Paper of the Month – April

Upon formation, rock minerals trap samples of fluid and atmosphere that can be locked away for billions of years

Upon formation, rock minerals trap samples of fluid and atmosphere that can be locked away for billions of years

April’s ‘Paper of the Month’ comes from the Institute of Light and Matter (Université Claude Bernard Lyon 1 and French National Centre for Scientific Research (CNRS)), where the project was conceived by Professor Frédéric Caupin.

Climate change is a controversial subject in both the scientific and political communities, but with the world’s fauna and flora at risk it is one which needs addressing. Modelling future climatic conditions relies heavily on historical records, but this data does not date back far enough as the technology was only developed in the last century. To predict a more accurate climatic future, a technique known as paleothermometry is becoming ever more widely used. Professor Caupin’s group focused on identifying issues in current methods of extracting paleothermometry data and constructed a novel method which bypasses current practical and theoretical problems. 

Rock minerals almost always contain Fluid Inclusions (FIs). These inclusions contain snippets of atmospheric and fluid data trapped at the time of the rock’s formation and thus have been used in the past as proxies to estimate the variability of the Earth’s surface temperature as well as determining natural processes – such as fluid distribution in the earth’s mantle. 
These fluid inclusions – upon cooling – can nucleate bubbles within the rock and it is these bubbles that can be studied to determine the ambient temperature at the time the fluid was trapped. 

However this method of determining historical ambient temperature from rock minerals has limitations – as highlighted by Professor Caupin – for two reasons. Firstly, there is bias in the current methodology and, secondly, the method requires the nucleation of a bubble, which does not always occur within the rock sample.

In this study, Professor Caupin’s group created a new approach which bypasses the need for a nucleation bubble and other limitations. Their method follows the interaction between laser light and fluid droplets – Raman spectroscopy and Brillouin microscopy – from which paleothermometry data can be drawn. They used FIs in quartz crystals, because of the relative ease in comparison between these results, and that of the more standard bubble based method – a technique where paleothermometry data is taken from the nucleation bubble. Their experimental findings show both methods to closely agree with each other and, as such, proves the validity of their new method. 

The group used the Linkam THMS600 to allow application of the wide thermal cycles with the precise temperature control they required for their work whilst also allowing them to observe the spectroscopic measurements. 

The group now aim to use this method as a new approach to find paleothermometry data in more paleoclimatic relevant samples, such as speleothems and evaporites. This approach may provide a novel route to understanding the earth’s climatic history. 


Linkam's Interview with Professor Frédéric Caupin.

El Mekki-Azouzi, M. Tripathi, C.S.P. Pallares, G. Gardien, V. and Caupin, F. (2015).  Brillouin Spectroscopy of Fluid Inclusions Proposed As A Paleothermometer For Subsurface Rocks. Scientific Reports 5, 13168.

By Tabassum Mujtaba