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  • Asahi, Hirofumi  (2)
  • 1
    Online-Ressource
    Online-Ressource
    Cambridge University Press (CUP) ; 2014
    In:  Quaternary Research Vol. 81, No. 1 ( 2014-01), p. 151-157
    In: Quaternary Research, Cambridge University Press (CUP), Vol. 81, No. 1 ( 2014-01), p. 151-157
    Kurzfassung: Biogenic opal content and mass accumulation rate (MAR) at IODP Expedition 323 Site U1343 were found to fluctuate consistently, generally being high under warm conditions and low under cold conditions during the last 2.4 Ma. Continuous wavelet transform analysis of the normalized biogenic opal content indicates that export production in the Bering Sea varied predominantly at 41-ka periodicity before 1.25 Ma, and shifted to 100-ka periodicity at the onset of the Mid-Pleistocene Transition (MPT; 1.25–0.7 Ma). The 100-ka cycles dominated until the Holocene. Export production in the Bering Sea decreased markedly in the Bering Sea two times during the MPT: the first occurred at the beginning of the MPT (1.25 Ma) and the second in the middle of the MPT (0.9 Ma). These decreases coincided with both increases in the relative abundance of sea-ice diatoms and decreases in the warm-water diatom species Neodenticula seminae , indicating that reductions in export production in the Bering Sea during the MPT were associated with climate cooling. Decreases in export production in the Bering Sea during the MPT were most likely associated with the increased influence of polar/Arctic domains on the high-latitude North Pacific.
    Materialart: Online-Ressource
    ISSN: 0033-5894 , 1096-0287
    RVK:
    Sprache: Englisch
    Verlag: Cambridge University Press (CUP)
    Publikationsdatum: 2014
    ZDB Id: 1471589-2
    ZDB Id: 205711-6
    SSG: 13
    SSG: 14
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    In: Nature Communications, Springer Science and Business Media LLC, Vol. 9, No. 1 ( 2018-12-19)
    Kurzfassung: The Mid-Pleistocene Transition (MPT) is characterised by cooling and lengthening glacial cycles from 600–1200 ka, thought to be driven by reductions in glacial CO 2 in particular from ~900 ka onwards. Reduced high latitude upwelling, a process that retains CO 2 within the deep ocean over glacials, could have aided drawdown but has so far not been constrained in either hemisphere over the MPT. Here, we find that reduced nutrient upwelling in the Bering Sea, and North Pacific Intermediate Water expansion, coincided with the MPT and became more persistent at ~900 ka. We propose reduced upwelling was controlled by expanding sea ice and North Pacific Intermediate Water formation, which may have been enhanced by closure of the Bering Strait. The regional extent of North Pacific Intermediate Water across the subarctic northwest Pacific would have contributed to lower atmospheric CO 2 and global cooling during the MPT.
    Materialart: Online-Ressource
    ISSN: 2041-1723
    Sprache: Englisch
    Verlag: Springer Science and Business Media LLC
    Publikationsdatum: 2018
    ZDB Id: 2553671-0
    Standort Signatur Einschränkungen Verfügbarkeit
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