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

Published online by Cambridge University Press:  25 October 2011

Jenny Webster-Brown ,
Ian Hawes ,
Karl Safi ,
Brian Sorrell  and
Nathaniel Wilson
Jenny Webster-Brown*
Affiliation:
University of Canterbury, Private Bag 4800, Christchurch, New Zealand
Ian Hawes
Affiliation:
University of Canterbury, Private Bag 4800, Christchurch, New Zealand
Karl Safi
Affiliation:
NIWA Ltd, PO Box 11-115, Hamilton, New Zealand
Brian Sorrell
Affiliation:
Dept Biological Sciences, Aarhus University, 8000 Aarhus 3, Denmark
Nathaniel Wilson
Affiliation:
University of Bayreuth, Bayreuth, Germany
*
[email protected]
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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, SO4, As, U and Mn as ions and trace elements that behave mainly conservatively during freezing, from those which are affected by biological processes (removing HCO3) and the precipitation of mineral phases such as calcite (removing Ca and more HCO3). 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 H2S. 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.

Keywords

freeze concentrationmajor ionMcMurdo Ice ShelfPHREEQC modellingtrace element
Type
Biological Sciences
Information
Antarctic Science , Volume 24 , Issue 2 , 28 February 2012 , pp. 121 - 130
Copyright
Copyright © Antarctic Science Ltd 2011

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