Steady state ocean

In unbuffered systems, kinetic limitation may come either from slow transport to the cell surface or from slow dissolution of solid species resulting in depletion of the bulk medium. Simple calculations show (Table 1) that, in the open ocean, steady state diffusion of such elements as zinc of iron to the cell surface may match the uptake rate of fast growing algae. This is in accordance with the postulate that, in a stable environment, all potentially limiting elements should effectively be co-limiting primary production and that the average uptake rates should match the diffusion rates (Morel and Hudson, 1985). 

Figure 34 5 Mean ocean steady-state Nisotope balance. Vertical arrows represent global input and output fluxes, in which the flux is proportional to the length of the arrow and the isotopic composition is shown by the position on the horizontal axis (showing in %o). The yellow...

Fig. 8. Steady-state model for the earth s surface geochemical system. The kiteraction of water with rocks ki the presence of photosynthesized organic matter contkiuously produces reactive material of high surface area. This process provides nutrient supply to the biosphere and, along with biota, forms the array of small particles (sods). Weatheriag imparts solutes to the water, and erosion brings particles kito surface waters and oceans.

In an oversimplified way, it may be stated that acids of the volcanoes have reacted with the bases of the rocks the compositions of the ocean (which is at the fkst end pokit (pH = 8) of the titration of a strong acid with a carbonate) and the atmosphere (which with its 2 = 10 atm atm is nearly ki equdibrium with the ocean) reflect the proton balance of reaction 1. Oxidation and reduction are accompanied by proton release and proton consumption, respectively. In order to maintain charge balance, the production of electrons, e, must eventually be balanced by the production of. The redox potential of the steady-state system is given by the partial pressure of oxygen (0.2 atm). Furthermore, the dissolution of rocks and the precipitation of minerals are accompanied by consumption and release, respectively. 

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... 

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. 

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. 

However, with "only" 1000 Pg emitted into the system, i.e. less than 3% of the total amount of carbon in the four reservoirs, the atmospheric reservoir would still remain significantly affected (20%) at steady state. In this case the change in oceanic carbon would be only 2% and hardly noticeable. The steady-state distributions are independent of where the addition occurs. If the CO2 from fossil fuel combustion were collected and dumped into the ocean, the final distribution would still be the same. 

A requirement of the heat balance for a steady-state ocean is that the input of new cold abyssal water (Antarctic Bottom Water and North Atlantic Deep Water) sinking in the high-latitude regions must be balanced by input of... 

As shown in Fig. 10-13, there is also a flux of O2 produced during net photosynthesis from the ocean to the atmosphere and an export flux of particulate and dissolved organic matter out of the euphotic zone. For a steady-state system, new production should equal the flux of O2 to the atmosphere and the export of organic carbon (Eppley and Peterson, 1979) (when all are expressed in the same units, e.g., moles of carbon). Such an ideal state probably rarely exists because the euphotic zone is a dynamic place. Unfortunately, there have been no studies where all three fluxes were measured at the same time. Part of the difficulty is that each flux needs to be integrated over different time scales. The oxygen flux approach has been applied in the subarctic north Pacific (Emerson et al, 1991) and subtropical Pacific (Emerson et al, 1995, 1997) and Atlantic (Jenkins and Goldman, 1985). The organic carbon export approach has... 

The steady-state flux from the atmosphere to the ocean across the layer is given by Pick s Pirst Law ... 

Carbon is released from the lithosphere by erosion and resides in the oceans ca. 10 years before being deposited again in some form of oceanic sediment. It remains in the lithosphere on the average 10 years before again being released by erosion (Broecker, 1973). The amount of carbon in the ocean-atmosphere-biosphere system is maintained in a steady state by geologic processes the role of biological processes is, however, of profound importance... 

The subsequent fate of the assimilated carbon depends on which biomass constituent the atom enters. Leaves, twigs, and the like enter litterfall, and decompose and recycle the carbon to the atmosphere within a few years, whereas carbon in stemwood has a turnover time counted in decades. In a steady-state ecosystem the net primary production is balanced by the total heterotrophic respiration plus other outputs. Non-respiratory outputs to be considered are fires and transport of organic material to the oceans. Fires mobilize about 5 Pg C/yr (Baes et ai, 1976 Crutzen and Andreae, 1990), most of which is converted to CO2. Since bacterial het-erotrophs are unable to oxidize elemental carbon, the production rate of pyroligneous graphite, a product of incomplete combustion (like forest fires), is an interesting quantity to assess. The inability of the biota to degrade elemental carbon puts carbon into a reservoir that is effectively isolated from the atmosphere and oceans. Seiler and Crutzen (1980) estimate the production rate of graphite to be 1 Pg C/yr. 

