For a moment, the camera shows an inflatable boat, bobbing in the water near a remote Pacific coral reef where Kelton McMahon ’05 does fieldwork.

Then the camera drops into the clear blue water, revealing the subject of his research: hundreds of grey reef sharks and blacktip reef sharks, each five to six feet long, swimming together in massive schools around the reef.

“How can coral reefs be so productive and biodiverse with a backdrop of such low nutrients?”

McMahon, an assistant professor of biological oceanography at the University of Rhode Island, showed the footage during his Jan. 14 talk at �ֲ���ý because it was awesome, yes, but also because it represents a paradox first noticed by Charles Darwin aboard the HMS Beagle in the 1830s.

Kelton McMahon gestures while speaking to a junior seminar taught by Larissa Williams, associate professor of biology, on Jan. 14. A Purposeful Work infusion course, the seminar features speakers who help students make connections between coursework and the types of work they’d like to pursue after graduation. (Phyllis Graber Jensen/�ֲ���ý College)

The paradox: Since Pacific coral reefs are in the nutrient-poor open ocean, there shouldn’t be enough food for two species of apex predator to coexist in such big numbers.

In other words, “How can coral reefs be so productive and biodiverse with a backdrop of such low nutrients?” McMahon said.

McMahon was the first of several scientists Associate Professor of Biology Larissa Williams invited to campus this semester, to speak with the students in her junior seminar and then give a public talk. Williams’ class is a Purposeful Work infusion course, where students learn about ways they can take course material into the real world.

McMahon is an ocean ecogeochemist, a title that suggests the depth of his interdisciplinary work. Over the course of his career, he and his colleagues have been developing and applying a suite of geochemistry tools, collectively called compound-specific stable isotope analysis (CSIA), that help scientists understand food webs better than ever before.

Kelton McMahon ’05 takes a tissue sample from a grey reef shark off the Phoenix Islands, home to pristine coral reefs. (Mark Priest)

McMahon told his �ֲ���ý audience about two of his current projects, which apply CSIA to real-world problems.

But first, a few terms:

Trophic level: A living thing’s place in the food chain. For example, plants are at trophic level 1, herbivores are at trophic level 2, carnivores that eat herbivores are at trophic level 3, and so on.

Producers/consumers: Producers are organisms that make their own food, as plants do through photosynthesis. Consumers get their food by eating other organisms.

Amino acids: The compounds that make up proteins — essential for life.

Isotope: Atoms of a given element with the same number of protons and electrons, but different numbers of neutrons. An atom of carbon-12 has six protons and six neutrons (light carbon), while carbon-13 has six protons and seven neutrons (heavy carbon).

Isotope analysis: Measuring the ratio of heavy to light isotopes in a sample, which provides a chemical “fingerprint” of physical, chemical, and biological processes that have impacted those atoms. For example, by measuring the isotope ratios of a piece of shark muscle, we can understand how energy moves through a food web, from coral at the bottom to shark at the top.

CSAI gets specific

Scientists have used conventional “bulk” isotope analysis for decades, but it has its limitations, McMahon said. The bulk method gives you the average isotope value of all the atoms in an element in an organism. It doesn’t distinguish whether an isotope of carbon, for example, came from one or another compound in the body of a shark.

That means a lot of detail gets lost.

“All the different compounds in the body tell a different piece of the story about how organic matter is made by primary producers and passed on to upper trophic level consumers through the food web,” McMahon said.

As a result, if you sample two animals and get back different isotope ratios, it’s difficult to know why. It could be because the animals have a different trophic position — they feed at different levels of the food chain.

Or it could be because different producers are at the bottom of each animal’s food web. Or it could be a combination of both.

Sharks! Watch this video clip of sharks swarming in the waters near the Phoenix Islands in the South Pacific Ocean. Video by Camrin Braun.

In other words, McMahon said, you can’t figure out who’s eating what at what time.

