pCO2 is the partial pressure of CO2 in a liquid or gas. In oceanography, it is used to investigate carbon dioxide (CO2) dissolved in the surface layers of the ocean in order to better understand changes in ocean carbon chemistry and ocean acidification due to enhanced atmospheric CO2. The RV Celtic Explorer has a pCO2 Underway System. pCO2 data was collected as part of the CE18016 Celtic Sea Herring Acoustic Survey on board the RV Celtic Explorer in October 2018. Collect pC02 data (partial pressure of CO2 in a liquid or gas) to investigate carbon dioxide (CO2) dissolved in the surface layers of the ocean which contributes towards our understand of changes in ocean carbon chemistry and ocean acidification due to enhanced atmospheric CO2.