CO2全球循环及其同位素示踪研究

极地冰盖气泡研究表明,工业革命前大气圈天然ＣＯ₂浓度约为２８０×１０－６,天然ＣＯ₂浓度变化反映了冰期－间冰期循环这一长期气候变化固有特征。工业革命后,大量人为ＣＯ₂进人大气圈,人为ＣＯ₂收支明显不平衡,一个大于２．６ＧＴＣ／ａ的未知陆地生态汇很可能存在于北半球中纬度地带。土壤、岩溶作用、河流作用、地球化学作用、干旱－半干旱环境等系统以及海洋内部ＣＯ₂循环的同位素示踪研究,可为人为ＣＯ₂未知汇即“ＭｉｓｓｉｎｇＳｉｎｋ”的探求提供线索。

CO2 GLOBAL CYCLE AND ITS ISOTOPIC TRACING INVESTIGATION

The Pre-industrial Revolution's records of natural CO₂in the atmosphere has been reconstructed by measuring CO₂in air bubbles from polar ice sheets. All these records in both Antarctic and Arctic show that: (1) there was a strong correlation beween CO₂ and δ¹⁸O; (2) the CO₂ concentration was (250-300) ×10^-6 during 0.13-0.12Ma B. P., i.e. the last interglacial period, similar to that in Holocene;(3) the CO₂ concentration w4s (180-200) × 10^-6 during the last but one coldest period of glaciation, about 0.15Ma B. P., corresponding to that of the Last Glacial Maximum about 18000a B. P. Natural CO₂ variations are characteristic of the longterm climate mechanisms causing glacial-interglacial cycles. During the transition from the glacial to the interglacial, the natural CO₂concentration increased by (80-100) × 10^-6. Before the Industrial Revolution, the natural CO₂ concentration in the atmosphere was kept about 280 × 10^-6and the interhemispherical distribution of CO₂ showed a gradually decreasing tendency from the south to the north.After the Industrial Revolution, much of anthropogenic CO₂ entered the atmosphere owing to the burning fossil fuel. The CO₂ concentration in the atmosphere increased in average by 1.8 × 10^-6/a during 1958-1988, and the rising curve shows a interannual oscillation. Meanhile, the interhemispherical distribution of CO₂ show ed a gradually descreasing tendency from the north to the south. The CO₂ produced by burning fossil fuel during the period of 1981-1987 made up 57% of all anthropogenic CO₂. The anthropogenic CO₂ uptaken by entire oceans is less than I GTC/a during the same lperiod. So there must be terrestrial ecology sinks(including soils) more than 2.6GTC/a to keep the balance of anthropogenic CO₂. Such an unknown sink,' so called "Missing Sink", is likely located in the northern middle latitude. Existing models about the oceanic CO₂, cycle all are based on isotopic tracing.But the behavior of one isotopic tracer is not completely the same as that of CO₂, so multi-isotopic tracers have been used. Radionuclides such as ¹⁴C (called "bomb ¹⁴C" for short below), ³⁹Ar and ⁸⁵Kr produced in nuclear explosion have a global distribution. This distribution relatively simple boundary condition and is very helpful for tracing of the CO, global cycle. Today, however, the use of ³⁹Ar and ⁸⁵Kr limited. In models of the CO, cycle in soil, the cycle ratio of C is a very important parameter, whose information can be drawn from measuring ¹⁴C in organic matter and soil-forming CaCO₃. Since the absorption of natural ¹⁴C and bomb ¹⁴C varies from soil to soil, determining the cycle ratio of C is complicated. For this reason, ¹⁴C measurement in soils must be carried out widely.The CO₂ cycle in karst can be studied by tracing of ³H, ⁴He, ¹⁴C, ^37,39Ar, ^81,85Kr and U-Th. Models to couple the CO₂-(CH₂O)n-CO₃²-system to the CO₂-H₂O-CO₃²system can used to reveal relationships between the variation of natural and anthropogenic CO₂ and climatic records for a variety of karst regions.By determining the distribution of bomb ¹⁴C in suspended matter, sediment, water body in rivers and estuaries and by determining the air-sea partial pressure differences of CO, (△PCO₂) over coastal regions with a higher spatial and temporal resolution, we can relate the CO₂ exchange in continental shelf regions of East Asia to the large-scale oceanic CO₂ distribution, and then estimate the CO₂ flux entering oceans through rivers. CO, fluxes produce mainly in geoclemical processes such as carbonate weathering,silicate weathering, and the production and modification of organic carbon. By tracing of, ¹⁰Be, ²⁶Al, ³⁶Cl, ¹⁴C and by precisionly determining of δ¹³C distribution in the atmosphere, we can exactly estimate the weathering rates of both terrestrial carbonates and silicates and the transporting rates of organic and' inorganic carbon to obtain the income and expenses of CO₂ during geochemical processes.The variation of CO₂ par.tial presure in the paleoatmosphere can be estimated further by establishing the soil CO, diffusion model an