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  • 1. Agnini, C
    et al.
    Fornaciari, E
    Rio, D
    Tateo, F
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Giusberti, L
    Responses of calcareous nannofossil assemblages, mineralogy and geochemistry to the environmental pertubartions across the Paleocene/Eocene boundary in the Venetian Pre-Alps2007In: Marine micropaleontology, Vol. 63Article in journal (Refereed)
  • 2.
    Agnini, Claudia
    et al.
    University of Padova.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    An early Eocene carbon cycle perturbation at ~52.5 Ma from the southern Alps: Chronology and biotic response2009In: Paleoceanography, ISSN 0883-8305, E-ISSN 1944-9186, Vol. 24, no PA2209, p. 1-14Article in journal (Refereed)
  • 3.
    Agnini, Claudia
    et al.
    University of Padova.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    It Paleognee inferiore in facies pelagica ne Venetor nord-orientalie2009In: Rendiconto online Soc. Geol. It, Vol. 4, p. 5-12Article in journal (Refereed)
  • 4. Agnini, Claudia
    et al.
    Fornaciari, Eliana
    Raffi, Isabella
    Catanzariti, Rita
    Paelike, Heiko
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Rio, Domenico
    Biozonation and biochronology of Paleogene calcareous nannofossils from low and middle latitudes2014In: Newsletters on stratigraphy, ISSN 0078-0421, Vol. 47, no 2, p. 131-181Article in journal (Refereed)
    Abstract [en]

    Calcareous nannofossils have provided a powerful biostratigraphic tool since the 1950's and 1960's, when several milestone papers began to highlight their potential use in dating Cenozoic sediments and rocks. Here, we present a new calcareous nannofossil biozonation for the Paleogene Period, which is based on biostratigraphic data collected during the past 30 years. Semi-quantitative counting methods applied on DSDP/ODP drill sites and marine on-land sections have been used to demonstrate the details of the abundance patterns of each biostratigraphically useful calcareous nannofossil taxon. This new biozonation still partly relies on older biozonations and thus represents an integration between those classical biohorizons that proved reliable and new biohorizons proposed as substitutes for bioevents considered problematic. Thirty-eight new Paleogene biozones are proposed using a new code system: 11 Paleocene biozones (CNP1-CNP11), 21 Eocene biozones (CNE1-CNE21) and 6 Oligocene biozones (CNO1-CNO6). The new scheme uses a limited number of biohorizons, one for each biozone boundary, which guarantees more stability although with a coarser resolution. A series of additional biohorizons are included in almost every biozone. This new Paleogene biozonation has an average duration of 1.1 Myr per biozone, ranging from 0.9 Myr in the Paleocene, to 1.0 Myr in the Eocene, and 1.8 Myr in the Oligocene. Age estimates provided for calcareous nannofossil biohorizons are calculated using both magnetostratigraphic and astronomically tuned cyclostratigraphic data.

  • 5. Alexanderson, Helena
    et al.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cronin, Thomas M.
    Funder, Svend
    Ingólfsson, Ólafur
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Landvik, Jon Y.
    Löwemark, Ludvig
    Mangerud, Jan
    März, Christian
    Möller, Per
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Spielhagen, Robert F.
    An Arctic perspective on dating Mid-Late Pleistocene environmental history2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, p. 9-31Article in journal (Refereed)
    Abstract [en]

    To better understand Pleistocene climatic changes in the Arctic, integrated palaeoenvironmental andpalaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologicage control are required, not least for correlation to extra-Arctic records. In this paper we discuss,from an Arctic perspective, methods and correlation tools that are commonly used to date ArcticPleistocene marine and terrestrial events. We review the state of the art of Arctic geochronology, withfocus on factors that affect the possibility and quality of dating, and support this overview by examples ofapplication of modern dating methods to Arctic terrestrial and marine sequences.Event stratigraphy and numerical ages are important tools used in the Arctic to correlate fragmentedterrestrial records and to establish regional stratigraphic schemes. Age control is commonly provided byradiocarbon, luminescence or cosmogenic exposure ages. Arctic Ocean deep-sea sediment successionscan be correlated over large distances based on geochemical and physical property proxies for sedimentcomposition, patterns in palaeomagnetic records and, increasingly, biostratigraphic data. Many of theseproxies reveal cyclical patterns that provide a basis for astronomical tuning.Recent advances in dating technology, calibration and age modelling allow for measuring smallerquantities of material and to more precisely date previously undatable material (i.e. foraminifera for 14C,and single-grain luminescence). However, for much of the Pleistocene there are still limits to the resolutionof most dating methods. Consequently improving the accuracy and precision (analytical andgeological uncertainty) of dating methods through technological advances and better understanding ofprocesses are important tasks for the future. Another challenge is to better integrate marine andterrestrial records, which could be aided by targeting continental shelf and lake records, exploringproxies that occur in both settings, and by creating joint research networks that promote collaborationbetween marine and terrestrial geologists and modellers.

