Spectrophotometric measurement of calcium carbonate saturation states in seawater. Easley, R., a., Patsavas, M., C., Byrne, R., H., Liu, X., Feely, R., & Mathis, J., T. Environmental science & technology, 12, 2012.
Spectrophotometric measurement of calcium carbonate saturation states in seawater. [pdf]Paper  Spectrophotometric measurement of calcium carbonate saturation states in seawater. [link]Website  abstract   bibtex   
Measurements of ocean pH and carbonate ion concentrations in the North Pacific and Arctic Oceans were used to determine calcium carbonate saturation states (Ω(CaCO3)) from spectrophotometric methods alone. Total carbonate ion concentrations, [CO(3)(2-)](T) were, for the first time at sea, directly measured using Pb(II) UV absorbance spectra. The basis of the method is given by: -log[CO(3)(2-)](Tspec) = log((CO3)β(1))/e(2) + log(R - e(1))/(1 - Re(3)/e(2)) where (CO3)β(1) is the PbCO(3)(0) formation constant, e(i) are molar absorptivity ratios, and R = (250)A/(234)A (ratio of absorbances measured at 250 and 234 nm). Based on shipboard and laboratory Pb(II) data and complementary carbon-system measurements, experimental parameters were determined to be (25 °C): log((CO3)β(1))/e(2) = 5.513 - 5.358x10(-2)S + 5.166x10(-4)S(2) e(1) = 0.2293 - 5.554x10(-4)S + 8.440x10(-5)S(2) e(3)/e(2) = 3.091 - 8.730x10(-2)S + 9.363x10(-4)S(2) The resulting mean difference between the shipboard spectrophotometric and conventional determinations of [CO(3)(2-)](T) was ±2.03 µmol kg(-1). The shipboard analytical precision of the Pb(II) method was ~1.71 µmol kg(-1) (2.28%). Spectrophotometric [CO(3)(2-)](T) and pH(T) were then combined to calculate Ω(CaCO3). For the case of aragonite, 95% of the spectrophotometric aragonite saturation states (Ω(Aspec)) were within ±0.06 of the conventionally calculated values (Ω(Acalc)) when 0.5 ≤ Ω(A) ≤ 2.0. When Ω(A) > 2.0, 95% of the Ω(Aspec) values were within ±0.18 of Ω(Acalc). Our shipboard experience indicates that spectrophotometric determinations of [CO(3)(2-)](T) and Ω(CaCO3) are straightforward, fast, and precise. The method yields high-quality measurements of two important, rapidly changing aspects of ocean chemistry and offers capabilities suitable for long-term automated in situ monitoring.
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 title = {Spectrophotometric measurement of calcium carbonate saturation states in seawater.},
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 year = {2012},
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 abstract = {Measurements of ocean pH and carbonate ion concentrations in the North Pacific and Arctic Oceans were used to determine calcium carbonate saturation states (Ω(CaCO3)) from spectrophotometric methods alone. Total carbonate ion concentrations, [CO(3)(2-)](T) were, for the first time at sea, directly measured using Pb(II) UV absorbance spectra. The basis of the method is given by: -log[CO(3)(2-)](Tspec) = log((CO3)β(1))/e(2) + log(R - e(1))/(1 - Re(3)/e(2)) where (CO3)β(1) is the PbCO(3)(0) formation constant, e(i) are molar absorptivity ratios, and R = (250)A/(234)A (ratio of absorbances measured at 250 and 234 nm). Based on shipboard and laboratory Pb(II) data and complementary carbon-system measurements, experimental parameters were determined to be (25 °C): log((CO3)β(1))/e(2) = 5.513 - 5.358x10(-2)S + 5.166x10(-4)S(2) e(1) = 0.2293 - 5.554x10(-4)S + 8.440x10(-5)S(2) e(3)/e(2) = 3.091 - 8.730x10(-2)S + 9.363x10(-4)S(2) The resulting mean difference between the shipboard spectrophotometric and conventional determinations of [CO(3)(2-)](T) was ±2.03 µmol kg(-1). The shipboard analytical precision of the Pb(II) method was ~1.71 µmol kg(-1) (2.28%). Spectrophotometric [CO(3)(2-)](T) and pH(T) were then combined to calculate Ω(CaCO3). For the case of aragonite, 95% of the spectrophotometric aragonite saturation states (Ω(Aspec)) were within ±0.06 of the conventionally calculated values (Ω(Acalc)) when 0.5 ≤ Ω(A) ≤ 2.0. When Ω(A) > 2.0, 95% of the Ω(Aspec) values were within ±0.18 of Ω(Acalc). Our shipboard experience indicates that spectrophotometric determinations of [CO(3)(2-)](T) and Ω(CaCO3) are straightforward, fast, and precise. The method yields high-quality measurements of two important, rapidly changing aspects of ocean chemistry and offers capabilities suitable for long-term automated in situ monitoring.},
 bibtype = {article},
 author = {Easley, Regina a and Patsavas, Mark C and Byrne, Robert H and Liu, Xuewu and Feely, Richard and Mathis, Jeremy T},
 journal = {Environmental science & technology}
}
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