Extracting formation temperatures from stalagmites 

As part of our NERC ‘Exploring the frontiers’ grant, Dr Peter Wynn of Lancaster University and I have been out undertaking fieldwork in the Matienzo valley in northern Spain. The Matienzo valley is a fantastic karstic depression; it’s over two million years old and contains hundreds of kilometres of natural cave systems. Beyond its fantastic history of use as a repository for scientific data, the region is also heavily used by recreational cavers and cave explorers.  

Our current work is focused on a small cave system called Llanio, just outside the main Matienzo karst depression. The work aims to develop a novel method for extracting cave speleothem (stalagmite) formation temperatures.

Cave temperatures

Caves have stable annual temperatures, only fluctuating within one degree over the annual cycle. This stable temperature reflects the average external annual temperature very accurately. For this reason, the development of a palaeothermometer from speleothem carbonate has been something of a ‘holy grail’ for palaeoclimate scientists over the last 50 or more years.  

The entrance to Llanio involves a flat-out crawl for several metres before some more small passages lead into the larger sections of the cave, where our water and speleothem sampling takes place. This spring, the crawl was made even worse than normal as the entrance had numerous large spiders in residence and the remains of some unidentifiable animal that we had to crawl over on both the way in and way out of the cave!  

Inside the caves

Once we entered the cave, we had an excellent and productive research trip. We were able to collect numerous water samples and extract the phosphate from them using an in-cave chemical extraction method. The data from these samples will be compared to what we would expect at the known cave temperature. We also collected some already-broken calcite, which we will dissolve later back in the BGS Stable Isotope Facility. 

Further work

All these samples will be collated with samples that have been sent to us from collaborators from around the world, to see if we can use our new method to develop a reliable cave palaeothermometer in the BGS laboratories.  

About the author

Dr Andrew Smith

Dr Andrew Smith

Isotope geochemist

BGS Keyworth

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