Sea—air interface

The fundamental control on the chemical contribution of the ocean to climate is the rate of gas exchange across the air-sea interface. The flux, F, of a gas across this interface, into the ocean, is often written as... 

Loss of radon in the ocean occurs typically through radioactive decay (producing four short-lived daughters before decaying to °Pb) or loss to the atmosphere at the air-sea interface. Loss of radon owing to turbulence or diffusion at the air-sea interface leads to a depletion of radon with respect to "Ra, allowing for studies on gas exchange at this interface. ... 

Fig. 4-16 A simplified model of flux resistances and concentration gradients in the viscous sublayers at the air-sea interface.

Because seawater signatures of temperature and salinity are acquired by processes occurring at the air-sea interface we can also state that the density characteristics of a parcel of seawater are determined when it is at the sea surface. This density signature is locked into the water when it sinks. The density will be modified by mixing with other parcels of water but if the density signatures of all the end member water masses are known, this mixing can be unraveled and the proportions of the different source waters to a given parcel can be determined. 

There are two different classes of surface-active materials in seawater, those that are naturally present and those that have been added to the oceans by man s activities. Most of the analytical methods proposed for use in seawater actually measure the anthropogenic input, and attempt as much as possible to eliminate interferences from naturally occurring compounds. Yet sea foam was known to exist long before detergents. It is to be expected that both kinds of surfactants would be concentrated at the air-sea interface. 

C is introduced into the oceans mainly through the exchange of 14C02 at the air-sea interface. 14C once produced in the atmosphere gets quickly oxidized to 14C02 and enters the exchangeable carbon system. 

Liss, P.S. and P.G. Slater (1974), Flux of gases across the air-sea interface. Nature, 247, 181-184. Matos, J.S. (1992), Aerobiose e septicidade em sistemas de drenagemde aguas residuais, Ph.D. thesis, 1ST, Lisbon, Portugal. 

Hsu, S. A. (1974). A dynamic roughness equation and its application to wind stress determination at air-sea interface. J. Phys. Oceanogr. 4, 116-120. 

The major ions are transported across the air-sea interface by the ejection of water droplets from the sea surfece. These droplets result from water turbulence at the sea surface that causes microscopic bubbling. Some of these bubbles burst, ejecting seawater into the atmosphere. Since not all of the salt ions are ejected to the same degree, bursting bubbles can alter the ion ratios in the remaining water. 

In this chapter, the fundamentals of aqueous gas chemistry are described, such as the factors that determine gas solubility and the rate of gas exchange across the air-sea interface. This background information is important to understanding the biogeochem-ical processes discussed through the rest of the text, because many involve gaseous species. 

A net transfer of gas across the air-sea interface will spontaneously take place if the gas is not at equilibrium. In the case where the aqueous gas concentration exceeds... 

The effects of photosynthesis are clearly seen in the low TDIC and nutrient concentrations of the surface water. The O2 concentrations are high because of contact with the sea surfece and production by phytoplankton. The temperature and O2 concentration data have been used to compute the percent saturation with respect to O2. The high degree of supersaturation in the surfece water suggests that the rate of O2 supply via photosynthesis is exceeding its removal via the dual processes of aerobic respiration and degassing across the air-sea interface. 

DOM also tends to be concentrated at boimdaries, such as the sediment-water and air-sea interfeces. The latter is also characterized by enrichments of POM, such as bacteria. Under calm conditions, the DOM and POM that collects at the air-sea interface forms a visible surfece slick or microlayer. On windy days, this organic matter can be whipped up into an emulsion that has the appearance of a very sturdy foam. DOM can also be transferred into the POM pool by adsorbing onto organic particles. 

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