CSAI can help, as McMahon and his team demonstrated by sampling grey reef sharks and blacktip reef sharks who live near the coral reefs around the Phoenix Islands, a 10-day boat ride from Hawaii.

Over the course of several years and many controlled feeding studies — where scientists know the isotope values in both the food and the consumer — McMahon and his colleagues figured out that certain amino acids, called “trophic” amino acids, change their isotope value as they move through the food chain, whereas other amino acids, called “source” amino acids, stay the same from phytoplankton to shark.

By measuring the changes in trophic amino acids as they move up the food chain, you can find an animal’s trophic level, McMahon said. CSAI can also reveal how an amino acid was made — important, since different producers like coral and phytoplankton make the same amino acids in different ways.

So, using a single analysis, McMahon can determine how many steps removed an animal is from the bottom of the food chain and identify the isotope signal at the bottom of the food web.

Pacific coral reefs are home to some of the most biodiverse systems on Earth — a paradox, since reefs exist in the nutrient-poor open ocean. (Mark Priest)

“This has been a really powerful tool for looking at trophic dynamics, who’s eating what in complex systems,” McMahon said. “That information gets recorded in the biochemical signals in our consumers’ tissues.”

For years, oceanographers thought that grey and blacktip reef sharks coexisted because they fed at different trophic levels. CSAI, however, revealed that even though the sharks are similar in size, swim together, and both eat a variety of smaller fish, they feed in two totally different food webs.

The base of a grey reef shark’s food chain is largely phytoplankton, which exist in the open water. Blacktip reef sharks, on the other hand, rely on a food web with corals on the reef itself at the base.

Kelton McMahon ’05 speaks with students in a junior seminar taught by Associate Professor of Biology Larissa Williams on Jan. 14. (Phyllis Graber Jensen/�ֲ���ý College)

“It’s this compartmentalization of the food web, the division of resources, that’s helping promote the coexistence of these apex predators,” McMahon said.

CSIA can also tell us about the effects of climate change, McMahon said. In January, he’ll return to Antarctica — one of several �ֲ���ý alumni who conduct research there — to continue a study on how climate change and human activity, like past whaling, affect the lives of penguins over the course of hundreds or even thousands of years.

On the Antarctic Peninsula, his team will take feathers from living penguins and also dig penguin tissue out of the ground, searching for samples that show what penguins were eating throughout the last 10,000 years.

CSIA helps scientists trace the past, McMahon said, but it could also afford a view forward.

In this video, Kelton McMahon ’05 conducts a test excavation of penguin tissue, which could potentially provide thousands of years of data on the penguins’ diets and the environmental conditions in which they lived. (Video courtesy of Kelton McMahon)

“By exploring how past ecosystems responded to disturbance, we can begin to predict how the food web supporting these penguins in the future will change, in response to, say, continued warming,” McMahon said.

CSIA has “allowed us to shed some really interesting light on how organic matter moves through a wide range of systems,” he said. “The molecular isotope tools we are developing provide a powerful tool to help us start predicting what the future might look like.”

In Kongsfjorden on the west side of Svalbard, Will Ambrose (facing) and Kelton McMahon ’05 haul a dredge to collect Serripes groenlandicus and other clam species for McMahon’s thesis in 2004. Photograph by Glenn Lopez, SUNY–Stony Brook.

Professor Will Ambrose, a bearded biologist specializing in Arctic sea-floor ecology, is a pioneer in the science of deciphering the past — including past climates — 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’s 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 “sentinel of climate change.”

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.

Seen here is the cross section of a small portion of aSerripes groenlandicus shell, near the umbo, or hinge. The lines indicate annual growth: dark lines for slow winter growth; light areas indicate fast summer growth. For an image showing the complete shell, click the image above. Will Ambrose has discovered a correlation between growth and climate shifts. This image is a composite of 18 images produced by the College’s new Imaging and Computing Center using a Nikon SMZ 1500 stereo microscope. Collected in 1926, the shell’s actual length is 2.5 inches.