  • 6.
    Backman, Jan
    Stockholm University.
    Cenozoic marine microfossils from the North Pole2008In: Drilling for the Future, ECORD Workshop, May 2008, Edinburgh, 2008Conference paper (Other (popular science, discussion, etc.))
  • 7.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Fornaciari, Eliana
    University of Padova, Department of Geosciences.
    Rio, Domenico
    University of Padova, Department of Geoscience.
    Biochronology and paleoceanography of late Pleistocene and Holocene calcareous nannofossils across the Arctic Basin2009In: Marine Micropaleontology, ISSN 0377-8398, E-ISSN 1872-6186, Vol. 72, p. 86-98Article in journal (Refereed)
  • 8.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Frank, M.
    Sangiorini, F.
    Brinkhuis, H.
    Stickley, C.
    O´Regan, M.
    Løvlie, R.
    Pälike, H.
    Spofforth, D.
    Gattcecca, J.
    Moran, K.
    King, J.
    Heil, C.
    Age model and core-seismic integration for the Cenozoic Arctic Coring Expedition sediments from the Lomonosov Ridge2008In: Paleoceanography, Vol. 23, no PA1S03, p. PA1S03-Article in journal (Refereed)
  • 9.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Frank, Martin
    Sangiorgi, F
    Brinkhuis, Henk
    Sluijs, Appy
    Stickly, Catherine
    Gattacecca, Jerome
    Age/depth relationships for the ACEX sedimentary section recovered from the Lomonosov Ridge2007Conference paper (Other (popular science, discussion, etc.))
  • 10.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Rudels, B
    Moran, K
    O'Regan, M
    Moore, T
    Jokat, W
    Mayer, L.A.
    Cenozoic Depositional Regimes and the Onset of Ventilated Conditions in the Central Arctic Ocean2006In: EOS Transactions, American Geophysical Union, v. 87(52): Fall Meet. Suppl.,, 2006, p. Abstract U24A-01Conference paper (Other (popular science, discussion, etc.))
  • 11.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Moran, K.
    More, T.
    King, J.
    Gattacecca, J.
    Brinkhuis, H.
    Mathiessen, J.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Paelike, H.
    O’Regan, M.
    Frank, M.
    Kubik, P.
    Cenozoic Ridge Crest Sediments From the Central Arctic Ocean Yield cm/ka-Scale Sedimentation Rates2005In: EOS Transactions, American Geophysical Union, v. 86(52): Fall Meet. Suppl.,, 2005, p. Abstract PP51C-0607Conference paper (Other academic)
  • 12.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Moran, Kathryn
    University of Rhode Island.
    Expanding the Cenozoic paleoceanographic record in the central Arctic Ocean: IODP Expedition 302 synthesis2009In: Central European Journal of Geoscience, ISSN 1896-1517, Vol. 1, no 2, p. 157-175Article in journal (Refereed)
    Abstract [en]

    The Arctic Coring Expedition (ACEX) proved to be one of the most transformational missions in almost 40 year of scientific ocean drilling. ACEX recovered the first Cenozoic sedimentary sequence from the Arctic Ocean and extended earlier piston core records from ≈1.5 Ma back to ≈56 Ma. The results have had a major impact in paleoceanography even though the recovered sediments represents only 29% of Cenozoic time. The missing time intervals were primarily the result of two unexpected hiatuses. This important Cenozoic paleoceanographic record was reconstructed from a total of 339 m sediments. The wide range of analyses conducted on the recovered material, along with studies that integrated regional tectonics and geophysical data, produced surprising results including high Arctic Ocean surface water temperatures and a hydrologically active climate during the Paleocene Eocene Thermal Maximum (PETM), the occurrence of a fresher water Arctic in the Eocene, ice-rafted debris as old as middle Eocene, a middle Eocene environment rife with organic carbon, and ventilation of the Arctic Ocean to the North Atlantic through the Fram Strait near the early-middle Miocene boundary. Taken together, these results have transformed our view of the Cenozoic Arctic Ocean and its role in the Earth climate system.

  • 13.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Moran, Kathryn
    Introduction to special section on Cenozoic Paleoceanography of the central Arctic Ocean2008In: Paleoceanography, Vol. 23Article in journal (Refereed)
  • 14.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Moran, Kathryn
    New results from ACEX2008In: ECORD Newsletter, Vol. 10Article, review/survey (Other (popular science, discussion, etc.))
  • 15.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Raffi, Isabella
    Ciummelli, Marina
    Baldauf, Jack
    Species-specific responses of late Miocene Discoaster spp. to enhanced biosilica productivity conditions in the equatorial Pacific and the Mediterranean2013In: Geo-Marine Letters, ISSN 0276-0460, E-ISSN 1432-1157, Vol. 33, no 4, p. 285-298Article in journal (Refereed)
    Abstract [en]

    Census data of a major Cenozoic calcareous nannofossil genus (Discoaster) have been acquired from Site U1338, located near the Equator in the eastern Pacific Ocean and drilled in 2009 during Integrated Ocean Drilling Program (IODP) Expedition 321. The investigated 147.53 m thick upper Miocene sediment sequence is primarily composed of biogenic carbonate and biogenic silica. Diatom biostratigraphic data were used to develop a revised biomagnetostratigraphic age model, resulting in more variable late Miocene sedimentation rates. Carbonate content variations mainly reflect dilution by biogenic silica production, although intense carbonate dissolution affects a few shorter intervals. Abundance variations of discoasters show no distinct correlation with either carbonate or biosilica contents. The two dominant Discoaster taxa are D. brouweri and D. variabilis, except for a 12 m thick interval where D. bellus outnumbers the sum of all other discoasters by a factor of 4.6. Data presented indicate that first D. hamatus and then D. berggrenii both evolved from D. bellus. Three unusual morphotypes, here referred to as Discoaster A, B and C, increase in relative abundance during episodes of enhanced biosilica production in the upper half of the investigated sequence (Messinian). Strikingly similar morphotypes have been observed previously in Messinian age sediments from the Mediterranean, characterized by alternating deposition of biogenic carbonate and biosilica. This suggests a species-specific response among some of the late Miocene discoasters to broader oceanographic and climatic forcing that promoted episodes of enhanced deposition of biogenic silica.

