Millennial-scale environmental modulation of reductive diagenesis in hemipelagic marine sediments and Asian monsoon variations

Abstract:

Magnetic mineral diagenesis occurs in all sedimentary environments to varying extents; however, non-steady state diagenesis is relatively poorly understood. We present results of a high-resolution multi-proxy analysis of a hemipelagic sediment core from the western Pacific Ocean in which large down-core magnetic property fluctuations broadly correlate with geochemical and sedimentological variations. Localized stratigraphic intervals of enhanced relative magnetic mineral preservation are linked to millennial-scale variations in supply of organic carbon that gave rise to non-steady state diagenetic variations. We provide the first direct microscopic observations of fine-grained magnetic mineral inclusions that were protected against sulfidic dissolution by their coarse-grained silicate host minerals, and demonstrate that magnetic mineral diagenesis was modulated by millennial-scale environmental and climatic variability. Such environmentally modulated diagenesis is likely to be common in organic-rich marine sedimentary environments with high deposition rates. Non-steady state diagenesis is an important process that can drive modification of magnetic mineral concentration in many types of studies, including high-resolution paleoenvironmental reconstructions, tracing of terrigenous mineral provenance and relative paleointensity analyses. We also present a lagged marine diagenetic record of Asian monsoon intensity. A ~3-5 ka offset between climate and diagenetic response arises from the downward diffusion of pore fluids during diagenesis. Correlation of the diagenetic signature in our record with Heinrich events supports previous hypotheses of teleconnections between the Asian monsoon and North Atlantic climatic events.