乐播传媒

Professor Will Ambrose, a bearded biologist specializing in Arctic sea-floor ecology, is a pioneer in the science of deciphering the past 鈥� including past climates 鈥� by studying the annual hard-tissue accretions of organisms such as mollusks.

As an expert in sclerochronology, Ambrose has discovered a link between Arctic clam growth and regular shifts in the region鈥檚 climate. In short, Arctic clams grow more rapidly during regimes of warm and wet weather and less during cold and dry regimes. This sensitivity to climate change, says Ambrose, makes the humble bivalve a 鈥渟entinel of climate change.鈥�

While Ambrose is collaborating on no fewer than five clamshell research projects at the moment, the scientific paper that detailed the initial findings of a correlation between climate change and Arctic clamshells appeared in Global Change Biology in September 2006.

The paper emerged from work done three years earlier, when Ambrose dispatched divers to the bottom of a high Arctic fjord in the Svalbard archipelago, a popular Arctic research site about halfway between the Norwegian mainland and the North Pole. From the ocean bottom, the divers returned with four Greenland cockles (Serripes groenlandicus).

After encasing the shells in epoxy and slicing them apart, Ambrose and a team of scientists, including Kelton McMahon 鈥�05, analyzed the growth bands. First, the team found that growth bands were indeed deposited annually. Then the team was able to correlate annual differences in shell growth with a measurement of Arctic weather oscillations known as the Arctic Climate Regime Index.

鈥淲hat makes the work exciting,鈥� says Ambrose, interviewed in his cluttered office on Carnegie鈥檚 third floor, 鈥渋s that this is the first time in the Arctic that we鈥檝e been able to track a large-scale climatic oscillation and see that large-scale regional event reflected in animals living on the bottom.鈥�

While scientists have for decades analyzed growth lines in shells (Ambrose and others call them 鈥渢rees of the sea鈥�) in order to reconstruct past environments, the intensity around climate-change research has 鈥渞eally made the field of sclerochronology take off,鈥� he says.

In this hot field, Ambrose鈥檚 research is distinctive for its location, on the Arctic continental shelf. 鈥淎 lot of the work has been done at lower latitudes, mostly because it鈥檚 harder to get clams in the Arctic and there are simply fewer people available to help,鈥� he says. 鈥淭hat鈥檚 why we鈥檙e ahead of the ball.鈥�

If it鈥檚 true that Arctic clams grow faster in warmer weather (and grow faster when there鈥檚 less of a seasonal ice pack, another signal that Ambrose saw hints of), a simplistic response might be, 鈥淕reat 鈥� fatter clams for walruses to munch on.鈥� But, explains Ambrose, fat clams won鈥檛 offset the problems walruses are having due to less pack ice to rest on. And less ice will also affect tiny creatures inside the ice that are the first link in a food chain for polar cod, seabirds, and seals. And so on, throughout the Arctic food web.

In the end, changes in water temperature and salinity (due to runoff from melting glaciers) and increased sea levels, leading to erosion and turbidity, will all take their toll on the Arctic ecology. 鈥淓cosystems operate at the interface of physics, chemistry, and biology, with both complementary and contradictory interactions,鈥� Ambrose writes in a forthcoming article predicting that 鈥渞egional, and perhaps global, biodiversity will suffer.鈥�

Until recently, Ambrose researched other organisms of the benthic community, such as bloodworms along Maine鈥檚 coast. A simple matter of funding helped bring bivalves into focus, as a 乐播传媒 grant (from the Philip J. Otis Endowment) and an external one (from the Howard Hughes Medical Institute) helped purchase a pricey Isomet low-speed saw for preparing shell cross-sections. 鈥淰ery expensive,鈥� Ambrose says.

In researching the biological response of Arctic bivalves to climate change, Ambrose has depended on the interests and expertise of colleagues and students at 乐播传媒 and abroad.

Geology professor Beverly Johnson, for example, has been invaluable in co-advising biology students so they can learn to use the College鈥檚 stable isotope ratio mass spectrometer, a tool to help identify the age and origins of molecules in various materials. Johnson herself has used the instrument to look at amino acids in dinosaur eggs, and it can likewise be used to tease out the chemical components of clamshells.

