Tropical plankton invade arctic waters

The Earth Institute at Columbia University: 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. 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. 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—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.

Coauthor O. Roger Anderson, a specialist in one-celled organisms at Columbia University’s Lamont-Doherty Earth Observatory, 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...

Radiolaria, from the Challenger Expedition, 1873-1876