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How snail shells are shedding light on the Gulf's nomadic traditions and fishing heritage
Snail shells collected at an archaeological site in Oman can be used to trace the Gulf's climate going back thousands of years, a new study reveals.
This work can help us understand how people adapted to increasingly arid conditions in the region around 3000 to 2000 BCE, becoming more nomadic and settling in coastal areas.
'This was a time of major change in how societies were organised in the region, when the first monumental stone structures were built, people produced copper for trade with the civilisations of Mesopotamia and the Indus, and the date palm first came under cultivation,' Dr Lucas Proctor, one of the study's two primary authors, said.
Central to the study in Ash Sharqiyah North province was the analysis of two types of oxygen in the shells of a land snail. Researchers compared the abundance of a heavier form of oxygen, Oxygen-18, to that of a much more common type, Oxygen-16.
The study found that the extent to which the creatures incorporated Oxygen-18 correlated with how the area's climate had changed. Higher ratios of Oxygen-18 to Oxygen-16 were associated with arid conditions, while a lower ratio suggested a more humid climate.
How shells document the past
'[The ratio has] become more positive since 6000 BCE, indicating drier conditions,' said Dr Katharina Schmitt, the study's other primary author. 'Prior to this period, there was a recurring fluctuation between higher and lower values.'
The paper, Unlocking the potential of the terrestrial gastropod species Zootecus insularis as a climate archive for arid regions, has been published in Nature Scientific Reports.
The work links to a wider increase in the analysis of climatic data. In a 2021 paper, Prof Scott Elias, of Royal Holloway University of London, wrote that the drier results are partly due to natural variations in the Earth's climate in the era before human beings had any influence on climate change.
As well as offering clues into the climate of the past, the shells also indicated a change in the type of vegetation growing as the region became much more arid.
Dr Proctor said snails were 'great climate indicators' because they were very sensitive to alterations in the environment and were preserved in the ground for a long time.
How many shells were analysed?
More than 300 snails, including fossils, were collected, of which 169 were analysed in detail and dated.
'The snails are abundant in sediments throughout the Gulf region, so they can easily be collected from areas of interest,' Dr Proctor said.
'This is so important in arid locations like Arabia, where many of the traditional high-resolution climate records … struggle with preservation issues, gaps in their records, or only form in specific areas far away.
'Using these shells allows us to create a bridge between local conditions and these existing regional records to understand how different areas experienced these regional patterns.'
While the approach used in the study has often been used to reconstruct climates and environments going back millions of years, it is 'much less common' to use land snails rather than aquatic snails, and to look at more recent timescales.
Dr Proctor hopes the research 'will spur a wider interest in using a combination of preserved land and aquatic snail shells for climate reconstruction in the future'.
How has the climate changed?
Previous evidence indicates that between 12000 and 3000 BCE, global fluctuations in climate caused the Khareef monsoon – which now affects only southern Oman – to shift north, possibly as far as Abu Dhabi.
This was caused by factors including the position of the Earth's orbit, the melting of ice sheets and the interaction of ocean currents and air masses, with both Arabia and the Sahara receiving far more seasonal rainfall than they do now.
'We think much of Oman and UAE could have supported savannah-like grasslands and seasonal lakes during this time,' Dr Proctor said. 'Eventually, around 6,000 to 5,000 years ago, this climate pattern began to change and the Khareef shifted south to its current position and a much more arid climate pattern took shape by about 4,000 years ago.'
When it was humid the people living in the area could have nomadic foraging lifestyles in the interior, but more arid conditions meant communities had to retreat to the coasts or develop new strategies for living in the interior.
'This corresponds to the Late Neolithic transition, where we see the adoption of herding and specialised fishing economies,' Dr Proctor said.
'It probably also contributed to the adoption of date palm agriculture in the Bronze Age and the eventual invention of aflaj [irrigation systems] and the oasis system even later.'
