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Pleistocene variations of beryllium isotopes in central Arctic Ocean sediment cores
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
IFM-Geomar, Leibniz Institute of Marine Sciences.
Paul Scherrer Institute, ETH Zurich.
2009 (English)In: Global and Planetary Change, ISSN 0921-8181, E-ISSN 1872-6364, Vol. 68, no 1-2, 38-47 p.Article in journal (Refereed) Published
Abstract [en]

Neogene marine sediments can be dated via decay of the cosmogenic radionuclide 10Be. Two cores from theAlpha and Mendeleev Ridges in the Arctic Ocean have been analyzed for seawater-derived beryllium (Be)isotopes in order to date the sediments and to calculate sedimentation rates. The decrease of 10Be concentrationin the cores was used to calculate first order sedimentation rates. To eliminate the dilution effect of berylliumcaused by short-term changes in sedimentation rate and grain size, the 10Be concentrationswere normalized tothe terrigenous stable isotope 9Be determined in the same sample aliquot. The measured 10Be concentrationsyield low average sedimentation rates for the Alpha and Mendeleev Ridges of 2.3 mm ka−1 and 2.7 mm ka−1,respectively. Sedimentation rates calculated from the 10Be/9Be ratios result in similarly low values, rangingfrom 0.2 to 6.8 mm ka−1 for the Alpha Ridge core and from 1.9 to 6.9 mm ka−1 for the Mendeleev Ridge core.However, amino acid racemization dating for the past 150 ka of a core adjacent to the Mendeleev Ridge corestudied here indicates significantly higher sedimentation rates than calculated from the downcore decreaseof 10Be and 10Be/9Be. If such higher rates also prevailed at the locations of our cores, for which there isbiostratigraphic evidence, either the supply of 10Be was much lower than assumed or that of 9Be was muchhigher. This could imply that the signature of the deepwaters in this part of the Arctic Ocean compared to todaywas largely different for most of the past approximately one million years with a significantly lower 10Be/9Beratio. Our study also addresses the variability of beryllium isotopes in sediment cores across the Arctic Oceanthrough a comparison of previously published results. Calculated 10Be fluxes reveal low values in the AmerasianBasin and highest values in the Eurasian Basin, near the Fram Strait. The decrease of Be isotopes in the twostudied Amerasian Basin cores may thus have been caused by environmental factors such as significantlyreduced inflow of Atlantic waters in the past, reduced input of 10Be and/or increased input of 9Be from theshelves, combined with a more efficient sea ice shielding in this part of the Arctic Ocean.

Place, publisher, year, edition, pages
2009. Vol. 68, no 1-2, 38-47 p.
National Category
Geology
Research subject
Geology
Identifiers
URN: urn:nbn:se:su:diva-30890DOI: 10.1016/j.gloplacha.2009.03.024ISI: 000269401100005OAI: oai:DiVA.org:su-30890DiVA: diva2:274693
Available from: 2009-10-30 Created: 2009-10-30 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Quaternary paleoceanography of the Arctic Ocean: A study of sediment stratigraphy and physical properties
Open this publication in new window or tab >>Quaternary paleoceanography of the Arctic Ocean: A study of sediment stratigraphy and physical properties
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A Quaternary perspective on the paleoceanographic evolution of the central Arctic Ocean has been obtained in this PhD thesis by studying sediment cores from all of the Arctic’s major submarine ridges and plateaus. The included cores were mainly recovered during the Healy-Oden Trans-Arctic expedition in 2005 and the Lomonosov Ridge off Greenland expedition in 2007. One of the main thesis objectives is to establish whether different sediment depositional regimes prevailed in different parts of the central Arctic Ocean during the Quaternary and, if so, establish general sedimentation rates for these regimes. This was approached by dating key cores using the decay of the cosmogenic isotopes 10Be and 14C, and through stratigraphic core-to-core correlation using sediment physical properties. However, the Arctic Ocean sea ice complicated the use of 10Be for dating because a solid sea ice cover prevents the 10Be isotopes from reaching the seafloor, resulting in too old ages. Dating using 14C is also complicated due to uncertain marine reservoir age corrections in the central Arctic Ocean. The core-to-core correlations show five areas with different depositional regimes; the northern Mendeleev Ridge and Alpha Ridge, southern Mendeleev Ridge, Morris Jesup Rise, Lomonosov Ridge and Yermak Plateau, listed in the order of increasing sedimentation rates from ~0.5cm/ka to ~4.8 cm/ka. A detailed study of the relationship between sediment bulk density and grain sizes suggests a strong link between variations in clay abundance and bulk density. Grain size analysis of a Lomonosov Ridge core show that fine silt and clay dominates the interglacials, possibly due to increased suspension freezing of these size fractions into sea ice and/or nepheloid transport. Sediments younger than the marine isotope stage (MIS) 7 generally contain more coarse silt, attributed to a regime shift during the Quaternary with increased iceberg transport into the central Arctic Ocean from MIS 6 and onwards.

Place, publisher, year, edition, pages
Stockholm: Department of Geology and Geochemistry, Stockholm University, 2009. 37 p.
Series
Meddelanden från Stockholms universitets institution för geologi och geokemi, ISSN 1101-1599 ; 337
Keyword
Arctic Ocean, sedimentology, Quaternary, stratigraphy, physical properties
National Category
Earth and Related Environmental Sciences Geology Geology
Research subject
Marine Geoscience
Identifiers
urn:nbn:se:su:diva-30895 (URN)978-91-7155-968-5 (ISBN)
Public defence
2009-11-27, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: In progress. Paper 4: In progress. Paper 5: In progress. Paper 6: In progress. Available from: 2009-11-05 Created: 2009-10-30 Last updated: 2009-10-30Bibliographically approved

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