5 NATURAL ABUNDANCE OF THE STABLE ISOTOPES ... - Falw.vu

Stable Isotopes of Hydrogen, Carbon and Oxygenatmospheric CO 2marine HCO 3marine carbonatemarine plantsmarine planktonland plants C 4 typeland plants C 3 typegroundwater HCO 3fresh-water carbonatewoodpeatcoaloilnatural gasbacterial CH 4animal bonediamond80 60 40 20 0 +2013 VPDB (‰)Fig.7.2General view of 13 C/ 12 C variations in natural compounds. The ranges are indicative forthe materials shown.Fig.7.2 presents a broad survey of natural abundances of various compounds, at the low- 13 Cend bacterial methane (marsh-gas), at the high end the bicarbonate fraction of groundwaterunder special conditions. In the carbonic acid system variations up to 30‰ are normallyobserved. Wider variations occur in systems in which carbon oxidation or reduction reactionstake place, such as the CO 2 (carbonate) CH 4 (methane) or the CO 2 (CH 2 O) x(carbohydrate) systems.7.1.2 CARBON ISOTOPE FRACTIONATIONSIt will later be shown that the presence of dissolved inorganic carbon (DIC) in sea-, ground-,and surface water presents the possibility of studying gas-water exchange processes and ofmeasuring water transport rates in oceans and in the ground. In connection with studyingthese phenomena, the stable and radioactive isotopes of carbon and their interactions pay animportant contribution, often together with the water chemistry.91