For years, scientists have warned that the steady loss of sea ice around the North Pole, which is linked to human-driven climate change, is placing Arctic wildlife at risk of habitat loss and food shortages.

Now, researchers have identified yet another threat that sea ice decline presents for polar ecosystems: A spike in the spread of viruses between marine mammals.

A team led by Elizabeth VanWormer, a marine scientist at UC Davis, found that outbreaks of phocine distemper virus (PDV)—which is deadly to seals, sea lions, and otters—correlated with periods of more severe ice loss.

The findings, which were published on Thursday in Scientific Reports, reveal that sea routes opened up by sea ice melt enable marine mammal populations that don’t typically meet to become exposed to each other, which amplifies the risk of transmitting PDV.

"The loss of sea ice is leading marine wildlife to seek and forage in new habitats and removing that physical barrier, allowing for new pathways for them to move," said co-author Tracey Goldstein, associate director of the One Health Institute at the UC Davis School of Veterinary Medicine, in a statement.

"As animals move and come in contact with other species, they carry opportunities to introduce and transmit new infectious disease, with potentially devastating impacts," she added.

The team discovered this troubling link between PDV transmission and Arctic sea ice loss by analyzing samples collected from more than 2,500 live mammals and 165 carcasses between 2001 and 2016. The sampled species included Steller sea lions, northern fur seals, and northern sea otters, as well as bearded, ringed, ribbon, and spotted seals. These animals migrate through the North Pacific Ocean between the eastern coast of Russia and Alaska.

The samples confirmed that there was a major peak in PDV infections in North Pacific sea mammals in 2003, 2004, and 2009. These epidemics followed a devastating outbreak in the Atlantic in 2002, which killed an estimated 30,000 seals.

VanWormer and her colleagues probed how the virus was introduced from the Atlantic to the Pacific by studying patterns of Arctic sea ice loss since 2002 in satellite imagery. The space-down view, combined with maps of the mammals’ movements, confirmed that PDV spread from one ocean to another in years of unusually low sea ice extent.