Analysing the Global Carbon Cycle; The Interaction of Sources and Sinks


Why analyse the carbon cycle? Carbon is the central building block of all


living organisms. On earth, carbon cycles in vast quantities through the atmosphere,


biosphere and geosphere interconnected by pathways of exchange that undergo various chemical, physical, geophysical and


biological processes. These exchanges are very complex and each process change has an impact on other processes within the cycle and on the total carbon balance. If an


organism absorbs more carbon dioxide (CO2) than they emit they are known as a carbon


sink. If they emit more CO2 than they absorb they are a carbon source.


Despite some recent press reports to the contrary, the vast majority of scientific evidence demon - strates that global warming is as a


result of rising CO2 levels in the atmosphere. CO2 is a prominent greenhouse gas, acting as a


blanket to prevent heat leaving the earth’s atmosphere. Research


suggests that atmospheric CO2 levels have risen dramatically and at increasing rates in recent history and are now at their highest levels in at least 650,000 years. Ice core measurements indicate that


ambient CO2 was approximately 284ppm (parts per million) back in 1832. This increased to 350ppm in 1988 and is around 389ppm today.


If atmospheric CO2 levels continue to rise global temperatures are expected to also rise. Some reports suggest that a rise in CO2 to 700ppm would increase global temperatures by around 1.5o climate, ecology and social economics.


C, impacting on our It is widely accepted that man-made activity, by burning fossil fuels,


accounts for about 50% of atmospheric CO2. Natural biomass respiration and volcanic activity account for the remainder. Natural carbon sinks such as plant photosynthesis and ocean biota take up about half of this released CO2.


Increased uptake of CO2 by the world’s oceans has its own environmental impact as the seas become more acidic and so


potentially damaging the marine life and ecology. There are also


questions as to whether the oceans can sustain current CO2 uptake levels due to the effects of the climate change.


The concerns regarding rapidly rising atmospheric CO2 conc - entrations and its potential impact on future climate is an issue of global, economic and political significance. Much emphasis, therefore, is being


placed on CO2 exchange research. Due to the complexities of these flux exchanges, the research draws on expertise from a number of geoscience disciplines requiring a variety of high quality and versatile gas exchange instrumentation. ADC Bioscientific is one of the world leaders in the development and manufacture of this environmental research instrumentation employed in carbon exchange research.


Infrared Gas Analyser


ADC BioScientific instrumentation measures CO2 concentrations by Infrared Gas Analysis. Infrared gas analysers, often affectionately known


by researchers as IRGAs, measure the energy absorbed by


heteroatomic gases, such as CO2, at very precise wavelengths within the infrared region.


First produced in the UK in the 1940s, IRGAs were initially simple, bulky, mains powered and laboratory based instruments. However, researchers’ requirements and expectations have lead to these instruments becoming ever more powerful, sophisticated, reliable and


Folded open path IRGA design of ADC OP-2.


field portable. ADC BioScientific gas exchange instrumentation is regarded as market leaders in portability and ease of use.


This highly specialised instrumentation is utilised in various areas of


CO2 exchange research. Atmospheric CO2


There are many instruments and techniques available for measuring the


absolute atmospheric CO2 concentration. However few are able to directly analyse the relationship and interaction between the atmosphere and terrestrial carbon sinks.


Eddy covariance is a technique, used by meteorologists, biologists and ecologists, that determine the momentum of 3-dimential vertical


CO2 fluxes within atmospheric boundary layers, for instance directly above a crop, grassland or forest canopy. The methodology is mathematically complex and requires highly specialised field instrumentation. This fundamentally includes a fast response, high


resolution CO2/H2O analyser synchronised with a fast sampling sonic anemometer providing combined data at 20Hz. It is common for this instrumentation to be located on flux towers many meters high above a forest canopy or even on an aircraft or blimp.


Typically the analysis cell of an infrared gas analyser is of a closed construction with gas being pumped through it. Unfortunately this design is not completely suitable for Eddy covariance experimentation as there is a lag time between the sampling point and the analysis cell that may be several meters of gas tubing away. To overcome these delays an analyser is designed with an analysis cell directly open to the


environment, so any changes in atmospheric CO2 is measured instantaneously. One such instrument is the ADC BioScientific OP-2 CO2/H2O open path analyser.


The longer the path length of an infrared gas analyser cell, the higher the possible resolution. With a path length of 80cm the OP-2 is able to


resolve CO2 to 0.02ppm. At the same time the novel folded path design, where the energy signal is reflected back 4 x 20cm, maintains the compact nature of the instrument.


The ADC OPEC (Open Path Eddy Covariance) system is a complete, fully integrated and synchronised measurement station. In addition to the OP-2, it also features the highly regarded Windmaster sonic anemometer, manufactured by Gill Instruments Ltd. and EDDYSOFT, Eddy covariance data collection and calculation software written by flux researchers at the Max Plank Institute.


Plant Photosynthesis


Vegetation is a prime natural carbon sink absorbing CO2 for photo- synthesis, a key biochemical process, providing essential energy and building materials for plant tissue.


Improving our understanding of plant growth and crop production is an ongoing necessity for the global community. By measuring


photosynthesis, by CO2 uptake, it is possible to monitor plant health and efficiency. There is now the added environmental aspect of this re-


ADC OPEC system at CFERN field station Jianxi Province, China.


search regarding how crops will respond to rising CO2 concentrations and how their anticipated increased photosynthesis rates could impact on the carbon balance.


AET August/September 2010


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