| Summary: | This chapter is about the ongoing human-induced shifts in fundamental ocean carbonate chemistry that are occurring globally and are a growing concern to scientists studying marine organisms. It reviews the current state of ocean pH and related carbonate system variables, how they have changed during the industrial era, and how they are expected to continue to change during this century and beyond. Surface-ocean pH has been relatively stable for millions of years, until recently. Over the 800 000 years prior to industrialization, average surfacewater pH oscillated between 8.3 during cold periods (e.g. during the Last Glacial Maximum, 20 000 yr ago) and 8.2 during warm periods (e.g. just prior to the Industrial Revolution), as reviewed by Zeebe and Ridgwell in Chapter 2. But human activities are upsetting this stability by adding large quantities of a weak acid to the ocean at an ever increasing rate. This anthropogenic problem is referred to as ocean acidification because ocean acidity is increasing (i.e. seawater pH is declining), even though surface-ocean waters are alkaline and will remain so. The cause of the decline in seawater pH is the atmospheric increase in the same gas that is the main driver of climate change, namely carbon dioxide (CO2). Due to increasing atmospheric CO2 concentrations, the ocean takes up large amounts of anthropogenic CO2, currently at a rate of about 106 metric tons of CO2 per hour (Brewer 2009), which is equivalent to one-fourth of the current global CO2 emissions from combustion of fossil fuels, cement production, and deforestation (Canadell et al. 2007 Le Quéré et al. 2009 ). If we would partition these emissions equally per capita, each person on the planet would be responsible for 4 kg per day of anthropogenic CO2 invading the ocean. To grasp the size of the problem, this invisible invasion may be compared with a recent, highly visible environmental disaster. The ocean currently absorbs anthropogenic carbon at a rate that is about a thousand times greater than from when ...
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