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

Daniel E Kerr,Peter J Brown,Anthony Grey,Brian P Kelleher

doi:10.1016/j.marchem.2021.104050

Daniel E Kerr, Peter J Brown + Show 2 more

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https://doi.org/10.1016/j.marchem.2021.104050

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Abstract

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.

Highlights

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
The latter is commonly used to track ocean acidification because it is a measure of carbonate ion concentration. pH is one of the four main parameters, the other three being dissolved inorganic carbon (DIC), fugacity of CO2 and total alkalinity (TA) (Dickson et al, 2007)
The purpose of this review is to provide an overview of organic alkalinity (OrgAlk) contributions to TA, how it is quantified, as well as discuss the implications of its omission in carbonate system studies conducted in coastal waters

Summary

Introduction

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. Accurate TA assessment is important in our understanding of the risks associated with the acidification of marine waters This is especially relevant in littoral systems, as the carbonate chemistry of coastal waters is substantially more dynamic than the open ocean (Borges and Gypens, 2010).

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