Biogenic silicate dissolution

While rapid burial enhances preservation, the type of sediment produced is determined by the relative particle composition of the deposit. For example, rapid burial of biogenic silicate by clay minerals helps protect the shells against dissolution, but the resulting deposit is classified as an abyssal clay, rather than a siliceous ooze, if the sediment is less than 30% by mass BSi. Thus, prediction of the sediment type likely to be found at a given location requires knowledge of the relative magnitudes of the accumulation rates of all particle types. 

Figure 5 Graphical approach to resolving silicate originating via biogenic silica dissolution from that generated via clay-mineral dissolution during the alkaline leach technique used to quantify biogenic silica abundance. This sample was from the Gulf of California, Carmen Basin.

Li XG, Song JM, Yuan HM, Li FY, Sun S (2005) High contents of biogenic silicate in Jiaozhou Bay sediments-evidence of Si-hmitation to phytoplankton primary production. Oceanol Limnol Sin 36(6) 92-98 (in Chinese with English abstract) Li XJ, Chen F, Liu J, Huang XH (2004) Distribution and its dissolution of carbonate in seafloor surface sediment in the western South China Sea. Geochimica 33(3) 254-260 (in Chinese with English abstract)... 

Changes in phosphate, nitrate, ammonia, and silicate concentrations associated with the biogenic production and destruction of POM can alter seawater alkalinities. These effects are usually so small in scale that they can be ignored. Since the largest biotic impact on alkalinity in oxic seawater is exerted by the formation and dissolution of... 

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. 

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. 

The dynamics of the process of dissolution and sorption of biogenic silica from siliceous rocks, diatomite and opoka, has been studied. 

In addition to the considerable amount of dissolution of biogenic silica that takes place in the oceanic water column, further dissolution of siliceous tests and spicules occurs within the marine sedimentary pile. Recent estimates of the proportion of deposited particulate silica that redissolves... 

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