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 ’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.

“What makes the work exciting,” says Ambrose, interviewed in his cluttered office on Carnegie’s third floor, “is that this is the first time in the Arctic that we’ve been able to track a large-scale climatic oscillation and see that large-scale regional event reflected in animals living on the bottom.”

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

In this hot field, Ambrose’s research is distinctive for its location, on the Arctic continental shelf. “A lot of the work has been done at lower latitudes, mostly because it’s harder to get clams in the Arctic and there are simply fewer people available to help,” he says. “That’s why we’re ahead of the ball.”

If it’s true that Arctic clams grow faster in warmer weather (and grow faster when there’s less of a seasonal ice pack, another signal that Ambrose saw hints of), a simplistic response might be, “Great — fatter clams for walruses to munch on.” But, explains Ambrose, fat clams won’t 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.

These Serripes groenlandicus clams were collected in Storfjord at a site last visited by 19th-century Russian explorers. Photograph by Greg Henkes '08.

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. “Ecosystems operate at the interface of physics, chemistry, and biology, with both complementary and contradictory interactions,” Ambrose writes in a forthcoming article predicting that “regional, and perhaps global, biodiversity will suffer.”

Until recently, Ambrose researched other organisms of the benthic community, such as bloodworms along Maine’s coast. A simple matter of funding helped bring bivalves into focus, as a �ֲ���ý 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. “Very expensive,” 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 �ֲ���ý and abroad.

Geology professor Beverly Johnson, for example, has been invaluable in co-advising biology students so they can learn to use the College’s 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.

“I work with Will to understand how modern systems work,” says Johnson, “and then go back to old shells, using the geochemistry of shells from 125,000 years ago to reconstruct the environment.”

Ambrose also depends on Matt Duvall, who directs �ֲ���ý’ new Imaging Center, to create elegant microscopic images of his clamshell sections that Ambrose calls “just incredible.”

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 Áslaug Ásgeirsdóttir. What started informal — an interdisciplinary coffee klatsch — has given rise to “North Atlantic Studies,” a thematic grouping of �ֲ���ý courses, known as a concentration, under the College’s new general education requirements. “We represent an area of study, rather than just a bunch of us sitting around having coffee,” Ambrose says.

“It’s a truly special group,” Retelle adds. “The 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.”

Ambrose himself is quick to point out that “students here are the ones driving the bus in terms of getting the work done.” As he speaks, Greg Henkes ’08 of Chapel Hill, N.C., is downstairs in the environmental geochemistry lab cutting shells and extracting organic material. Henkes’ 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.

Greg Henkes ’08, one of Will Ambrose’s thesis students, took this photograph at 3 a.m. on June 3, 2007, as the research shipLance heads through sea ice in Storfjord in the Svalbard archipelago, about halfway between the North Pole and Norway.

“It’s pretty incredible to be able to do this at �ֲ���ý,” says Henkes. “It’s the way science is going,” 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. “People aren’t doing their own little thing anymore.”

“That’s the way science should be done,” emphasizes Kelton McMahon, co-author of the Serripes groenlandicus paper. “In certain circles, it is. But a lot of people come from departments that don’t share data because they feel funding is in direct competition. �ֲ���ý takes a very progressive approach to interdisciplinary research.”

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 — a New Wave Research UP213 laser ablation system coupled to a Thermo Finnigan Element 2 single collector field inductively coupled plasma mass spectrometer — 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. “If it wasn’t for Kelton getting us access to those machines,” says Ambrose, “the paper wouldn’t have been anywhere near as good.”

As he sits in his Carnegie office discussing his work — Ambrose also hopes to extend his sclerochronology research to coral in part because “they live much longer than clams” — 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, “growth didn’t track ice cover the way it did before. Something happened, but we’re not sure what,” he says. “Are the last four years unnatural? That’s why I want those new clams. It’s another four years of data that will help establish some baselines.” And baselines will help provide more answers, which will probably just beget more questions. It’s the wayscientific inquiry works. “People like simple answers,” Ambrose says. “Nature doesn’t.”

