Preparation and quality control of in‐house reference materials for marine dissolved inorganic carbon and total alkalinity measurements

Abstract

Accurate measurements of seawater carbonate chemistry are crucial for marine carbon cycle research. Certified reference materials (CRMs) are typically analyzed alongside samples to correct measurements for calibration drift. However, the COVID‐19 pandemic led to a limited access to CRMs. In response to this shortage, we prepared and monitored in‐house reference materials (IHRMs) for total alkalinity (TA) and dissolved inorganic carbon (DIC), over 12 and 15 months, respectively. Overall, TA was stable, but a slight increase in DIC of about 2 μmol kg−1 occurred over 15 months. The increase could potentially be attributed to bacterial growth, despite mercuric chloride fixation and repeated UV exposure. It is noted that this small increase was most likely within our instrument and measurements uncertainties. Our repeated measurements also identified a few bottles that had TA or DIC concentrations 4–5 μmol kg−1 higher than the rest, indicating issues during cleaning, fixation, or storage of individual bottles. This study emphasizes the importance of careful and continuous monitoring if self‐prepared IHRMs are used. Given that the amount of work required is very high, IHRM preparation is only recommended when CRMs are not available.

Effects of grain size and seawater salinity on magnesium hydroxide dissolution and secondary calcium carbonate precipitation kinetics: implications for ocean alkalinity enhancement

“…The entire contents of the jerry cans were then sterile filtered using a peristaltic pump and a 0.2 µm Whatman Polycap 75 AS filter, before being stored in cleaned and autoclaved 25 L polycarbonate bottles. Prior to conducting the experiments, each seawater batch was equilibrated to laboratory air pCO2 by bubbling them with H2O-saturated air for at least a week (Moras et al, 2023). For the grain size experiments, three grain size ranges were produced using two stainless steel sieves with 63 µm and 180 µm mesh sizes.…”

“…The DIC concentration was measured using an Automated Infra-Red Inorganic Carbon Analyzer (AIRICA) coupled to a LI-COR Li7000 Infra-Red detector (Gafar and Schulz, 2018). Both TA and DIC measurements were corrected against in-house reference material (previously calibrated against certified reference material), with measurement uncertainties of ±2.20 and ±1.98 μmol kg -1 (Moras et al, 2023). ΩA and carbonate chemistry speciation were calculated from TA and DIC, providing temperature and salinity measurements, using CO2SYS (Sharp et al, 2021).…”

Guide to Best Practices in Ocean Alkalinity Enhancement Research

“…Sec-ond, bubbling with dry CO 2 gas directly leads to evaporation of water, increasing TA. It is unclear at this stage how relevant this problem is for a short bubble burst, but it could be avoided by saturating the CO 2 gas stream with H 2 O before bubbling the sample, as for example described in Moras et al (2023b).…”