The search for soil carbon... by Barry Rawlins

Last week a team of BGS scientists spent 5 days in one of the worlds most advanced scientific facilities firing light, 10 billion times brighter than the sun, at soil samples! Barry Rawlins explains more about their hunt for organic carbon and why it's so important for the future…

At the UK's synchrotron 'Diamond Light Source' in Harwell we're trying to find where the organic carbon is locked away inside soil aggregates. If we know this we can understand whether the structure of the soil might influence whether it is available for bacteria to feed on. If the carbon is freely available then the organic matter becomes an active source of CO2, and may change with changing climate scenarios.  If the organic matter is locked deep inside the aggregates then it might not be available to bacteria. So different soil types could potentially be sources or sinks of CO2.  It's all about understanding the processes within the carbon cycle.
Here's a video explaining exactly what we got up to with our soil aggregates (aka clumps of soil held together by clay and organic matter including bacteria etc) at Diamond:

We used a chemical (osmium) to stain the organic matter. It is possible using the beamline at Diamond to locate where this osmium and organic matter is in 3 dimensions by scanning the sample at different energy levels using X-ray computed tomography (on the I12 beamline). 
As many visitors find when they visit the beamline, it took us some time to set up our experiment and because the scientists there had recently installed some new optics it took a while to get this working.  Once we were up and running the procedure was really effective.   We worked through the night to capture our data – changing samples at 4am is something I have never experienced before!  We now have nearly 10 terra-bytes of data to process so our results will take some time to generate. 
We did make a short video about the experiments which you can see above, and a short visualization showing where the carbon is in the aggregate (coloured gold) below. The Diamond Light Source is an incredible facility and I am really pleased to have had the opportunity to work there. I hope we'll be writing another blog when we know more from our results.
By Barry Rawlins, the Team Leader for Sustainable Soils at the BGS