Oceanic reservoirs reactions

In an oversimplified way one can say that acids of the volcanoes have reacted with the bases of the rocks the composition of the ocean (which is at the first endpoint (pH = 8) of the titration of a strong acid with a carbonate) and the atmosphere (which with its pco2 = 10 3 5 atm is nearly in equilibrium with the ocean) reflect the proton balance of reaction (5.25). Oxidation and reduction are accompanied by proton release and proton consumption, respectively. (In order to maintain charge balance, the production of e will eventually be balanced by the production of H+.) Furthermore, the dissolution of rocks and the precipitation of minerals are accompanied by H+-consumption and H+-release, respectively. Thus, as shown by Broecker (1971), the pe and pH of the surface of our global environment reflect the levels where the oxidation states and the H+ ion reservoirs of the weathering sources equal those of the sedimentary products. 

Grustal reservoirs are also variable in Gl-isotope compositions (Figs. 1-6) due to fractionation of the Gl-isotope compositions inherited from their mantle source through fluid-mineral reactions, incorporation of G1 derived from the oceans and fractionation within fluid reservoirs by diffusion (see below). For example, the oceanic crust is enriched in Gl (and pore fluids depleted in Gl) through reaction of seawater with basaltic crust derived from the depleted mantle (Fig. 1 Magenheim et al. 1995). Undoubtedly, future investigations of Gl-isotopes in whole rocks and mineral separates will address the Gl-isotope compositions of these reservoirs and their evolution. 

Equation 1.2 assumes that the concentration of C is constant throughout the ocean, i.e., that the rate of water mixing is much fester than the combined effects of any reaction rates. For chemicals that exhibit this behavior, the ocean can be treated as one well-mixed reservoir. This is generally only true for the six most abundant (major) ions in seawater. For the rest of the chemicals, the open ocean is better modeled as a two-reservoir system (surface and deep water) in which the rate of water exchange between these two boxes is explicitly accoimted for. 

Carbon dioxide is one of the maj or global warming gases. The ocean acts as a reservoir for carbon dioxide and therefore will slow the effects of this gas on global warming. How is this air-water transfer rate dependent on the rate of reaction of carbon dioxide with liquid water to form H2CO3 ... 

Kinetics of Reactions in Natural Waters. In considering equilibria and kinetics in natural water systems, it is usually necessary to recall that widely different time scales need to be identified with chemical reactions in different systems. Relatively short times (days to weeks) are available for approach to equilibrium in rivers, smaller lakes, reservoirs, and estuaries. Times for reaction in large lakes, seas, and perhaps typical ground waters are of the order of tens to hundreds of years. In ocean waters, the reaction time may range from thousands of years to... 

To begin the discussion, we will present briefly a view of the modern carbon cycle, with emphasis on processes, fluxes, reservoirs, and the "CO2 problem". In Chapter 4 we introduced this "problem" here it is developed further. We will then investigate the rock cycle and the sedimentary cycles of those elements most intimately involved with carbon. Weathering processes and source minerals, basalt-seawater reactions, and present-day sinks and oceanic balances of Ca, Mg, and C will be emphasized. The modern cycles of organic carbon, phosphorus, nitrogen, sulfur, and strontium are presented, and in Chapter 10 linked to those of Ca, Mg, and inorganic C. In conclusion in Chapter 10, aspects of the historical geochemistry of the carbon cycle are discussed, and tied to the evolution of Earth s surface environment. 

In conclusion, it should be noted that the dissolved silica and cations brought to the ocean by streams must be removed, if the ocean is a steady-state reservoir. Also, the anions Cl- and SO42 must enter into chemical reactions for the same reason. Bicarbonate should be removed by reactions resulting in return of CO2 to the atmosphere. During the past two decades controversy has raged over the steady-state ocean concept, the mechanisms and fluxes responsible for element removal from the ocean, and the time scale for removal of these elements and return of CO2 to the atmosphere, i.e., early or late diagenesis or metamorphism. 

There are two major carbon cycles on Earth. The two cycles operate in parallel. One cycle is slow and abiotic. Its effects are observed on multimillion-year timescales and are dictated by tectonics and weathering (Berner, 1990). In this cycle, CO2 is released from the mantle to the atmosphere and oceans via vulcanism and seafloor spreading, and removed from the atmosphere and ocean primarily by reaction with silicates to form carbonates in the latter reservoir. Most of the carbonates are subsequently subducted into the mantle, where they are heated, and their carbon is released as CO2 to the atmosphere and ocean, to carry out the cycle again. The chemistry of this cycle is dependent on acid-base reactions, and would operate whether or not there was life on the planet (Kasting et al., 1988). This slow carbon cycle is a critical determinate of the concentration of CO2 in Earth s atmosphere and oceans on timescales of tens and hundreds of milhons of years (Kasting, 1993). 

On geological time scales, CO2 cycles between rocks, often by way of the ocean and atmosphere. The rock reservoirs include the mantle, continental carbonates, carbon in reduced form mostly in continental shales, and carbon (mostly carbonate) in or on the sea floor. The small volatile reservoir (ocean plus atmosphere) cycles through carbonate rock in a hundred thousand to a million years. Over longer periods free CO2 is dynamically controlled by processes that form carbonates at low temperatures and processes that decompose carbonates at high temperatures by (Urey) reactions of the form... 

In an ideal steady-state world the flux of organic carbon from the upper ocean would be equal to net community production, which would be related via a stoichiometric ratio of C N to new production. This relationship was first suggested by Eppley and Peterson (1979) who termed the ratio of new to total production the/-ratio. A schematic picture of the processes that lead to the creation and transport of organic matter from the surface to the deep ocean is presented in Fig. 1.15. Nearly all the reaction rates and reservoir fluxes for N, C and O2 in the figure have been measured. Relating the fluxes of the... 

The true reservoir size for carbon dioxide, however, is larger than its concentration, [CO2], because of the carbonate system reactions. The ratio of the reservoir of DIG that exchanges carbon to the CO2 gas reservoir in the mixed layer is ADIC / A[C02]. Thus, the residence time for carbon in the surface ocean with respect to gas exchange from Eq. (11.23) is ... 

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