Tracing climate history through giant clams
Scientists need ancient records of climate to understand background variability and to better simulate Earth’s climate system, ultimately to make predictions for its future. Giant clams live long lives, forming growth bands in their shells as they quickly grow. The layers in fossil clam shells are essentially archives of the environmental past. “Giant clams are excellent recorders of environmental and climatic parameters, and because of their rapid growth rate, they can record very high-resolution variability – monthly if not higher!” explains Eleanor John, a palaeoclimatologist from Cardiff University. In the EU-funded REEFCLAM project, undertaken with the support of the Marie Skłodowska-Curie Actions programme, John studied giant clam shells from the tropical Pacific, an area where palaeoclimate data is both particularly valued and relatively scarce. Giant clams were used for food and tools in early tropical Pacific societies, and their shells were left behind in large deposits called middens. The project explored shells in middens roughly 3 000 years old in Fiji, and the results are helping to build up a picture of the pre-industrial climate of this tropical region. “We now know that climate variations such as the El Niño Southern Oscillation and the Pacific Decadal Oscillation have dramatic regional and global effects,” says John. “To understand how these are likely to change in future, we need to understand how they have varied through time. This is why archives such as the fossil giant clams in REEFCLAM are so valuable,” she adds.
Collaboration with local museums
The REEFCLAM project involved collaboration with Fiji Museum, who assisted John in collecting samples from known archaeological sites in the field. They also gave access to giant clams in their archives. The clams were then shipped to the United Kingdom, where John prepared the shells so that their growth layers could be imaged, measured and analysed. Using geochemical methods, she was able to examine changes in trace element concentrations and stable isotope ratios in the shell material as the shell grew, which reveal details about the environment at the time the growth bands were formed. “The clams are the property of Fiji Museum and will be returned once all analyses have been completed and will hopefully be the focus of a new exhibit at the museum, explaining the results of our research,” notes John.
Sub-annual palaeoclimate records
John was able to successfully obtain sub-annually resolved palaeoclimate records from two fossil giant clams in the final throes of the project, and secured funding from the United Kingdom’s Natural Environment Research Council’s Isotope Facility to generate high-resolution stable isotope records from more shells. There is still some data pending analysis, and the results of these are imminent. “As such, I can say that the project will have successfully achieved its aim in generating sub-annually resolved pre-industrial climate records from Fiji,” says John. “I expect the results to fill in an important gap in our understanding of seasonal and inter-annual climatic variability around 3 000 years ago,” she adds.
New clam collaborations
John plans to apply for follow-up funding on both the Fijian giant clams and other giant clam fossils from the region, in collaboration with new networks. “I see huge potential in using giant clam archives to answer important questions in the Pacific!”
Keywords
REEFCLAM, giant clams, archive, past, environment, growth