![]() ![]() ![]() These three quantities are used commonly to trace hydrothermal water. Another independent source of silica are the hydrothermal vents which spew water of extremely high temperature, silica content, and helium content, as well as many other minerals, into the ocean. Dissolution from the bottom sediments constitutes a source of silica for the water column which is not available for nitrate, phosphate or oxygen. Much of the silica thus falls to the bottom of the ocean and accumulates in the sediments. However, silica in marine organisms is associated with skeletons rather than fleshy parts and so dissolves more slowly in the water. Subsurface distributions of silica look something like nitrate and phosphate and mirror oxygen since silica is also regenerated in situ below the euphotic zone. This nutrient is also depleted in surface waters similarly to nitrate and phosphate - completely depleted in downwelling areas and small but measurable quantities in upwelling areas. In seawater it is present as H2SiO4 (silicic acid) rather than silicate (SiO3), but many people use the term silicate. This indicates very stagnant deep waters.ĭissolved silica - non-conservative. In the Black Sea there is no oxygen (anoxic) but hydrogen sulphide is present instead (from reduction of sulphate by bacteria). However, low values of oxygen, such as those found in the North Pacific deep and intermediate layers, are an indication of waters that have been away from the sea surface for a long time. Also, since waters of different oxygen content mix, the age is not simply related to concentration. However, it is not a precise age tracer because the consumption rate is not a constant. Therefore, oxygenĬontent decreases with age, so it can be used in a rough way to date the water, particularly at depth where consumption is very small. Knowing the age of water masses is important in estimating anthropogenic CO2. Below the surface, oxygen concentration decays as a result of consumption by organisms and by oxidation of detritus (marine snow). Global Ocean Repeat Hydrography, Carbon, and Tracer Measurements, 2015-2020. Per cent saturation of oxygen depends strongly on temperature. The atmosphere is the primary source of oxygen in the ocean and surface waters are usually close to saturation. ![]()
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