July 3, 2003. Copyright 2003. Graphic News. All rights reserved.

Old Man River sheds new light on Òcarbon cycleÓ

LONDON, July 3, Graphic News: Scientists analysing data from North AmericaÕs largest river, the mighty Mississippi, say that the amounts of carbon flowing into the sea have increased by two thirds in the last half-century.

A study published in the July 4 issue of the journal Science suggests that the increase in carbonate compounds is in part the result of higher rainfall and streamflow in the Mississippi basin and changes in the amount and type of land cover.

Peter A. Raymond of Yale University and Jonathan J. Cole of the Institute of Ecosystem Studies say that these observations have important implications for the potential management of carbon dioxide -- considered a culprit in global warming -- in the United States.

Mother Nature packages carbon in numerous stores known as sinks. These include organic molecules in the soil and living and dead organisms; the gas carbon dioxide in the atmosphere; fossil fuels in the EarthÕs crust; marine sediments and sedimentary rocks; and dissolved carbon dioxide and calcium carbonate shells in marine organisms in the oceans.

Carbon from the atmosphere and soil regularly combines with water and components from weathering rocks to form carbonates and bicarbonates. These compounds flow off the land and through streams and rivers until they reach the sea. This part of the Òcarbon cycleÓ has up to now been considered constant over millions of years and is frequently left out of shorter-term global warming discussions. 

The Mississippi, the "Old Man River" which begins as a tiny brook and 2,350 miles (3,780 kilometres) later empties into the Gulf of Mexico, collects water and carbon compounds from over 1.2 million square miles (3.1 million square kilometres) of land. Once in the oceans, these weathering products -- carbonate and bicarbonate ions, known as carbonate alkalinity -- are removed by sedimentation. When the sedimented minerals are subjected to high temperature and pressures in EarthÕs interior, carbon dioxide is again released and returned via volcanic activity to the atmosphere.

Carbon dioxide emissions from burning fossil fuels and increased rainfall in the Mississippi basin may have driven up the amount of these carbon compounds that the river carries. The authors also conclude that alkalinity export rates are linked to patterns of land use. Increased rainfall and temperatures are resulting in agricultural lands pulling more carbon from the atmosphere for incorporation into alkalinity than forests, reversing the conventional wisdom that planting millions of trees will reduce atmospheric carbon dioxide and gloal warming.

This kind of research will be especially important for tracking man-made or anthropogenic carbon emmissions in Asia, where the expansion of croplands is still a major contributor to deforestation.
/ENDS

Source: Science