CE18005 Blue Whiting Acoustic Survey — pCO2

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. pC02 data was collected as part of the CE18005 Blue Whiting Acoustic survey on board the RV Celtic Explorer in March/April 2018 by the Marine Institute (MI) in the North East Atlantic Ocean. Instrument information: — SST (± 0.05 deg C): During this cruise the data from the thermosalinograph were not available. Based on 9 cruises in 2018 (spread over the course of the year) where both, SST and equilibrator temp (Equ_T), were available we established a relation to calculate SST from Equ_T: The data from SST were shifted by 2 minutes to account for the time the water needs from the intake to the equilibrator. The resulting Linear function is SST = 1.01181 * Equ_T — 0.434. By Comparing the calculated SST with measured SST from cruises that were not used for establishing th erelationship we found the standard deviation of SST-SST_calc was always lower then 0.05 °C. —Equilibrator temp (± 0.05 °C): Temperature equilibrator is measured by a Fluke Hart 1523, wich is known to be stable over a longer period. It was calibrated in 2016. —SSS (± 0.5 PSU): SSS was measured with a thermosalinograph from Seabird (SBE21) which was calibrated approximately every 12 months. —Atmospheric press. (± 0.1 mbar): Atmospheric pressure was measured using a Druck barometer with a Precision of 0.2 %. The sensor is installed at approximately 5 m height and pressure is corrected to sea level. —Equilibrator press (± 2 mbar): The equilibrator is open to the atmosphere. Since no absolute pressure sensor was installed the pressure from the atmospheric pressure sensor was used. A SETRA difference pressure sensor is attached to the equilibrator. —pCO2/fCO2 (± 3 µatm): Accuracy of pCO2/fCO2 data was recalculated to be better than 2 µatm. IR sensor: Licor 7000, calibrated with 3 non-zero standard gases. Standard gases: Manufactued — Air Products, Calibrated — Mace Head Research Station (198.29 399.28 606.52]) Water flow rate: 2-3 L min-1 Stem flow rate: 80-220 mL min-1 (equilibrator stem flow was 220 mL min-1) A General Oceanics pCO2 system (model 8050) was used for pCO2 measurements. The system is described in detail in Pierrot et al.(2009). Surface water is pumped continuously from the intake to the equilibrator. The equilibrator contains a water spray head, and as the water flows through it the dissolved CO2 equilibrates with the Headspace. The Headspace is dried and xCO2 is determined by an Infrared sensor. Calculations were performed following Pierrot (2009) and are described in detail in Steinhoff (2010).