The 30th anniversary of a CSIRO stalwart

August 7th, 2020

ACC’s greenhouse gases team are celebrating 30 years of carbon dioxide (CO2) isotope measurements from their MAT252 mass spectrometer in the Global Atmospheric Sampling Laboratory (GASLAB).

This instrument commenced operations at CSIRO’s Aspendale laboratories on August 6, 1990 under the guidance of Research Scientists, Dr. Roger Francey and Dr. Colin Allison. It replaced an older mass spectrometer in use since 1977, as part of a broader upgrade of CSIRO’s atmospheric greenhouse gas research capability. Arrival of new instrumentation and personnel from 1990 marked the commencement of the GASLAB facility.

The MAT252 was manufactured by Finnigan MAT (Bremen, Germany) as state-of-the-art technology for high precision measurement of the 13C/12C and 18O/16O ratios in atmospheric CO2. The system includes a custom-built module for cryogenic separation of CO2 from air, interfaced to an isotope-ratio-mass-spectrometry (IRMS) analyser. It was designed with a capability to process very small sample volumes, a feature that has been advantageous for maintaining multi-decadal records from a global network of sampling sites (Figure 1), and critical for measuring ancient air retrieved from air bubbles trapped in polar ice sheets (Figure 2, 3).

In the field of atmospheric composition research, most cutting-edge analytical systems are quickly superseded through ongoing technological advances, and few instruments remain viable over 30 years. But despite its age, the MAT252 still produces world-class quality data, thus continuing CSIRO’s benchmark records of the changing isotopic composition of CO2 in the global atmosphere. Records from the Southern Hemisphere, especially those from the Cape Grim Baseline Air Pollution Station in Tasmania, provide unparalleled definition of changes in the background atmosphere.

Defining the variation of CO2 isotopes in time and space helps constrain the fluxes of CO2 between the atmosphere and linked reservoirs, such as the land biosphere, oceans and fossil fuels. This is because the exchange processes can discriminate against different isotopes based on their mass. For example, photosynthesis by plants preferentially removes lighter isotopically labelled CO2 from the atmosphere, whereas atmosphere-ocean exchange has weaker mass discrimination.

One important use of CSIRO’s atmospheric 13C/12C records has thus been to determine the relative uptake of global fossil carbon emissions by the land biosphere and the oceans (Figure 2, 3). The 18O/16O records hold information about the hydrological cycle, and cycling of atmospheric carbon through the land biosphere.

Written by: Ray Langenfelds, Colin Allison, Roger Francey, Elise-Andree Guerette, Zoe Loh, Christopher Roulston.