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Siliceous oozes are the rarest type of oceanic sediment and are formed by the "tests" of radiolarians and diatoms that accumulate on the ocean floor (DeMaster, 2002). These biogenic oozes accumulate slowly on the ocean floor over millions of years (DeMaster, 2002). Diatomaceous oozes are found along continental margins in higher latitudes (Keller and Barron, 1983), while radiolarian oozes are found in equatorial areas (Stoecker, et al. 1996). The thickest band of siliceous ooze found in the ocean encircles Antarctica and is dominated by the skeletons of diatoms (Burckle and Cirilli, 1987). Another region where diatomaceous oozes are found is the Northern Pacific where there is an ooze that extends from the Alaskan Peninsula to the East Asian continental margin (Keller and Barron, 1983). Radiolarians dominate siliceous oozes in tropical zones and have formed a lateral reaching ooze that runs along the equator of the Pacific basin. This same ooze extends vertically along the Eastern boundary of the Pacific basin to the reaches of the tropical zone boundaries. Radiolarian oozes make up a sizable portion of oceanic sediment found in the Indian Ocean and are found in smaller amounts in tropical areas of the East Atlantic Ocean basin (Stoecker et al. 1996).

Siliceous oozes form in "upwelling" zones and in areas that are well suited for primary production by siliceous organisms (Keller and Barron, 1983). Major ocean currents around the world provide such conditions for the formation of siliceous oozes. The "North Equatorial Current" and the "Humboldt Current" in the Pacific, the "Canary Current" in the Atlantic, and the "Somali Current" in the Indian Ocean are upwelling currents that provide valuable nutrients for phytoplankton to flourish in the surface waters (Marshall and Plumb, 2008). In the Southern ocean along the Antarctic coastal margin, there is extensive upwelling of North Atlantic Deep Water and Circumpolar Deep Water, and the abundance of primary production here is evident by the siliceous ooze that encircles the continental margin (Burckle and Cirilli, 1987).

Siliceous oozes and carbon sequestration

Siliceous oozes are a major sink for long-term sequestration of carbon dioxide (armbrust). Because atmospheric levels of carbon dioxide have been increasing exponentially since the industrial revolution (IPCC), there has been a push to figure out how to concomitantly increase rates of carbon sequestration in ocean sediments (armbrust). Diatoms take up large amounts of atmospheric carbon dioxide, and have therefore been a primary focus in carbon sequestration experiments (Silver).

Because of this, projects like the SERIES iron-enrichment experiments have dumped iron into ocean basis, in hopes of increasing rates primary productivity and ultimately, carbon sequestration (armbrust). Iron is often a limiting trace element for diatom production, which was evident from the diatom blooms that occurred soon after iron introduction (Armbrust). Although iron fertilization produces massive blooms and takes up more atmospheric carbon, the carbon sequestration rate is low (how much--find another paper). Most of the carbon dioxide taken up from the atmosphere is recycled within the surface layer and stays there for long periods of time before making it to the deep ocean to be sequestered (Armbrust).

A byproduct of diatom blooms is the biosynthesis of domoic acid (Silver). This is a neurotoxin produced by diatoms that bioaccumulates up the food web and has detrimental effects on marine mammals and humans (silver). It was first discovered to be harmful to humans in the 1980s when 107 people became sick and 3 people died from eating mussels that had fed on toxic diatoms (armbrust). It is unknown why diatom blooms produce domoic acid, but one theory suggests that it is an adaptation that aids in iron absorption (silver).

Importance of diatoms for primary production

Siliceous oozes implemented in modern products (Armbrust, Diatomaceous earth)

References

Stoecker, D.K., Gustafon, D.E., Verity, P.G. 1996. Micro- and mesoprotozooplankton at 140W in the equatorial Pacific: heterotrophs and mixotrophs. Aquat Microb Ecol. Vol. 10:273-282.

DeMaster, D.J. 2002. The accumulation and cycling of biogenic silica in the Southern Ocean: revisiting the marine silica budget. Deep-Sea Research II. Vpl. 49. pp. 3155-3167.

Buckle, L.H. Cirilli, J. 1987. Origin of Diatom Ooze Belt in the Southern Ocean: Implications for Late Quaternary Paleoceanography. The Micropaleontology Project., Inc. Vol. 33, No. 1 pp. 82-86.

Armbrust, V.E. 2009. The life of diatoms in the world's oceans. Nature. Vol. 459.

Silver, M. 2000. Understanding Domoic Acid and Toxic Diatom Blooms. Coastal Ocean Research. R/CZ-145: 3.1.

IPCC Fifth Assessment Report. 2013. Carbon and other Biogeochemical Cycles. Climate Change 2013. Ch. 6.

Keller, G., Barron, J.A. 1983. Paleoceanographic implications of Miocene deep-sea hiatuses.

Marshall, J. Plumb, R.A. 2008. Atmosphere, Ocean, and Climate Dynamics: An Introductory Text. Elsevier Academic Press, Burlington, MA.