The 30th anniversary of a CSIRO stalwart

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.

Installation of the MAT252 at Aspendale in August, 1990. From left: Roger Francey, Colin Allison, and Finnigan MAT representatives Winfried Schmidt and Jim Bearpark

Colin Allison analysing air samples on the MAT252, circa 1990.

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In the field of atmospheric composition research, most cutting-edge analytical systems are quickly superseded through ongoing technological advances, and few instruments remain viable over 30 years.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.

Figure 1. MAT252 measurements of CO2, δ13C and δ18O (retained ◊, rejected +) in flask samples collected at Cape Grim, Tasmania

Figure 2. CO2 and δ13C from direct air sampling at Cape Grim, and Law Dome ice and firn; and fluxes since 1840 for the main carbon sources and sinks.

Figure 3: The low CO2 levels from 1550 to 1750 AD were linked by d13CO2 to increased carbon uptake by the land biosphere during cool conditions (the Little Ice Age).

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