Researchers from the United States, Norway and Russia say that while the protozoa were carried thousands of miles on a rare type of warm water pulse from the Atlantic that has occurred in the past, the pulses are becoming more frequent with climate change.
Writing in the British Journal of Micropalaeontology, they say that the tropical plankton were swept northward from the Caribbean on warm Gulf Stream currents, which normally fade out somewhere between Greenland and Northern Europe.
But a repeat of a kind of current pulse that occurred in the 1920s, 1930s and 1950s is believed to have brought the non-native plankton much farther north than ever before observed.
Arctic waters are also reaching record warmth and have undergone more extensive sea ice melt in recent years than ever seen before.
The tropical plankton may represent some of the first evidence of a climate-induced change in species redistribution into the Arctic, the researchers say. The plankton samples were netted northwest of the Norwegian archipelago of Svalbard in 2010.