Atmospheric gases exchange

The role of the World Ocean in the global cycle of C02 is mainly manifested through the process of its exchange at the atmosphere-ocean boundary. The intensity of ocean-atmosphere gas exchange is determined by the dynamic and diffusive behavior of the turbulent layers of water and air near the interface. Here numerous physical schemes appear which reflect the situations of wave formation, their collapse, and the... 

The atmospheric gas exchange rate depends on the CO2 fugacity difference between the air, /co , and water where superscript ml indicates CO2 fugacity in the ocean mixed layer. Fugacity and concentration are related through the Henry s Law coefficient, KH(molm atm ). The net organic carbon flux from the euphotic zone, Jc, has been expanded in the above equation to show that it is the difference between photos5mthesis. Pc, and respiration, Rc (Jc = Pc-Rc). 

Let us now assume that the residence time of a system is equivalent to the period of time that the system behaves as a closed system thermodynamically. With this assumption it is useful to qualitatively compare the residence times of different aqueous systems in the hydrosphere to the halftimes of some example reactions and reaction types. This has been done schematically in Fig. 2.2. In essence, as we examine the diagram, we can assume reactions are at equilibrium in waters whose residence times significantly exceed the half-times of reactions of interest. Note that the half-times of some solute-solute and solute-water reactions (these include some complexation and acid-base reactions [see Chaps. 3 and 5]) are shorter than the residence times of raindrops and so can be assumed to be at equilibrium in rain. These are homogeneous reactions. However, the other types of reactions shown, including atmospheric gas exchange, which is heterogeneous, are too slow to have... 

Noble gases are widely used in studies of the basic properties and dynamics of natural systems including the ocean. This chapter describes some of the more extensive applications of noble gases (mainly helium isotopes) to studies of oceanographic problems. They include the modem oceanic circulation, paleo-oceanography, hydro-thermal and cold brine systems in the deep ocean, and ocean/atmosphere gas exchange. 

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. ... 

What functions do the stomates serve in gas exchange with the atmosphere ... 

The process of equilibration of the atmosphere with the ocean is called gas exchange. Several models are available, however, the simplest model for most practical problems is the one-layer stagnant boundary-layer model (Fig. 10-18). This model assumes that a well-mixed atmosphere and a well-mixed surface ocean are... 

Example Obtain a relationship for the residence time of gases in the atmosphere with respect to gas exchange ... 

The carbonate system plays a pivotal role in most global cycles. For example, gas exchange of CO2 is the exchange mechanism between the ocean and atmosphere. In the deep sea, the concentration of COi ion determines the depth at which CaCOs is preserved in marine sediments. 

The major function of cutin is to serve as the structural component of the outer barrier of plants. As the major component of the cuticle it plays a major role in the interaction of the plant with its environment. Development of the cuticle is thought to be responsible for the ability of plants to move onto land where the cuticle limits diffusion of moisture and thus prevents desiccation [141]. The plant cuticle controls the exchange of matter between leaf and atmosphere. The transport properties of the cuticle strongly influences the loss of water and solutes from the leaf interior as well as uptake of nonvolatile chemicals from the atmosphere to the leaf surface. In the absence of stomata the cuticle controls gas exchange. The cuticle as a transport-limiting barrier is important in its physiological and ecological functions. The diffusion across plant cuticle follows basic laws of passive diffusion across lipophylic membranes [142]. Isolated cuticular membranes have been used to study this permeability and the results obtained appear to be valid... 

In calculations two periods were considered—the accumulation time (5 years), during which PCB atmospheric concentration was 1 ng/m3 and the clearance interval with air concentration assumed equal to zero. It was considered that pollutant input to soil takes place only due to gas exchange with the atmosphere. The calculations resulted in the profile of pollutant vertical distribution. This profile allows drawing conclusions about the penetration depth variation. 

Gas exchange Dissolution of gases into seawater or degassing from seawater to the atmosphere or into occluded gas bubbles... 

The thin-film model is the simplest and, therefore, most commonly used approach to estimate air-sea fluxes of gases. In this model, molecular diffusion is assumed to present a barrier to gas exchange in each of two layers. As illustrated in Figure 6.5, one layer is composed of a shallow region of the atmosphere that lies in direct contact with the sea surface. The second is a shallow layer of seawater tliat lies at the sea surface. These layers have depths less than 100 (am and, hence, are referred to as thin films. 

The resulting CO2 gas is returned to the atmosphere by two means (1) volcanic emissions associated with eruptions near subduction zones, i.e., back-arc volcanoes or (2) diffusion through the sediments of the continental rise into the ocean, followed by gas exchange across the air-sea interfece. The combined production of CO2 from these two settings is thought to exceed that from the high-temperature hydrothermal reaction zones. 

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