Monsoon fluctuations over the past 350 kyr: High-resolution evidence from northeast Asia northwest Pacific climate proxies (marine pollen and radiolarians)

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Quaternary Science Reviews
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High-resolution analyses of pollen and radiolarians from northwest Pacific cores V28-304 and RC14-99 provide continuous, directly-linked evidence of oceanic-atmospheric climate processes through the past three Pleistocene glacial-interglacial cycles. Systematic fluctuations in marine pollen assemblages, which reflect changes in the forest communities of Japan, are compatible with fluctuations in faunal assemblages and inferred oceanographic properties offshore. Each interglacial has distinguishable characteristics which imply that the sequence, timing and magnitude of climatic change were not identical during the three most recent interglacial intervals. Most interglacials contain at least one 10-15 kyr period of exceptionally high percentages (>20%) of Cryptomeria, which we interpret as reflecting increased levels of precipitation in response to intensification of the summer monsoon. With the exception of Oxygen Isotope Substage 5e in RC14-99. integlacial summer sea-surface temperatures were similar to or slightly warmer than today.Glacial environments in central Japan and in the northern subtropical gyre were similar to those which now support cold-temperate and boreal forests on northernmost Japan and a dominant subpolar fauna and associated low sea-surface temperatures offshore. Climatic change was apparently not as severe in southern Japan (where temperate vegetation largely replaced warm-temperate flora) or in the southern subtropical gyre (where only winter SSTs were cooler than present). We attribute these changes in vegetation and surface-water conditions to shifts in the atmospheric polar and oceanographic subarctic fronts in response to the seasonal variations in the Siberian High. Maxima in Cryptomeria systematically lag maxima in solar insolation at 30 degrees N. This correlation between our summer monsoon indicator and summer insolation substantiates the view that the strength of the Asian monsoon is linked to variations in northern hemisphere solar radiation. (C) 1997 Elsevier Science Ltd.


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