Wednesday, February 18, 2015

Water, water everywhere and not a drop of acid!

Update 1, 2 and 3:


  1. FYI - good comment from Carbon Brief link you posted above

    Jean-Pierre Gattuso • 2 days ago

    It is unfortunate that this blog post is inaccurate and misleading, even after the correction mentioned at the end of the post.

    The paper this blog post refers to (Land et al., in press) describes how salinity estimated from space could advance the monitoring of ocean acidification. Salinity is indeed a parameter required to describe the carbonate system. It has also been used as a proxy of total alkalinity (the charge balance in seawater).

    1- Misunderstanding of basic carbonate chemistry and terminology

    The massive input of CO2 in the ocean has no effect on total alkalinity:

    CO2 + H2O -> HCO3- + H+ -> CO32- + 2H+

    It can readily be seen that the charge balance is not altered when CO2 dissolves in seawater as, at each step of the process, an equal number of positive and negative charges is released. It must be noted that other processes such as the precipitation and dissolution of calcium carbonate do affect total alkalinity. The projected decline of calcification and increase in CaCO3 dissolution as a result of ocean acidification will therefore alter total alkalinity but on centennial time scales. Hence, changes in total alkalinity and pH are totally decoupled on shorter timescales. The former, therefore, cannot be used as a proxy of the later.

    The use of the term "acidic" is also unfortunate. The definition of “acidic” in the Oxford English dictionary is “having the properties of an acid; having a pH of less than 7″. Despite the process of ocean acidification, the oceans are alkaline (pH higher than 7) and will not become acidic in the foreseeable future. Hence, the "acid" or “acidic” should not be used when referring to seawater. Note that there are few exceptions, seawater can be acidic in the immediate vicinity of CO2 vents or in purposeful perturbation experiments.

    2- Description of the carbonate system

    Two carbonate chemistry parameters are required, together with salinity and temperature, to characterise the carbonate system. Total alkalinity is one of them but it is not enough. One needs either the partial pressure of CO2, pH or the concentration of dissolved inorganic carbon. However, region-specific algorithms (described in the paper) were developed to assess the carbonate system with a limited number of parameters which can be measured at the global scale. Hence, having salinity estimates from space is an important step forward. It should be noted, however, that the precision of pH derived is quite poor and very sensitive to regional algorithms. Such approximation does not enable to use this approach to monitor the rate of ocean acidification, which is typically around 0.0002 units per year, far below the resolution of these algorithms. They can, however, be useful to monitor large swings in pH such as those generated by the upwelling of deep water.


    Dickson A., 2010. The carbon dioxide system in seawater: equilibrium chemistry and measurements. In: Riebesell U., Fabry V. J., Hansson L. & Gattuso J.-P. (Eds.), Guide to best practices for ocean acidification research and data reporting, pp. 17-40. Luxembourg: Publications Office of the European Union.

    Gattuso J.-P. & Hansson L., 2011. Ocean acidification: background and history. In: Gattuso J.-P. & Hansson L. (Eds.), Ocean acidification, pp. 1-20. Oxford: Oxford University Press.

    Land P. E., Shutler J. D., Findlay H., Girard-Ardhuin F., Sabia R., Reul N., Piolle J. F., Chapron B., Quilfen Y., Salisbury J. E., Vandemark D., Bellerby R. & Bhadury P., in press. Salinity from space unlocks satellite-based assessment of ocean acidification. Environmental Science & Technology.

    Zeebe R. E. & Gattuso J.-P., 2011. Chemistry of the seawater carbonate system. In: Gattuso J.-P. & Hansson L. (Eds.), Ocean acidification, pp. 2-3. Oxford: Oxford University Press.

  2. Thanks for the comment. This is another interesting link:
    NOAA however says acidification is the correct term, no matter it's scary in connotations: