Fast Geochemistry

Melt water streams of the McMurdo Dry Valleys connect glaciers to lakes carrying dilute glacial melt water that exchanges through streambed sediments dissolving them very rapidly.
M. Gooseff, Penn State University

The ubiquitous dissolution of soils and sediments results in dissolved loads of major ions and nutrients to streams. In most temperate watersheds, the rate of weathering is generally positively correlated to temperature and precipitation. In the cold and dry McMurdo Dry Valleys of Antarctica, dilute glacial melt water generated during 8-10 weeks in the austral summer flows into well-defined stream channels, which spill into closed basin lakes. The sediments of these streambeds are unconsolidated and relatively 'fresh' (i.e., minimally weathered), underlain by permafrost at depths of ~75 cm. Stream water actively exchanges between the open channel and the thawed streambed sediments, known as the hyporheic zone ("hypo-" from the Greek meaning 'under' and "rheos" meaning 'river'). When thawed, water stored in the streambed actively dissolves the minerals there. Thus, as the dilute stream water exchanges with the high-solute hyporheic water and stream water, concentrations of silica, potassium, etc. increase downstream. Watershed areas of dry valley streams are small because there is no rain. Hence, chemical weathering yields per unit area watershed are some of the highest on earth.

Comparison of published silica weathering rates for several watersheds in the continental United States, separated by main bedrock mineral, and the bulk weathering rate from studies in the McMurdo Dry Valleys, Antarctica (MCM LTER). Note the log scale of the y-axis.
Data reported in Gooseff et al., 2002.
For further reading: 
Maurice, P. A., D. M. McKnight, L. Leff, J. E. Fulghum, and M. Gooseff (2002), Direct observations of aluminosilicate weathering in the hyporheic zone of an Antarctic Dry Valley stream, Geochimica et Cosmochimica Acta, 66(8), 1335-1347. Gooseff, M. N., D. M. McKnight, W. B. Lyons, and A. E. Blum (2002), Weathering reactions and hyporheic exchange controls on stream water chemistry in a glacial meltwater stream in the McMurdo Dry Valleys, Water Resources Research, 38(12), WR000834. Nezat, C. A., W. B. Lyons, and K. A. Welch (2001), Chemical weathering in streams of a polar desert (Taylor Valley, Antarctica), Geological Society of America Bulletin, 113(11), 1401-1408.
For further information: 
Dr. W. Berry Lyons
Dr. Michael N. Gooseff

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