Dissolved inorganic carbon (DIC) and its stable isotope (δ¹³C-DIC) are powerful tools for exploring aquatic biogeochemistry and the carbon cycle. Traditionally, they are determined separately with a DIC analyzer and an isotope ratio mass spectrometer. We present an approach that uses a whole-water CO₂ extraction device coupled to a Cavity Ring-Down Spectroscopy (CRDS) CO₂ and isotopic analyzer to measure DIC and δ¹³C-DIC simultaneously in a 3–4 mL sample over an ~11 min interval, with an average precision of 1.5 ± 0.6 μmol kg⁻¹ for DIC and 0.09 ± 0.05‰ for δ¹³C-DIC. The system was tested on samples collected from a Chesapeake Bay cruise in May 2016, achieving a precision of 0.7 ± 0.5 μmol kg⁻¹ for DIC and 0.05 ± 0.02‰ for δ¹³C-DIC. Using the simultaneously measured DIC and δ¹³C-DIC data, the biogeochemical controls on DIC and its isotope composition in the bay during spring are discussed. In the northern upper bay, the main controlling processes were CO₂ outgassing and carbonate precipitation, whereas primary production (surface) and degradation of organic carbon (subsurface) dominated in the southern upper bay and middle bay. By improving the mode of sample introduction, the system could be automated to measure multiple samples. This would give the system the potential to provide continuous shipboard measurements during field surveys, making this method more powerful for exploring the complicated carbonate system across a wide range of aquatic settings.

溶解的无机碳（DIC）和其稳定同位素（δ ¹³ C-DIC）是浏览水生生物地球化学和碳循环的强大工具。传统上，它们是使用DIC分析仪和同位素比质谱仪分别确定的。我们提出了一种方法，使用一个全水CO ₂耦合到一个光腔衰荡光谱法（CRDS）CO提取装置₂和同位素分析仪测量DIC和δ ¹³ 3-4毫升的样品通过一个在同时C-DIC〜 11分钟的时间间隔，用1.5±0.6微摩尔千克的平均精度^-1为DIC和0.09±0.05‰，δ ¹³C-DIC。该系统上2016年5月从切萨皮克湾巡航收集的样品进行测试，获得0.7±0.5微摩尔公斤的精度^-1为DIC和用于δ0.05±0.02‰ ¹³ C-DIC。使用同时测量DIC和δ ¹³ C-DIC数据，对DIC和生物地球化学控制弹簧期间在托架其同位素组成进行了探讨。在北部上海湾，主要控制过程是CO ₂出气和碳酸盐沉淀，而主要的生产（表面）和有机碳的降解（地下）主要在南部上海湾和中海湾。通过改进样品引入方式，可以使系统自动化以测量多个样品。这将使该系统有潜力在实地调查期间提供连续的船上测量结果，从而使该方法对于在广泛的水生环境中探索复杂的碳酸盐系统更为有效。