SOCAT Quality Control Cookbook - for version 2025 of the Surface Ocean CO 2 Atlas.

Abstract

This is the SOCAT quality control (QC) cookbook for SOCAT version 2025. It is an update to the cookbooks for version 1 (Olsen and Metzl, 2009), version 3 (Olsen et al., 2015; Wanninkhof et al., 2013) and version 2019 (version 7) (Lauvset et al., 2018). It incorporates the data set quality control flags defined in earlier cookbooks and reflects community discussions during the 2023 Surface Ocean pCO2 Workshop at the Flanders Marine Institute (VLIZ), Oostende, Belgium (IOCCP, 2024; Steinhoff et al., 2024). This document focuses on the quality control of a submitted dataset and does not provide information on how to upload data to SOCAT. This revision aims to maintain the quality and integrity of the SOCAT synthesis and gridded products. The outcomes of the 2021 pCO2 instrument intercomparison at VLIZ (Steinhoff et al., 2025) indicate that membrane-based sensors, including those with calibration gases, do not have a consistent uncertainty of less than 5 μatm, for reasons that we do not understand. This provides compelling justification for not assigning a flag of C to any membrane-based systems in SOCAT.