Abstract: Carbonates constitute a critical component of marine sediments, and accurate determination of their content is fundamental to understanding global shifts in carbonate deposition and dissolution within the oceans, as well as the influence of carbonate system evolution on climate change. The gasometric method and weight-loss are typical non-instrumental approaches to carbonate quantification; however, the precision and reliability of both techniques in the analysis of marine sediment carbonates remain insufficiently evaluated. This study investigates the solubility characteristics of carbon dioxide (CO₂) gas in hydrochloric acid (HCl) solutions, and finds that under typical temperature and pressure conditions, the solubility of CO₂ within a 20ml approximately 18% hydrochloric acid solution in the gasometric device ranges from 0.3% to 21.5%, with a mean of 9%. Furthermore, using both the gasometric method and an improved weight-loss method, we conducted a comparative analysis of carbonate content in prepared samples with varying calcium carbonate concentrations, and in a deep-sea sedimentary sequence. The experimental results reveal that, due to CO₂ dissolution in HCl, the gasometric method induces an absolute error in carbonate concentration analysis ranging from 0.3% to 18.2% (mean = 4.4%), with a standard deviation of 5.4%. In contrast, the improved weight-loss method yields errors of only 0.2-2.4% (mean = 1.0%) and a substantially lower standard deviation of 1.2%. These findings indicate that the accuracy and stability of the weight-loss method for carbonate quantification are superior to those of the gasometric method. Moreover, a comparison of carbonate content results obtained by both methods in this study for samples derived from IODP (International Ocean Discovery Program) Site U1553 with those determined by coulometric titration reveals that the improved weight-loss method more accurately reproduces the carbonate content variations observed at Site U1553, further validating its reliability and applicability for determining carbonate content in deep-sea sediments.

Key words: Carbonate, gasometric method, weight-loss method, measurement error, deep-sea sediments