The long necks protruding from a geoduck's giant shell have led some to believe that the world's largest burrowing clam is an aphrodisiac. Whether or not that is true, the sea creature may offer another—albeit less sexy—benefit for humanity, according to new research. The long-lived geoduck (pronounced "gooey duck") could help us deduce what climate conditions were like hundreds of years ago and more accurately predict future patterns.
"Unlocking climate and ecosystem records in the marine environment is equally as useful as tree rings are in the terrestrial environment," says Bryan Black, a tree-ring analyst at Oregon State University. "Geoducks and trees each capture climate variability from their own unique perspective."
Gaps in climate records continue to force substantial variability into climate projections, including those found in the most recent Intergovernmental Panel on Climate Change (IPCC) report. These limitations are mostly due to the length and global distribution of instrumental climate records. But scientists are now discovering that data from a suite of animal proxies has the potential to fill in some of these holes. And holes in the sand created by geoducks' squirting siphons are one place where researchers have begun digging for those clues.
Parallel arcs on the hinge of the Pacific Northwest clam's shell record growth increments, much like tree rings. Sea surface temperatures—which strongly influence regional climate—are one of the key variables that can be inferred from these records. Hotter temperatures drive metabolism in geoducks; wider increments mean warmer years. The same goes for trees. Inland, old-growth Douglas firs have a longer growing season when the snow melts earlier.
"We can take those different perspectives—each explaining a different part of the story—and put them together to get a full view of what the climate was like in the past, and a more robust forecast for the future," says Black, who was the lead author of a paper on proxies for climate reconstruction recently published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology. "And from the ecology side," he adds, "once we know which variables a marine organism is sensitive to, we can better inform how future climate changes could affect it." This information could be especially useful for fishery managers.
The researchers collected and compared more than 30 individual trees and geoducks, at each of several locations in the Pacific Northwest. Through a process called cross-dating, they ensured that annual growth increments were indeed representative of climatic variation rather than an individual's unique experience. "When you are looking at multiple samples, you see some rings are narrow and some are wide," says Carolyn Copenheaver, a forestry expert at Virginia Polytechnic Institute and State University and co-author on the paper. One individual tree, she explains, may have unusually narrow increments compared with its neighbors if it lost branches the previous year. But comparing them as a group, Copenheaver says, helps eliminate that noise and allows scientists to say, "This one was 1977; that one was 1944."
In the end the team found that almost 50 percent of the variability in the sea surface temperatures—obtained from instrumental records dating back to the 1940s—correlated with the variable widths of the tree rings. Once the tree rings were combined with geoducks' incremental record, the amount of variability explained rose to close to 70 percent.