Intercomparison of carbonate chemistry measurements on a cruise in northwestern European shelf seas

[摘要] Four carbonate system variables were measured in surface waters during acruise aimed at investigating ocean acidification impacts traversingnorthwestern European shelf seas in the summer of 2011. High-resolutionsurface water data were collected for partial pressure of carbon dioxide(pCO₂; using two independent instruments) and pH using the total pHscale (pH_T), in addition to discrete measurements of totalalkalinity and dissolved inorganic carbon. We thus overdetermined thecarbonate system (four measured variables, two degrees of freedom), whichallowed us to evaluate the level of agreement between the variables on acruise whose main aim was not intercomparison, and thus where conditions weremore representative of normal working conditions. Calculations of carbonatesystem variables from other measurements generally compared well with directobservations of the same variables (Pearson's correlation coefficient alwaysgreater than or equal to 0.94; mean residuals were similar to the respectiveaccuracies of the measurements). We therefore conclude that four of theindependent data sets of carbonate chemistry variables were of high quality.A diurnal cycle with a maximum amplitude of 41 μatm was observed inthe difference between the pCO₂ values obtained by the two independentanalytical pCO₂ systems, and this was partly attributed to irregularseawater flows to the equilibrator and partly to biological activity insidethe seawater supply and one of the equilibrators. We discuss how these issuescan be addressed to improve carbonate chemistry data quality on futureresearch cruises.

[学科分类] 地球化学与岩石