  • 16.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Raffi, Isabella
    Università Chieti-Pescara.
    Rio, Domenico
    Università di Padova.
    Fornaciari, Eliana
    Università di Padova.
    Pälike, Heiko
    Universität Bremen.
    Biozonation and biochronology of Miocene through Pleistocene calcareous nannofossils from low and middle latitudes2012In: Newsletters on stratigraphy, ISSN 0078-0421, Vol. 45, no 3, p. 221-244Article in journal (Refereed)
    Abstract [en]

    Calcareous nannofossils are widely used in Cenozoic marine biostratigraphy. At present, the two most widely used calcareous nannofossil biozonations were established approximately 40 years ago. These were derived from marine land sections and Deep Sea Drilling Project rotary cored sediments. Over nearly three decades, we have generated Miocene through Pleistocene calcareous nannofossil data from deep sea sediments in low and middle latitude regions. The sediments used here have been mostly recovered using the advanced piston coring technique, generating less core disturbance and complete recovery via multiple penetration of the sediment column at single sites. A consistent trait in our work on calcareous nannofossil biostratigraphy has been to use semi-quantiative methods in combination with short sample distances, close enough to capture the details of the abundance behaviour of individual calcareous nannofossil taxa. Such data represent the foundation of the new biozonation presented here, which still partly relies on the pioneering work presented by Er lend Martini and David Bukry about 40 years ago. A key aim here has been to employ a limited set of selected biohorizons for the purpose of establishing a relatively coarsely resolved and stable biozonation. We present 31 biozones using a new code system: CNM1-CNM20; Calcareous Nannofossil Miocene biozones 1 through 20. CNPL1-CNPL11; Calcareous Nannofossil Plio-Pleistocene biozones 1 through 11. As the new biozonation encompasses 23 million years, the average biozone resolution becomes 0.74 million years, ranging from 0.15 to 2.20 million years. A single biohorizon is used for the definition of each biozone boundary. Auxiliary markers are avoided, as well as subzones, in order to maintain stability to the new biozonation. Virtually every biozone holds one or several additional biohorizons. These, together with all biozone boundary markers, are assigned age estimates derived chiefly from astronomically tuned cyclostratigraphies.

  • 17. Beltran, Catherine
    et al.
    Rousselle, Gabrielle
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wade, Bridget S.
    Sicre, Marie Alexandrine
    Paleoenvironmental conditions for the development of calcareous nannofossil acme during the late Miocene in the eastern equatorial Pacific2014In: Paleoceanography, ISSN 0883-8305, E-ISSN 1944-9186, Vol. 29, no 3, p. 210-222Article in journal (Refereed)
    Abstract [en]

    Repeated monospecific coccolithophore dominance intervals (acmes) of specimens belonging to the Noelaerhabdaceae familyincluding the genus Reticulofenestra and modern descendants Emiliania and Gephyrocapsaoccurred during the Neogene. Such acme was recognized during the late Miocene (similar to 8.6Ma), at a time of a major reorganization of nannofossil assemblages resulting in a worldwide temporary disappearance of larger forms of the genus Reticulofenestra (R. pseudoumbilicus) and the gradual recovery and dominance of its smaller forms (< 5 mu m). In this study we present a multiproxy investigation of late Miocene sediments from the east equatorial Pacific Integrated Ocean Drilling Program Site U1338 where small reticulofenestrid-type placoliths with a closed central areaknown as small Dictyococcites spp. (< 3 mu m)formed an acme. We report on oxygen and carbon stable isotope records of multispecies planktic calcite and alkenone-derived sea surface temperature. Our data indicate that, during this 100 kyr long acme, the east equatorial Pacific thermocline remained deep and stable. Local surface stratification state fails to explain this acme and thus contradicts the model-based hypothesis of a Southern Ocean high-latitude nutrient control of the surface waters in the east equatorial Pacific. Instead, our findings suggest that external forcing such as an extended period of low eccentricity may have created favorable conditions for the small Dictyococcites spp. growth. Key Points < list list-type=bulleted id=palo20081-list-0001> < list-item id=palo20081-li-0001> EEP thermocline deep during the late Miocene small Dictyococcites acme <list-item id=palo20081-li-0002>Low eccentricity favorable for the small Dictyococcites spp. growth

  • 18. Björck, S
    et al.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Bengtsson, S
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Rodhe, Henning
    Stockholm University, Faculty of Science, Department of Meteorology .
    Uttalande från klimatgruppen inom akademiens klass för geovetenskaper angående Climate Change 2007: The Physical Science Basis2007Other (Other (popular science, discussion, etc.))
    Abstract [sv]

    Björck S., Backman J., Bengtsson S., Destouni G., Rodhe H., Uttalande från klimatgruppen inom akademiens klass för geovetenskaper angående Climate Change 2007: The Physical Science Basis (Statement on Climate Change 2007: The Physical Science Basis; in Swedish), Climate Group of the Class of Geosciences at the Royal Swedish Academy of Sciences, 5 June, 2007.

  • 19. Björk, Göran
    et al.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Marin geovetenskap.
    Rudels, Bert
    Swift, Jim
    Anderson, Leif
    Darby, Dennis
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Marin geovetenskap.
    Winsor, Peter
    Polyak, Leonid
    Edwards, Margo
    Bathymetry and deep-water exchange across the central Lomonosov Ridge at 88°-89°N2007In: Deep-Sea Research I, Vol. 54, p. 1197-1208Article in journal (Refereed)
    Abstract [en]

    Seafloor mapping of the central Lomonosov Ridge using a multibeam echo-sounder during the Beringia/Healy–Oden Trans-Arctic Expedition (HOTRAX) 2005 shows that a channel across the ridge has a substantially shallower sill depth than the 2500m indicated in present bathymetric maps. The multibeam survey along the ridge crest shows a maximum sill depth of about 1870 m. A previously hypothesized exchange of deep water from the Amundsen Basin to the Makarov Basin in this area is not confirmed. On the contrary, evidence of a deep-water flow from the Makarov to the Amundsen Basin was observed, indicating the existence of a new pathway for Canadian Basin Deep Water toward the Atlantic Ocean. Sediment data show extensive current activity along the ridge crest and along the rim of a local Intra Basin within the ridge structure.

