For the first time, scientists have identified tropical and subtropical species of marine protozoa（原生动物） living in the Arctic Ocean. Apparently, they traveled thousands of miles on Atlantic currents and ended up above Norway with an unusual -- but naturally cyclic -- pulse of warm water, not as a direct result of overall warming climate, say the researchers. On the other hand: arctic waters are warming rapidly, and such pulses are predicted to grow as global climate change causes shifts in long-distance currents. Thus, colleagues wonder if the exotic（外来的） creatures offers a preview of climate-induced changes already overtaking the oceans and land, causing redistributions of species and shifts in ecology. The study, by a team from the United States, Norway and Russia, was just published in the British Journal of Micropalaeontology.

The creatures in question are radiolaria（放射虫类） -- microscopic one-celled plankton that envelop themselves in ornate glassy shells and graze on marine algae, bacteria and other tiny prey. Different species inhabit characteristic temperature ranges, and their shells coat much of the world's ocean bottoms in a deep ooze going back millions of years; thus climate scientists routinely analyze layers of them to plot swings in ocean temperatures in the past. The new study looks at where radiolarians are living now.

In 2010, a ship operated by the Norwegian Polar Institute netted plankton samples northwest of the Norwegian archipelago of Svalbard, about midway between the European mainland and the North Pole. When the coauthors analyzed the samples, they were startled to find that of the 145 taxa they spotted, 98 had come from much farther south -- some as far as the tropics. Furthermore, the southern radiolaria were in different sizes and apparently different stages of growth for each species, indicating they were reproducing, despite the harsh conditions. It was the first time since modern arctic oceanographic research began in the early 20th century that researchers had spotted a living population of such creatures in the northern ocean.