Doctor Blum Measures the World

No scientist has pointed a mass spectrometer at more mysteries than Joel Blum. Give him a few isotopes and he can tell where salmon survive, birds fly, or dinos died. The answers} he reveals, are elemental

NOTHING IN THE " CLEAN LAB " on the second floor of the earth sciences building is made of metal. The walls are painted with non-flaking plastic epoxy. Air is filtered three times before it enters the room. People enter through a kind of filter, too. Scuffed athletic shoes line the corridor outside the lab. Lab workers in stocking feet move through an anteroom, cover hair and clothes with surgeons' hats and gowns, and slip into clean "lab shoes" everything from Kmart tennies to fluffy-poodle slippers. Earth science professor Joel Blum, thirty something, favors Birkenstocks.

Inside the lab, Blum, along with his Ph.D. and undergraduate honors students, takes samples from soil and rocks, from feathers, fish scales, even maple syrup, and chemically deconstructs them into their elemental components. He dissolves them in cocktails of pure acids and loads them onto thin ribbons of refractory metals such as rhenium, tantalum, and tungsten. Then he takes them down the hall past the scuffed athletic shoes and around the corner, to a machine that is helping him solve some of science's most frustrating problems. Behind door number two, the Finnigan MAT 262 Thermal lonization Mass Spectrometer awaits.

It doesn't look that exciting—more like something you'd find in a doctor's office or a low-budget sci-fi movie: enameled metal, polished stainless steel, flashing lights, a few dials. Appearances are deceiving, though. The instrument cost a cool half-million. It's one of only about 25 such high-powered machines operating in the United States, and the only one north of Boston. From the vacuum-pumped interiors of its precision-tooled stainless-steel cylinders come "very, very precise measurements" of concentrations as small as a few parts per trillion. That's a pinhead-sized drop in an Olympic swimming pool. "This," says Blum, "is one of the things that I love about my work. I have the facilities to measure anything!"

What Blum measures in such small amounts are isotopes—stable forms of chemical elements. And if he has the facilities to measure anything, then his research agenda seems to cover everything, from "Why did the dinosaurs die?" to "What controls the Earth's climate?" to "What streams make the best homes for salmon?" to "Where do songbirds go in winter?" In a field of focused, diligent, patient gatherers of information, Blum's range of inquiry is astounding.

Caltech professor GeraldJ. Wasserburg, Blum's former advisor, insists that Blum does not have a problem with focus. "I think he's just having fun," Wasserburg says, and cheerfully takes credit for encouraging Blum to think outside of the box. "My students are required to work in diverse fields," he explains. "I want them to be able to stand on more than one leg and preferably on more than two."

"He's got this technique, and he just keeps coming up with neat ways to apply it," says professor James Drever, who studies lowtemperature geochemistry at the University of Wyoming. "If you take any one thing Joel does, there are others doing it. But no one else does the range of things that he does."

JOEL BLUM DIDN'T START OUT as an environmental scientist, although his passion for the out-of-doors may have been a factor in his decision to focus on environmental problem-solving when he came to Dartmouth in 1990. After all, we're talking about a guy who got his master's degree at the University of Alaska in Fairbanks because of the nearby peakbagging opportunities. But Blum spent his Ph. D.-student career studying the origins of the solar system. Now he's using a technique invented by a chemist and formerly used mostly by geologists to solve environmental problems right here on Earth.

The technique involves analyzing isotopes. Back in the 1950s, the Nobel Prize-winning chemist Harold Urey had the insight that isotopes could serve as a kind of "natural fingerprint." An isotope is a variation on an element. An element, you may recall, is a fundamental substance made up of atoms. The number of protons in each atom tells you which element. For example, carbon has six protons, oxygen has eight, and Blum's favorite element, strontium, has 38. The number of neutrons in an atom sometimes varies, and these variations are different isotopes. An element can have many isotopes.

