A theoretical evaluation of mineral stability in Don Juan Pond, Wright Valley, Victoria Land

• Published in: Antarctic Science
• Main Author: Marion, G.M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1997
• Subjects: Geology; Ecology, Evolution, Behavior and Systematics; Oceanography; Antarctic; The Antarctic; Victoria Land; Wright Valley; Don Juan Pond; Antarc*; Antarctic Science
• Online Access: http://dx.doi.org/10.1017/s0954102097000114; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102097000114

Don Juan Pond, located in the Wright Valley, Victoria Land, is unique for several reasons. It is the most saline of the Antarctic lakes, being a near-saturated CaCl 2 solution. As a consequence of this high salinity, Don Juan Pond generally remains unfrozen in winter, even at temperatures below -50°C. Don Juan Pond is the site where antarcticite (CaCl 2 ·6H 2 O) was first identified forming naturally. The objective of this paper is to demonstrate the utility of a chemical thermodynamic model (FREZCHEM) by developing theoretical stability diagrams for ice, halite (NaCl), hydrohalite (NaCl·2H 2 O), and antarcticite in Don Juan Pond, using experimental data collected on 34 days between 1961 and 1983. The composition of Don Juan Pond at the calculated eutectic temperature (-51.8°C) was CaCl 2 = 3.72 mol kg −1 and NaCl = 0.50 mol kg −1 , which is similar but not identical to a pure NaCl–CaCl 2 –H 2 O system. The low eutectic temperature and high CaCl 2 concentrations of Don Juan Pond account for lack of freezing during winter. The model is compatible with the experimental data, and predicts the formation of ice during rare high water periods, halite, and antarcticite. These solid phases have all been reported from Don Juan Pond. The model also predicts the formation of hydrohalite at subzero temperatures; hydrohalite has never been observed at Don Juan Pond, but this may simply reflect that most sampling was done during the summer when halite is thermodynamically more stable than hydrohalite. The FREZCHEM model may prove useful in elucidating the physicochemical behaviour, the origin of salinity, and the evolution of Antarctic lakes.