Quantifying the opal belt in the Atlantic and southeast Pacific sector of the Southern Ocean by means of 230Th normalization

Abstract

A set of 114 samples from the sediment surface of the Atlantic, eastern Pacific and western Indian sectors of the Southern Ocean has been analyzed for 230Th and biogenic silica. Maps of opal content, Th‐normalized mass flux, and Th‐normalized biogenic opal flux into the sediment have been derived. Significant differences in sedimentation patterns between the regions can be detected. The mean bulk vertical fluxes integrated into the sediment in the open Southern Ocean are found in a narrow range from 2.9 g m−2 yr−1 (Eastern Weddell Gyre) to 15.8 g m−2 yr−1 (Indian sector), setting upper and lower limits to the vertically received fraction of open ocean sediments. The silica flux to sediments of the Atlantic sector of the Southern Ocean is found to be 4.2 ± 1.4 × 1011 mol yr−1, just one half of the last estimate. This adjustment represents 6% of the output term in the global marine silica budget.