Freezing-induced acidification of sea ice brine

Veselý, L.; Štůsek, R.; Mikula, O.; Yang, X. ORCID: https://orcid.org/0000-0002-3838-9758; Heger, D.. 2024 Freezing-induced acidification of sea ice brine. Science of the Total Environment, 946, 174194. 14, pp. 10.1016/j.scitotenv.2024.174194

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Abstract/Summary

The acidity of sea ice and snow plays a key role in the chemistry of the cryosphere; an important example lies in the photochemical catalytic release of reactive bromine in polar regions, facilitated at pHs below 6.5. We apply in-situ acid-base indicators to probe the microscopic acidity of the brine within the ice matrix in artificial sea water at a range of concentrations (0.35–70 PPT) and initial pHs (6–9). The results are supported by analogous measurements of the most abundant salts in seawater: NaCl, Na2SO4, and CaCO3. In the research herein, the acidity is expressed in terms of the Hammett acidity function, H2−. The obtained results show a pronounced acidity increase in sea water after freezing at −15 °C and during the subsequent cooling down to −50 °C. Importantly, we did not observe any significant hysteresis; the values of acidity upon warming markedly resembled those at the corresponding temperatures at cooling. The acidity increase is attributed to the minerals' crystallization, which is accompanied by a loss of the buffering capacity. Our observations show that lower salinity sea water samples (≤ 3.5 PPT) reach pH values below 6.5 at the temperature of −15 °C, whereas higher salinity ices attain such values only at −30 °C. The ensuing implications for polar chemistry and the relevance to the field measurements are discussed.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1016/j.scitotenv.2024.174194
ISSN:	0048-9697
Additional Keywords:	Fractional crystallization; Buffering capacity; Acidification; Sea ice; Brine
Date made live:	01 Jul 2024 09:15 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/537655

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.1016/j.scitotenv.2024.174194

ISSN:

0048-9697

Additional Keywords:

Fractional crystallization; Buffering capacity; Acidification; Sea ice; Brine

Date made live:

01 Jul 2024 09:15 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/537655