Supersaturation ocean

An increase in seawater alkalinity (for example, by the dissolution of CaCOa) would decrease pC02 in seawater and decrease the Revelle factor (10), Thus CaCOa dissolution would provide a a strong negative feedback in response to an increased level of CO2 in the atmosphere and ocean. However, the surface water of temperate and tropical oceans is supersaturated with respect to CaCOa by several fold. It is not likely that the dissolution of CaCOa would provide a negative feedback to the air-sea CO2 transfer process in the near future. 

Oceanic surface water is everywhere supersaturated with respect to the two solid calcium carbonate species calcite and aragonite. Nevertheless carbonate precipitation is exclusively controlled by biological processes, specifically... 

The solubility of calcite and aragonite increases with increasing pressure and decreasing temperature in such a way that deep waters are undersaturated with respect to calcium carbonate, while surface waters are supersaturated. The level at which the effects of dissolution are first seen on carbonate shells in the sediments is termed the lysocline and coincides fairly well with the depth of the carbonate saturation horizon. The lysocline commonly lies between 3 and 4 km depth in today s oceans. Below the lysocline is the level where no carbonate remains in the sediment this level is termed the carbonate compensation depth. 

According to Equation 48 calcite should precipitate from waters having a Mg/Ca ratio below a certain value, while dolomite should precipitate from waters having a Mg/Ca ratio above that critical value. This rule is obeyed under conditions of precipitation from very slightly supersaturated aqueous solutions like those occurring in certain areas of the ocean. Ocean water is close to equilibrium with both calcite and dolomite (53). 

Piston velocity The rate at which supersaturated gases are moved from the surface ocean into the atmosphere by molecular diffusion. Transfer velocity. 

Near-surface seawater is typically supersaturated by over six times with respect to calcite, and over four times with respect to aragonite (see Chapter 4). When it flows over shallow areas of the world s oceans, its chemistry can be modified by several different processes. The extent of modification is strongly dependent on the residence time of the water over the shallow areas. Morphologic controls on flow, such as embayments, barrier islands, and reefs, can often lead to significant restriction of the flow of seawater. In areas where these restrictions occur, major changes in the chemistry of the seawater are usually observed. 

Swinnerton, Linnebom and Cheek (239) and Seiler and Junge (226) reported that the ocean, which they found to be supersaturated with CO, might be an important source. It is also possible that the oxidation of nonmethane hydrocarbons, particularly those whose production occurs over land, may be another huge source. Since, as we will see later, methane is thought to have a uniform distribution throughout the troposphere, some... 

Schmidt also measured the H2 content of surface waters in the North and South Atlantic Oceans. The data varied from 0.8 to 5.0 x 10 mL/L(H20), corresponding to saturation factors of E = 0.8 5.4, where F = represents equilibrium conditions between surface water and air, while F < 1 or E > 1 indicate undersaturation or supersaturation, respectively. The H2 supersaturation in ocean water may be due to the production of hydrogen by microbiological activity. 

When high iron and silica concentrations were reached, chemical deposition of iron and silica became possible, on the arrival of supersaturated volcanic solutions. The oldest (Archean) BIF, closely associated with volcanic rocks (formations of Algoma type) were deposited from supersaturated solutions formed when acid thermal waters mixed with ocean waters saturated with carbonic acid but devoid of free oxygen. 

Concentrations of N2 in non-denitrifying waters are generally close to the equibbrium concentrations. For example, dissolved N2 concentrations in the upper 200m of the western North Pacific Ocean and eastern Okhotsk Sea were in the range from 500 to 650 pmol kg (i.e. 1-4.3% supersaturated) (Nakayama et al.. 

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