Siliceous ooze
[2] Siliceous oozes are largely composed of the silica based skeletons of microscopic marine organisms such as diatoms and radiolarians.
Other components of siliceous oozes near continental margins may include terrestrially derived silica particles and sponge spicules.
Despite the unfavorable conditions, organisms can use dissolved silicic acid to make opal silica shells through biologically controlled biomineralization.
[4] The amount of opal silica that makes it to the seafloor is determined by the rates of sinking, dissolution, and water column depth.
[5] The dissolution rate of sinking opal silica (B-SiO2) in the water column affects the formation of siliceous ooze on the ocean floor.
Only four percent of opal silica produced in the surface ocean will, on average, be deposited to the seafloor, while the remaining 96% is recycled in the water column.
[6] The fastest accumulation rates of siliceous ooze occur in the deep waters of the Southern Ocean (0.1 mol Si m−2 yr−1) where biogenic silica production and export is greatest.
[7] The diatom and radiolarian skeletons that make up Southern Ocean oozes can take 20 to 50 years to sink to the sea floor.
[6] Once deposited, silica continues to dissolve and cycle, delaying long term burial of particles until a depth of 10–20 cm in the sediment layer is reached.
[6] When opal silica accumulates faster than it dissolves, it is buried and can provide a diagenetic environment for marine chert formation.
[9] A notable example is in the Southern ocean, where the consistent upwelling of Indian, Pacific, and Antarctic circumpolar deep water has resulted in a contiguous siliceous ooze that stretches around the globe.
Diatomaceous oozes are predominantly formed of diatom skeletons and are typically found along continental margins in higher latitudes.
A small surface area of deep sea sediment is covered by radiolarian ooze in the equatorial East Atlantic basin.
[10] Deep seafloor deposition in the form of ooze is the largest long-term sink of the oceanic silica cycle (6.3 ± 3.6 Tmol Si year−1).
[10] Rapid dissolution in the surface removes roughly 135 Tmol opal Si year−1, converting it back to soluble silicic acid that can be used again for biomineralization.
[13] The opal silicate skeletons enhance the sinking velocity of diatomaceous particles (i.e. carbon) from the surface ocean to the seafloor.
Most of the carbon dioxide taken up during the process of photosynthesis is recycled within the surface layer several times before making it to the deep ocean to be sequestered.
[16] Radiolarites evolved in upwelling regions in areas of high primary productivity and are the oldest known organisms capable of shell secretion.
[16] Scientists hypothesize that competition with diatoms for dissolved silica during the Cenozoic is the likely cause for the mass extinction of most radiolarian species.
[19] Free-floating diatoms, known as bipolar and multipolar centrics, began evolving approximately 100 million years ago during the Cretaceous.
[9] The sediment distribution and deposition patterns of oozes inform scientists about prehistoric areas of the oceans that exhibited prime conditions for the growth of siliceous organisms.
[9] Paleo-ooze accretion rates can be used to determine deep sea circulation, tectonic activity, and climate at a specific point in time.
[20] The Burubaital Formation is primarily composed of chert which was formed over a period of 15 million years (late Cambrian-middle Ordovician).
[20] The late Cambrian (497-485.4 mya) marks a time of transition for marine biodiversity and is the beginning of ooze accumulation on the seafloor.
[9] The formation of NADW and AABW dramatically transformed the ocean, and resulted in a spatial population shift of siliceous organisms.
This boom in siliceous plankton was greatest during the first one million years of the Tertiary period and is thought to have been fueled by enhanced upwelling in response to a cooling climate and increased nutrient cycling due to a change in sea level.
