Chemical pROxIES

Both organic and mineral lake sediments undergo reactions that vary depending on their chemical compositions, and on environmental factors such as temperature, and the light and nutrients available to organisms. Compounds containing arsenic (As) carbon (C), chlorine (Cl), iron (Fe), mercury (Hg), nitrogen (N), phosphorus (P), silicon (Si), Sodium (Na), and sulfur (S) are among those that have been used as proxies for the climate conditions prevailing at the time sediments were deposited. Iron-bearing compounds align themselves with the Earth's magnetic field; changing alignments in different strata track changes in the field itself. As some minerals form, they can even trap samples of lake water in microscopic spaces. Many different combinations of particle size, composition, and chemical interaction are possible, making it necessary to understand and account for many different processes in order to use lake sediments as effective proxies for the climatic conditions in the past.

SEE ALSO: Biogeochemical Cycles; Cenozoic Era; Chemistry; Climatic Data, Nature of the Data; Climatic Data, Proxy Records; Climatic Data, Sediment Records; Foraminifera; Phytoplankton; Plants; Salinity.

BIBLIOGRAphY. W.M. Last and J.P. Smol, eds., Tracking Environmental Change Using Lake Sediments (Kluwer, Dordrecht, 2001); P.S. Murdoch, J.S. Baron, and T.L. Miller, "Potential Effects of Climate Change on Surface-Water Quality in North America," Journal of the American Water Resources Association (v.36/2, 2000).

Matthew K. Chew Arizona State University

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