Radioactive elements decay over time, transforming an isotope of one element into another; the more time passes, the greater the change in the amount of a particular isotope. Thus, measuring isotopes can reveal exactly how old a chunk of rock is.

Even elements that aren't radioactive are naturally made up of isotopes, in varying amounts. Since elements make up rocks, water, soil, and organic materials, and since the exact mix of isotopes in each of these materials differs from place to place, depending on how nature dealt the deck, the "isotope ratio" can reveal the geographic origin of a sample—sort of the geologic equivalent of a Boston accent or a Texas drawl.

Blum learned about isotope analysis from Wasserburg, who developed many of these techniques in the 1960s and 1970s to tell the age of rocksamples returned from the moon. As a Ph.D. candidate in the 1980s, Blum worked in Wasserburg's California Institute of Technology lunar research lab, affectionately nicknamed "The Lunatic Asylum." "Everyone in academia calls it that," says Blum, who routinely used "Lunatic Asylum" as his address on research papers. "Although I do remember that after one of my first publications it was in the British journal Nature—a reader wrote to question this American practice of using lunatics in scientific research."

Blum's first isotope investigation at Dartmouth was, in a way, a transition between space studies and Earth-based investigation. It had to do with why the dinosaurs died. Many scientists think a giant comet or asteroid smashed into the Earth 65 million years ago, sending up a cloud of dust that darkened the sun and made the planet inhospitable for giant reptiles. Blum and fellow earth sciences professor Page Chamberlain first set out to resolve what killed the critters and later focused on where the crucial impact occurred.

Two hot possibilities were huge craters in lowa and on Mexico's Yucatan Peninsula. Using mass spectrometers, Blum and Chamberlain fingered Mexico as die probable point of impact. The evidence was the isotopic composition of tiny glass beads called microtekites. Formed around the time of mass dinosaur extinctions, these beads are "impact glass," created when molten rock was hurled skyward. Blum and Chamberlain found them to be isotopically identical to Yucatan but not lowa samples.

Further analysis of the beads yielded even more information about how the dinosaurs died. The impact caused limestone and gypsum to melt. And melting rocks of this kind would have released clouds of carbon dioxide and sulfates. In other words, say Blum and Chamberlain, around the time of mass dino dieoffs, the Earth may have first been cloaked for a few years in chilling sulfate gases, followed by a few thousand years of an enhanced layer of greenhouse gases perhaps making things first too cold and then too hot for T. rex.

Blum has also used isotopes to study animals that aren't extinct—though they might be at risk. Migratory birds, for instance, leave their North American breeding grounds each fall and fly to winter quarters in Central America. Many of those species are declining in numbers. Is that because of problems up North or down South? If we could match northern populations with their southern destinations, we could set priorities for habitat protection. But so far, labor-intensive studies that tagged thousands of migrating birds with metal ID bracelets have shed little light on the question of exactly where each population spends the winter.

When biology professor Richard Holmes explained the problem to him, Blum suggested that isotopes could serve as a natural, built-in bird tag. His reasoning was simple: isotope ratios in soil and water identify geographic location; birds eat insects that eat leaves that grow on trees rooted in soil and refreshed by water. The identifying isotopes get handed up the food chain.

So far, a team of Dartmouth researchers including Blum, Chamberlain, and Holmes have made measurements of isotope ratios in one migratory bird species, the black-throated blue warbler. It's a bird that's not in any danger of disappearing; the black-throated blue was tapped for preliminary studies because feather samples from a wide variety of locations were available. The results are suggestive: carbon and hydrogen isotope ratios are highest in feathers from the southern end of the bird's breeding range and lowest in feathers from the northern end. Strontium isotope ratios are highest in bone samples from Appalachian birds, lower in samples from the western part of the range. Now the three reseachers are eyaluating other isotopes that could help fine-tune the natural tagging system. They're also turning their attention to the bones and feathers of American redstarts, colorful warblers that are declining on their Adirondack breeding grounds.

