhat different conclusions with respect to the behavior of the trace maker, and diametrically opposed conclusions regarding the ichnotaxonomy. The two studies (Löwemark & Hong, 2006; Nara, 2006) were published in parallel without taking the other into consideration. During the 2nd International Ichnological Congress in Krakow 2008 the authors had the opportunity to compare their results (Löwemark and Nara, 2008). We therefore feel that a clarifying note is timely.

    Morphologically, S. coronus is shown to typically consist of three distinct parts: a bundle of thickly lined, often crossing tubes that have been constructed after each other, a feeding funnel connected to one end of the burrow system, and a fecal mound connected to the other end (Nara, 2006). Löwemark & Hong (2006) introduced a new ichnospecies, S. formosus, based on the differences in morphology to the original description of S. coronus that outlined a congruent bundle as the typical form. However, subsequent comparison of S. formosus with Nara's (2006) descriptions of S. coronus showed that the former can be accommodated in the latter. S. formosus therefore should be considered as a junior synonym of S. coronus and be abandoned.

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  • 28.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Alfred Wegener Institute for Polar and Marine Research, Climate Science Division, Germany.
    O'Regan, Matthew
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Cardiff University, UK.
    Hanebuth, T. J. J.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Late Quaternary spatial and temporal variability in Arctic deep-sea bioturbation and its relation to Mn cycles2012Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 365-366, s. 192-208Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Changes in intensity and composition of bioturbation and trace fossils in deep-sea settings are directly related to changes in environmental parameters such as food availability, bottom water oxygenation, or substrate consistency. Because trace fossils are practically always preserved in situ, and are often present in environments where other environmental indicators are scarce or may have been compromised or removed by diagenetic processes, the trace fossils provide an important source of paleoenvironmental information in regions such as the deep Arctic Ocean. Detailed analysis of X-ray radiographs from 12 piston and gravity cores from a transect spanning from the Makarov Basin to the Yermak Plateau via the Lomonosov Ridge, the Morris Jesup Rise, and the Gakkel Ridge reveal both spatial and temporal variations in an ichnofauna consisting of ChondritesNereitesPhycosiphonPlanolitesScoliciaTrichichnusZoophycos, as well as deformational biogenic structures. The spatial variability in abundance and diversity is in close correspondence to observed patterns in the distribution of modern benthos, suggesting that food availability and food flux to the sea floor are the most important parameters controlling variations in bioturbation in the Arctic Ocean. The most diverse ichnofaunas were observed at sites on the central Lomonosov Ridge that today have partially ice free conditions and relatively high summer productivity. In contrast, the most sparse ichnofauna was observed in the ice-infested region on the Lomonosov Ridge north of Greenland. Since primary productivity, and therefore also the food flux at a certain location, is ultimately controlled by the geographical position in relation to ice margin and the continental shelves, temporal variations in abundance and diversity of trace fossils have the potential to reveal changes in food flux, and consequently sea ice conditions on glacial–interglacial time scales. Down core analysis reveal clearly increased abundance and diversity during interglacial/interstadial intervals that were identified through strongly enhanced Mn levels and the presence of micro- and nannofossils. Warm stages are characterized by larger trace fossils such as ScoliciaPlanolites or Nereites, while cold stages typically display an ichnofauna dominated by small deep penetrating trace fossils such as Chondrites or Trichichnus. The presence of biogenic structures in glacial intervals clearly show that the Arctic deep waters must have remained fairly well ventilated also during glacials, thereby lending support to the hypothesis that the conspicuous brown layers rich in Mn which are found ubiquitously over the Arctic basins are related to input from rivers and coastal erosion during sea level high-stands rather than redox processes in the water column and on the sea floor. However, the X-ray radiograph study also revealed the presence of apparently post-sedimentary, diagenetically formed Mn-layers which are not directly related to Mn input from rivers and shelves. These observations thus bolster the hypothesis that the bioturbated, brownish Mn-rich layers can be used for stratigraphic correlation over large distances in the Arctic Ocean, but only if post sedimentary diagenetic layers can be identified and accounted for in the Mn-cycle stratigraphy.

