800,000-year-old plankton

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A single-celled alga that went extinct in the North Atlantic Ocean about 800,000 years ago has returned after drifting from the Pacific through the Arctic thanks to melting polar ice. And while its appearance marks the first trans-Arctic migration in modern times, scientists say it signals something potentially bigger.

“It is an indicator of rapid change and what might come if the Arctic continues to melt,” said Chris Reid, a professor of oceanography at the Sir Alister Hardy Foundation for Ocean Science in the United Kingdom.

Arctic sea ice has been in decline for roughly three decades, and in several more recent summers, a passage has opened up between the Pacific and Atlantic. In as little as 30 years, Arctic summers are projected to become nearly ice free.

The findings, first reported in 2007, are among the 300 European Union-funded research papers being synthesized by a collaborative project dubbed CLAMER for Climate Change & European Marine Ecosystem Research. All of this work explores the effects of climate change on marine environments, documenting evidence of major transitions under way in the waters around Europe and the North Atlantic.

Many shifts

The alga, called Neodenticula seminae, belongs to a group of organisms with glasslike walls known as diatoms. The diatom is not the only living thing that may have taken advantage of retreating Arctic sea ice to travel.

In 2010, a gray whale appeared in the Mediterranean Sea. This species was thought to be confined to the Pacific Ocean, disappearing from the North Atlantic in the 1700s. This whale’s voyage was most likely made possible by shrinking Arctic sea ice, concluded researchers writing in the journal Marine Biodiversity Research.

Work compiled so far by CLAMER contains evidence of many changes within European waters. Species are moving northward