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Siliceous ooze is a type of pelagic sediment that covers large areas of the deep ocean floor. Siliceous oozes consist of terrestrial derived particles as well as the remains of microscopic sea creatures, mostly those of diatoms and radiolarians. Sometimes siliceous oozes also contain silicoflagellates and the spicules of sponges.


 * Diatoms are golden-brown algae that construct an opaline silica microscopic shell that is known as a "frustule".
 * Silicoflagellates are a minor group of marine algae that construct microscopic shells composed of opaline silica.
 * Radiolarians are marine protists that also construct microscopic shells composed of opaline silica and are distant relatives of the foraminifera.

Siliceous ooze accumulates on the ocean floor where the bottom waters are close to saturation with respect to silica, and the opaline remains of either diatoms, radiolarians, silicoflagellates, and sponge spicules, or combinations of these are rapidly buried. These conditions exist within areas of high biological productivity associated with volcanic islands and nutrient-rich upwelling zones. ''Continental margin upwelling areas such as the, Gulf of California, have the most rapid biogenic silica accumulation rates. However, since these upwelling areas are so small, less than 5% of silica in the marine environment is accounted for from upwelling. ''As the least common type of pelagic sediment, it covers only 15% of the ocean floor. It accumulates at a slower rate than calcareous ooze: 0.2–1 cm / 1000 yr.

After burial, most siliceous oozes remain unconsolidated. However, a fraction of siliceous oozes dissolve and reprecipitate as a result of diagenesis to form chert beds or nodules. When siliceous oozes are incorporated into orogenic belts associated with subduction zones, they are also altered by diagenesis, and lithified to form chert, i.e. radiolarian chert.

______________________________--my edits are in italics above

-process of accumulation on the seafloor?

-Creatures make it up?

Things to include:

-River inputs

-Implications for global Si cycle and oceanic Si isotopic budgets?

Distance from land masses, water depth, and ocean fertility are all factors that affect the composition of siliceous ooze.. About 6 X10^14 to 6.1 X 10^12 mol yr^-1 of dissolved silica is transported from continents to the oceans by rivers. Amorphous silica, which is likely to dissolve in seawater is also transported by rivers. It has been found that as much as 75% of oceanic silica originates from continents and as much as 90% of oceanic silica is delivered by rivers. Continental margin upwelling areas such as the, Gulf of California, have the most rapid biogenic silica accumulation rates. However, since these upwelling areas are so small, less than 5% of silica in the marine environment is accounted for from upwelling.



-Silicifying organisms changed the way in which marine silicon cycle functions opposed to calcifying organisms which took advantage of the exsisting carbonate-seawater system. (re-do wording)

-Aluminum is an important regulator for the longterm production of marine biosillicia.

-Si is one of many ( N, P, S, K, Ca) bioessential elements that are efficiently recycled in a marine ecosystem 

-The loss of bioessential elements to the lithosphere is minor on short timescales. However, the cumulative loss of bioessential elements to the lithosphere over time is signifiant. As stated by Van Cappellen (2003), "the lithosphere is the largest reservoir of the major nutrient elements. As compared to the combined contents of the atmosphere, hydrosphere, pedosphere and biosphere, sediments and rock contain orders of magnitude more C, P, Fe, Si, CA, and K. Incorporation of elements as marine sedimentary deposits is the principle means of loss. (?) Sedimentary burial would deplete the ocean reservoirs of these nutrients unless compensated by volcanic outgassing and chemical weathering of rocks. <??Then talk about river transport??>

-Shell fragments from calcareous and siliceous organisms are subject to recrystallization and cementation.

-Younger rocks tend to release more dissolved silic acid into rivers than other rocks even though older rock contain more Si.

-Skeletal hard part production creates coupling in elemental cycles, particularly of the calcium carbonate and biogenic opal cycles in oceans. B-SIO2 and calicum carbonate are secreted by organism living in the surface waters. .

Will: new stuff to look at::

-According to findings by Tréguer et al., only about 50% of the biogenic silica dissolves in the upper 200 m of the water column.

-Biogenic materials are removed from surface waters either by sinking into the deep ocean or as deposits in shallow sediments. Less than 1% of the organic matter that originated in the surface waters becomes preserved in sediment. However, more B-SIO2 is dissolved than CaCO3 because of undersaturated oceans. Of all the B-SIO2 that is created by organisms (diatoms, silicoflagelates, and radiolarians), only about 3% is buried as marine sediment.

-Because of the low trophic level, organismal origins of B-SIO2, the flux of BiSO2 is related to the amount of organic matter.

-"The relative proportion of siliceous versus calcareous production is of global significance because it regulates the uptake of CO2 by marine surface waters. When silica-secreting organisms dominate, more CO2 can be extracted from the atmosphere, because there is no release of CO2 by reaction." , <-Van Cappellen, page 369>.

-The Si biogeochemical cycle in the ocean is dependent upon the biological uptake during the synthesis and skeletal secretion in the surface water and the regeneration of Si in deeper waters and surface sediments. (rephase)

-The estimated turnover time of Si is 1.5x10^4

-There is little evidence to suggest that the secretion of mineralized body parts occurred any earlier than 600 mya.

-In circumstances with abundant nutrients, diatoms can displace other primary producers which is why diatoms are common in early marine blooms in the open ocean as well as coastal and upwelling zones.

-It is well documented the primary source of new silica in the oceans is through river transport of H4SiO4 from the weathering of rocks from the continents. *Strong covalent bonds* Because weathering is such a dominant process in the abundance of H4SiO4 delivered to the ocean climate could also play a major role.

-Conceptually speaking, all biogenic silica should dissolve in the oceans. However dissolution in living organisms is does not occur because of the protection of organic membranes. Once a siliceous organism dies, bacteria immediately break down the membranes and the dissolution process begins. Despite the dissolution, some siliceous shell materials persist and accumulate along the seafloor. biddle azam 1999. berger 1992 konin 2001 brezeszinski 2002

-Silicic acid in the pore waters of marine sediments can be a result of the preservation and burial of biogenic silica. H4SiO4 concentration increases with depth. The biogenic silica that reaches the depth of asymptotic concentration is preserved because thermodynamic equilibrium as been reached. However, asymptotic concentration varies widely with location and with different sediments.

-Aluminum decreases the solubility of biosiliceous fragments. Most aluminum uptake bu biogenic silica happens once it has reached the seafloor, after deposition.

**** Table 3 in Van Cappellen is a table illustrating fluxes of bioessential elements, if we need it***

**** Figure 3 Van Cappellen is a box model of ocean silica cycle***Its pretty good***pg 373**

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Areas of high productivity -->ooze; need saturation for ooze, need lots of organisms -> areas with diatom blooms

ooze is silica shells mixing with other minerals like clay and basalt (most common ocean salt)

Low productivity -> no ooze because silica dissolves