Whale earwax could tell us more about carbon dioxide in our oceans

A physiologist with wide-ranging interests, Stephen Trumble studies everything from rats to zebrafish, but these days whale earwax is taking over his Baylor University lab in Texas. There are already 30 pieces of it lined up, each requiring about a year’s worth of analysis – and he hopes to obtain five times as many. He’s doing this because hidden in all that wax is information that could tell us how life has been changing for whales and the Arctic in the past 100 years or more.

For decades, cetologists, the marine scientists who study whales and dolphins, have had to gather data from dozens of different sources to reconstruct the life story of a specific sea mammal. For example, studying the scars in the ovaries could reveal the number of pregnancies a female whale had experienced; the bristly, filter-like baleen used to feed could give scientists information on what sorts of contaminants might have entered the whale’s food source in the most recent decade or two. Whale earwax has long had some use in this accounting. Earplugs – the scientific term for the lengths of wax that accumulate in the ears of some whales – grow in annual layers like tree rings, revealing the number of years a whale has lived.

But Trumble’s team has discovered that much more can be learned from the aquatic mammal’s earwax – a veritable one-stop shop for all the whale data they’ve been dreaming of. Using the foot-and-a-half-long earplug from one bowhead whale, Trumble and his lab collaborators were able to obtain the whale’s history, including its age, migrations and pregnancy. That small piece of wax – at 2 pounds, it’s 1/100,000th the size of a typical bowhead whale’s body – has also given Trumble and his team a history of the buildup and decline of pesticides like DDT in recent decades, as well as today’s rapidly growing carbon concentrations in the Arctic.

A research group with unlimited resources could attempt to track a whale throughout its life, showing up every year to take a skin sample. That’d provide great information on where the whale had been and what sorts of things it had been exposed to. But the logistical and financial costs of that sort of project make it essentially impossible. Trumble’s work offers a realistic way to obtain all that Arctic intelligence.

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Since US and international regulations protect whales – even when they wash ashore dead – fresh earplugs are hard to come by, so Trumble’s project is at least as much about searching for earplug samples as making sense of them. Evolutionary biologist Hans Thewissen says he happened to be in Barrow, Alaska, the day that bowhead was brought ashore in a traditional, tightly controlled annual subsistence hunt. Native communities in the region can take at most 67 bowheads in a year.

Every animal harvested during such a hunt is towed back to the beach, and the meat is divvied up for the community; then wildlife managers begin taking measurements for research and extracting body parts to learn more about the whale population. At that point, “the scientists stand around, and when there’s an organ they want they ask for permission to sample it,” says Thewissen, a professor at Northeast Ohio Medical University. He had his eye on the earplug because Trumble had told Thewissen how much information this tiny piece of whale might hold.

Trumble describes extracting the earplug of a beached whale as “a crazy amount of work”. The dead whale needs to be turned the right way, and bones and tissues – particularly their massive jawbone – might be obstacles. Heavy-duty construction equipment like front-end loaders are sometimes used. And that’s assuming the whale has an earplug. Not every species does, and sometimes within a species some individuals do and others don’t – an apparent randomness researchers don’t fully understand. “It’s like humans,” says Thewissen. “Some people have more earwax than others.”

Trumble has been travelling all over the world to raid museum collections for earplugs, and the backlog of work is growing at his lab. The analysis is labour-intensive; it takes about a year to separate each wax layer from adjacent ones. Researchers then run numerous tests to determine chemical composition. Each layer becomes its own sample, its own record of that year in Arctic living, and requires its own extensive tests and calculations. It adds up, but Trumble says “it’s cheaper than taking skin samples each year for 30 years from a live whale in the wild.”

The bowhead from Barrow, the team determined, was 65 years old. Each layer of its earplug was further divided into two sections, one dark and the other light – the colour change was due to the different prey the whale found and ate in the two seas it migrated between every year. Differences in the levels of the pregnancy hormones progesterone and estradiol in the earplug layers revealed she had been pregnant between 11 and 14 times, approximately every three to four years after reaching sexual maturity. Trumble says that his lab found a huge spike in the stress hormone cortisol during her first mating-and-pregnancy experience. By measuring nitrogen isotopes left by the whale’s plankton prey in the layers of wax, researchers could determine when and where she was feeding, and thus her movements. This whale, it seems, spent most of her decades moving between the Bering and Beaufort seas.

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Scientists already know the Arctic ocean accounts for a disproportionate amount of the carbon dioxide that is absorbed by the world’s oceans – gases dissolve more easily in colder water. But most of what they know about the effects and extent of that increased carbon dioxide is only about specific, localised parts of the Arctic. The wider effects, and even whether the Arctic ocean’s ability to absorb carbon dioxide is increasing or decreasing, are still a matter of scientific debate. Bowhead whales spend at least some part of every year of their lives – sometimes as long as 100 years – in that changing Arctic, and their earplugs are something of an Arctic scorecard. The bands of wax extracted from a whale’s ear chart, year by year, carbon and nitrogen isotope levels.

The whale wax also acts as a record of which poisonous chemicals produced in the US and other more southerly latitudes make their way up north, and how long that trip takes. Trumble’s team was able to figure out that approximately 10 years passed between the time now-banned pesticides like DDT, hexachlorobenzene and chlordane were produced in the US and when they showed up in the whale. The same was true of PCBs, carcinogenic chemicals previously used in things like electrical coolant but banned in the US since 1979. Though not much can be done to remove these chemicals from the Arctic waters now, pinpointing the exact lag time could inform future regulatory decisions on pesticides and other synthetic compounds.

In addition, all of this information can inform how native Alaskans manage their annual subsistence hunts. Eventually, global earplug analysis could help other regions set more sustainable rules for their traditional hunts – like that of minke whales in the Faroe Islands – since it can nail down with near certainty how frequently female whales can and do give birth. “If they can have a baby every year or every two years, that really affects how fast the population can grow,” says Thewissen. That information – as well as knowledge of what contaminants are affecting the whales and when – can help regulators make better decisions regarding ship traffic, oil exploration and all the other human activities that interfere with whales’ lives and have the potential to irrevocably damage the Arctic.

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