KARST PROCESSES AND THE CARBON CYCLE

The IGCP379 has been involved in global change study in two ways: assessing the modern contribution of karst processes to the content of CO2 in the atmosphere,and collecting karst records as paleoenvironmental proxies.

It is straightforward from the basic chemical reaction of karst processes that it can be both a sink or a source of CO2 in atmosphere. With every tonne of limestone dissolution,120 kg of carbon must have been taken as CO2 from the atmosphere; or in contrary,the same percentage of emission will take place when carbonate rock is deposited.

Some basic points regarding karst processes in global carbon cycle have been reached in IGCP 379's five year international collaboration:(1) carbonate rocks,the world biggest carbon reservoir which covers 99.55% of the world's total,are still active in global carbon cycle. According to monitoring,the variation of CO2 taken from atmosphere by limestone dissolution can be monthly and daily in the time scale,or even daily or hourly in CO2 emission;(2) Biogenic processes play a major role in limestone dissolution. These two changes occur almost synchronically. It is hard to take the limestone dissolution as a slow,merely inorganic chemical process,and seperate it from terrestrial biosphere as a long-term cycling; (3)the limestone denudation acts basically as a sink of atmospheric CO2. IGCP 379 has estimated the global annual removal of carbon from the atmosphere by karst processes as 6.08 hundred million tonnes annually,i.e, one-third of the missing sink in the current global carbon cycle model. The emission of CO2 from plate margin is considered as a source of atmospheric CO2.

The major contribution which Geology has ever made to global change study is providing information on paleoclimatic changes. The General Circulation Model was tested by records from deep sea sediments,corals,ice cores,lake deposits,and loess. Karst records are advantageous in this direction to some broad area of carbonate rocks without other paleoenvironmental proxies. IGCP379 members have worked on 34 sites for paleoclimatic reconstruction,which cover almost all the continents. For instance, with a 210cm long stalagmite taken from the DongGe Cave, Libo county,Guizhou province,south China,the paleoclimatic change from MIS 6 to 5c was reconstructed at an average resolution of 620 year. The end of Penultimate Glaciation was determined.