Eric T. Sundquist
Niel Plummer
1982
<p><span>We have calculated the total individual ion activity coefficients of carbonate and calcium, </span><span id="mmlsi1" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si1.gif" alt="" width="49" height="17" data-inlimgeid="1-s2.0-0016703782902526-si1.gif" data-loaded="true" /></span><span> and </span><span id="mmlsi2" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si2.gif" alt="" width="47" height="12" data-inlimgeid="1-s2.0-0016703782902526-si2.gif" data-loaded="true" /></span><span>, in seawater. Using the ratios of stoichiometric and thermodynamic constants of carbonic acid dissociation and total mean activity coefficient data measured in seawater, we have obtained values which differ significantly from those widely accepted in the literature. In seawater at 25°C and 35%. salinity the (molal) values of </span><span id="mmlsi3" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si3.gif" alt="" width="49" height="15" data-inlimgeid="1-s2.0-0016703782902526-si3.gif" data-loaded="true" /></span><span> and </span><span id="mmlsi4" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si4.gif" alt="" width="47" height="14" data-inlimgeid="1-s2.0-0016703782902526-si4.gif" data-loaded="true" /></span><span> are </span><span id="mmlsi5" class="mathmlsrc"><span class="formulatext stixSupport mathImg" title="Click to view the MathML source" data-mathurl="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-0016703782902526&_mathId=si5.gif&_user=111111111&_pii=0016703782902526&_rdoc=1&_issn=00167037&md5=c4d1b5c6500dfcea4f27e42ca1f665a6">0.038 ± 0.002</span></span><span> and </span><span id="mmlsi6" class="mathmlsrc"><span class="formulatext stixSupport mathImg" title="Click to view the MathML source" data-mathurl="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-0016703782902526&_mathId=si6.gif&_user=111111111&_pii=0016703782902526&_rdoc=1&_issn=00167037&md5=ddfd94fcad1351b0539d76c9086cfc23">0.173 ± 0.010</span></span><span>, respectively. These values of </span><span id="mmlsi7" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si7.gif" alt="" width="49" height="17" data-inlimgeid="1-s2.0-0016703782902526-si7.gif" data-loaded="true" /></span><span> and </span><span id="mmlsi8" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si8.gif" alt="" width="47" height="12" data-inlimgeid="1-s2.0-0016703782902526-si8.gif" data-loaded="true" /></span><span> are independent of liquid junction errors and internally consistent with the value </span><span id="mmlsi9" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si9.gif" alt="" width="102" height="16" data-inlimgeid="1-s2.0-0016703782902526-si9.gif" data-loaded="true" /></span><span>. By defining </span><span id="mmlsi10" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si10.gif" alt="" width="47" height="12" data-inlimgeid="1-s2.0-0016703782902526-si10.gif" data-loaded="true" /></span><span> and </span><span id="mmlsi11" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si11.gif" alt="" width="49" height="17" data-inlimgeid="1-s2.0-0016703782902526-si11.gif" data-loaded="true" /></span><span> on a common scale (</span><span id="mmlsi12" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si12.gif" alt="" width="40" height="12" data-inlimgeid="1-s2.0-0016703782902526-si12.gif" data-loaded="true" /></span><span>), the product </span><span id="mmlsi13" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si13.gif" alt="" width="47" height="12" data-inlimgeid="1-s2.0-0016703782902526-si13.gif" data-loaded="true" /></span><span id="mmlsi14" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si14.gif" alt="" width="49" height="17" data-inlimgeid="1-s2.0-0016703782902526-si14.gif" data-loaded="true" /></span><span> is independent of the assigned value of </span><span id="mmlsi15" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si15.gif" alt="" width="34" height="12" data-inlimgeid="1-s2.0-0016703782902526-si15.gif" data-loaded="true" /></span><span> and may be determined directly from thermodynamic measurements in seawater. Using the value </span><span id="mmlsi16" class="mathmlsrc"><img class="imgLazyJSB inlineImage" title="" src="http://ars.els-cdn.com/content/image/1-s2.0-0016703782902526-si16.gif" alt="" width="171" height="21" data-inlimgeid="1-s2.0-0016703782902526-si16.gif" data-loaded="true" /></span><span> and new thermodynamic equilibrium constants for calcite and aragonite, we show that the apparent constants of calcite and aragonite are consistent with the thermodynamic equilibrium constants at 25°C and 35%. salinity. The demonstrated consistency between thermodynamic and apparent constants of calcite and aragonite does not support a hypothesis of </span><i>stable</i><span> Mg-calcite coatings on calcite or aragonite surfaces in seawater, and suggests that the calcite critical carbonate ion curve of Broecker and Takahashi (1978,</span><i>Deep-Sea Research</i><span class="boldFont">25</span><span>, 65–95) defines the calcite equilibrium boundary in the oceans, within the uncertainty of the data.</span></p>
application/pdf
10.1016/0016-7037(82)90252-6
en
Elsevier
Total individual ion activity coefficients of calcium and carbonate in seawater at 25°C and 35%. salinity, and implications to the agreement between apparent and thermodynamic constants of calcite and aragonite
article