Abstract
<p> Spectrophotometric open-ocean seawater pH measurements are simple, fast and precise. The sulfonephthalein indicator <em> m </em> -cresol purple ( <em> m </em> CP) is recommended for open-ocean surface-to-deep pH measurements. The salinity- and temperature-dependence of such measurements (293⩽ <em> T </em> ⩽303 and 30⩽ <em> S </em> ⩽37) is given as: pHT(sw) =1245.69T+ (2.11 × 10−3)(35 − S) + log(R − 0.00692.2220− R0.1330)">pHT(sw) =1245.69T+ (2.11 × 10−3)(35 − S) + log(R − 0.00692.2220− R0.1330) on the total hydrogen ion concentration scale ([H <sup> + </sup> ] <sub> T </sub> = [H <sup> + </sup> ] <sub> f </sub> + [HSO <sub> 4 </sub> <sup> − </sup> ]), in units of mol·(kg-soln) <sup> −1 </sup> . <em> R </em> is the ratio of indicator absorbances at molar absorptivity maxima (i.e. <em> R </em> + <sub> 578 </sub> <em> A </em> / <sub> 434 </sub> <em> A </em> ). The at-sea analytical precision of the technique, evaluated on two recent NOAA cruises, is approximately 0.0004 pH units.</p>
Original language | American English |
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Journal | Deep Sea Research Part I: Oceanographic Research Papers |
Volume | 40 |
DOIs | |
State | Published - Jan 1 1993 |
Disciplines
- Life Sciences