Biogenic silica dissolution

Preservation versus Dissolution of Sinking Detrital Biogenic Silica... 

PRESERVATION VERSUS DISSOLUTION OF SINKING DETRITAL BIOGENIC SILICA... 

Silicon isotope variations in the ocean are caused by biological Si-uptake through siliceous organisms like diatoms. Insofar strong similarities exist with C-isotope variations. Diatoms preferentially incorporate Si as they form biogenic silica. Thus, high 5 °Si values in surface waters go parallel with low Si-concentrations and depend on differences in silicon surface water productivity. In deeper waters dissolution of sinking silica particles causes an increase in Si concentration and a decrease of 5 °Si-values. 

Fujii, M., and Chai, P. (2005). Effects of biogenic silica dissolution on silicon cycling and export production. Geophys. Res. Lett. 32, doi 10.1029/2004GL022054. 

Alexandre et al. (1997) found that the biogenic sihca input into the biogeochemical silica cycle from the dissolution of phytoliths is twice as large as silica input from primary silicate mineral weathering in the tropical Congo rainforest. Biogenic (opaline) silica dissolves faster than sihcate minerals. While most of the phytoliths dissolve rapidly with a mean residence time of 6 months (Alexandre et al., 1994), and the sihca is recycled by the forest, a small part (7.5%) does not dissolve and is preserved in the soil. 

Koning E., Brummer G.-J., van Raaphorst W., van Bennekom J., Helder W., and van Iperen J. (1997) Settling dissolution and burial of biogenic silica in the sediments off Somalia (northwestern Indian Ocean). Deep-Sea Res. II 44, 1341-1360. 

Rickert D. (2000) Dissolution kinetics of biogenic silica in marine environments. PhD Thesis, Ber. Polarforsch., 351. 

Van Cappellen P. and Qiu L. (1997a) Biogenic silica dissolution in sediments of the Southern Ocean ... 

Dixit S. (2001) Dissolution of biogenic silica solubility, reactivity and the role of aluminum. PhD Dissertation, Georgia Institute of Technology. 

Martin W. R., Bender M., Leinen M., and Orchardo J. (1991) Benthic organic carbon degradation and biogenic silica dissolution in the central equatorial Pacific. Deep-Sea Res. 38, 1481-1516. 

Van Cappellen and Qiu (1997a) have shown that the dissolution of biogenic silica in the highly undersaturated water column is inherently different than that in the seabed, where pore waters reach near-saturation levels. In areas of high undersaturation the dissolution rate of biogenic silica increases exponentially with the increasing departure from undersaturation. In contrast, most sedimentary environments exhibit a linear relationship between departure from undersaturation and dissolution rate. The difference in dissolution mechanism is believed to be related to the onset of localized dissolution centered on surface defects (Van Cappellen and Qiu, 1997a). 

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