Freezing-induced acidification of sea ice brine
| Authors | |
|---|---|
| Year of publication | 2024 |
| Type | Article in Periodical |
| Magazine / Source | Science of the Total Environment |
| MU Faculty or unit | |
| Citation | |
| web | https://www.sciencedirect.com/science/article/abs/pii/S0048969724043420?via%3Dihub |
| Doi | http://dx.doi.org/10.1016/j.scitotenv.2024.174194 |
| Keywords | Fractional crystallization; Buffering capacity; Acidification; Sea ice; Brine |
| Description | 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 degrees C and during the subsequent cooling down to -50 degrees 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 degrees C, whereas higher salinity ices attain such values only at -30 degrees C. The ensuing implications for polar chemistry and the relevance to the field measurements are discussed. |
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