Preservation of fossil diatoms in Atlantic sediment cores: control by supply rate

Abstract

Dissolution of fossil diatoms in piston cores from the North and equatorial Atlantic Ocean is generally severe only in areas of low primary productivity, and hence low fluxes of diatoms to the sea floor. In silica-rich sediments, initial dissolution increases the silica content of pore waters, which acts as a buffer against continued dissolution. Thus down-core decrease in accumulation rates reflects relative loos compared to initial supply rates, rather than absolute dissolution. Most records show either very strong or very weak impact by post-depositional dissolution. An empirical model suggest that in pelagic sediments, dissolution measurably affects diatom accumulation only when supply is below approximately 2.5 × 10 8 diatom fragments cm −2 1000 y −1, or 6.4 × 10 6 whole diatoms cm −2 1000 y −1. Other factors may also influence the preservation of siliceous microfossils; however, water depth has no discernible effect on the relative severity of opal dissolution in sediments of the abyssal Atlantic.