Chemical conditions beneath glaciers are difficult to observe and are usually studied by sampling meltwaters emerging from glacial oulets or drill holes. These waters average chemical signals over a large area and cannot record small-scale spatial and temporal variability.
By contrast, subglacial sediments contain minute (nanometer-sized) particles of iron oxides that can only have formed in transient geochemical "hotspots." Raiswell et al. have found minute crystals of schwertmannite, an iron hydroxy-sulfate mineral, in glaciers from the Antarctic and Arctic.
Schwertmannite is typically found in acid mine drainage, where it forms by the oxidation of pyrite at low pH. These conditions can also be created in subglacial environments, but only in minute hotspots or "microenvironments."
There, schwertmannite forms rapidly but is very unstable, and its survival requires freezing into ice within 100 years. So, frozen nanoparticle schwertmannite indicates the presence of transient geochemically active microenvironments deep within glacial ice.
The formation, preservation, and delivery of nanoparticles of schwertmannite (and iron oxides) into the Southern Ocean may partially relieve iron-limited photosynthesis and assist in the removal of manmade carbon dioxide from the atmosphere.
This study, "Schwertmannite in wet, acid, and oxic microenvironments beneath polar and polythermal glaciers," by R. Raiswell et al. was published in the May 2009 edition of Geology.
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