Spectrophotometric Measurement of Calcium Carbonate Saturation States in Seawater

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• 作者：Regina A. Easley ; Mark C. Patsavas ; Robert H. Byrne ; Xuewu Liu ; Richard A. Feely ; Jeremy T. Mathis
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2013
• 出版时间：February 5, 2013
• 年：2013
• 卷：47
• 期：3
• 页码：1468-1477
• 全文大小：633K
• 年卷期：v.47,no.3(February 5, 2013)
• ISSN：1520-5851

文摘

Measurements of ocean pH and carbonate ion concentrations in the North Pacific and Arctic Oceans were used to determine calcium carbonate saturation states (惟_CaCO3) from spectrophotometric methods alone. Total carbonate ion concentrations, [CO₃^{2鈥?/sup>]_T, were for the first time at sea directly measured using Pb(II) UV absorbance spectra. The basis of the method is given by the following: where _CO3尾₁ is the PbCO₃0 formation constant, e_i are molar absorptivity ratios, and R = ₂₅₀A/₂₃₄A (ratio of absorbances measured at 250 and 234 nm). On the basis of shipboard and laboratory Pb(II) data and complementary carbon-system measurements, the experimental parameters were determined to be (25 掳C) the following: The resulting mean difference between the shipboard spectrophotometric and conventional determinations of [CO₃2鈥?/sup>]_T was 卤2.03 渭mol kg鈥?. The shipboard analytical precision of the Pb(II) method was 1.71 渭mol kg鈥? (2.28%). Spectrophotometric [CO₃2鈥?/sup>]_T and pH_T were then combined to calculate 惟_CaCO3. For the case of aragonite, 95% of the spectrophotometric aragonite saturation states (惟_Aspec) were within 卤0.06 of the conventionally calculated values (惟_Acalc) when 0.5 鈮?惟_A 鈮?2.0. When 惟_A > 2.0, 95% of the 惟_Aspec values were within 卤0.18 of 惟_Acalc. Our shipboard experience indicates that spectrophotometric determinations of [CO₃2鈥?/sup>]_T and 惟_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.}