Antarctic Science


Special Issue: The Latitudinal Gradient Project (LGP)

PChemistry and stratification of Antarctic meltwater ponds I: Coastal ponds near Bratina Island, McMurdo Ice Shelf


B.R. Wait a1, J.G. Webster-Brown a2c1, K.L. Brown a3, M. Healy a3 and I. Hawes a4
a1 Gateway Antarctica, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
a2 SGES, University of Auckland, Private Bag 92019, Auckland, New Zealand
a3 Department of Geology, University of Auckland, Private Bag 92019, Auckland, New Zealand
a4 National Institute of Water and Atmospheric Research, PO Box 8602, Christchurch, New Zealand

Article author query
wait br   [PubMed][Google Scholar] 
webster-brown jg   [PubMed][Google Scholar] 
brown kl   [PubMed][Google Scholar] 
healy m   [PubMed][Google Scholar] 
hawes i   [PubMed][Google Scholar] 

Abstract

The geochemistry and vertical stratification of shallow meltwater ponds at 78°S near Bratina Island (McMurdo Ice Shelf) have been determined for late winter (October) and summer (January) conditions as part of the Latitudinal Gradient Project. Of the five frozen ponds investigated in October, all were stratified with respect to conductivity, and three had highly saline basal brines beneath the ice at temperatures of −16 to −20°C. In the ice column, inclusions of saline fluid were observed in channels between ice crystals; the abundance increasing with depth and decreasing ice crystal size. In January, seven of the ten ponds investigated (including ponds sampled in October) retained conductivity stratification, whereas significant thermal stratification was observed in only three ponds (maximum ΔT = 5.5°C). Basal brines, ice and meltwaters were Na-Cl or Na-SO4 dominated. FREZCHEM52 modelling, supported by changes in ion ratios, indicated that the precipitation of mirabilite (Na2SO4.10H2O) and gypsum (CaSO4.2H2O) during progressive freezing is an important determinant in chemical evolution of the basal brine. High pH (8.8–11.2) and over-saturation with respect to dissolved oxygen (> 20 mg L−1) in summer, and the presence of sulphide ions in basal brines in winter, occurred in those ponds which experienced high biological productivity during the summer months.

(Published Online November 14 2006)
(Received December 14 2005)
(Accepted June 12 2006)


Key Words: freeze concentration; FREZCHEM52; geochemistry; ice; Latitudinal Gradient Project; salt exclusion.

Correspondence:
c1 Corresponding author: j.webster@auckland.ac.nz


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