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Fundamentals of Ocean pH

R. Cohen and W. Happer – September 18, 2015 (republished November 21, 2021)

1 Introduction

We are often told that the CO2 released from burning fossil fuels will cause dangerous ocean acidification. Actually the oceans will remain comfortably alkaline and hospitable to life for the foreseeable future. This brief note is a quantitative review of the physical chemistry of ocean pH. High school chemistry and algebra should provide enough background to follow the discussion. An excellent introduction to the chemistry of the oceans can be found in the book: Seawater: Its Composition, Properties and Behavior, by Wright and Colling. More details on ocean pH can be found in a recent review by Tans.

2 Alkalinity of the Unbuffered Ocean

Ocean water is salty because of the weathering of the earth’s rocks by rainwater, and because of salts dissolved from the ocean floor, especially near plate-spreading boundaries. The salt water contains positive ions (cations), mainly sodium Na+, magnesium Mg2+, calcium Ca2+ and potassium K+. For clarity, we can think of the ions as coming from the strong bases NaOH, and potassium hydroxide, KOH (lye) and much less soluble magnesium hydroxide, Mg(OH)2 and calcium hydroxide Ca(OH)2 (slaked lime). The ocean also contains negative ions (anions), mainly chloride Cl− and sulfate SO2 , which we can think of the anions as coming from the strong acids, hydrochloric acid, HCl and sulfuric acid, H2SO4. For want of a better word, we will refer to the cations of strong bases, and anions of strong acids as pH-independent ions. The concentration of pH-independent ions is unaffected by normal changes in the pH of water.

Download the entire paper here: 2015 Cohen Happer Fundamentals of Ocean pH

Roger Cohen was a co-founder of the CO2 Coalition and a highly regarded physicist with major contributions to materials science and industrial management. He passed away on September 10, 2016, less than one year after completing this important paper.

 

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