BRIEF RESEARCH REPORT article
Front. Mar. Sci.
Sec. Marine Pollution
Silver nitrate preserves seawater carbonate chemistry for short-term storage
Kuria Ndungu
Caroline Mengeot
Louise Valestrand
Kai Sørensen
Andrew King
Norwegian Institute for Water Research (NIVA), Oslo, Norway
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Abstract
Seawater samples for total dissolved inorganic carbon (CT) and total alkalinity (AT) measurements of the seawater carbonate system are typically preserved with mercuric chloride (HgCl₂), but mercury use is globally regulated under the Minamata Convention. We tested silver nitrate (AgNO₃; 25 and 50 μM) as an alternative preservative for oligotrophic seawater. No significant differences (p > 0.05) in CT were observed between HgCl₂-treated samples (2177 ± 2 μmol kg⁻¹) and either 25 μM (2178 ± 2 μmol kg⁻¹) or 50 μM (2177 ± 1 μmol kg⁻¹) AgNO₃ treatments after 2 d storage. Untreated samples showed significant CT increase over the same period. After 21 d, both AgNO₃ treatments showed significantly elevated CT compared to HgCl₂. AT remained stable across all treatments for 3 months. This initial investigation demonstrates that AgNO₃ is suitable for short-term (≤2 d) 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.
Summary
Keywords
Carbonate chemistry, Dissolved Inorganic Carbon, Mercury alternative, ocean acidification, Seawater preservation, Silver Nitrate, Total alkalinity
Received
29 October 2025
Accepted
19 February 2026
Copyright
© 2026 Ndungu, Mengeot, Valestrand, Sørensen and King. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Kuria Ndungu
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