JERICO-NEXT TNA: Intercomparison of instruments for carbonate system measurements (INTERCARBO)

Continental margins are among the most biologically active areas on Earth. Although they cover only a small portion of the oceans, they contribute up to 15% of ocean primary production, are responsible for over 40% of the total oceanic carbon sequestration and for the vast majority of commercial fisheries. Carbon fluxes in coastal seas are more complex than those in the open ocean, in part due to high spatiotemporal variability in biological activity and physical processes. In the European coastal areas, complications also rise from the highly variable hydrography: sea surface temperature may vary from below zero degrees on the coast of Spitsbergen up to 30°C in the Mediterranean Sea, while salinity varies from 0 ‰ at the Bothnian Bay, the Baltic Sea, up to more than 38 ‰ in the Mediterranean Sea. This large variability creates challenges related to instrument accuracy, reliability and maintenance. As there are only a limited number of instruments available for such a highly variable range of environmental conditions, different research groups have often built their own instruments or modified the commercial instruments suitable for their own needs. This has led to a situation which sometimes makes assimilation of the data observed in different areas challenging. The aim of the INTERCARBO experiment, partly funded by TransNational Access (TNA) of H2020 infrastructure project Joint European Research Infrastructure network for Coastal Observatory – Novel European eXpertise for coastal observaTories (JERICO-NEXT) was to bring together a large number of carbon dioxide partial pressure (pCO2), pH and total alkalinity sensors used on European coastal seas and to compare measurements using different sensors on the same seawater samples. During the activity, 17 experiments were carried out in three 1 m3 tanks that were filled with seawater that was obtained from Oslofjord. The seawater was manipulated in order to meet predetermined physical and chemical properties. Three salinity conditions (5, 20, and 35 PSU) were generated by introducing fresh water from a local well. Three carbon dioxide target values of approximately 200, 400, and 800 parts per million (ppm) were targeted by equilibrating the water with the corresponding CO2 gases (due to high alkalinity and limited duration of the experiment, these target values were not always reached). The measurements were made on seawater at 10 °C and 20 °C. This data set presented here contains currently available pCO2 a