A SHIFT IN THE MODE OF DEEP-SEA SILICON BURIAL AND CENOZOIC COOLING

Deep-sea sedimentation rates increased and bottom-water temperatures declined in the later Cenozoic, which diagenetic modeling suggests would have resulted in a greater proportion of the silica reaching the seafloor being buried prior to its dissolution. If the influx of silica to the global ocean was consistent through the Cenozoic, mass balance constraints necessitate that the proportion of silica buried in other settings — namely, shallow marine environments or incorporated into clays (i.e. reverse weathering) — would have had to have been greater earlier in the Cenozoic than today. Unlike the burial of weathering products in the form of SiO2 and CaCO3, which removes carbon from the coupled ocean-atmosphere system, reverse weathering releases carbonic acid back into the system and thus does not constitute a sink for carbon. Here, we investigate the implications of a lower deep-sea silica burial efficiency on the silicon and carbon cycles. We further explore the potential climatic consequences of a secular shift in the mode of Si burial from biogenic silica to authigenic clays, particularly in the context of Cenozoic cooling.