Comment of tracing environmental change with organic carbon isotopes

Abstract

As global change becomes a more important research topic, scientists tried different ways on various geologic records in their research. This paper introduces and reviews the organic carbon isotope method used to trace environmental change, including its mechanism, research objects, obtained results and problems. It is considered that 12C prefers to enrich in C-H bond rather than in C-O bond, causing much lower negative δ13C for biotic matter or organic carbon than that for inorganic carbon. Difference in photosynthesis distinguishes plants into three groups with distinctive δ 13C, i. e. C3, C4, and CAM. The C3, plants have δ13C=-20‰- -32‰ , average -28‰ and the C4, plants have 13C= -9‰- -l7‰, average -14‰. Climate affects the style and strength of photosynthesis, causing distinctive development of plant group in unique environment with distinctive total organic δ 13C value. The difference in δ13C of total plants can further result in local characteristic δ 13C of animal fossils on the biological chain, such as fossil teeth, and even characteristic inorganic δ13C. Therefore, carbon-isotopic study of biotic chains and their ramifications or products is an effective way to understand local or temporal environments. Accordingly, the geologic records are divided into two large classes, i. e. organic and inorganic records. Organic records include fossil plants, such as tree rings, fossil animals, such as teeth, continental sedimentary organic matter, such as coal, marine sedimentary organic matter and soils (ramification of biotic matter). These research records have been used successfully to trace environmental changes of various aims. The authors believe that organic carbon isotopic study will play a more important role in revealing significant mass extinction, finding oldest C4 plants, understanding origin of earliest life on earth, verifying the existence of extraterrestrial life and determining the relation between organic matter and mineral resources. More attention will be paid to the detail of fractionation of carbon isotopes during carbon cycling. Obviously, complexity of these problems needs the inter-discipline collaboration.