Dartmouth scientist Rachel Obbard was looking at samples of Arctic sea ice for small organisms when something else caught her eye: tiny, bright-colored bits and pieces and miniature string-like objects that did not seem to belong.

Those small specks turned out to be a type of pollution known as microplastics. Their presence in sea ice collected from the central Arctic Ocean showed that some of the vast quantities of garbage and pollution floating in the world’s seas has traveled to the northernmost waters.

For Obbard, an assistant engineering professor who specializes in polar-ice studies, the appearance of microplastics in Arctic sea ice was an unpleasant surprise. “I was kind of shocked. I said, ‘This shouldn’t be here in such a remote place,’ ” she said.

Worse yet, that sea ice holding the small bits of trash is thinning and likely to shed them back into the water, where they can be ingested by fish, birds and mammals, said a study by Obbard and fellow scientists that was published online Tuesday in the scientific journal Earth’s Future.

Extrapolating the findings from the examined cores and factoring in the ongoing transformation of thick multiyear ice to thinner, single-year ice, Obbard and her colleagues found that […]