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31_acidifiation - Oceanacidification GS222D.Lund Lecture31...

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Ocean acidification GS222 – D. Lund Lecture 31
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Overview - this lecture 1) Acidity 2) The carbonate system 3) Saturation state 4) Impact on marine organisms
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Acidity and dissolved CO 2 When CO dissolved in seawater it forms carbonic  acid, which releases hydrogen ions (H + ) into  solution.  Acidity is a measure of the hydrogen ions in  solution, measure on the pH scale. pH = -log [H + ] as [H + ] increases, pH decreases.  log scale  means every unit decrease in pH is a 10-fold  increase in [H + ] Draw pH vs. [H + ]
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The carbonate system Increase in [H + ] causes consumption of carbonate  ion (CO 3 2- ) Step 1.         CO 2  + H 2   H 2 CO 3        carbonic acid Step 2.         H 2 CO   H +  + HCO 3 -        bicarbonate ion Step 3.         HCO 3    H +  + CO 3 2-          carbonate ion Carbonate ion is used by many organisms to build  calcium carbonate shells: CO 3 2-  + Ca 2+    CaCO 3   Less carbonate ion in the water makes CaCO 3   more  likely to dissolve. 
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Saturation state When seawater is saturated with respect to  carbonate ion, calcium carbonate can precipitate Draw picture of carbonate ion vs. water depth. Calcium ion not a limiting factor Why does deep water have lots of CO 2 ? As a result, carbonate ion content is low in deep  water.
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Carbonate-rich sediments do not occur in the  deepest ocean Draw picture of carbonate capped ridge.
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Rate of acidity increase In last 50 years, atmospheric CO 2  increased by  ~75 ppm, or  1.5 ppm/year
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