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. Oceanographers have previously shown that sometimes pulses of warm water penetrate along the Norwegian coast and into the arctic basin; such pulses have occurred in the 1920s, 1930s and 1950s. Further, the authors say that well-dated fossils of foraminiferaprotozoans closely related to radiolariafound on the arctic seafloor suggest that warm-water plankton may have temporarily established themselves at least several times beforearound 4200 and 4100 BC, and again around 220, 370 and 1100 AD. "All the evidence is that this isn't necessarily immediate evidence of global warming of the ocean," said Anderson. Lead author Kjell Bjrklund, of the University of Oslo Natural History Museum said of the invaders, "This doesn't happen continuouslybut 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 who tracks fish global populations. Could this be the start of a switch in currents predicted by climate models? The most recent pulse began in the early 1980s, and has lasted more or less to the present. Even without that, the arctic ocean itself is warming rapidly; with progressive loss of summe
|Contact: Kevin Krajick|
The Earth Institute at Columbia University