  • 29.
    Löwemark, Ludvig
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Steinke, S
    Wang, C.-H.
    Chen, M.-T.
    Müller, A.
    Shiau, L.-J.
    Kao, S.-J.
    Song, S.-R.
    Lin, H.-L.
    Wei, K.-Y.
    New evidence for a glacioeustatic influence on deep watercirculation, bottom water ventilation and primaryproductivity in the South China Sea2009Ingår i: Dynamics of atmospheres and oceans (Print), ISSN 0377-0265, E-ISSN 1872-6879, Vol. 47, nr 1-3, s. 138-153Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We provide new evidence for the development of a stable estuarinecirculation characterized by stagnating water bodies, nutrientrecycling and increased primary productivity in the South ChinaSea (SCS) during glacial intervals. This circulation was caused bythe closure of the shallow and narrow straits connecting the SCSin the south and west. Our main evidence is derived from newlymeasured Mn concentrations and Mn/Al ratios in two sedimentcores from the northern and southeastern SCS covering the last500 ky. Concentrations and Mn/Al ratios of the redox sensitive elementMnshowclearglacial–interglacial cycles with maxima duringinterglacial periods and minima during glacial periods. These cyclesindicate ventilation cycles of the bottom water, and are connectedto the glacial–interglacial changes in sea level. In contrast, totalorganic carbon (TOC) concentrations display an opposite patternwith pronounced maxima during glacial times, especially in thesouthern part of the basin. The variations in TOC can be ascribed totwo factors. Firstly, variations in primary productivity are controlledby variations in the intensity of the winter monsoon. Secondlyto the degree of preservation of TOC controlled by variations inventilation, which in turn is ultimately controlled by sea level.

    Consequently, variations in TOC represent a superimposition ofprimarily sea level influenced preservation control and wintermonsoon driven variations in primary productivity intensity. Thedecrease in Mn correspond to times when sea level dropped40–60m below the present level. The larger amplitude of the variationsin TOC and Mn in the southern part of the basin compared tothe northern site suggest that oxygen depletion and nutrient recyclingwas stronger in the parts of the basin situated the furthest away from the only remaining opening to the open Pacific, the LuzonStrait.

  • 30. Mellquist, M.
    et al.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Itrax XRF-core scanner data provide new evidence for a mega event in the Arctic Ocean in cores from the YMER-80, ARCTIC OCEAN-96 and LOMROG-07 expeditions2008Ingår i: Transactions, American Geophysical Union, v. 89(53): Fall Meet. Suppl., 2008, s. Abstract PP51A-1481Konferensbidrag (Övrigt vetenskapligt)
  • 31. Rodriguez-Tovar, Francisco J.
    et al.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Pardo-Iguzquiza, Eulogio
    Zoophycos cyclicity during the last 425 ka in the northeastern South China Sea: Evidence for monsoon fluctuation at the Milankovitch scale2011Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 305, nr 1-4, s. 256-263Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In a deep-sea piston core, covering the last 425 ka from the northeastern South China Sea, power spectrum analysis of several core data from sediment parameters has been conducted and compared with that obtained from time-series analysis of the distribution of the trace fossil Zoophycos through the core. Power spectra show a more or less well developed cyclical pattern, with similar cyclostratigraphic patterns for sand and carbonate content, oxygen isotopes and Zoophycos distribution, but different for carbon isotopes and total organic carbon content (TOC). Temporal calibration allows the recognition of Milankovitch orbital-scale cycles, with a duration of 111-100 ka for short-term eccentricity, 63-55 ka for the combined effect of both precession and obliquity, 42-40 ka for the obliquity cycle, and 28-21 ka for the precessional cycle band. The variable Milankovitch-scale cyclicity suggests the influence of a complex interaction of variable processes. East Asian monsoon variability at the Milankovitch orbital-scale cycles could determine variations in environmental conditions, including changes in the organic material reaching the sea floor, and in turn influencing the cyclical occurrence of the Zoophycos trace makers. The cyclicity of Zoophycos is of special interest to basin analysis, where Zoophycos has the potential of being used as a proxy for cyclical monsoon fluctuations at the Milankovitch scale.

