4.8 Article

North Pacific freshwater events linked to changes in glacial ocean circulation

期刊

NATURE
卷 559, 期 7713, 页码 241-+

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NATURE PUBLISHING GROUP
DOI: 10.1038/s41586-018-0276-y

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  1. Bundesministerium fur Bildung and Forschung
  2. Helmholtz Postdoc program [PD-301]
  3. Helmholtz funding through the Polar Regions and Coasts in the Changing Earth System (PACES) program of the Alfred Wegener Institute
  4. Qingdao National Laboratory for Marine Science and Technology [QNLM201703]

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There is compelling evidence that episodic deposition of large volumes of freshwater into the oceans strongly influenced global ocean circulation and climate variability during glacial periods(1,2). In the North Atlantic region, episodes of massive freshwater discharge to the North Atlantic Ocean were related to distinct cold periods known as Heinrich Stadials(1-3). By contrast, the freshwater history of the North Pacific region remains unclear, giving rise to persistent debates about the existence and possible magnitude of climate links between the North Pacific and North Atlantic oceans during Heinrich Stadials(4,5). Here we find that there was a strong connection between changes in North Atlantic circulation during Heinrich Stadials and injections of freshwater from the North American Cordilleran Ice Sheet to the northeastern North Pacific. Our record of diatom delta O-18 (a measure of the ratio of the stable oxygen isotopes O-18 and O-16) over the past 50,000 years shows a decrease in surface seawater delta O-18 of two to three per thousand, corresponding to a decline in salinity of roughly two to four practical salinity units. This coincided with enhanced deposition of ice-rafted debris and a slight cooling of the sea surface in the northeastern North Pacific during Heinrich Stadials 1 and 4, but not during Heinrich Stadial 3. Furthermore, results from our isotope-enabled model(6) suggest that warming of the eastern Equatorial Pacific during Heinrich Stadials was crucial for transmitting the North Atlantic signal to the northeastern North Pacific, where the associated subsurface warming resulted in a discernible freshwater discharge from the Cordilleran Ice Sheet during Heinrich Stadials 1 and 4. However, enhanced background cooling across the northern high latitudes during Heinrich Stadial 3-the coldest period in the past 50,000 years(7)-prevented subsurface warming of the northeastern North Pacific and thus increased freshwater discharge from the Cordilleran Ice Sheet. In combination, our results show that nonlinear ocean-atmosphere background interactions played a complex role in the dynamics linking the freshwater discharge responses of the North Atlantic and North Pacific during glacial periods.

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