Bicarbonate concentration ocean

Rainwater and snowmelt water are primary factors determining the very nature of the terrestrial carbon cycle, with photosynthesis acting as the primary exchange mechanism from the atmosphere. Bicarbonate is the most prevalent ion in natural surface waters (rivers and lakes), which are extremely important in the carbon cycle, accoxmting for 90% of the carbon flux between the land surface and oceans (Holmen, Chapter 11). In addition, bicarbonate is a major component of soil water and a contributor to its natural acid-base balance. The carbonate equilibrium controls the pH of most natural waters, and high concentrations of bicarbonate provide a pH buffer in many systems. Other acid-base reactions (discussed in Chapter 16), particularly in the atmosphere, also influence pH (in both natural and polluted systems) but are generally less important than the carbonate system on a global basis. 

Equation 8.26 predicts a concentration of CO2 in one litre of water at 25°C of 3.32 x 10-2 moll-1 at a pressure of 1 bar. The pH of the oceans is related to the amount of dissolved C02 but also to the equilibria controlling the formation of carbonic acid and the bicarbonate and carbonate ions ... 

Vertical concentration profiles of (a) temperature, (b) potential density, (c) salinity, (d) O2, (e) % saturation of O2, (f) bicarbonate and TDIC, (g) carbonate alkalinity and total alkalinity, (h) pH, (i) carbonate, ( ) carbon dioxide and carbonic acid concentrations, and (k) carbonate-to-bicarbonate ion concentration ratio. Curves labeled f,p have been corrected for the effects of in-situ temperature and pressure on equilibrium speciation. Curves labeled t, 1 atm have been corrected for the in-situ temperature effect, but not for that caused by pressure. Data from 50°27.5 N, 176°13.8 W in the North Pacific Ocean on June 1966. Source From Culberson, C., and R. M. Pytkowicz (1968). Limnology and Oceanography, 13, 403-417. 

Concentrations of bicarbonate and calcium in many rivers conform to the mass balance for Reaction A [HC03 ] 2[Ca24 ]. [Data from w. stumm and J. J. Morgan, Aquatic Chemistry, 3rd ed. (New York Wiley-lnterscience. 1996). p. 189 and H. D. Holland. The Chemistry of the Atmosphere and Oceans (New York Wiley-lnterscience, 1978).]... 

Infrared absorption in the atmosphere can have the same effect. Over the last century the concentration of carbon dioxide in the atmosphere has risen dramatically because of combustion. As a result, the atmosphere now absorbs more infrared radiation than it did in the past, and cooling into space is less efficient. A likely consequence is global warming, although a detailed calculation of the magnitude of the expected effect is far from simple. For example, while is it not difficult to estimate total CO2 emissions from combustion, most of these molecules end up in the ocean as carbonates or bicarbonates, and do not directly contribute to global warming. Nonetheless, there is broad consensus in the scientific community that carbon dioxide emissions will tend to increase the Earth s temperature over the next few decades, with environmental consequences which may be severe. 

Highly saline environments are not only directly associated with present seas and oceans, but also with former seas which have led to salt deposition. These are generally hypersaline environments and may include salt lakes such as the Dead Sea, where salt concentrations may reach 4-5 M NaCl (Buchalo et al., 1998), together with salt pans and flats. In many cases, these are dominated by other ions such as potassium, magnesium, calcium, sulphate, carbonate and bicarbonate, as well as sodium and chloride. Flowers et al. (1986) estimated that about 10% of global land area was occupied by soils too saline for the growth of non-halophiles. 

There is —50 times more carbon in the ocean than in the atmosphere, and it is the amount of Die in the ocean that determines the atmospheric concentration of CO2. In the long term (millennia) the most important process determining the exchanges of carbon between the oceans and the atmosphere is the chemical equilibrium of dissolved CO2, bicarbonate, and carbonate in the ocean. The rate at which the oceans take up or release carbon is slow on a century timescale, however, because of lags in circulation and changes in the availability of calcium ions. The carbon chemistry of seawater is discussed in more detail in the next section. 

At steady state the rate of bicarbonate removal by CaCOs precipitation in the ocean is given by two times the flux of calcium from rivers, based on the river flow rate and Ca + concentration in Table 2.3. (This is an upper limit for the removal of HCOif by precipitation of CaCOs because a small amount of the Ca + from rivers is precipitated as anhydrite in the Mackenzie and Carrels mass balance, Table 2.4.)... 

