Researchers see a natural cycle, but note that such migrations are occurring more often and penetrating deeper into the Arctic Ocean, which raises the question if climate change has a role to play.
For the first time, scientists have identified tropical and subtropical species of marine protozoa living in the Arctic Ocean. Apparently, they travelled 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 creatures offers a preview of climate-induced changes already overtaking the oceans and land, causing redistributions of species and shifts in ecology.
O. Roger Anderson, a specialist in one-celled organisms at Columbia University and a co-author of the study which detailed this finding, said: "When we suddenly find tropical plankton in the arctic, the issue of global warming comes right up, and possible inferences about it can become very charged. So, it's important to examine critically the evidence to account for the observations."
He said the invaders were apparently swept up in the warm Gulf Stream, which travels from the Caribbean into the north Atlantic, but usually peters out somewhere between Greenland and Europe.
Oceanographers have previously shown that sometimes pulses of warm water penetrate along the Norwegian coast and into the arctic basin. Lead author Kjell Bjørklund, of the University of Oslo Natural History Museum said of the invaders, "This doesn't happen continuously—but it happens."
That said, oceanographers have noted that such pulses seem to be coming more often and penetrating further—"exactly what one would expect from global warming," said Rainer Froese, an oceanographer at the Helmholtz Centre for Ocean Research.
Louis Fortier, an arctic oceanographer at Laval University in Quebec, said: "Whether or not [such] intrusions are signs of this predicted increased advection in response to climate change, nobody can tell yet, I believe. But for me, the observations so far certainly support the models."
Whatever the answer, this is the first time a living population of the southern radiolaria plankton has been found so far north. Changes in global ocean ecology are already being detected in many places elsewhere. A 2011 global study on the impact of climate change on fisheries says that many marine species are moving poleward or into deeper, cooler waters in response to warming--among other places, along the U.S. east coast, the Bering Sea, and off Australia.
The North Sea, off Scandinavia and the United Kingdom, has warmed about 2 degrees F in the last 50 to 100 years; there, 15 of 36 fish species studied have moved northward; fish more common nearer the Mediterranean—anchovy, red mullet, sea bass—are being caught by commercial fishermen, while cod, which prefer colder waters, are moving out. There is also evidence that zooplankton similar to the radiolaria are shifting northward in the North Atlantic. In the Pacific, poisonous algal blooms harmful to the shellfish industry are being detected farther north, into Alaskan waters.