The oceans have absorbed approximately 30% of the atmospheric carbon dioxide (CO2) emitted by humankind since the beginning of the Industrial Revolution and they serve as an important net carbon sink (Sabine et al. 2004.) Although oceans, as carbon sinks, reduce the rate of CO2 increase in the atmosphere, the absorption process has a direct and measurable impact on ocean chemistry. Since the late 18th century, the mean surface ocean pH has dropped 0.1 units from 8.2 to 8.1. Because pH is measured on a logarithmic scale (a unit change of 1.0 is equal to a tenfold change in concentration), this change is roughly equivalent to a 30% increase in the concentration of hydrogen ions ...view middle of the document...
It has been hypothesized that there was an input of CO2 to the deep ocean, presumably the result of a massive volcanic methane release of about 2000 gigatons of carbon over approximately 10,000 years (Zachos et al. 2005, 2008.) In this scenario, methane would have been rapidly oxidized into CO2, lowering the pH and carbonate ion concentration in the deep sea. The fossil record indicates that this massive methane-release event was followed by the extinction of several bottom-dwelling foraminifera species, single-celled organisms with calcareous shells (Zachos et al. 2005.) Although knowledge of this ancient event may help us to predict what might happen to ocean pH and biota under contemporary conditions (Zachos et al. 2005,) today's world is much different. Current rates of ocean acidification are faster, preindustrial levels of CO2 and temperature were lower, and a vastly different marine biota occupies the oceans today (Doney et al. 2009.)
Review of Literature:
Changes in ocean chemistry will probably impact marine life in three different ways. Decreased carbonate ion concentration could affect the calcification process for calcifying organisms (e.g., corals), the lowered pH could affect acid-base regulation, as well as a variety of other physiological processes, and increased dissolved CO2 could alter the ability of primary producers, such as phytoplankton, to photo-synthesize. Most of the research in the field has focused on calcification effects.
Many organisms use calcium and carbonate ions from seawater to produce calcium carbonate, a compound used for skeletal support (e.g., corals) and protection (e.g., snail shells). The three mineral forms of calcium carbonate commonly produced are aragonite, calcite, and high-magnesium calcite (Raven et al. 2005.) Aragonite calcifiers (e.g., stony corals and shelled pteropods) and high-magnesium calcite calcifiers (e.g., coralline algae and sea urchins) are likely to be affected by ocean acidification more strongly than calcite calcifiers (e.g., foraminifera and coccolithophores). This distinction is because of differences in the solubility of mineral forms; for example, aragonite is approximately 50% more soluble than calcite (Doney et al. 2009.)
For many organisms, a decrease in the calcium carbonate saturation state has been correlated with a reduction in calcification rates, even when waters remain supersaturated with respect to aragonite and calcite (Kleypas et al. 2005, Fabry et al. 2008.) Under laboratory conditions, several calcifying organisms, including abundant planktonic species (e.g., coccolithophores, pteropods, foraminifera) and benthic invertebrates (e.g., coral, calcifying algae, molluscs, echinoderms), have shown a reduction in calcification rates as a result of reduced carbonate ion concentration (Raven et al. 2005, Fabry et al. 2008.) However, the impact of lower carbonate concentration on calcification rates varies among species, and there is evidence that acidification may even...