Several narwhals and its spiral-shaped tusks Image: wiki
The researchers report in the journal Current Biology that the tusks of narwhals record environmental information over decades, clearly showing changes in the Arctic. Each year, spiraling tusks grow new layers containing isomers of carbon and nitrogen, isotopes, as well as some mercury consumed by narwhals. The researchers purchased 10 narwhal tusks from Inuit hunters in northwestern Greenland and found that they contained information for nearly 50 years.
Having data available over such a long time span "has helped us take a surprising step forward in figuring out which factors affect diet and mercury (content)." The study's lead author, Jean-Pierre Desforges, a marine biologist at McGill University, said.
The researchers cut open the whale's tusks (actually the human equivalent of teeth, made of dentin), ground them into a powder, and analyzed the isotopic content of the samples. The findings show where the narwhal may have eaten and how well it came into contact with mercury. Mercury is a powerful toxin whose accumulation affects the animal's immune and reproductive systems.
Mercury is one of the common preservatives in cosmetics. Image source: Pixabay
When sea ice covered much of the narwhal's habitat in the 1960s and 1990s, carbon and nitrogen isotopes suggested that narwhals eat fish located upstream in the food chain, such as halibut, which are close to ice or the ocean floor. After 1990, the sea ice cover declined sharply, and the carbon isotopic composition in whale tusks began to change. This suggests that its diet at this time came from an ice-free ocean, including polar cod and woolly scales, which were several links downstream in the food chain and therefore generally contained less mercury. However, narwhals still ingest most of the toxic metals. Researchers say this could be due to climate change or increased emissions, or both.
Arctic ice floes Image source: unsplash
Altering food sources can affect narwhals' pollution exposure and nutrient access, and may eventually alter their population levels. Cortney Watt, a marine biologist at the University of Manitoba, said the study shows the potential of narwhal tusks in tracking the region and its organisms in climate change adaptation. Watt studied whales but was not involved in the new study. "I think they're very competent sentinels that can give us a hint at what's really going on in our environment," she said. They are also good historical archives of what is happening in the Arctic. ”
Author: Susan Cosier, freelance writer in science and the environment
Translation: Liu Chan
Reviewer: Zhang Naixin
Source of introduction: Scientific American