The gross flux of carbon from atmosphere to ocean is thus ca. 80 Pg C/yr. There are several complications with the above calculation. The isotopic ratios must be steady-state values, which are unavailable due to the changes resulting from atmospheric atom bomb testing. The few available pre-bomb measurements from the late 1950s (Broecker et ah, 1960) together with determinations in corals (Druffel and Linick, 1978) are invaluable tools for determin-... 

In a steady-state ocean the sediment deposition rate of a nutrient like phosphorus ought to be balanced by riverbome influx to the oceans 1.5. 0Tg P are transported to the oceans by rivers (Richey, 1983). Assuming a C/P molar... 

Deffeyes, K.S. (1970) The axial valley a steady-state feature of the terrain. Chapter 9 in Johnson, H. and Smith, B.L. (eds.). The Megatectonics of continents and oceans. New Brunswick, New Jersey Rutgers U. Press. 

Paul UH (2001) Melt retention and segregation beneath mid-ocean ridges. Nature 410 920-923 Feineman MD, DePaolo DJ, Ryerson FJ (2002) Steady-state Ra/ °Th disequilibrium in hydrous mantle minerals. Geochim Cosmochim Acta 66 A345 (abstr)... 

Nozaki Y, Yamada M, Nikaido H (1990) The marine geochemistry of actinium-227 evidence for its migration through sediment pore water. Geophys Res Lett 17 1933-1936 Nozaki Y (1993) Actinium-227 a steady state tracer for the deep-se basin wide circulation and mixing studes. In Deep Ocean Circulation, Physical and Chemical Aspects. Teramoto T (ed) Elsevier p 139-155... 

Thus, the global thermal pollution will at steady state have increased the sea surface temperature by 1.9 °C, the land area temperature by 3.9 °C and the global mean temperature by 2.5 °C. Since part of this heating has already begun, further temperature increases of 1.4 °C (Ocean), 2.7 °C (Land), and 1.8 °C (Mean) should be expected (Figure 11). 

The problem is to calculate the steady-state concentration of dissolved phosphate in the five oceanic reservoirs, assuming that 95 percent of all the phosphate carried into each surface reservoir is consumed by plankton and carried downward in particulate form into the underlying deep reservoir (Figure 3-2). The remaining 5 percent of the incoming phosphate is carried out of the surface reservoir still in solution. Nearly all of the phosphorus carried into the deep sea in particles is restored to dissolved form by consumer organisms. A small fraction—equal to 1 percent of the original flux of dissolved phosphate into the surface reservoir—escapes dissolution and is removed from the ocean into seafloor sediments. This permanent removal of phosphorus is balanced by a flux of dissolved phosphate in river water, with a concentration of 10 3 mole P/m3. 

Program 0GC03 solves the steady state ocean model using Gaussian elimination and back substitution. 

The difference between the total dissolved carbon in the surface and in deep-sea reservoirs depends on productivity. And the difference between the alkalinity in these reservoirs depends on productivity and also corat, the calcium-carbonate-to-organic-carbon ratio. The carbon dioxide partial pressure depends on the difference between total carbon and alkalinity in the surface reservoir, and all these depend on the total amount of carbon and alkalinity at the start of the calculation in the three reservoirs combined. By adjusting the values of these various parameters and repeating the calculation, I arrive at the following values for a steady-state system that is close to the present-day ocean with a preindustrial level of atmospheric carbon dioxide ... 

For radiocarbon, the standard ratio s is provided by the preindustrial atmosphere, for which 8 = 0. Cosmic rays interacting with atmospheric nitrogen were the main source of preindustrial radiocarbon. In the steady state, this source drsource is just large enough to generate an atmospheric delta value equal to zero. The source appears in equation 9 for atmospheric radiocarbon. Its value, specified in subroutine SPECS, I adjust to yield a steady-state atmospheric delta value of 0. The source balances the decay of radiocarbon in the atmosphere and in all of the oceanic reservoirs. Because radiocarbon has an overall source and sink—unlike the phosphorus, total carbon, 13C, and alkalinity in this simulation—the steady-state values of radiocarbon do not depend on the initial values. 

The results for 14C are plotted in Figure 6-3. Again, the response of the atmosphere is quite pronounced. The response of the shallow ocean is less marked, and the deep ocean shows no response at all on this time scale. Radiocarbon ratios are lower in the ocean than in the atmosphere because radioactive decay reduces the 14C ratio. The difference between the steady-state atmosphere and the steady-state values in the oceanic reservoirs is an indication of how much time has elapsed since these masses of water last equilibrated with the atmosphere. Measurements of radiocarbon are an important source of information on the circulation of the deep ocean, and the differences between 13C ratios in the different reservoirs have quite different causes The deep ocean is lighter than the surface ocean because... 

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