Worm poo could reveal secrets of climate history

...many of the existing climate proxies originate from the oceans. Calcium carbonate granules left by earthworms, therefore, could enable climatologists to learn more about geographical areas that have hitherto been beyond their reach.
Dr Emma Versteegh
Earthworm excrement could be used to enhance and to benchmark climate change models, according to UK researchers...

UK academics have devised a way of using earthworm excrement to reveal what the prevailing weather conditions were thousands of years ago. The scientists, whose research was funded by the Natural Environment Research Council (NERC) and published in the journal Geochimica et Cosmochimica Acta, intend to use their novel method to enhance and to benchmark existing climate change models.

Researchers from the University of Reading and the University of York conducted a laboratory study to investigate balls of calcium carbonate commonly found within the faeces of the earthworm Lumbricus terrestris. During the course of the study, the team housed earthworms at different temperatures before conducting isotopic tests on the excreted calcite granules.

The researchers discovered that the calcium carbonate balls retained ‘memories’ of the temperatures at which they originally formed. It should therefore be possible to use soil samples from archaeological digs and geological surveys to provide exciting new insights into our climate history.

To find out more about the potential climatic applications of worm poo, I spoke with the study’s lead author Dr Emma Versteegh from the Department of Geography and Environmental Science at the University of Reading.

'Accurate to within 1°C'

"The temperature reconstructions that we conducted were accurate to within 1°C," she began. "Of course, as this was a proof-of-concept study, we still need to investigate how our method translates to real soils. For example, it might transpire that factors such as depth and water evaporation affect accuracy outside of the laboratory."

Essentially, Dr Versteegh and her colleagues have developed a method of finding out how hot it was when a lump of calcium carbonate was formed. By dating these granules, scientists should be able to use earthworm excrement as a tool to learn more about the climate at specific points in history.

"These temperature reconstructions are, by definition, local ones," said Dr Versteegh. "However, by collecting and comparing data taken from different sites, it should be possible to develop a much broader picture."

Luckily for the researchers, calcium carbonate granules excreted by earthworms are abundant. Moreover, under favourable circumstances, these deposits can persist for long periods of time, offering scientists the opportunity to dig deep into our climatic past.

"Calcium carbonate deposits are actually very common," Dr Versteegh explained. "Indeed, it is possible to find hundreds of these granules in small amounts of soil. Over the past few years, I have approached a number of archaeologists who work with shells and other types of carbonate. Not only did they tell me that they regularly encounter these granules, but they also revealed that they already collect them. This, of course, is extremely convenient from the perspective of our research.

'Intact for millions of years'

"We are now in the process of working out how best to analyse and to date these calcite granules," she continued. "Sadly, in acidic soils, they do not tend to last for a long time. However, under the right conditions, they can remain intact for millions of years – far beyond typical archaeological timeframes."

The ability to enhance and to benchmark climate change models is one of the NERC-funded research project’s most exciting potential applications. By adding worm poo to the existing portfolio of proxies, researchers could gain fresh insights into our climatic history.

"I am confident that data collected using the method that we have developed will help to fill in some of the gaps that exist within existing reconstructions," said Dr Versteegh. "Our laboratory tests have demonstrated that worm excrement can be used to provide terrestrial, or land-based, climate reconstructions. This could prove to be especially useful because many of the existing climate proxies originate from the oceans. Calcium carbonate granules left by earthworms, therefore, could enable climatologists to learn about the histories of geographical areas that have hitherto been beyond their reach."

Further research

Now that the proof-of-concept study is complete, the team intends to conduct isotopic tests on real-life samples. If the accuracy of this method is proven to extend beyond the walls of the laboratory, earthworm excrement could help to significantly enhance our understanding of past climates.

"We are currently applying our method to granules taken from archaeological studies and geological samples," concluded Dr Versteegh. "We want to learn more about what happens in soil outside of a controlled laboratory environment. We are also looking deeper into the chemistry of these granules. For example, by analysing carbon isotopes, it might be possible to gain insights into non-climatic historical factors such as the type of vegetation growing in a particular area. These are just a few of the areas in which we intend to conduct further research."

If you'd like to learn more about the climatic applications of worm excrement, check out the full paper: 'Earthworm-produced calcite granules: a new terrestrial palaeothermometer?'



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