Asian monsoon modulation of nonsteady state diagenesis in hemipelagic marine sediments offshore of Japan

Abstract

We have identifiedmillennial-scale variations inmagneticmineral diagenesis from Pacific Ocean sediments offshore of Japan that we correlate with changes in organic carbon burial that were likely driven by Asian monsoon fluctuations. The correlation was determined by identifying offsets between the positions of fossil diagenetic fronts and climatically induced variations in organic carbon burial inferred frommagnetic and geochemical analyses. Episodes of intense monsoon activity and attendant sedimentmagneticmineral diagenesis also appear to correlate with Heinrich events, which supports the existence of climatic telecommunications between Asia and the North Atlantic region. Several lines of evidence support our conclusions: (1) fluctuations in down-coremagnetic properties and diagenetic pyrite precipitation are approximately coeval; (2) localized stratigraphic intervals with relatively strongermagneticmineral dissolution are linked to enhanced sedimentary organic carbon contents that gave rise to nonsteady state diagenesis; (3) down-core variations in elemental S content provide a proxy for nonsteady state diagenesis that correlate with key records of Asianmonsoon variations; and (4) relict titanomagnetite that is preserved as inclusions within silicate particles, rather than secondary authigenic phases (e.g., greigite), dominates the strongly diagenetically altered sediment intervals and are protected against sulfidic dissolution.We suggest that such millennial-scale environmentalmodulation of nonsteady state diagenesis (that creates a temporal diagenetic filter and relict magneticmineral signatures) is likely to be common in organic-rich hemipelagic sedimentary settingswith rapidly varying depositional conditions. Ourwork also demonstrates the usefulness of magnetic mineral inclusions for recording important environmentalmagnetic signals.