Polar ice

FIGURE 6.24 The polar ice caps on Mars extend and recede with the seasons. They are mostly solid carbon dioxide and form by direct conversion of the gas into a solid. They disappear by sublimation. Although some water ice is also present in the polar caps, the temperature on Mars never becomes high enough to melt it. On Mars, ice is just another rock. 

Once the model was complete, it was adjusted to a steady state condition and tested using historic carbon isotope data from the atmosphere, oceans and polar ice. Several important parameters were calculated and chosen at this stage. Sensitivity analysis indicated that results dispersal of the missing carbon - were significantly influenced by the size of the vegetation carbon pool, its assimilation rate, the concentration of preindustrial atmospheric carbon used, and the CO2 fertilization factor. The model was also sensitive to several factors related to fluxes between ocean reservoirs. 

Craig, H., Horibe, Y. and Sowers, T. 1988. Gravitational separation of gases and isotopes in polar ice caps. Science 242,1675-1678. 

Neftel, A., Moor, E., Oeschger, H. and Stauffer, B. (1985). Evidence from polar ice cores for the... 

Records of past environmental change are preserved in a broad range of Earth materials. Past environments are inferred from "proxy" records, meaning measurements of physical and chemical parameters of marine and terrestrial sediment, polar ice, and other materials that were in some way influenced by their environment during accumulation. Examples of proxy records are the distribution of glacial deposits, the isotopic composition of terrestrial and marine sediments and ice, the abundance and species composition of plant and animal fossils, and the width of tree rings. 

A very important complication in interpreting ice core records, and in defining depth-age relations, is the fact that snow transforms to ice 50 to 100 m below the surfaces of most polar ice sheets. This means the gas trapped in ice is actually younger than the solid ice at the same depth, and that a variety of processes can transport and redistribute gases in this snowy upper layer (called the fim). To imderstand this, and to prepare for subsequent discussions, we must discuss how snow converts to ice near the ice sheet surface. 

Fig. 18-6 Characteristic air-mass trajectory and corresponding per mil isotopic composition of precipitation, along a transect from the subtropics to a polar ice sheet. This is a highly schematic view of the true atmospheric system.

Other trace gases important in atmospheric chemistry and climate (for example carbonyl sulfide and carbon monoxide) may also be measured in polar ice, and development of these and other measurements is underway in a number of laboratories around the world. 

Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in polar ice. Nature 391,141-146. 

Whilst the effects of global warming are still somewhat controversial it is likely to cause more storms and flooding, melting of the polar ice caps and changes in animal distributions. 

Analyzing the samples back at Caltech, Patterson, Masayo Murozumi, and Chow demonstrated that polar ice is naturally extremely pure but that snow deposited in modern times on Greenland contained roughly 100 times more lead than did preindustrial snow. Most of the lead deposits dated from the twentieth century. Geochemists later used the unique ratio of lead-206 and lead-207 isotopes in the lead to prove that these deposits originated in the United States. 

Water vapor enriched in oxygen-16 is transported by wind in the atmosphere from the sea to land. When the water vapor condenses and precipitates as rain, snow, or hail, the water becomes rich in oxygen-16. Eventually the oxygen-16 rich water is incorporated into rivers, lakes, glaciers, and polar ice, which are, therefore, also rich in oxygen-16. Thus the isotopic composition of groundwater and the water of rivers, lakes, and glaciers is not the same as in seas and oceans. 

New enzymes to address industrial problems are searched among a collection of more than 25,000 classified microorganisms. These microorganisms cover a broad range of habitats, from garden soil to extreme conditions (volcanoes, polar ice, and deep-sea environments). This biodiversity multiplies the number of possible derivable enzymes nature is the basis for all its products. 

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