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

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 we...

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Bibliographic Details
Published in:Antarctic Science
Main Authors: Wait, B.R., Webster-Brown, J.G., Brown, K.L., Healy, M., Hawes, I.
Format: Article in Journal/Newspaper
Language:English
Published: Cambridge University Press (CUP) 2006
Subjects:
Geology
Ecology, Evolution, Behavior and Systematics
Oceanography
Antarc*
Antarctic
Antarctic Science
Bratina Island
Ice Shelf
McMurdo Ice Shelf
Online Access:http://dx.doi.org/10.1017/s0954102006000563
https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102006000563
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Summary: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-SO 4 dominated. FREZCHEM52 modelling, supported by changes in ion ratios, indicated that the precipitation of mirabilite (Na 2 SO 4 .10H 2 O) and gypsum (CaSO 4 .2H 2 O) 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.

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