Using clam shells to help build 1,000-year record of ocean climate
AMES, Iowa: lan Wanamaker, working as a postdoctoral researcher from 2007 to 2009, was charged with beginning to compile a 1,000year record of the marine climate for a spot in the North Atlantic just off the fjords and fishing villages of North Iceland.
He was at Bangor University in Wales, working with James Scourse and Chris Richardson, professors in the School of Ocean Sciences. Before Wanamaker were thousands of clams, each specimen of Arctica islandica taken from 80 metres of seawater on the North Icelandic Shelf.
Those clams – dead and alive, some able to live up to 500 years in the icy water – were the research group’s sensors under the sea. Just like tree rings say a lot about growing seasons over time, annual growth increments in the shells can tell researchers a lot about ocean conditions over time.
Wanamaker, now an Iowa State University associate professor of geological and atmospheric sciences, started building the marine archive by processing all those clams – painstaking lab work that involved sectioning shells, embedding shell slices in epoxy blocks, measuring down to a millionth of a metre, drilling samples, radiocarbon dating and determining oxygen isotopes.
Then he’d eye cross sections of shells, looking for patterns, matching growth rings, finding overlaps, all with the goal of eventually lining up enough shells to build a master chronology of growth increments covering a millennium.
That open-access record, based on 10 years of work and analysis of nearly 1,500 isotope samples from dozens of clams, is now complete.
“Here we report a new 1,048-year precisely dated, annually resolved marine oxygen isotope record that spans the entirety of the last 1,000 years (AD 953-2000),” the researchers wrote in their paper. — Newswise