Ancient snails diagnose past climates
27 February 2013, by Harriet Jarlett
Snail shells dug out of archaeological excavations have given a unique insight into past climates.
An international team has shown that 9000-year-old land snail shells, collected from excavations in the Iberian Peninsula and Italy, contain much lower amounts of oxygen compared with modern day snails' shells.
'By putting together research on snails from multiple sites across Spain and Italy, we were able to produce a large scale regional picture for weather conditions over the western Mediterranean area. This allowed us to observe differences in climate across the region.' explains Dr André Colonese from the é, lead author of the study, published in Quaternary International.
Snail shells are known to vary the amounts of oxygen they contain based on the temperature and humidity of their surroundings. This is because the shells are made of calcium carbonate, a mineral which they obtain from water in their surroundings.
Land Snails 'seldom receive the attention they deserve.'
Dr André Colonese - University of York
Depending on the climate there may be different ratios of heavy oxygen isotopes available in the water compared to the light isotopes.
This isotope ratio can be measured in the calcium carbonate which makes the snail shells, using mass spectrometry. It was this ratio in the shell carbonate that the researchers used to discover what the weather was like 9000 years ago.
A lower ratio in the shells suggests that they grew up in a much wetter Mediterranean than we see today.
At that time the first farmers were starting to cultivate the land and domesticate animals in Italy and Spain, but this study shows they would have had to cope with much hotter, stickier conditions than the balmy climate the regions now boast.
Snails, including Pomatias elegans, inside a glass vial.
'The study of past climate is fundamental to a better understanding of past environmental and cultural dynamics, and vital to predicting future scenarios,' says Colonese.
Archaeological sites in the region contain an abundance of snail shells because the people who lived there ate them as snacks. 'The peculiarly large amount of large snails in sites from 12,000 to 6000 years ago suggests that our ancestors made a widespread dietary use of these animals,' Colonese says.
'But small species which were unlikely to have been eaten by humans – at least intentionally – are also abundant. These probably accumulated by natural processes instead.'
Dr Colonese and his co-authors believe that land snails from archaeological digs have great potential as a source of information about human behaviour and palaeoclimatic conditions but, 'unfortunately seldom receive the attention they deserve.'
The team hope to be able to extend this study to make more regional comparisons.
A.C. Colonesea, G. Zanchettab, A.E. Fallicke, G. Manganellif, M. Sañag, G. Alcadeh, J. Neboti (2013) Holocene snail shell isotopic record of millennial-scale hydrological conditions in western Mediterranean: Data from Bauma del Serrat del Pont (NE Iberian Peninsula) Quaternary International In Press
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