Blum is also applying the isotope tag technique to migratory Atlantic salmon—silvery, yard-long fish that spend most of their lives at sea but swim inland and upstream to spawn. In this century, dams and hydroelectric projects have barred salmon from many of their traditional spawning grounds. Restoration efforts include not only providing ways around the dams, but restocking young salmon in their native streams.

"The question is, which streams have the highest survival rates? " says Blum. "If we could find out, restocking efforts could be focused there." Fisheries biologists would like to sample schools of salmon at sea to find out where they came from. Unfortunately, there's no external tag you can apply to a fingersized salmon in its native stream that will survive the trip downstream and three years of ocean life.

Blum and Chamberlain have been working with Dartmouth biology professor Carol Folt and grad student Brian Kennedy to determine which isotopes could be a natural tag for salmon. They've been measuring the relative proportion of strontium isotopes (86-Sr and 87-Sr) in salmon backbones and earstones. In a recent effort, the researchers successfully-matched 18 out of 20 salmon to their home streams. Now, as with the bird research, they're looking for other isotopes that will make the matching process even more exact.

At Dartmouth, undergraduates are getting a chance to put the Finnigan MAT 262 Thermal lonization Mass Spectrometer through its paces in a spring-semester course taught by Blum. A year ago, the class investigated the isotopic composition of bottled spring water from countries around the world. The field work was done at the Hanover Co-op Food Store. The class confirmed that bottled waters really did come from the exotic sources blazoned on the labels. "The water from Iceland, especially, was unmistakable," says Blum. "There's nowhere else water with those ratios could have come from."

Last spring, the class studied another liquid made locally: maple syrup. Blum got the idea when local papers raised concerns that Vermont maple syrup contains traces of lead, which can cause brain damage at low doses, especially in children. When in the production process does syrup get contaminated? According to the class's findings, it often comes from the use of those quaint collection buckets. The modern practice of running tubing from trees to sugar house, though less esthetically pleasing, turns out to produce purer syrup.

While they were at it, the students also checked carbon isotope ratios to see if the sticky samples really were "pure maple syrup"—or whether they were diluted with less-expensive corn syrup. (Some were.) And since syrup labeled "Made in Vermont" fetches the I fanciest price, they checked to see if strontium isotope ratios differed in syrups from the Green Mountains and the granite of New Hampshire (They did.)

And Blum's diverse research doesn't end here. He is part of a team of Dartmouth scientists investigating the effects of heavy metals on human health. He's used isotope tracers to measure how acid rain affects the fertility of forest soils in New England. He's investigated global climate change during the last Ice Age and how the Earth regulates its temperature. His track record makes this business of using lunatics for scientific research seem like a pretty smart practice.

For his research and teaching accomplishments, Blum was named a Presidential Faculty Fellow in 1993. Says colleague James Drever, "He's a star. Not only does Joel find innovative ways to look at old problems, he addresses big issues, really important problems." If you ask Blum how he determines whether his work is truly important, truly worthwhile, he'll tell you that awards and grants and recognition are less important than whether his projects pass muster with his own personal Senator Proxmire: his mother-in-law. "I used to talk about supernova explosions and meteorite inclusions, and her eyes would glaze over," he says. "Now, I'm doing research that touches people's day-to-day lives, work that benefits people and the environment. She approves of that."

Blum and his Finnigan MAT 262 Thermal lonization Mass Spectrometer play isotopic tag with the living and the dead.

"This is what I LOVE about my work. I have the facilities to measure anything! Even Mexico's ChicxulubCrater (right). maybe the epicenter of dinosaur extinction.

CYNTHIA BERGER '79 producers the nationally syndicated radio program. The Ocean Report. She was formerly part of a NASA group, nicknamed "The N Team," that used remote sensing to study nutrient cycling in forests. Her favorite element is nitrogen.