Seawater carbonate

The evolution of the profiles of the isotope ratio is shown in Figure 8-12, which plots the profiles at various times in the calculation. Early in the calculation, isotope ratios at shallow depths have been driven more negative by the release of isotopically light respiration carbon, but little change has occurred at greater depths. As the evolution proceeds, the ratios at shallow depths become more positive as the result of the dissolution and diffusion of heavier carbon from both above and below. In the final steady state, after some 15,000 years, the isotope ratio is nearly constant at about -0.6 per mil at depths below 100 centimeters, rising rapidly to the seawater value, +2 per mil in the top 100 centimeters. The final values reflect a balance between the release of isotopically light carbon by respiration and the release of isotopically heavy carbon by dissolution, with the additional influence of the diffusion of isotopically heavy seawater carbon. 

Lithium isotope data from carbonate shells of other marine invertebrates have been reported. Hoefs and Sywall (1997) determined isotopic compositions of seven different species of modem bivalves from the North Sea coast. These samples had a relatively small range in 5 Li (+15 to +21), which corresponds well to the seawater-carbonate offset from inorganic calcite and modem corals (Marriott et al. 2004). 

Spero HJ, Bijma J, Lea DW, Bemis BE (1997) Effect of seawater carbonate concentration on foraminiferal carbon and oxygen isotopes. Nature 390 497-500 Spivack AJ, Edmond JM (1986) Determination of boron isotope ratios by thermal ionization mass spectrometry of the dicesium metaborate cation. Anal Chem 58 31-35 Spivack AJ, Edmond JM (1987) Boron isotope exchange between seawater and the oceanic crust. Geochim Cosmochim Acta 51 1033-1043... 

Zachos J, Pagani M, Sloan L, Thomas E, BiUups K (2001) Trends, rhythms and aberrations in global climate 65 Ma to present. Science 292 686-693 Zeebe RE (1999) An explanation of the effect of seawater carbonate concentration on foraminiferal oxygen isotopes. Geochim Cosmochim Acta 63 2001-2007 Zeebe RE (2005) Stable boron isotope fractionation between dissolved B(OH)3 and BlOH). Geochim Cosmochim Acta 69 2753-2766... 

Sea salt aerosol initially consists mainly of seawater (see Table 1). Organic carbon is present in sea salt particles as well, typically enriched in smaller sea salt aerosols compared to bulk seawater carbon (e.g., Blanchard, 1964 Hoffman and Duce, 1977 Blanchard and Woodcock, 1980 Middlebrook et al., 1998 Turekian et al., 2003). This organic carbon originates from three... 

Spero H. J., Bijma J., Lea D. W., and Bemis B. (1997) Effect of seawater carbonate chemistry on planktonic foraminiferal carbon and oxygen isotope values. Nature 390, 497-500. 

Another practical consideration when dealing with the seawater carbonic acid system is that in addition to carbonate alkalinity, H and OH , a number of other components can contribute to the total alkalinity (TA). The seawater constituent that is usually most important is boric acid. Under most conditions, boric acid contributes — 0.1 mmol alkalinity it is usually taken into consideration when making calculations. Nutrient compounds, such as ammonium, phosphate, and silica, whose concentrations in seawater are highly variable, can also influence alkalinity. They must be taken into account for very precise work. In anoxic pore waters a number of compounds, such as hydrogen sulfide and dissolved organic matter, can be significant contributors to alkalinity (e.g., see Berner et al, 1970). 

Carbon disulfide is stable to hydrolysis in the pH region of environmental concern (pH 4-10). At pH 13, carbon disulfide has a hydrolysis half-life at of about 1 hour at 25 C by extrapolation, at pH 9, carbon disulfide has a half-life of 1.1 years (EPA 1978a). In oxygenated seawater, carbon disulfide was found to be stable for over 10 days (Lovelock 1974). The volatilization half-life from a saturated water solution has been estimated to be 11 minutes (EPA 1978a). The compound apparently does not undergo biodegradation at rates that are competitive with its volatilization from surface waters. 

The profound consequences of controlled culture experiments for palaeoceanographic interpretations were widely recognized in 1997, when Spero and coworkers demonstrated that the seawater carbonate chemistry significantly affects and 8 0 in planktonic foraminifera (Spero et al. 1997 Bijma et al. 1999). This phenomenon has been referred to as the carbonate ion effect . While palaeoceanogra-phers had long been aware that temperature and seawater 8 0 affect foraminiferal 8 0 (Emiliani 1955 Shackleton 1967), another important player, the ocean s CO2 chemistry, had to be added to the... 

Zeebe, R. E. 1999. An explanation of the effect of seawater carbonate concentration on foraminiferal oxygen isotopes. Geochimica et Cosmochimica Acta, 63, 2001-2007. 

Culturing experiments revealed that the stable isotopic composition of planktic foraminiferal tests responds to changes in seawater carbonate ion concentration (Spero et al. 1997). Recently, this so-called carbonate ion effect (CIE) was applied to interpret deviations of values of planktic... 

Effect of seawater carbonate concentration on foraminiferal carbon and oxygen isotopes. Nature, 390, 497-500. 

A pressure- and temperature-independent property of seawater that determines in part the carbon content of seawater. Carbonate alkalinity is the sum of the concentration of bicarbonate plus two times the concentration of the... 

Fig. 2.95 Relationship between atmospheric CO2 mixing ratio and seawater pH assuming a pH of 8.25 at a CO2 mixing ratio of 280 ppm and constant seawater carbonate concentration.

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