  • 20.
    Blaj, Teodora
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Raffi, Isabella
    Chieti University, Italy.
    Late Eocene to Oligocene preservation history and biochronology of calcareous nannofossils from paleo-equatorial Pacific Ocean sediments2009In: Rivista italiana di paleontologia e stratigrafia, ISSN 0035-6883, E-ISSN 2039-4942, Vol. 1, p. 67-85Article in journal (Refereed)
    Abstract [en]

    A continuous late Eocene through Oligocene carbonate sequence was recovered at Ocean Drilling Program (ODP) Site 1218 in the paleo-equatorial Pacific Ocean. The preservation history of selected calcareous nannofossil species across the Eocene/Oligocene (E/O) boundary is presented together with late Eocene and Oligocene calcareous nannofossil biochronology. The astronomically calibrated timescale of Pälike et al. (2006) is used here. Across the E/O boundary, placolith preservation is controlled by variation in carbonate content. Taxa less prone to dissolution are Reticulofenestra  umbilicus, Coccolithus  pelagicus, Ericsonia formosa and Dictyococites bisectus, while Cyclicargolithus floridanus is more susceptible to dissolution. A biochronologic framework has been established for the following taxa: the highest occurrences (HO) of Discoaster barbadiensis (34.773 Ma), D. saipanensis (34.435 Ma), E. formosa (32.919 Ma), R. umbilicus (32.021 Ma), Sphenolithus predistentus (26.928 Ma), S. distentus (26.812 Ma), and S. ciperoensis (24.432 Ma), and the lowest occurrences (LO) of S. distentus (29.997 Ma) and S. ciperoensis (27.142 Ma). The first consistent appearance of Triquetrorhabdulus carinatus occurs at 26.556 Ma, while the onset of the peak interval of T. carinatus was determined at 24.669 Ma. Biochronological comparisons are made with other sites from the Atlantic Ocean. A Triquetrorhabdulus morphotype, labeled as T. aff. carinatus, was recorded for the first time in the studied sediments, and precedes the LO of T. carinatus by ~ 0.7 Myr. Its stratigraphic range has a duration of about 3.3 Myr. T. aff. carinatus disappears concomitantly with the beginning of a sharp increase in abundance of T. carinatus.

  • 21. Capraro, L.
    et al.
    Massari, F.
    Rio, D.
    Fornaciari, E.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Channell, J. E. T.
    Macri, P.
    Prosser, G.
    Speranza, F.
    Chronology of the Lower-Middle Pleistocene succession of the south-western part of the Crotone Basin (Calabria, Southern Italy)2011In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, no 9-10, p. 1185-1200Article in journal (Refereed)
    Abstract [en]

    Biostratigraphy based on calcareous nannofossils, integrated by magnetostratigraphic, geochronological and isotopic data, allowed establishing a precise chronological framework for the Pleistocene succession within the south-western sector of the Crotone Basin (Calabria, Southern Italy), where the Pliocene-Pleistocene global stratotype section and point is defined, thus demonstrating that sedimentation was quasi-continuous during most of the Lower and Middle Pleistocene. At a large scale, the Pleistocene succession in this sector of the Crotone Basin is characterized by an evident shallowing-upwards trend, showing facies changes from bathyal to shelfal to littoral/continental. However, comparison between adjacent sectors within the investigated area demonstrates that stratigraphic architectures change vastly on very short distances. Our chronological constraints indicate that such changes in sedimentation styles probably occurred in response to differential subsidence rates, which originated tectonically-controlled synsedimentary structures where accommodation space and sediment yield were allotted unevenly. This articulated physiography led to striking differences in the overall thicknesses and organization of Pleistocene stratigraphies and, eventually, to a distinct diachroneity in the first appearance of shallow-marine deposits. In addition, superimposed are complex interplays between regional and local tectonics, eustasy and orbitally-forced climate changes. These interactions have been highlighted by the oxygen isotope stratigraphy established for a part of the studied succession, which is likely to document almost continuously the interval from Marine Isotope Stage (MIS) 26 to MIS 17. In its younger part (post-MIS 17), chronological ties are poor, as the succession is dominated by shallow-water to continental deposits showing a prominent organization into cyclothems. Nevertheless, based on the chronology of the underlying units, it is feasible that basin infill ended during MIS 15-MIS 14 times.

  • 22. Ciummelli, Marina
    et al.
    Raffi, Isabella
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Biostratigraphy and evolution of Miocene Discoaster spp. from IODP Site U1338 in the equatorial Pacific Ocean2017In: Journal of Micropalaeontology, ISSN 0262-821X, E-ISSN 2041-4978, Vol. 36, p. 137-152Article in journal (Refereed)
    Abstract [en]

    Assemblages of upper lower through upper Miocene Discoaster spp. have been quantified from Integrated Ocean Drilling Program (IODP) Site U1338 in the eastern equatorial Pacific Ocean. These assemblages can be grouped into five broad morphological categories: six-rayed with bifurcated ray tips, six-rayed with large central areas, six-rayed with pointed ray tips, five-rayed with bifurcated ray tips and five-rayed with pointed ray tips. Discoaster deflandrei dominates the assemblages prior to 15.8 Ma. The decline in abundance of D. deflandrei close to the early-middle Miocene boundary occurs together with the evolution of the D. variabilis group, including D. signus and D. exilis. Six-rayed discoasters having large central areas become a prominent member of the assemblages for a 400 ka interval in the late middle Miocene. Five-and six-rayed forms having pointed tips become prominent in the early late Miocene and show a strong antiphasing relationship with the D. variabilis group. Discoaster bellus completely dominates the Discoaster assemblages for a 400 ka interval in the middle late Miocene. Abundances of all discoasters, or discoasters at the species level, show only (surprisingly) weak correlations to carbonate contents or oxygen and carbon isotopes of bulk sediment when calculated over the entire sample interval.

