Dissolved inorganic carbon (DIC) concentration and stable carbon isotope values (δ¹³C_DIC) are valuable for understanding aquatic carbon cycles and assessing anthropogenic carbon accumulation in the oceans. The advancement of Cavity Ring-Down Spectroscopy (CRDS) technology has enabled high-resolution δ¹³C_DIC data collection on both temporal and spatial scales, globally. However, the absence of appropriate standard materials has hindered the reliability and comparability of measurements across different laboratories and seawater sample batches. This study addresses this limitation by developing a novel secondary δ¹³C_DIC reference material specifically for laboratory use. By dissolving, mixing, and purifying commercially available ¹²C enriched NaHCO₃ and NaH¹³CO₃, we produced a solid reference material optimized for δ¹³C_DIC analysis of seawater samples. The preparation process is highly controllable and reproducible, resulting in a uniform and stable reference material that is suitable for long-term storage. Compared to traditional calcium carbonate solid standards and CO₂ gas standards, the developed reference material offers a simpler preparation process, high reproducibility, and greater applicability for shipboard measurements of seawater. During a three-month period of Arctic seawater sample analysis, this secondary reference material exhibited excellent stability, and the measured deep-water data were consistent with historical records, demonstrating the reliability of the newly developed reference material. The new reference material facilitates more accurate measurements of high temporal and spatial resolution seawater δ¹³C_DIC distribution, enhancing our ability to quantify anthropogenic CO₂ uptake and storage rates by the ocean, and providing a pathway to improve the comparability of δ¹³C_DIC data across different regions and research cruises.
 

dissolved inorganic carbon, stable carbon isotope, reference material, discrete sample, anthropogenic carbon