Seawater has nearly equal amounts of alkalinity and DIG because the main source of these properties is riverine bicarbonate ion, which makes equal contributions to both constituents. The processes of CaCOs precipitation, hydrothermal circulation, and reverse weathering in sediments remove alkalinity and DIG from seawater and maintain present concentrations at about 2 mmol (meq) kg . Reconciling the balance between river inflow and alkalinity removal from the ocean is not well rmderstood, and is discussed in much greater detail in Ghapter 2. 

Seawater has remarkably constant relative concentrations of major ions in all the world s oceans. For example the Na+ CF ratio changes by less than 1% from the Arabian Gulf to the Southern Ocean. In the oceans, bicarbonate ions (HCO3) and Ca2+ are biologically cycled (Section 6.4.4), causing vertical gradients in their ratios relative to the other major ions. However, the differences in the ratios to Na+ are small—less than 1% for calcium. 

Thus in the Archaean, when initially there was no life - or life of a different kind, when the atmosphere was more C02-rich and less oxygenic, and when landmasses were smaller, but weathering processes more aggressive, it is to be expected that sea water had a very different composition from the present day. In fact, in an early study Walker (1983) suggested that in the Archaean oceans had a lower pH and a lower carbonate and sulfate content, but higher concentrations of Ca, Fe2+, Ba, Si, Na, Cl and bicarbonate. 

Figure 9.4 shows the distribution of carbonate and calcium species in ocean water and in an anoxic pore water, calculated with the program PHREEQC (Parkhurst 1995). It is evident that about 10 % of total calcium is prevalent in the form of ionic complexes and 25 - 30 % of the total dissolved carbonate in different ionic complexes other than bicarbonate. These ionic complexes are not included in the equations of Sections 9.3.1 and 9.3.2. Accordingly, the omission of these complexes would lead to an erraneous calculation of the equilibrium. The inclusion of each complex shown in Figure 9.4 implies further additions to the system of equations, consisting in another concentration variable (the concentration of the complex) and a further equation (equilibrium of the complex concentration relative to the non-... 

Once CO2 dissolves in water, an equilibrium is established among dissolved C02 (C02 H20), bicarbonate ions (HCOJ), and carbonate ions (C03 ) (see Chapter 7). Thus, while the sea-to-air fluxes F2i and F31 can be linearly related to dissolved C02 (C02 H20), they are not linearly related to the total dissolved carbon (M2 and M3), which is the sum of C02 H20, HCO, and C03. This relationship depends on seawater temperature and pH, the latter of which depends in a complex way on salinity and concentrations of dissolved salts. Seawater pH varies between 7.5 and 8.4, and therefore most of the C02 that dissolves in the ocean is not in the C02 H20 form (Chapter 7). For the purpose of a global carbon cycle model, one wishes to avoid the complication of an explicit ocean chemistry model to relate F21 and F3J to M2 and M3, respectively. The following empirical relationship has been developed (Ver et al., 1999)... 

Although Pu(V) readily disproportionates at concentrations 10 M in acidic solutions, it is the state observed in more basic natural and ocean waters, partly due to the stability of the bicarbonate complex, cf. Ch. 22. 

Figure 8 Conceptual diagram of a simplified carbonate pump . Some marine organisms form calcareous skeletal material, a portion of which sinks as calcium carbonate aggregates. These aggregates are preserved in shallow ocean sediments or dissolve at greater depths (3000-5000 m), thus increasing DIG concentrations in the deep ocean. The calcium and bicarbonate are returned to the surface ocean through upwelling.

Adult Fish Water 90 mg/L sodium bicarbonate (Sigma or Aquatic Ecosystems), 50 mg/L Instant Ocean Salt (Aquatic Ecosystems), 10 mg/L calcium sulfate. Due to differences in local water sources, these parameters should be used as a guideline in particular, the amount of Sodium Bicarbonate may vary and should be added at a concentration that yields a pH of around 7.5. 

Furthermore, CO2 uptake leads to so-called oceanic acidification. With a very good approximation (i.e. neglecting the carbonate concentration compared with that of bicarbonate), equation (2.130) can be reduced to ... 

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