Ocean flux

In hydrological studies, the transfer of water between reservoirs is of primary interest. The magnitudes of the main reservoirs and fluxes (volume per time) are given in Figure 7. The oceans hold ca 76% of all the earth s water. Most of the remainder, ie, ca 21%, is contained in pores of sediments and in sedimentary rocks. A Httle more than 1% (or 73% of freshwater) is locked up in ice. The other freshwater reservoir of significant size is groundwater. Lakes, rivers, and the atmosphere hold a surprisingly small fraction of the earth s water. 

Residence times were computed hy r = M/Q where M for a particular constituent is equal to its concentration in seawater times the mass of the oceans, and is equal to the concentration of the constituent in average river water times the annual flux of river water to the ocean. 

Momentum is mostly transferred from the atmosphere to the ocean, having the effect of driving the ocean circulation through the production of a wind-driven flow. Of course, the resultant flow carries heat and water, so contributing to fluxes of these quantities to the atmosphere in ways that would not have occurred without the establishment of the wind-driven circulation in the first place. 

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... 

Figure 4 Mean annual net CO2 flux over the global oceans (in 10 " grams of C per year per 5" square)"...

Global uranium flux calculations have typically been based on the following two assumptions (a) riverine-end member concentrations of dissolved uranium are relatively constant, and (b) no significant input or removal of uranium occurs in coastal environments. Other sources of uranium to the ocean may include mantle emanations, diffusion through pore waters of deep-sea sediments, leaching of river-borne sediments by seawater," and remobilization through reduction of a Fe-Mn carrier phase. However, there is still considerable debate... 

The quantity of primary production that is exported from the upper ocean is said to be equivalent to new production (18, 19) New primary production is that associated with allocthonous nutrients (i.e., those upwelled or mixed into the euphotic zone or input via rivers and rain). In order for steady state to be maintained, an equivalent flux out of the euphotic zone is required. Earlier studies (19) suggested that sediment-trap measurements of particulate organic carbon (POC) flux were equivalent to new primary production however, recently it has become clear that these measurements probably represent only a... 

An important issue that remains unresolved, because of the lack of adequate quantitative data on reservoirs and fluxes, is the location of the so called "missing" carbon. Missing carbon is the carbon added to the atmosphere from the burning of fossil fuel that cannot be accounted for by the measured increase in atmospheric concentration or by diffusion into the ocean (5). 

The most common way in which the global carbon budget is calculated and analyzed is through simple diagrammatical or mathematical models. Diagrammatical models usually indicate sizes of reservoirs and fluxes (Figure 1). Most mathematical models use computers to simulate carbon flux between terrestrial ecosystems and the atmosphere, and between oceans and the atmosphere. Existing carbon cycle models are simple, in part, because few parameters can be estimated reliably. 

Fluxes are linear functions of reservoir contents. Reservoir size and the residence time of the carbon in the reservoir are the parameters used in the functions. Between the ocean and the atmosphere and within the ocean, fluxes rates are calculated theoretically using size of the reservoir, surface area of contact between reservoirs, concentration of CO2, partial pressures of CO2, temperature, and solubility as factors. The flux of carbon into the vegetation reservoir is a function of the size of the carbon pool and a fertilization effect of increased CO2 concentration in the atmosphere. Flux from vegetation into the atmosphere is a function of respiration rates estimated by Whittaker and Likens (79) and the decomposition of short-lived organic matter which was assumed to be half of the gross assimilation or equal to the amount transferred to dead organic matter. Carbon in organic matter that decomposes slowly is transferred... 

Once the model was complete, it was adjusted to a steady state condition and tested using historic carbon isotope data from the atmosphere, oceans and polar ice. Several important parameters were calculated and chosen at this stage. Sensitivity analysis indicated that results dispersal of the missing carbon - were significantly influenced by the size of the vegetation carbon pool, its assimilation rate, the concentration of preindustrial atmospheric carbon used, and the CO2 fertilization factor. The model was also sensitive to several factors related to fluxes between ocean reservoirs. 

This chapter focuses on types of models used to describe the functioning of biogeochemical cycles, i.e., reservoir or box models. Certain fundamental concepts are introduced and some examples are given of applications to biogeochemical cycles. Further examples can be found in the chapters devoted to the various cycles. The chapter also contains a brief discussion of the nature and mathematical description of exchange and transport processes that occur in the oceans and in the atmosphere. This chapter assumes familiarity with the definitions and basic concepts listed in Section 1.5 of the introduction such as reservoir, flux, cycle, etc. 

CO2 ) The ocean to atmosphere flux, which is dependent on the concentration of the dissolved species C02(aq), is related to the total carbon content in the surface layer (Ms) by... 

If all fluxes are proportional to the reservoir contents, the percentage change in reservoir content will be equal for all the reservoirs. The non-linear relations discussed above give rise to substantial variations between the reservoirs. Note that the atmospheric reservoir is much more significantly perturbed than any of the other three reservoirs. Even in the case with a 6000 Pg input, the carbon content of the oceans does not increase by more than 12% at steady state. 

The cycles of carbon and the other main plant nutrients are coupled in a fundamental way by the involvement of these elements in photosynthetic assimilation and plant growth. Redfield (1934) and several others have shown that there are approximately constant proportions of C, N, S, and P in marine plankton and land plants ("Redfield ratios") see Chapter 10. This implies that the exchange flux of one of these elements between the biota reservoir and the atmosphere - or ocean - must be strongly influenced by the flux of the others. 

The magnitude and direction of the net flux density, F, of any gaseous species across an air-water interface is positive if the flux is directed from the atmosphere to the ocean. F is related to the difference in concentration (Ac), in the two phases by the relation... 

The flux of particles in the other direction, deposition on the ocean surface, occurs intermittently in precipitation (wet deposition) and more continuously as a direct uptake by the surface (dry deposition). These flux densities may be represented by a product of the concen-... 

The sediment surface separates a mixture of solid sediment and interstitial water from the overlying water. Growth of the sediment results from accumulation of solid particles and inclusion of water in the pore space between the particles. The rates of sediment deposition vary from a few millimeters per 1000 years in the pelagic ocean up to centimeters per year in lakes and coastal areas. The resulting flux density of solid particles to the sediment surface is normally in the range 0.006 to 6 kg/m per year (Lerman, 1979). The corresponding flux density of materials dissolved in the trapped water is 10 to 10 kg/m per year. Chemical species may also be transported across the sediment surface by other transport processes. The main processes are (Lerman, 1979) ... 

Although fluxes of precipitation and river discharge can be quite accurately determined on a local scale, large portions of the globe, especially the oceans and Antarctica, are essentially ungauged, requiring extensive extrapolation of existing data. Evaporation fluxes are even less well known, since calculation requires... 

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