“You are what you eat and where you live” – INE/WERC introduces teachers to the fascinating world of stable isotope research

October 22, 2012 • Filed under: News — melanie.rohr

On Friday October 5, 2012, INE/WERC along with the Alaska Stable Isotope Facility (ASIF) hosted high school teachers from all across Alaska to learn more about the multitude of applications in stable isotope research as part of an outreach and education event jointly organized by the University of Alaska Corporative Extension Service (CES) and the Center for Ocean Science Education Excellence (COSEE).

Crowd of adults in classroom listening to presentation
A group of teachers from all over Alaska are given an introduction to stable isotope research.

The crowd of roughly 20 teachers listened intently as ASIF Director Dr. Mat Wooller explained how a person’s diet can influence the isotope signature of carbon and nitrogen in humans.
“You are what you eat and where you live, and stable isotopes are able to track a person’s diet. Your isotopic composition is reflected by the food you consume and what kind of food is available at the place you live.”

“A person living near the ocean with access to seafood could have a different isotopic signature than someone living in the interior of Alaska. Salmon, for example, is enriched in the heavier nitrogen isotope 15N. A sample from a person consuming large amounts of salmon can therefore show an enriched isotopic signal.”

Crowd of adults in classroom listening to presentationMat Wooller from ASIF is giving an introduction on stable isotope

Alaska Stable Isotope Facility Director Dr. Mat Wooller explains how different diets plot on the carbon and nitrogen isotope chart.

Dr. Wooller, a native of Great Britain, admitted that he himself has become “isotopically more American” since moving to the United States of America. “Many things we eat in this country are corn-based or contain corn or sugar from sugar cane. Corn is isotopically enriched, meaning it contains a larger proportion of the heavier carbon isotope which in turn shows up in our samples.”

Many attendees wondered whether these results could potentially be used for a qualitative analysis of human diets. Wooller referred to the ongoing research of his colleague, UAF researcher Dr. Diane O’Brien, who examines the use of isotope ratios as biomarkers in order to qualify health and diet among Alaskan Natives. Dr. O’Brien works with the Center of Alaska Native Health Research and the Institute of Arctic Biology at UAF.

Carbon versus nitrogen stable isotope plot
A chart showing the relationship of different food sources to carbon versus nitrogen stable isotope compositions.

After a brief introduction to isotopes, the attending teachers toured ASIF’s research laboratories where they had a chance to see a mass spectrometer up close and peek inside the instrument. Dr. Wooller explained that measuring isotopes is a fairly straightforward process, based on the fact that one of the isotopes is heavier and thus acts a bit more sluggish than it’s lighter counterpart. Thus, the different isotopes can easily be measured by examining their trajectories in the mass spectrometer when they are accelerated past an electromagnet in the instrument.
To demonstrate the procedure, two volunteers from the group of visiting teachers provided samples – a tiny chip of a finger nail – which were readily processed by ASIF’s lab manager Tim Howe. The difference in sample results was quite striking as the volunteers placed their numbers on the carbon/nitrogen isotope graph (Note the location of the smiley stickers on the chart above).

View across mass spectrometer trayResearch weighing and preparing sample

Image left: View across the sample tray of a mass spectrometer. Image center: Dr. Woller answers questions about mass spectrometry after the attendees had a chance to examine the inner workings of the instrument. Image right: ASIF Lab Manager Tim Howe prepares finger nail samples from two volunteers. These samples were immediately analyzed in the mass spectrometer so the group was able to see the difference in isotopic signatures between the two individuals.

Soon it became clear to the audience that stable isotope analysis isn’t just limited to tracking human diets; it’s a tool that can be applied to other organisms, modern and ancient. WERC researcher Dr. Nicole Misarti presented preliminary results from her research in South America showing how stable isotopes can be used for food web analysis.

Female holds video camera and films bone samplesFemale researcher in laboratory standing in front of two laptops pointing at graph on one of the computer screens

Image left: One of the teachers carefully examines a 2000 year old otter bone. Image right: Dr. Misarti presents preliminary data from South America, including samples from humans, penguins, birds and sea mammals.

In addition to carbon and nitrogen isotopes, researchers can use strontium isotope analyses to track the natal origin and migration of salmon, an application WERC PhD candidate Sean Brennan is using in his research on Chinook salmon in the Nushagak River in Bristol Bay, AK. Brennan samples otoliths, which are calcium carbonate structures located behind the brains of the fish that aid in balance as well as hearing.

“Because otoliths are laid down throughout the life of a fish, the isotopic signature provides not only information on the natal origin of the salmon but also enable us to trace the environmental life history throughout a fish’s lifetime.”

Grinding down otolith samplesOtolith on computer screen

Image left: PhD Candidate Sean Brennan demonstrates the preparation of otoliths for further analysis. In order to reveal the otolith’s layered structure, the sample has to be ground down first. Image right: An otolith sample under the microscope.

In the lab, Brennan demonstrated the rather labor-intensive, multi-step process of grinding and embedding the otoliths in order to prepare them for analysis. In a short presentation following the lab tour, Brennan discussed the importance of looking at isotope data to trace fish origin for management purposes, particularly biodiversity conservation.
“While current genetic analysis reveals information about the broad population structure of the salmon in a particular area, isotopic information provides additional, sometimes more detailed information about natal origins.“

Presenter points at screen that shows a close-up image of an otolith shown in the image of a fish’s head while explaining the architecture and function of this structure.
WERC Ph.D. candidate Sean Brennan points at an otolith shown in the close-up image of a fish’s head while explaining the architecture and function of this structure.

Because strontium isotopes derive from the bedrock surrounding the watershed and are taken up through the water itself, they imprint a unique, local signature that may differ between different tributaries of the same watershed, which may report only as a single genetic fish ‘stock’. When managing salmon resource use and potential perturbations, such as mineral development in the Bristol Bay area, this may become a crucial piece of information.

All photos by Melanie Rohr, INE