Dead Clams Talking

Field Notes
By Randall Hyman
Aug 21, 2014 8:35 PMNov 20, 2019 1:47 AM


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This is the first is a series of three posts from researchers' expedition to northern Norway. Read others in the series here.

Growth increments on these common clams hold untold insights into past climate. This past Sunday, as I was setting sail with a team of scientists aboard a coastal steamer bound from Tromsø, Norway, to a tiny island near the northernmost tip of the country, paleoclimatologist Al Wanamaker surprised me with a bit of news. “I guess you heard about our Ming nightmare,” he had said as brisk Arctic winds chiselled white caps across the frigid seas before us. We had only met by email up till then and he wanted to broach this sensitive subject in person. At the center of the storm was a tiny clam: Arctica islandica, or the “Ming clam.” In 2007, Wanamaker and colleagues at Bangor University discovered it was the world's longest living non-colonial animal.

Handful of Arctica islandica. After that discovery, “I was shaking in my boots when I walked out of the lab,” says Wanamaker. “Before I knew it, friends were calling me from all over the world.” But then things changed. “When others realized we had to kill individuals to date them, everything went haywire and headlines changed to 'Scientist kills world's oldest living animal.' It was a nightmare. There were even crazy stories about me clubbing and shucking them overboard. It took some coverage from National Geographic and other good journalists to set the record straight.” Wanamaker and I were on the same page. We both wanted to focus on the science and get any distractions out of the way. The straight dope is that, if there's one amazingly old Arctica islandica, there are many others happily living nearby. And where we’re headed, the coastal ocean is teeming with them.

History Written in Rings

The living Arctica islandica Wanamaker and colleagues had identified was over 500 years old. Going one step farther, the team was able to use isotopic analysis to track the tug-of-war between Arctic and North Atlantic currents on an annual basis, just by examining the chemicals in the layers of the clam’s shell. Like tree dating (dendrochronology), the science of sclerochronology matches rings – in this case shell rings – among individuals to establish accurate ages. And like dendrochronology, sclerochronology is accurate to the single year, not decades or centuries like ice cores and geologic strata.

Fishing boats sit at dock at Ingøya. Though people have been counting such rings in shells – called increments – since at least Leonardo da Vinci’s time, isotopic analysis, electron microscopes and other innovations have given the field a shot in the arm in recent years, propelling it toward answering ever bigger climate questions. A key study Wanamaker and colleagues published in 2012 showed it could be done: His team reconstructed over a millennium of climate change based on clam shells collected off Iceland's northern coast. We’re here, in Ingøya, the critical gateway between the North Atlantic and Barents Sea, to build on that study. Here Arctica islandica, dead or alive, has tales to tell that are helping crack open mysteries of climate change, past and present. By connecting the dots between clams from Iceland to the British Isles to northern Norway, the team I’m with hopes to add another piece to the big puzzle, detailing how Atlantic Ocean currents impact Arctic climate.

PhD students Irene Ballesta Artero and Maddie Mette examine Arctica islandica clams just dredged at their study site.

Climate Over Millennia

By the time we arrived at Ingøya on Monday, it was clear to me that I'd be witnessing groundbreaking science this week. Our crew – Wanamaker of Iowa State University, Will Ambrose and Mike Retelle of Bates College, Michael Carroll of Norway's Akvaplan-niva and Rob Witbaard of the Royal Netherlands Institute for Sea Research, plus students – were buzzing with excitement, and the island's austere, treeless beauty only added to the electricity. Nordic light has always delighted my photographer's eye, but here, 20 miles off the mainland where the precipitous continental shelf lies right at our doorstep, the effect is mesmerizing. No sooner did we unpack gear than plans were made for the next day’s first fieldwork. Oceanographer Ambrose, a co-principal investigator, dubs their work “Dead Clams Talking,”a wry twist on the movie title Dead Man Walking that only a scientist steeped in mollusks could dream up. He and his colleagues specialize in reading the series of bands striping clams’ calcareous lids that casual beachcombers would consider mere decoration. Scientists see entire biographies in these annual growth bands, much like tree rings or ice cores, and they are able to discern lean years from fat years and icy from warm. But the team reads more than just growth bands. Using the same techniques Wanamaker employed in his Iceland research, they are pulverizing annual growth increments and analyzing oxygen and carbon isotope levels to infer, year by year, marine salinity and temperature.

Marine ecologist Michael Carroll discusses map of Ingoya and field work plans with oceanographer Will Ambrose and paleoclimatologist Al Wanamaker. In Iceland, Wanamaker showed that a major shift in ocean currents there had contributed to overall climate over the past millennium. He did this courtesy of a handy isotope tracer: radiocarbon. Radiocarbon is produced in the upper atmosphere and transferred into the global ocean whenever seawater is in contact with the atmosphere. Arctic waters, locked under ice and submerged at great depths for centuries, contain less radiocarbon than the northward flowing Gulf Stream. Knowing all this, Wanamaker and colleagues confirmed that the Gulf Stream had filled the region during the warm Medieval Climate Anomaly – roughly the Viking era – while older Arctic currents dominated the Little Ice Age. This week our team is going one step farther than the Iceland study by combining the talents of scientists from different disciplines to reveal an even more complete story about climate over the past 1000 years, and possibly beyond. While Wanamaker and his grad student collect clams for meticulous isotopic analysis to be performed back in Iowa, the Dutch team is continuing its long-range study of clam growth and energy expenditure by monitoring a live rack of mollusks wired with electronic loggers in deep water. Geologist Retelle will be studying the ancient beds of dead clams on raised beaches with the aim of establishing a continuous chronology from deep water clams to those marooned long ago. Oceanographer Ambrose and marine ecologist Carroll are lending years of Arctic experience and mollusk research to help put the pieces together. After a day of riding shotgun on a small boat dredging clams, I am exhausted with already lots to tell – with the help of the clams, of course. That’s to come, in my second post of the series. Stay tuned! All images by Randall Hyman

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