|The fossilised Antarctic clam shells which display different |
growth rates during the El Nino and La Nina phases
Now scientists have discovered 50 million year old clam shells and wood from a formation on Seymour Island in the Antarctic which could provide an answer. 50 million years ago, during an epoch known as the Eocene, an event called the Eocene Thermal Maximum occured. This event oversaw the highest average temperature ever in geological history; most continents would have been covered in lush, tropical forests and jungles.
The specific bivalve mollusc species, Cucullaea raea and Eurhomalea antarctica, were fossilised records of the temperature phases. Growth rings within the shells matched these shifts. We have similar records in modern clam shells today. Cold phases resulted in a narrow growth ring while warm phases caused a larger growth. Despite the Eocene Thermal Maximum, the shells still displayed classic signs of El Nino growth rates. The Eocene Thermal Maximum began around 58 million years ago, just 7 million years after the extinction of the dinosaurs.
It ends 50 million years ago, the same date as the Antarctic clam shells. This suggests that permament El Nino phases cannot last and will always relapse into its counterpart La Nina. Clams live up to 100 years, allowing them to experience up to 20 climatic shifts, making them a very useful and reliable indicator. The range of specimens give a comprehensive guide to the meteorological conditions that might occur in the future, in particular that an El Nino event can never be permanent.