By Edgar Allen Beem

Freelance writer Edgar Allen Beem wrote about the in the Fall 2007 issue of �ֲ���ý Magazine.

With help from a group of staff and faculty advisers at �ֲ���ý, biology major Kelton McMahon recently won a National Science Foundation fellowship to study ecological geochemistry at the Woods Hole Oceanographic Institution.

But what may be surprising about McMahon’s good fortune is that he hasn’t been a �ֲ���ý student for a while. He graduated last year. Still, even well after graduation, he was eligible for grant-application assistance from the �ֲ���ý Graduate Fellowships Committee.

“Having a committee like the BGFC at your disposal makes a tremendous difference” in the quest for support, McMahon says. “These fellowships are extremely competitive and nearly everyone applying has excellent grades, recommendations and so forth.” It was the BGFC’s guidance in polishing his application essay, he says, that made the crucial difference.

In fact, the committee works with students as early as their sophomore year and with alums as late as five years after graduation. Its assistance includes matching prospective awards to a student’s circumstances, coordinating grant applications, working with candidates on their application essays, coaching for interviews, and even helping with travel costs for grant finalists. And the committee is the college’s official intermediary between students and fellowship programs.

“The committee was extremely helpful in all aspects of the application process, from critiquing my fellowship proposal to helping me compile the application materials,” says McMahon, who is working toward his Ph.D. in the MIT-WHOI Joint Program in Biological Oceanography.

Matteo Pangallo, an English major who graduated from �ֲ���ý in 2003 and is building a career in theater, was accepted into a graduate program at King’s College London for 2005-06. But the acceptance came too late for most graduate scholarships and fellowships.

“The committee directed me toward the Jack Kent Cooke Scholarship,” he says. “They knew that it was still available for the upcoming academic year, and that I would probably be a good fit for it.” As indeed he was, winning the scholarship in April 2005.

Pangallo calls the committee “instrumental” in his receiving the Cooke scholarship, a generous award that has enabled him to stay focused on his educational goals. “Without it, I would have had to spend my entire savings, take out a substantial loan and find part-time work,” he says.

“By not having to pick up a part-time job,” he adds, “I have been able to secure an unpaid internship in the research department at the Globe Theatre,” the modern recreation of Shakespeare’s home theater. “That’s been one of the highlights of my time in London.”

Pangallo is now working on his dissertation, which involves preparing the first-ever modern critical edition of a rare manuscript play from 1632.

One of the most important aspects of the BGFC’s work is simply making students aware that financial aid for further study awaits them after graduation from �ֲ���ý. Statistics show that students who succeed in winning graduate support “are the ones who start early and work steadily over an extended period of time to develop truly outstanding applications,” says Robert Allison, professor of religion, a seven-year member of the BGFC and its acting chair during the sabbatical of anthropologist Elizabeth Eames.

“Events like the sophomore dinner and the fairs that we run to raise awareness and interest early in students’ careers at �ֲ���ý are critical to the program,” he says.

Fulbright, Ford Foundation and Mellon are a few of the better-known grant programs in the committee’s arsenal. Perhaps as important as the money itself is the cachet borne by certain programs. His NSF fellowship, says McMahon, “is one of the most prestigious awards given to an entering graduate student. It’ll be really helpful as I apply for future grants and a faculty position in academia.”

Many of the top fellowship programs require that the baccalaureate institution nominate the candidate or submit an application for her or him. In �ֲ���ý’ case, that’s the job of the BGFC. And some programs are invitation-only.

“We’ve worked proactively to get �ֲ���ý on the invitation lists of several of these programs,” says Allison. “But for the most part, �ֲ���ý’ own prestige as an excellent undergraduate college has won us those invitations.”