Silver nitrate preserves seawater carbonate chemistry for short-term storage

Seawater samples for total dissolved inorganic carbon ( C T ) and total alkalinity ( A T ) measurements of the seawater carbonate system are typically preserved with mercuric chloride (HgCl 2 ), but mercury use is globally regulated under the Minamata Convention. We tested silver nitrate (AgNO 3 ; 25 and 50 μM) as an alternative preservative for oligotrophic seawater. No significant differences ( p > 0.05) in C T were observed between HgCl 2 -treated samples (2,177 ± 2 μmol kg −1 ) and either 25 μM (2,178 ± 2 μmol kg −1 ) or 50 μM (2,177 ± 1 μmol kg −1 ) AgNO 3 treatments after a 2-day storage. Untreated samples showed a significant C T increase over the same period. After 21 days, both AgNO 3 treatments showed significantly elevated C T compared to HgCl 2 . A T remained stable across all treatments for 3 months. This initial investigation demonstrates that AgNO 3 is suitable for short-term (≤2 days) preservation, enabling shipboard carbonate chemistry analysis with simplified disposal compared to mercury-contaminated samples. Further studies with diverse marine waters are needed to establish broader applicability.