Constraining biogenic silica dissolution in marine sediments: A comparison between diagenetic models and experimental dissolution rates

Fractionation of silicon isotopes during biogenic silica dissolution

“…Two main factors argue against an overriding importance of isotope exchange in the observed isotope effect, however. First, any back reactions are expected to become more significant as dissolved silicon loads increase (Khalil et al, 2007) and the relative rate of the forward reaction decreases, yet systematic variation was not consistently observed in the measured D DSi-BSi as a function of either the Si(OH) 4(aq) concentration or the rate of bSiO 2 dissolution across the experiments (Table 1 and Fig. 2); while a slight increase in D DSi-BSi did occur as dissolution progressed in the serial dissolution data (Table 1 and Fig.…”

Sediment <sup>231</sup>Pa/<sup>230</sup>Th as a recorder of the rate of the Atlantic meridional overturning circulation: insights from a 2-D model

“…Krishnaswami et al, 1981;Rutgers van der Loeff and Berger, 1993;Scholten et al, 1995;Moran et al, 2001) range between 400-800 m y −1 . Since there are no clear indications of systematic variability in this parameter, we chose a uniform and intermediate value of 500 m y −1 (Table 1).…”

“…We could further address this question by using a diagenetic model (e.g. Khalil et al, 2007) to estimate the opal concentration in sinking particles reaching the seafloor from sediment mass accumulation rates and use this information to estimate the range of possible fractionation factors to be applied at this site using the sediment trap data compilation of Chase et al (2003). However, distinguishing between the importance of changes in circulation and opal flux will eventually be best addressed by generating a database large enough to obtain a near-synoptic view of the spatial distribution of sediment 231 Pa/ 230 Th for each time slice of interest, since the distribution generated by the overturning circulation is clearly distinct from the distribution generated by the distribution of opal productivity in the ocean.…”

Microbial mediation of benthic biogenic silica dissolution

“…Several one-dimensional early diagenesis models are available to investigate the constraints of BSi recycling and preservation on a local scale in surface sediments (Luce et al, 1972;Schink et al, 1975;Kamatani et al, 1988;Boudreau, 1990a,b;Archer et al, 1993;Truesdale et al, 2005;Khalil et al, 2007). Constructed to reproduce decreasing reaction kinetics with sediment depth, these models are usually based on a first-order kinetic expressing the direct proportionality of the dissolution rate to the saturation deficit, a function of the saturation concentration and the ambient pore water Si concentration.…”