And because ice shelves are melting so fast — and are expected to melt even faster in the future — “rates of phytoplankton productivity are likely to increase as well,” the paper says. That will be good news for the many forms of life that rely on phytoplankton — first krill and other sea organisms, such as fish, and then the mammals and birds that feed upon those, including penguins and whales.
“The phytoplankton are the base of the entire southern ocean food web,” says Arrigo. “Without them you’ve got no krill, you’ve got no seals and whales and penguins.”
Thus, the same phenomenon that could drive sea level rise around the world might ultimately also result in some pretty happy penguins. If that messes with your emotions, rest assured you’re not the only one — all of this is quite new for humanity.
Other research, to be sure, has uncovered different mechanisms by which climate change actually seems to threaten penguins — so this new study is a rare positive finding for the birds in what can often look like a sea of negative ones. The result is also not exclusive to penguins, of course — it would apply to all organisms ultimately dependent on phytoplankton as the base of the food chain.
The researchers reached their conclusions through satellite analysis of Antarctic coastal “polynyas,” or areas of open water encircled by sea ice. Polynyas form as winds blow the ice apart, or as warm water wells up from below, and they tend to persist for many years. There are 46 of them around Antarctica, ranging in size from several hundred square kilometers to several thousand, Arrigo explains.
Because they feature open ocean, polynyas provide enough sunlight to the ocean for phytoplankton to bloom. Polynyas “tend to be biological hotspots,” says Arrigo. “They’re the place where a lot of the action is going on in the Antarctic.” It’s where you find the most penguins and seals, and the most phytoplankton.
Organisms living there, however, generally need to be studied by satellite, because the areas are very hard to get to, even with ice-breaking ocean vessels.
Using satellite images, the researchers analyzed the chlorophyll content of each polynya — basically, its greenness, as seen from space — and then sought to find factors in the surrounding environment that could help account for just how teeming with life it was. Environmental factors considered included sea surface temperatures, the width of continental shelves beneath the polynyas, and the proximity to Antarctic ice shelves known to be losing a lot of mass — and thus, pouring a great deal of freshwater into the oceans.
And that’s what led to the big, unexpected new result. “By far the most important factor was how fast nearby glaciers were melting,” says Arrigo. “That was a real surprise to us.”
Indeed, in statistical terms, ice melt explained more than half the variability in how much chlorophyll was detected, by satellite analysis, in a given polynya. “Sixty percent of the productivity in these polynyas was explained by that one variable, how fast these glaciers are melting,” Arrigo continues. “That’s important because the rate of melting in these glaciers seems to be accelerating.”
The ancient ice contains a lot of iron, possibly because of eons spent sliding across land or bedrock, or because of similarly vast time periods accumulating the contents of winds and precipitation, which can carry iron from far afield.
And iron is a nutrient that phytoplankton need to feed — precisely why iron fertilization of the oceans is one popular “geoengineering” idea for counteracting global warming. It would lead to greater blooms of algae and phytoplankton that would, in turn, pull more carbon out of the atmosphere as they grow. Or so goes the thinking, anyway.
There has been considerable controversy over iron fertilization. But now, it looks as if melting ice sheets may be conducting a similar experiment of their own off the Antarctic coast.
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