Tropical Plankton Invade Arctic Waters: Researchers See Natural Cycle, but Questions Arise on Climate Change

For the first time, scientists have identified tropical and subtropical species of marine protozoa 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.