An investigation into the characteristics of reactive silicon pools of coastal marine sediments

Abstract

Many studies use traditional alkaline leach digestions to quantify biogenic silica (bSiO2) in sediments. Studies from river-plume systems demonstrate this methodology precludes information on other operational Si reactive pools, missing potentially valuable information on early diagenetic products. We build on previous studies by broadly examining the reactive Si pools in Mississippi River plume-influenced coastal sediments. The magnitude of Si released among operational pools across the region revealed large spatial variations in the conservation of detrital materials. Contrary to other analyses using different approaches, we suggest the availability of detrital sourced components (i.e. Al, Fe and Mn) may be a factor limiting authigenesis and resulting Si storage capacity in coastal sediments by this chemical mechanism. Overall, these data suggest authigenic precipitates may be forming as a function of bSiO2 accumulation, thereby implying that bSiO2 acts as the primary substrate for formation of authigenic products. The amount of authigenic Si products, relative to bSiO2, appears to be larger in this region than other systems studied to date, and this may be due to regional eutrophication which has led to an increase in sediment bSiO2 compounding the substrate available for authigenic precipitates. Thus, regions which have all experienced increased sediment bSiO2 accumulation coincident with eutrophication, may be primed for substantial authigenic product formation and increased Si sequestration.