Four carbonate system variables were measured in surface waters during a cruise traversing northwestern European shelf seas in the summer of 2011. High resolution surface water data were collected for partial pressure of carbon dioxide (pCO2; using two independent instruments) and pHT, in addition to discrete measurements of total alkalinity and dissolved inorganic carbon. We thus overdetermined the carbonate system (four measured variables, two degrees of freedom) which allowed us to evaluate the level of agreement between the variables. Calculations of carbonate system variables from other measurements generally compared well (Pearson’s correlation coefficient always ≥ 0.94; mean residuals similar to the respective uncertainties of the calculations) with direct observations of the same variables. We therefore conclude that the four independent datasets of carbonate chemistry variables were all of high quality, and as a result that this dataset is suitable to be used for the evaluation of ocean acidification impacts and for carbon cycle studies. A diurnal cycle with maximum amplitude of 41 µatm was observed in the difference between the pCO2 values obtained by the two independent analytical pCO2 systems, and this was partly attributed to irregular seawater flows to the equilibrator and partly to biological activity inside the seawater supply and one of the equilibrators. We discuss how these issues can be addressed to improve carbonate chemistry data quality on research cruises.
2793-2822. Article.
Intercomparison of carbonate chemistry measurements on a cruise in northwestern European shelf seas
Published 19 February 2014 Science ClosedTags: chemistry, field, methods, North Atlantic