  • 23.
    Coxall, Helen K.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Huck, Claire E.
    Huber, Matthew
    Lear, Caroline H.
    Legarda-Lisarri, Alba
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sliwinska, Kasia K.
    van de Flierdt, Tina
    de Boer, Agatha M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Zachos, James C.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Export of nutrient rich Northern Component Water preceded early Oligocene Antarctic glaciation2018In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 11, no 3, p. 190-196Article in journal (Refereed)
    Abstract [en]

    The onset of the North Atlantic Deep Water formation is thought to have coincided with Antarctic ice-sheet growth about 34 million years ago (Ma). However, this timing is debated, in part due to questions over the geochemical signature of the ancient Northern Component Water (NCW) formed in the deep North Atlantic. Here we present detailed geochemical records from North Atlantic sediment cores located close to sites of deep-water formation. We find that prior to 36 Ma, the northwestern Atlantic was stratified, with nutrient-rich, low-salinity bottom waters. This restricted basin transitioned into a conduit for NCW that began flowing southwards approximately one million years before the initial Antarctic glaciation. The probable trigger was tectonic adjustments in subarctic seas that enabled an increased exchange across the Greenland-Scotland Ridge. The increasing surface salinity and density strengthened the production of NCW. The late Eocene deep-water mass differed in its carbon isotopic signature from modern values as a result of the leakage of fossil carbon from the Arctic Ocean. Export of this nutrient-laden water provided a transient pulse of CO2 to the Earth system, which perhaps caused short-term warming, whereas the long-term effect of enhanced NCW formation was a greater northward heat transport that cooled Antarctica.

  • 24. Dickens, Gerald R.
    et al.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    A comment on "Pliocene climate change of the Southwest Pacific and the impact of ocean gateways" by C. Karas, D. Nurnberg, R. Tiedemann, D. Garbe Schonberg, EPSL 301, 117-124 (2011)2012In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 331, p. 364-365Article in journal (Other academic)
  • 25.
    Dickens, Gerald R.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Core alignment and composite depth scale for the lower Paleogene through uppermost Cretaceous interval at Deep Sea Drilling Project Site 5772013In: Newsletters on stratigraphy, ISSN 0078-0421, Vol. 46, no 1, p. 47-68Article in journal (Refereed)
    Abstract [en]

    Deep Sea Drilling Project Site 577 on Shatsky Rise (North Pacific Ocean) recovered a series of cores at three holes that contain calcareous nannofossil ooze of latest Cretaceous (late Maastrichtian) through early Eocene age. Several important records have been generated using samples from these cores, but the stratigraphy has remained outdated and confusing. Here we revise the stratigraphy at Site 577. This includes refining several age datums, realigning cores in the depth domain, and placing all stratigraphic markers on a current time scale. The work provides a template for appropriately bringing latest Cretaceous and Paleogene data sets at old drill sites into current paleoceanographic literature for this time interval. While the Paleocene Eocene Thermal Maximum (PETM) lies within core gaps at Holes 577* and 577A, the sedimentary record at the site holds other important events and remains crucially relevant to understanding changes in oceanographic conditions from the latest Cretaceous through early Paleogene.

  • 26. Dowdeswell, J. A.
    et al.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hogan, K. A.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Evans, J.
    Hell, Benjamin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Marcussen, C.
    Noormets, R.
    O'Cofaigh, C.
    Sellén, Emma
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sölvsten, M.
    High-resolution geophysical observations of the Yermak Plateau and northern Svalbard margin: Implications for ice-sheet grounding and deep-keeled icebergs2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3518-3531Article in journal (Refereed)
    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.

  • 27.
    Dowdeswell, Julian A.
    et al.
    University of Cambridge.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Hogan, K.A.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Antony, D
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Darby, Dennis
    Old Dominion University.
    Eriksson, Björn
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Evans, J
    Hell, Benjamin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Marcussen, Christian
    GEUS.
    Noormets, R.
    UNIS.
    Polyak, Leonid
    Ohio State University.
    Sellén, Emma
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Sölvsten, Morten
    Geophysical and geological observations from the Yermak Plateau and northern Svalbard margin: Implications for ice-sheet grounding and deep-keeled icebergs2009In: Third Conference on Arctic Palaeoclimate and its Extremes- beyond the frontier, Copenhagen: The Natural History Museum and University of Copenhagen , 2009, p. 22-22Conference paper (Other academic)
  • 28. Farrell, J W
    et al.
    Moran, K
    Backman, J
    Stockholm University.
    TI: Arctic coring expedition: how to beat the system and win2007In: Eos Transactions AGU, Fall Meeting 2007, 2007Conference paper (Other academic)
  • 29.
    Fitch, Peter
    et al.
    University of Leicester.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Heterogeneity and Cyclicity in the Physical Property Measurements of Cenozoic Sediments (IODP Expedition 320/321)2009In:  Eos Trans. AGU, 90(52), Fall Meet. Suppl., 2009Conference paper (Other academic)
    Abstract [en]

    The Cenozoic sediments of the Equatorial Pacific provide an ideal and unique record of oceanographic conditions and climate change over the last 50 million years of Earth’s history. Previous studies utilizing data and samples from ODP Leg 199 have provided great insight into astronomically calibrated time-scales which control depositional sequences and lithologies of the deep Pacific waters. IODP Expeditions 320 and 321 aimed to further our understanding of the time-scales, processes and geological signatures in this environment by recovering a more detailed and higher resolution record of data and samples through this important geological record.

    This study uses physical properties and wireline logging data together with detailed sedimentological descriptions from IODP Expedition 320 to investigate heterogeneity and cyclicity in the physical properties across a time-transect of six sites. The application of statistical techniques for the numerical quantification of heterogeneity to these data shows that the various discrete time periods (age units) studied along the transect (lower Eocene through upper Miocene) return consistent values allowing these age units to be traced laterally based on contrasts in heterogeneity values. Heterogeneities in bulk density, magnetic susceptibility, and natural gamma ray data are seen to vary with unit thickness and can be related to lithology, and the presence / abundance of bioturbated intervals and carbonate turbidite beds. Numerical heterogeneities are also shown to be consistent across three scale of investigation; wireline (meter scales), track (cm scales) and discrete (mm-cm scale) datasets. These results could significantly impact future sampling strategies for similar sites by guiding the minimum sampling density required to ensure resolving high-resolution heterogeneities and cyclicity.