  • 32. Rogerson, Mike
    et al.
    Colmenero-Hidalgo, Elena
    Levine, R.C.
    Rohling, E.J.
    Bigg, G.R.
    Schönfeld, Joachim
    Cacho, I
    Sierro, F.J.
    Völker, Antje
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Reguera, M.I.
    de Abreu, L.
    Garrick, K.
    Enhanced Mediterranean-Atlantic exchange during Atlantic freshening phases2010Ingår i: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 11, nr 8, s. Q08013-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Atlantic-Mediterranean exchange of water at Gibraltar represents a significant heat and freshwater sink for the North Atlantic and is a major control on the heat, salt and freshwater budgets of the Mediterranean Sea. Consequently, an understanding of the response of the exchange system to external changes is vital to a full comprehension of the hydrographic responses in both ocean basins. Here, we use a synthesis of empirical (oxygen isotope, planktonic foraminiferal assemblage) and modeling (analytical and general circulation) approaches to investigate the response of the Gibraltar Exchange system to Atlantic freshening during Heinrich Stadials (HSs). HSs display relatively flat W–E surface hydrographic gradients more comparable to the Late Holocene than the Last Glacial Maximum. This is significant, as it implies a similar state of surface circulation during these periods and a different state during the Last Glacial Maximum. During HS1, the gradient may have collapsed altogether, implying very strong water column stratification and a single thermal and δ18Owater condition in surface water extending from southern Portugal to the eastern Alboran Sea. Together, these observations imply that inflow of Atlantic water into the Mediterranean was significantly increased during HS periods compared to background glacial conditions. Modeling efforts confirm that this is a predictable consequence of freshening North Atlantic surface water with iceberg meltwater and indicate that the enhanced exchange condition would last until the cessation of anomalous freshwater supply into to the northern North Atlantic. The close coupling of dynamics at Gibraltar Exchange with the Atlantic freshwater system provides an explanation for observations of increased Mediterranean Outflow activity during HS periods and also during the last deglaciation. This coupling is also significant to global ocean dynamics, as it causes density enhancement of the Atlantic water column via the Gibraltar Exchange to be inversely related to North Atlantic surface salinity. Consequently, Mediterranean enhancement of the Atlantic Meridional Overturning Circulation will be greatest when the overturning itself is at its weakest, a potentially critical negative feedback to Atlantic buoyancy change during times of ice sheet collapse.

  • 33. Steinke, Stephan
    et al.
    Groeneveld, J
    Mohtadi, M
    Lin, L.-C.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Chen, M.-T.
    Rendle-Buehring, R
    Reconstructing the southern South China Sea upper water column structure since the Last Glacial Maximum: Implications for the East Asian winter monsoon development2010Ingår i: Paleoceanography, ISSN 0883-8305, E-ISSN 1944-9186, Vol. 25, s. PA2219-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Upper water column dynamics in the southern South China Sea were reconstructed in order to track changes in the activity of the East Asian winter monsoon (EAWM) since the Last Glacial Maximum. We used the difference in the stable oxygen isotopes (Δδ18O) and Mg/Ca-based temperatures (ΔT) of surface-dwelling (G. ruber) and thermocline-dwelling (P. obliquiloculata) planktonic foraminifera and the temperature difference between alkenone- and P. obliquiloculata Mg/Ca-based temperatures to estimate the upper ocean thermal gradient at International Marine Past Global Change Study (IMAGES) core MD01-2390. Estimates of the upper ocean thermal gradient were used to reconstruct mixed layer dynamics. We find that our Δδ18O estimates are biased by changes in salinity and, thus, do not display a true upper ocean thermal gradient. The ΔT of G. ruber and P. obliquiloculata as well as the alkenone and P. obliquiloculata suggest increased surface water mixing during the late glacial, likely due to enhanced EAWM winds. Surface water mixing was weaker during the late Holocene, indicating a weaker influence of winter monsoon winds. The weakest winter monsoon activity occurred between 6.5 ka and 2.5 ka. Inferred EAWM changes since the Last Glacial Maximum coincide with EAWM changes as recorded in Chinese loess sediments. We find that the intensity of the EAWM and the East Asian summer monsoon show an inverse behavior during the last glacial and deglaciation but covaried during the middle to late Holocene.

