Revisiting the dissolution of biogenic Si in marine sediments: a key term in the ocean Si budget

Of the *240 9 10 mol year of biogenic silica (bSi) produced by diatoms and other silicifying organisms, only roughly 3%–4% escapes dissolution to be permanently buried. At the global scale, how, where and why bSi is preserved in sediment is not well understood. To help address this, I compile 6245 porewater dissolved Si concentrations from 453 sediment cores, to derive the concentration gradient at the sediment–water interface and thus diffusive fluxes out of the sediment. These range from\0.002 to 3.4 mol m year, and are independent of temperature, depth and latitude. When classified by sediment lithology, predominantly siliceous sediments unsurprisingly have higher mean diffusive fluxes than predominantly calcareous or clay-rich sediment. Combined with the areal extent of these lithologies, the ‘best-guess’ global sedimentary bSi recycling flux is 69 9 10 mol year.