    Analysis of cyclicity within the physical properties data using the Fourier transform and semi-variogram analysis, with depth-scale converted to a time-series based on shipboard paleontological analysis, shows a number of large wavelength cycles have been captured, ranging from 100ka to 6Ma. Further analysis of the location and intensity of bioturbation and the occurrence of carbonate turbidites  at two key sites reveals that cyclicity of similar wavelengths can still be resolved, suggesting that it may be possible to identify  and remove the bioturbated layers and/or turbidite beds prior to a more detailed study of Milankovitch cyclicity.

  • 30. Fornaciari, E
    et al.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Holocene Calcareous Nannofossils from a HOTRAX site on the Lomonosov Ridge2006In: EOS Transactions, American Geophysical Union, v. 87(52): Fall Meet. Suppl.,, 2006, p. Abstract OS53B-1110Conference paper (Other academic)
  • 31. Fornaciari, E
    et al.
    Giusberti, L
    Luciani, V
    Tateo, F
    Agnini, C
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Oddone, D
    Rio, D
    An expanded Cretaceous-Tertiary transition in a pelagic setting of the Southern Alps (central-western Tethys)2007In: Palaeogeography, Palaeoclimatology, Palaeoecology, Vol. 255Article in journal (Refereed)
  • 32. Giusberti, L
    et al.
    Rio, D
    Agnini, C
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Fornaciari, E
    Tateo, F
    Oddone, M
    Mode and tempo of an expanded Paleocene Eocene Thermal Maximum section in the Venetian Pre-Alps2007In: Geological Society America Bulletin, Vol. 119Article in journal (Refereed)
  • 33. Giusberti, Luca
    et al.
    Rio, Domenico
    Agnini, Claudia
    Tateo, Fabio
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Fornaciari, Eliana
    Tateo, Fabio
    Oddone, Massimo
    Mode and tempo of an expanded Paleocene Eocene Thermal Maximum section in the Venetian Pre-Alps2007In: Geological Society of America Bulletin, Vol. 119, p. 391-412Article in journal (Refereed)
  • 34. Gyllencreutz, R
    et al.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Jakobsson, M
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Kissel, C
    Arnold, E
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Time-slice maps of postglacial palaeoceanography in the Skagerrak2007In: EGU 2007 General Assembly, 2007Conference paper (Other academic)
  • 35. Haley, B.A.
    et al.
    Frank, M
    Moran, K
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Cenozoic neodynium isotope evolution of Arctic Ocean deep water2007In: Geochimica et Cosmochimica Acta, Vol. 70Article in journal (Refereed)
  • 36.
    Hanslik, Daniela
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Björck, Svante
    Lund University, Department of Geology.
    Sellén, Emma
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Fornaciari, Eliana
    University of Padova, Department of Geosciences.
    Skog, Göran
    Lund University, Department of Geology.
    Quaternary Arctic Ocean sea ice variations and deep water isolation times2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3430-3441Article in journal (Refereed)
    Abstract [en]

    A short sediment core retrieved from a local depression forming an intra basin on the Lomonosov Ridge during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX) contains a record of the Marine Isotope Stages (MIS) 1-3 showing exceptionally high abundances of calcareous microfossils during parts of MIS 3. Based on radiocarbon dating, linear sedimentation rates of 7-9 cm/ka persist during the last deglaciation. Last Glacial Maximum (LGM) is partly characterized by a hiatus. Planktic foraminiferal abundance variations of Neogloboquadrina pachyderma sinistral and calcareous nannofossils reflect changes in Arctic Ocean summer sea ice coverage and probably inflow of subpolar North Atlantic water. Marine reservoir ages of 1400 years or more, at least during the last deglaciation, seem plausible from calibration of the radiocarbon ages using modeled reservoir corrections from previous studies in combination with the microfossil abundance record of the studied core. Paired benthic-planktic radiocarbon dated foraminiferal samples indicate a slow decrease in age difference between surface and bottom waters from the Late Glacial to the Holocene, suggesting circulation and ventilation changes.

  • 37.
    Hanslik, Daniela
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Marin geovetenskap.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Marin geovetenskap.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Marin geovetenskap.
    Björck, Svante
    Skog, Göran
    Fornaciari, Eliana
    Radiocarbon calibration of a high resolution core from the Central Arctic Ocean2008In: EOS Transactions: American Geophysical Union, 2008, p. PP51A-1483Conference paper (Other academic)
    Abstract [en]

    The big challenge in calibrating radiocarbon dates to calendar years for Arctic Ocean deep sea sediments is to estimate the marine reservoir age of the water masses. Most sediment cores from the central Arctic Ocean have a low resolution and the preserved record for the last 25 ka is in the order of 10-20 cm. Therefore, most AMS 14C dating results are presented either uncalibrated or corrected. The used reservoir values often vary between 400 and 550 years, close to the global mean ocean reservoir age, since all available regional reservoir differences (ΔR) are from coastal areas around the Arctic Ocean. Our study presents 14C ages and calibration attempts with different modelled reservoir ages from a high resolution record of Holocene and Late Glacial sediments from the Lomonosov Ridge. During the 2005 Healy-Oden Trans-Arctic Expedition (HOTRAX) an area of the central Lomonosov Ridge, between about 88°15’–89°N and 140°–180°E, was cored where a >1000 m deep depression characterizes the ridge morphology. Calcareous nannofossils (Fornaciari and Backman in prep.) and foraminifera analyzed in the upper 70 cm of core HLY0503-18TC show a sequence of the last ~130 ka. The chronology has been established through the nannofossil record in the lower 30 cm (Fornaciari and Backman in prep.) and 14C dating in the upper 40 cm. The data indicate very high accumulation rates during the Late Glacial of ~10 cm/ka, and times of extremely low to no accumulation during the Last Glacial Maximum, MIS 4 and parts of MIS 5. In addition, 14C dating on benthic and planktonic foraminifera from the same depth in the sediment core reveals age differences between surface and deep water masses. The age difference of such benthic-planktonic pairs shows a succession of ~1200 year older bottom watera in the Late Glacial to ~250 year in the late Holocene. This indicates circulation and/or ventilation changes through the last deglaciation and Holocene, which we hopefully will be able to date in greater detail with better model estimates of temporal changes in marine reservoir ages.

