Conclusions: The Role of Canopy Flux Measurements in Global C-Cycle Research
The carbon cycle is central to the Earth System, being inextricably coupled with climate, the water cycle, the nutrient cycles, and the production of bio-mass by photosynthesis on land and in the oceans. Over the past century, the Earth’s carbon cycle experienced large perturbations. Since the beginning of the industrial revolution, the mean global carbon dioxide (C02) concentra-ion has risen from about 280 ppm to over 368 ppm (Conway et al. 1994; Keeling and Whorf 2002). The worldwide rise in atmospheric C02 concentration is occurring due to an imbalance between the rate at which anthropogenic and natural sources emit C02 (by burning fossil fuel and respiring) and the rate at which biospheric and oceanic sinks remove C02 from the atmosphere by photosynthesis and physio chemical processes. Superimposed on the overall trend regarding C02 is a record of great interannual variability of sources and sinks in the rate of growth of atmospheric C02. Typical values are on the order of 0.5 to 3 ppm year-1. On a mass basis, these values correspond to 1 and 5 Gt C year-1, respectively. Potential sources of year-to-year changes in C02 remain a hot topic of debate. Such variation has been attributed to El Niño/La Nina events, which cause regions of droughts or excessive rainfall (Conway et al. 1994; Keeling et al. 1995), and alterations in the timing and length of the growing season (Myneni et al. 1997; Randerson et al. 1997).
KeywordsGross Primary Production Carbon Budget Eddy Covariance Global Change Biol Eddy Correlation
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