The influence of organic alkalinity on the carbonate system in coastal waters


  • Growing consensus that organic matter contributions to alkalinity is significant.
  • Organic alkalinity prevalent in the coastal ocean.
  • Methods to quantify and characterise organic alkalinity are detailed.
  • Possibile to reduce propagated errors in carbonate system descriptors.


Total alkalinity (TA) is one of the four main carbonate system variables and is a conventionally measured parameter used to characterise marine water carbonate chemistry. It is an important indicator of a waterbody’s buffering capacity and a measure of its ability to resist acidification, a matter of growing concern in the marine environment. Although TA is primarily associated with the inorganic components of seawater such as bicarbonate, there is a growing consensus that dissolved organic matter (DOM) can significantly contribute to TA in coastal waters. This organic fraction of TA (OrgAlk) is typically deemed negligible and is not accounted for in conventional TA expressions. However, omission of OrgAlk can lead to the propagation of errors in subsequent carbonate system calculations and to misinterpretation of key carbonate chemistry descriptors such as calcium carbonate saturation states. Here we provide an overview of OrgAlk contributions to TA and investigate the implications of its omission in carbonate system studies conducted in coastal waters. We examine the prevalence of OrgAlk across both coastal and pelagic waters using publicly available carbonate system data products, such as GLODAP and GOMECC. Current measures to account for, incorporate and characterise the contribution of OrgAlk to TA are also critically examined.

Kerr D. E., Brown P. J., Grey A. & Kelleher B. P., 2021. The influence of organic alkalinity on the carbonate system in coastal waters. Marine Chemistry: 104050. doi: 10.1016/j.marchem.2021.104050. Article.

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