In 1845, Arctic explorer Sir John Franklin and 134 crew members vanished while searching for the Northwest Passage to connect the Atlantic and Pacific Oceans through the Canadian Arctic Archipelago. Today, climate change has opened this once impossible route, but the mystery of the seamen's deaths continued to elude us.

We know a note found on King William Island reported the two ships were trapped in ice for about a year and a half. Over a century later, in 2014 and 2016, archeologists found the sunken remains of the two ships. They found objects carefully stowed away which conflicted with the theory that lead poisoning killed them. If so, the sailors would have become delirious, not neatly organized.

Lead was also suspected because high levels were found in a well-preserved crewman's body exhumed from permafrost in 1984 near the stranded ships. But a new look reveals he died from tuberculosis worsened by malnutrition.

Since the human nail is a good record keeper of the body's elements, scientists tested for levels of zinc, copper, lead and other metals in his nails and compared them with a healthy male's nails. To their surprise his lead levels were normal until the last weeks of his life.

Under starvation conditions, his body had begun to consume his muscle, fat and bone which released the lead in them and explains the high lead levels.Meanwhile, his zinc levels plummeted during the time they were stuck in the ice. Zinc is an essential element in all our cells and is crucial to our immune system. So, without zinc, his tuberculosis killed him quickly.

This finding may help to explain the challenges of other doomed Arctic expeditions which continue to mystify science.