Observations of the marine CO₂ system are important for understanding ocean acidification, air-sea CO₂ fluxes and the marine carbon cycle in general. A variety of autonomous in situ instruments have been developed and used towards this end. There is, however, a lack of inter-comparison studies of currently available sensor technologies. In this study, a total of 10 instruments including commercially available pH, partial pressure of CO₂ (pCO₂), and total alkalinity (A_T) sensors were tested and compared in a 5000 L seawater tank located at Scripps Institution of Oceanography (SIO), California, USA. The test took place over ~12 days (August 16 to 28, 2016) where conditions in the tank were artificially varied to encompass a wide range of A_T, pH and pCO₂ as well as temperature and salinity. To assess accuracy, independent measurements of pH, pCO₂, dissolved inorganic carbon (DIC) and A_T were made using benchtop instrumentation. We also evaluated internal consistency, comparing the measured parameter from the sensors with the calculated parameter, e.g. pCO₂ calculated from A_T and pH compared with directly measured pCO₂. DIC can be precisely derived (within ±5 μmol/kg) over a wide range of conditions from measured pH or pCO₂ paired with A_T. Sensor accuracy established by discrete samples is sufficient for short-term and seasonal dynamical studies, but their ability in determining long-term (e.g. climate) variability could not be evaluated because of the brevity of the study. These results provide insights into sensor performance and strategies for data quality control for future studies of ocean acidification and carbon cycling.

_{海洋CO 2}系统的观测对于了解海洋酸化、海气-CO ₂通量和海洋碳循环具有重要意义。为此，已经开发和使用了多种自主原位仪器。然而，目前可用的传感器技术缺乏相互比较研究。在这项研究中，共有 10 种仪器，包括市售的 pH 值、CO ₂分压( p CO ₂ ) 和总碱度 (A _T) 传感器在位于美国加利福尼亚州斯克里普斯海洋研究所 (SIO) 的 5000 L 海水箱中进行了测试和比较。测试进行了约 12 天（2016 年 8 月 16 日至 28 日），其中人为改变水箱中的条件以涵盖广泛的 A _T、pH 和p CO ₂以及温度和盐度。为了评估准确性，使用台式仪器对 pH、p CO ₂、溶解的无机碳 (DIC) 和 A _T进行了独立测量。我们还评估了内部一致性，将传感器的测量参数与计算的参数进行比较，例如从 A _T计算的p CO ₂和 pH 值与直接测量的p CO ₂相比。DIC 可以在广泛的条件下从测量的 pH 值或p CO ₂与 A _T精确导出（在 ±5 μmol/kg 范围内） 。由离散样本建立的传感器精度足以进行短期和季节性动态研究，但由于研究的简短性，无法评估它们确定长期（例如气候）变率的能力。这些结果为未来海洋酸化和碳循环研究的传感器性能和数据质量控制策略提供了见解。