鈥淚 work with Will to understand how modern systems work,鈥� says Johnson, 鈥渁nd then go back to old shells, using the geochemistry of shells from 125,000 years ago to reconstruct the environment.鈥�

Ambrose also depends on Matt Duvall, who directs 乐播传媒鈥� new Imaging Center, to create elegant microscopic images of his clamshell sections that Ambrose calls 鈥渏ust incredible.鈥�

Geology professor Mike Retelle, another Svalbard regular who specializes in reconstructing climates from lake sediments, has collaborated with Ambrose on researching climate-change information from fossilized Ice Age clams.

Beyond the sciences, Ambrose, Johnson, and Retelle belong to an informal North Atlantic Study Group on campus that also includes archeologists Gerald Bigelow and Bruce Bourque, historian Michael Jones, and political scientist 脕slaug 脕sgeirsd贸ttir. What started informal 鈥� an interdisciplinary coffee klatsch 鈥� has given rise to 鈥淣orth Atlantic Studies,鈥� a thematic grouping of 乐播传媒 courses, known as a concentration, under the College鈥檚 new general education requirements. 鈥淲e represent an area of study, rather than just a bunch of us sitting around having coffee,鈥� Ambrose says.

鈥淚t鈥檚 a truly special group,鈥� Retelle adds. 鈥淭he richness of discussion is such that the boundaries between disciplines disappear. The walls of the box dissolve. Will is a big part of that. As a model for an undergraduate institution, Will has really raised the bar.鈥�

Ambrose himself is quick to point out that 鈥渟tudents here are the ones driving the bus in terms of getting the work done.鈥� As he speaks, Greg Henkes 鈥�08 of Chapel Hill, N.C., is downstairs in the environmental geochemistry lab cutting shells and extracting organic material. Henkes鈥� senior thesis involves a study of 130 years of climate change in the Barents Sea and Svalbard using a historic Russian collection of Serripes groenlandicus. He will present his findings to an American Geophysical Union conference in San Francisco.

鈥淚t鈥檚 pretty incredible to be able to do this at 乐播传媒,鈥� says Henkes. 鈥淚t鈥檚 the way science is going,鈥� says Ambrose of the collaborative nature of scientific enquiry, noting his international partnerships with colleagues at the Norwegian Polar Institute and the research firm Akvaplan-niva. 鈥淧eople aren鈥檛 doing their own little thing anymore.鈥�

鈥淭hat鈥檚 the way science should be done,鈥� emphasizes Kelton McMahon, co-author of the Serripes groenlandicus paper. 鈥淚n certain circles, it is. But a lot of people come from departments that don鈥檛 share data because they feel funding is in direct competition. 乐播传媒 takes a very progressive approach to interdisciplinary research.鈥�

McMahon is now working on his Ph.D. in a program co-sponsored by MIT and the Woods Hole Oceanographic Institution. His contribution to the clamshell research has been to use two gizmos 鈥� a New Wave Research UP213 laser ablation system coupled to a Thermo Finnigan Element 2 single collector field inductively coupled plasma mass spectrometer 鈥� to measure the chemical components of shell samples. Ambrose et al. used changes in the ratio of strontium to calcium to establish that the external lines of the Greenland cockleshells were, in fact, annual growth lines. 鈥淚f it wasn鈥檛 for Kelton getting us access to those machines,鈥� says Ambrose, 鈥渢he paper wouldn鈥檛 have been anywhere near as good.鈥�

As he sits in his Carnegie office discussing his work 鈥� Ambrose also hopes to extend his sclerochronology research to coral in part because 鈥渢hey live much longer than clams鈥� 鈥� he is eagerly awaiting a new shipment of Svalbard shells that he hopes will solve a quirk in his findings. Until recent years, Ambrose found that annual clam growth was high in years when the extent of Arctic ice pack, as measured each March, was low. But over the last several years, 鈥済rowth didn鈥檛 track ice cover the way it did before. Something happened, but we鈥檙e not sure what,鈥� he says. 鈥淎re the last four years unnatural? That鈥檚 why I want those new clams. It鈥檚 another four years of data that will help establish some baselines.鈥� And baselines will help provide more answers, which will probably just beget more questions. It鈥檚 the wayscientific inquiry works. 鈥淧eople like simple answers,鈥� Ambrose says. 鈥淣ature doesn鈥檛.鈥�

By Edgar Allen Beem

Freelance writer Edgar Allen Beem wrote about the in the Fall 2007 issue of 乐播传媒 Magazine.