Summer–winter transitions in Antarctic ponds: III. Chemical changes

• Published in: Antarctic Science
• Main Authors: Webster-Brown, Jenny, Hawes, Ian, Safi, Karl, Sorrell, Brian, Wilson, Nathaniel
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2011
• Subjects: Geology; Ecology, Evolution, Behavior and Systematics; Oceanography; Antarctic; McMurdo Ice Shelf; Antarc*; Antarctic Science; Ice Shelf
• Online Access: http://dx.doi.org/10.1017/s0954102011000721; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102011000721

Abstract Observations were made of water column chemistry in four Na-Cl dominated ponds on the McMurdo Ice Shelf from the end of January to early April in 2008. During that time the ponds went from ice-free to predominantly frozen, with only a small volume of residual hypoxic, saline liquid trapped at the base of each pond. Changes in the concentrations of inorganic solutes with time distinguished Na, Cl, Mg, K, SO 4 , As, U and Mn as ions and trace elements that behave mainly conservatively during freezing, from those which are affected by biological processes (removing HCO 3 ) and the precipitation of mineral phases such as calcite (removing Ca and more HCO 3 ). Dissolved Fe, Mo, Cu and Zn also show evidence of precipitation from the water column during freezing; geochemical speciation modelling predicts the formation of stable insoluble mineral phases such as Fe oxides and oxyhydroxides while conditions are oxic, and Fe-, Cu-, Mo- and Zn-sulphide minerals in the presence of H 2 S. Consequently, under winter conditions, residual liquid beneath the ice in such ponds is anticipated to be an anoxic Na-Cl brine with the capacity to develop high concentrations of toxic trace elements such as As and U.