Millennial time scale changes in surface to intermediate-deep layer circulation recorded in sediment cores from the northwestern North Pacific

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  • Harada Naomi
    Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
  • Kimoto Katsunori
    Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
  • Okazaki Yusuke
    Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
  • Nagashima Kana
    Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
  • Timmermann Axel
    International Pacific Research Center, the School of Ocean and Earth Science and Technology, University of Hawaii
  • Abe-Ouchi Ayako
    Center for Climate System Research, The University of Tokyo Research Institute for Global Change, JAMSTEC

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Other Title
  • 北西部北太平洋海底堆積物に記録された表層および中・深層循環の1,000年スケール変動
  • ホクセイブ キタタイヘイヨウ カイテイ タイセキブツ ニ キロク サレタ ヒョウソウ オヨビ チュウ シンソウ ジュンカン ノ 1 000ネン スケール ヘンドウ

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Abstract

We have been focused on the high latitudes in the North Pacific Ocean and its marginal seas, which are sensitive to global climate changes and are a driver of regional climate changes in the East Asian region, including Japan. We are investigating and reconstructing changes in the westerly jet, surface water temperature, salinity, and intermediate-deep water ventilation over orbital and millennial time scales by using marine sediment cores. Our understanding of the paleo-environment of the western North Pacific as described by proxy records in marine sediments can be summarized as follows : (a) atmospheric circulation, in particular north and south migrations of the westerly jet axis, had a great impact on the subarctic Pacific sea surface environments ; (b) a mechanism propagated through atmospheric circulation is important for explaining the synchronization of climate changes between the subarctic Atlantic and the subarctic to mid-latitude Pacific ; and (c) changes not only in sea surface conditions (SST and SSS) but also in intermediate-deep layer conditions (ventilation rate and water temperature) and the carbon cycle are occurring in response to climate changes across millennial time scales. It is notable that the ventilation age of the intermediate-deep layer in the northwestern North Pacific was younger during the Heinrich event 1 (H1) and Younger Dryas (YD) cold period and older during the B/Å warm period than in the present. In other words, ventilation at the intermediate-deep layer was more active during H1 and YD, and less active during the B/Å compared with the present.<BR>Increased surface density during H1 may trigger deep convection in the high latitudes of the North Pacific. This hypothesis was tested using paleo climate models—so-called water-hosing experiments—that mimic a glacial meltwater pulse in the North Atlantic by prescribing anomalous freshwater fluxes. The model results were consistent with the proxy record, which indicates that the ventilation rate increased at intermediate depths in the northwestern North Pacific during H1. In the collaborative proxy-climate model intercomparison study, the propagation mechanisms of millennial-scale abrupt climate changes are discussed.

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