Natural sparkling mineral waters get their effervescence from gases coming from the Earth. While these waters have been long enjoyed for their taste and health benefits, we often don’t know exactly where in the Earth’s interior those bubbles come from. A recent study, led by Dr Rūta Karolytė (seen here on the left), now at Oxford Earth Sciences, together with an international team from the University of Edinburgh, the Scottish Universities Environmental Research Centre in Scotland and the Universities of Adelaide and Wollongong in Australia, has explored the relationship between natural springs and gas, with some surprising implications.
Where does the CO2 come from?
CO2 in mineral waters can come from a variety of sources, such as the breakdown of carbonate rocks and the activity of bacteria. CO2 can also migrate directly from the Earth’s mantle, which is around 40 km below the ground surface, or be degassed from hot magma chambers at depth.
Traditionally, the origin of CO2 is pinpointed by measuring the amount of one form of the noble gas helium, which was trapped in the Earth’s mantle during the big bang, and comparing that to the amount of CO2 present.
This new study of sparkling water mineral springs in south-east Australia showed that the balance between CO2 and helium can be easily overprinted when gases dissolve in natural mineral waters. In the past scientists thought these signatures showed that mantle CO2 only represented a tiny fraction of what is found in these springs. But the new results show that in many cases, what we see in the Australian springs and many other common sparkling mineral waters is pristine gas coming from the depths of the Earth’s mantle.
Findings apply to storing man-made CO2
While this could be a fun and geologically-sound marketing concept for mineral water retailers, the real applications of the study results are much wider.
Being able to determine the source of small amounts of gases dissolved in much larger volumes of water has very important applications for Carbon Capture and Storage (CCS). CCS is a technology which allows the injection of man-made CO2 into deep geological formations, preventing it from entering the atmosphere and contributing to climate change.
As Rūta explains: ‘We use these springs as a nature’s experiment of mixing CO2 with lots of water, transporting it over long distances and seeing if we can still determine what its original source is – and the answer is yes! The rocks that the Australian mineral waters flow through are highly fractured, and therefore no engineered CO2 storage would ever take place in this particular region. However, our work shows that we can use the same techniques to confidently trace and identify the unique fingerprint of the CO2 injected in formations which have a secure seal rock and can hold the gases for millions of years.’
Currently there are over 20 large scale CCS projects in the world, but many more are needed in the future to reduce the global CO₂ levels and help to limit the impact of climate change. Adoption of CCS technologies could greatly help the UK cut its greenhouse gas emissions to almost zero by 2050, and this will be necessary to meet recently announced targets.
The study, published in Geochimica et Cosmochimica Acta, was supported by the UK Engineering and Physical Sciences Research Council and the Australian research organisation CO₂CRC.
Full paper available here: https://doi.org/10.1016/j.gca.2019.06.002