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  • 34. Virtasalo, Joonas J.
    et al.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Papunenen, Heikki
    Kotilainen, Aarno T.
    Whitehouse, Martin J.
    Pyritic and baritic burrows and microbial filaments in postglacial lacustrine clays in the northern Baltic Sea2010Ingår i: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 167, nr 6, s. 1185-1198Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Holocene postglacial lacustrine clays in the northern Baltic Sea were studied for ichnofossils,petrography, and microscale elemental and 34S/32S composition to understand the impact of benthos-producedorganic matrices on the early diagenesis of sediments. X-radiographs of these clays display intense burrowmottling with discrete Palaeophycus, ‘Mycellia’ and rare Arenicolites. Small burrow-like and irregularlyshaped concretions were separated from these clays. The burrow-like concretions are composed of framboidalpyrite and poorly crystalline FeS2 cement. They formed within worm-produced burrows by the decompositionof mucous coatings on the burrow walls by sulphate reduction. 34SCDT composition of the framboidsindicates saline inflows from the North Sea as the sulphate source. The irregular concretions are microcrystallinepyritic masses that formed in pore spaces with less reactive organic compounds. Their 34SCDT valuesreflect precipitation from the ambient porewater sulphate by sulphate reduction. The burrow-like and irregularconcretions are microcrystalline barite in the lower parts of the clays. ‘Mycellia’ are mineral-replacedfilaments produced by large sulphur-oxidizing bacteria or mycelial fungi. They concentrate in monosulphidebands in the lower substrate levels, but are associated with organic patches upward. This study demonstratesthat substantial amounts of pyrite formed within organic matrices close to the sediment–water interface. Thisdiffers from previous studies that proposed a deeper-burial origin and allochthonous sulphur source.

  • 35.
    Wohlfarth, Barbara
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Klubseang, Wichuratree
    Inthongkaew, Suda
    Fritz, Sherilyn C.
    Blaauw, Maarten
    Reimer, Paula J.
    Chabangborn, Akkaneewut
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Chawchai, Sakonvan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Holocene environmental changes in Northeast Thailand as reconstructed from a tropical wetland2012Ingår i: Global and Planetary Change, ISSN 0921-8181, E-ISSN 1872-6364, Vol. 92-93, s. 148-161Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Geochemical variables (TOC, C/N, TS, delta C-13) and diatom assemblages were analyzed in a lake sediment sequence from Nong (Lake) Han Kumphawapi in northeast Thailand to reconstruct regional climatic and environmental history during the Holocene. By around c. 10,000-9400 cal yr BP, a large shallow freshwater lake had formed in the Kumphawapi basin. Oxygenated bottom waters and a well-mixed water column were characteristic of this early lake stage, which was probably initiated by higher effective moisture and a stronger summer monsoon. Decreased run-off after c. 6700 cal yr BP favored increased aquatic productivity in the shallow lake. Multiple proxies indicate a marked lowering of the lake level around 5900 cal yr BP, the development of an extensive wetland around 5400 cal yr BP, and the subsequent transition to a peatland. The shift from shallow lake to wetland and later to a peatland is interpreted as a response to lower effective moisture. A hiatus at the transition from wetland to peatland suggests very low accumulation rates, which may result from very dry climatic conditions. A rise in groundwater and lake level around 3200 cal yr BP allowed the re-establishment of a wetland in the Kumphawapi basin. However, the sediments deposited between c. 3200 and 1600 cal yr BP provide evidence for at least two hiatuses at c. 2700-2500 cal yr BP, and at c. 1900-1600 cal yr BP, which would suggest surface dryness and consequently periods of low effective moisture. Around 1600 cal yr BP a new shallow lake became re-established in the basin. Although the underlying causes for this new lake phase remain unclear, we hypothesize that higher effective moisture was the main driving force. This shallow lake phase continued up to the present but was interrupted by higher nutrient fluxes to the lake around 1000-600 cal yr BP. Whether this was caused by intensified human impact in the catchment or, whether this signals a lowering of the lake level due to reduced effective moisture, needs to be corroborated by further studies in the region. The multi-proxy study of Kumphawapi's sediment core CP3A clearly shows that Kumphawapi is a sensitive archive for recording past shifts in effective moisture, and as such in the intensity of the Asian summer monsoon. Many more continental paleorecords, however, will be needed to fully understand the spatial and temporal patterns of past changes in Asian monsoon intensity and its ecosystem impacts.