  • 38. Hebbeln, Dierk
    et al.
    Knudsen, Karen-Luise
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Kristensen, Peter
    Klitgaard-Kristensen, Dorthe
    Backman, Jan
    Scheurle, Carolyn
    Jiang, Hui
    Gil, Isabelle
    Smelror, Morten
    Jones, Phil
    Sejrup, Hans-Petter
    Late Holocene coastal hydrographic and climate changes in the eastern North Sea2006In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 16, no 7, p. 987-1001Article in journal (Refereed)
    Abstract [en]

    We present a high-resolution palaeoenvironmental reconstruction covering the late Holocene from the Skagerrak and other sites in the North Sea area. The data, which are based on the analyses of marine sediment cores, reveal a marked environmental shift that took place between AD 700 and AD 1100, with the most pronounced changes occurring at AD 900. Both surface and bottom waters in the Skagerrak were subject to major circulation and productivity changes at this time due to an enhanced advection of Atlantic waters to the North Sea marking the beginning of the 'Mediaeval Warm Period' (MWP). The observed increase in bottom current strength is especially remarkable as there is hardly any comparable signal in the older part of the record going back to 1000 BC. At the transition to the 'Little Ice Age' (LIA) the bottom current strength remains at a high level, now probably forced by atmospheric circulation. Thus, despite opposite temperature forcing, these two consecutive climate scenarios are apparently able to generate distinctly stronger bottom currents in the Skagerrak than observed in the preceding 2000 years, and demonstrate the significance of climatic forcing in shaping the marine environment. Indeed, both the MWP and the LIA are reported as strong climatic signals in northwest Europe, being the warmest (except the late twentieth century) and coldest periods, respectively, during at least the last 2000 years.

  • 39. Heil, J.
    et al.
    Heil, C.
    O’Regan, M.
    Moran, K.
    Gattacecca, J.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Moore, T.
    Paleomagnetic Results From the Pleistocene Sediments of Lomonosov Ridge, Central Artic Ocean, IODP Leg 3022005In: EOS Transactions, American Geophysical Union, v. 86(52): Fall Meet. Suppl.,, 2005, p. Abstract GP44A-04Conference paper (Other academic)
  • 40. Hüpers, Andre
    et al.
    Torres, Marta E.
    Owari, Satoko
    McNeill, Lisa C.
    Dugan, Brandon
    Henstock, Timothy J.
    Milliken, Kitty L.
    Petronotis, Katerina E.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bourlange, Sylvain
    Chemale, Farid
    Chen, Wenhuang
    Colson, Tobias A.
    Frederik, Marina C. G.
    Guèrin, Gilles
    Hamahashi, Mari
    House, Brian M.
    Jeppson, Tamara N.
    Kachovich, Sarah
    Kenigsberg, Abby R.
    Kuranaga, Mebae
    Kutterolf, Steffen
    Mitchison, Freya L.
    Mukoyoshi, Hideki
    Nair, Nisha
    Pickering, Kevin T.
    Pouderoux, Hugo F. A.
    Shan, Yehua
    Song, Insun
    Vannucchi, Paola
    Vrolijk, Peter J.
    Yang, Tao
    Zhao, Xixi
    Release of mineral-bound water prior to subduction tied to shallow seismogenic slip off Sumatra2017In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 356, no 6340, p. 841-844Article in journal (Refereed)
    Abstract [en]

    Plate-boundary fault rupture during the 2004 Sumatra-Andaman subduction earthquake extended closer to the trench than expected, increasing earthquake and tsunami size. International Ocean Discovery Program Expedition 362 sampled incoming sediments offshore northern Sumatra, revealing recent release of fresh water within the deep sediments. Thermal modeling links this freshening to amorphous silica dehydration driven by rapid burial-induced temperature increases in the past 9 million years. Complete dehydration of silicates is expected before plate subduction, contrasting with prevailing models for subduction seismogenesis calling for fluid production during subduction. Shallow slip offshore Sumatra appears driven by diagenetic strengthening of deeply buried fault-forming sediments, contrasting with weakening proposed for the shallow Tohoku-Oki 2011 rupture, but our results are applicable to other thickly sedimented subduction zones including those with limited earthquake records.

  • 41.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Världshavets gåtor2008In: Geologiskt Forum, no 57Article in journal (Other (popular science, discussion, etc.))
  • 42.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Marin geovetenskap.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Marin geovetenskap.
    Rudels, Bert
    Nycander, Jonas
    Department of Meteorology. Oceanografi.
    Frank, Martin
    Mayer, Larry
    Jokat, Wilfried
    Sangiorgi, Fransesca
    O'Regan, Matt
    Brinkhuis, Henk
    King, John
    Moran, Kathryn
    The Early Miocene Onset of a Ventilated Circulation Regime in the Arctic Ocean2007In: Nature, Vol. 447, no 7147, p. 986-990Article in journal (Refereed)
    Abstract [en]

