Surprising: despite subtropical temperatures, big difference between the seasons
In a new study, recently published in the journal Geochemistry, Geophysics, Geosystems, palaeontologists from the Vrije Universiteit Brussel (VUB) and KULeuven used the longest fossilised giant sea snail ever, Campanile giganteum, to get a better idea of what the Champagne region looked like millions of years ago. “Our research shows that the seawater in the Champagne region, with annual average temperatures of 26°C, must have been quite warm and that the difference in the water temperature between winter and summer was striking. This is surprising, because until now it has been assumed that in warmer climates the difference between summer and winter is smaller,” said dr. Niels de Winter, of the VUB research group Analytical, Environmental and Geo-Chemistry (AMGC), who carried out the research with, among others, dr. Johan Vellekoop (KULeuven).
Forty-five million years ago, the world’s climate was exceptionally warm. So hot, in fact, that there were no ice caps on the poles. As a result, the sea level was much higher than it is now, and large parts of Europe were covered with shallow subtropical seas, including what is now the Champagne region in France. Populated by numerous species of snails, molluscs, corals and sharks, the sea of the Champagne region was a hotspot for biodiversity.
With lengths of up to 90cm, the Campanile giganteum, which lived in this sea, was one of the longest sea snails ever. “The shell of such a snail is built up layer by layer. The chemical composition of those layers can give us an insight into annual temperature fluctuations during the snail’s life”, explains de Winter.
The researchers analysed the chemical composition of three fossilised snails and compared them to the only surviving modern relative of the giant snail, a giant creeper snail from Australia, to find out how warm the seawater was 45 million years ago, and why this shallow sea in the Champagne region was so rich in species. The research showed that the Campanile snails not only became very large, but also grew exceptionally fast, more than 10 times faster than most other sea snails. “Due to this high growth rate, these giant sea snails have a special potential as millions-of-years-old climate archives,” says de Winter. “Our research shows that the seawater in Champagne must have been warm, with temperatures of up to 32°C in summer. With relatively cool winter temperatures of 21°C, the difference between water temperatures in winter and summer was remarkable. The warm seawater and the large temperature changes throughout the year may have contributed to the exceptional diversity of species in the shallow sea in France. If we look at the temperature tolerance of modern species, we can see that these temperature variations are exactly right for shell growth, not too hot in summer but not too cold in winter either.”
The research thus also showed that the general assumption that periods with a warm climate, such as the Eocene studied here, also have a smaller seasonality – less difference between summer and winter – is not necessarily always correct. “This also has implications for our knowledge of climate change. Despite the warmer weather, we can still have a lot of differences between the seasons”, concludes de Winter.
Link to original publication: https://doi.org/10.1029/2019GC008794