  • 36. Yang, Tien-Nan
    et al.
    Lee, Teh-Quei
    Meyers, Philip A.
    Song, Sheng-Rong
    Kao, Shuh-Ji
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Chen, Rou-Fei
    Chen, Huei-Fen
    Wei, Kuo-Yen
    Fan, Cheng-Wei
    Shiau, Liang-Jian
    Chiang, Hong-Wei
    Chen, Yue-Gau
    Chen, Min-Te
    Variations in monsoonal rainfall over the last 21 kyr inferred from sedimentary organic matter in Tung-Yuan Pond, southern Taiwan2011Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, nr 23-24, s. 3413-3422Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Changes in paleorainfall intensity linked to the strength of the East Asian (EA) summer monsoon since 21 cal kyr BP are inferred from the organic matter contents of a 15-m sediment core from Tung-Yuan Pond in southern Taiwan. High total organic carbon/total nitrogen (TOC/TN) values in association with increased TOC content suggest that more soil-derived material containing terrestrial organic matter (OM) was delivered to the lake during periods of increased runoff associated with extensive precipitation that resulted from intensified summer monsoons, whereas low values indicate OM possessing a dominant algal origin during weakened summer monsoons. Rainfall intensity in terms of the proportion of terrestrial OM was high in four periods: the last deglaciation (similar to 17.2 to similar to 12.2 ka), the early Holocene (similar to 10.6 to similar to 8.6 ka), the middle Holocene Thermal Optimum (similar to 7.7 to similar to 5 ka) and the late Holocene (similar to 4.2 to similar to 2 ka), whereas it was low in the intervening time periods. High TOC/TN values coincide with peak values of summer insolation, and thus the strongest EA summer monsoon during the early and middle Holocene: small drops in these ratios correspond to increasing and decreasing solar radiation in the deglacial period and the late Holocene, respectively. The four intervals with low TOC/TN ratios, as well as episodic drops of the ratios during the deglaciation and the early and late Holocene are concordant with the late last glacial (similar to 21 to similar to 17.2 ka), the Oldest (similar to 14.8 ka), the Older (similar to 13.3 ka) and the Younger Dryas (similar to 13 to similar to 11.5 ka), the 8.2 cold event (similar to 8.6-7.7 ka) and a late Holocene cold event (similar to 5-4.2 ka), and suggest a weakened EA summer monsoon during these times. Moreover, high frequency hydrological variability occurred during the early Holocene, heavy rainfall persisted during the middle Holocene, and precipitation intensity generally diminished after similar to 5 ka. The Tung-Yuan Pond sediment record indicates that the TOC/TN ratio can be used as a paleorainfall intensity proxy to trace variations in the EA summer monsoon strength in other small lakes. Crown Copyright

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