High-resolution silica pore-water profiles in sediments of the Madeira Abyssal Plain, eastern North Atlantic

Abstract

High-resolution pore-water sampling has been undertaken to define the pore-water silica profile vs. depth for Holes 950A and 952A in the Madeira Abyssal Plain, eastern North Atlantic. The silica pore-water concentration in the upper 50 meters below seafloor (mbsf) faithfully records the presence of biogenic silica in organic-rich turbidites. Between 50 and 250 mbsf, that is, between 1 and 6.5 Ma, however, the silica pore-water concentration is low and stable, pointing to the absence of biogenic silica in the organic-rich turbidites in this interval. Such absence could indicate a change in source area, or in the northwest African upwelling system during that period.Near 280 mbsf in Hole 950A, and below 290 mbsf in Hole 952A, enhanced levels of silica are again observed in the pore waters, which indicates that biogenic silica is present in the deep organic-rich turbidites. For Hole 952A, this coincides with the interval where enhanced levels of diatoms have been reported. The high-resolution pore-water sampling in Holes 950A and 952A has resulted in the identification of potential intervals where authigenic silica phases are likely to have formed, thus enabling future studies on the diagenetic redistribution of silica in marine sediments.

Silica diagenesis and benthic fluxes in the Arctic Ocean

“…This sink could be explained by the uptake of DSi into newly precipitating authigenic minerals. The diagenetic transformation of biosilica into aluminosilicate minerals has been observed in the marine environment, both in tropical, deltaic Aller, 1995, 2004;Aller, 2014) and open marine deposits of the eastern and western North Atlantic Ocean (De Lange, 1998;Chong et al, 2014). Our pore water data indicate that authigenic clay minerals might be forming at depth at site 287: Decreasing DSi concentrations are paralleled by decreasing K + and Mg 2+ (Fig.…”