500- year- old clams open up history of the oceans
“The changes that we are seeing in ocean chemistry are unprecedented, relative to the last 1,000 years.” David Reynolds, Cardiff University
Clams are more than a tasty ingredient in chowder, they also are important in understanding Earth’s history.
The world’s oldest animals, 500- yearold clams have given scientists an unprecedented look at the climate history of the oceans.
By studying growth rings in the shells of quahog clams, scientists have pieced together the history of the North Atlantic Ocean over the past 1,000 years. The method is similar to how tree rings can serve as climate proxies by revealing clues about past weather and climate changes, including droughts.
Quahogs, also known as hard clams or chowder clams, are edible mollusks that live in the North Atlantic Ocean along North America and Europe.
By studying the clams’ shells, scientists from Cardiff University and Bangor University in Wales found that the ocean’s relationship with the atmosphere drastically changed over the centuries, probably because of the influence of greenhouse gases such as carbon dioxide and methane that have been pumped into the atmosphere from humans burning fossil fuels, which started with the Industrial Revolution.
Although clams have been used as climate proxies through the field called sclerochronology since the 1970s, the new study is the first time researchers have been able to obtain a 1,000- year record of the ocean with absolute dating precision, according to lead author David Reynolds of Cardiff University.
In the pre- industrial era, roughly before 1800, the climate was driven by natural factors such as volcanic eruptions and solar activity, he said. At that time, the ocean influenced the atmosphere. Since then, it has been the other way around: The atmosphere, with its increasing levels of carbon dioxide and other greenhouse gases, has driven major shifts underwater.
“The changes that we are seeing in ocean chemistry are unprecedented, relative to the last 1,000 years,” Reynolds said.
Scientists studied living and fossil clams from a seabed north of Iceland. By comparing the ring widths of live and fossil shells, they were able to date shells that lived during the same time period because they contained the same pattern.
“By using multiple fossil shells, we were therefore able to extend the record backwards through time to cover the entire last 1,000 years,” Reynolds said.