    Deep-water formation in the northern North Atlantic Ocean and the Arctic Ocean is a key driver of the global thermohaline circulation and hence also of global climate. Deciphering the history of the circulation regime in the Arctic Ocean has long been prevented by the lack of data from cores of Cenozoic sediments from the Arctic’s deep-sea floor. Similarly, the timing of the opening of a connection between the northern North Atlantic and the Arctic Ocean, permitting deep-water exchange, has been poorly constrained. This situation changed when the first drill cores were recovered from the central Arctic Ocean. Here we use these cores to show that the transition from poorly oxygenated to fully oxygenated (‘ventilated’) conditions in the Arctic Ocean occurred during the later part of early Miocene times. We attribute this pronounced change in ventilation regime to the opening of the Fram Strait. A palaeo-geographic and palaeo-bathymetric reconstruction of the Arctic Ocean, together with a physical oceanographic analysis of the evolving strait and sill conditions in the Fram Strait, suggests that the Arctic Ocean went from an oxygenpoor ‘lake stage’, to a transitional ‘estuarine sea’ phase with variable ventilation, and finally to the fully ventilated ‘ocean’ phase 17.5 Myr ago. The timing of this palaeo-oceanographic change coincides with the onset of the middle Miocene climatic optimum, although it remains unclear if there is a causal relationship between these two events.

  • 43.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Gardner, J.V.
    Vogt, P.
    Mayer, L.A.
    Armstrong, A.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Brennan, R.
    Calder, B.
    Hall, J.K.
    Kraft, B.
    New Multibeam bathymetric and sediment profiler data from the Chukchi Borderland provide pieces to the Arctic Ocean glacial puzzle2004In: Terminal QUEEN conference: Brorfelde, 2004, p. Denmark, Oct. 28-31Conference paper (Other academic)
  • 44.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Anderson, Leif
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Björk, Göran
    Cronin, Thomas M.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Koshurnikov, Andrey
    Mayer, Larry
    Noormets, Riko
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of New Hampshire, USA.
    Ananiev, Roman
    Barrientos Macho, Natalia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cherniykh, Denis
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Eriksson, Björn
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gemery, Laura
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Jerram, Kevin
    Johansson, Carina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Khortov, Alexey
    Mohammad, Rezwan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Semiletov, Igor
    Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation2016In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7, article id 10365Article in journal (Refereed)
    Abstract [en]

    The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions41-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (similar to 140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening.

  • 45.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Dowdeswell, J. A.
    Mayer, L.
    Polyak, L.
    Colleoni, Florence
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Anderson, L. G.
    Björk, G.
    Darby, D.
    Eriksson, Björn
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hanslik, Daniela
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hell, Benjamin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Marcussen, C.
    Sellén, Emma
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wallin, T.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    An Arctic Ocean ice shelf during MIS 6 constrained by new geophysical and geological data2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3505-3517Article in journal (Refereed)
    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.

  • 46.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark.
    Cronin, Thomas M.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Anderson, Leif G.
    Barrientos, Natalia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Björk, Göran
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    de Boer, Agatha
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mayer, Larry A.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Rattray, Jayne E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of New Hampshire, USA.
    Semiletov, Igor
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Post-glacial flooding of the Bering Land Bridge dated to 11 cal ka BP based on new geophysical and sediment records2017In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 13, no 8, p. 991-1005Article in journal (Refereed)
    Abstract [en]

    The Bering Strait connects the Arctic and Pacific oceans and separates the North American and Asian landmasses. The presently shallow (similar to 53 m) strait was exposed during the sea level lowstand of the last glacial period, which permitted human migration across a land bridge today referred to as the Bering Land Bridge. Proxy studies (stable isotope composition of foraminifera, whale migration into the Arctic Ocean, mollusc and insect fossils and paleobotanical data) have suggested a range of ages for the Bering Strait reopening, mainly falling within the Younger Dryas stadial (12.9-11.7 cal ka BP). Here we provide new information on the deglacial and post-glacial evolution of the Arctic-Pacific connection through the Bering Strait based on analyses of geological and geophysical data from Herald Canyon, located north of the Bering Strait on the Chukchi Sea shelf region in the western Arctic Ocean. Our results suggest an initial opening at about 11 cal ka BP in the earliest Holocene, which is later than in several previous studies. Our key evidence is based on a well-dated core from Herald Canyon, in which a shift from a near-shore environment to a Pacific-influenced open marine setting at around 11 cal ka BP is observed. The shift corresponds to meltwater pulse 1b (MWP1b) and is interpreted to signify relatively rapid breaching of the Bering Strait and the submergence of the large Bering Land Bridge. Although the precise rates of sea level rise cannot be quantified, our new results suggest that the late deglacial sea level rise was rapid and occurred after the end of the Younger Dryas stadial.

  • 47. Krylov, A
    et al.
    Andreeva, I
    Vogt, C
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    A shift in heavy and clay mineral provencances indicates a middle Miocene onset of a perennial sea-ice cover in the Arctic Ocean2008In: Paleoceanography, Vol. 23Article in journal (Other (popular science, discussion, etc.))
  • 48. Krylov, A
    et al.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Andreeva, I A
    Vogt, C
    Krupskaya, V V
    Grikurov, G E
    Moran, K
    : A middle Miocene onset of a permanent sea-ice cover in the Arctic Ocean2007In: Eos Transactions AGU, Fall Meeting 2007, 2007Conference paper (Other academic)
  • 49. Luciani, V
    et al.
    Agnini, C
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Giusberti, L
    Luchhi, R
    Muttoni, G
    Rio, D
    Planktonic foraminiferal response to the Early Eocene Climatic Optimum at the Tethyan Possagno section (Italy)2008In: EGU 2008 General Assembly, 2008Conference paper (Other (popular science, discussion, etc.))
  • 50. Luciani, V
    et al.
    Agnini, C
    Fornaciari, E
    Giusberti, L
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Rio, D
    High resolution study on planktonic foraminifera across the Paleocene-Eocene thermal maximum in the expanded Tethyan Forada section ( Italy): paleoecological and paleoenvironmental implications2007In: EGU 2007 General Assembly, 2007Conference paper (Other academic)
12 1 - 50 of 92
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