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Abstract

IODP Ex. 323 to the Bering Sea recovered a detailed record of Quaternary environmental variability adjacent to Alaska and eastern Siberia. The deep-sea sediment records show a dramatic bimodal environmental record of alternating high versus low magnetic susceptibility. Oxygen isotope records indicate that the interglacials are times of high clastic flux (high magnetic susceptibility) from the adjacent continents into the Bering Sea. Subsequent, more detailed chronostratigraphy indicates that Interstadial 3 and Interglacials 5, 7, and 9 are also intervals of large-amplitude, millennial-scale environmental variability alternating between warmer/wetter and cooler/drier intervals, with a quasi-cyclicity of ~5000 years. Comparative studies of North Atlantic Quaternary sediments associated with ODP Leg 172, with a similar dramatic glacial/interglacial variation in carbonate, show an almost identical millennial-scale (~5000 yrs) pattern of variability that we attribute to alternating warmer/cooler intervals in Interstadial 3 and Interglacials 5, 7, and 9. These results can also be compared to findings for Lake Elgygytgyn in Siberia. The chronology of this record is less certain than those of the other two regions, but it, too, shows large-amplitude changes in magnetic susceptibility in Interstadial 3 and Interglacials 5, 7, and 9 that can be attributed to oscillating warmer/cooler conditions on a millennial scale. These results suggest a coherent, hemispheric-scale pattern of climate variability in interstadial/interglacial periods of the last 400 ka with a quasi-cyclicity of ~5000 years. We speculate that this cyclicity is driven by a harmonic of the chaotic precession Milankovich cyclicity.