Beneath Arctic ice, scientists find an ecosystem never imagined (+video)
Scientists report finding a massive bloom of phytoplankton hidden under Arctic ice, suggesting that, as the ice thins and melts, the region is becoming vastly more biologically productive.
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Instead, the numbers started to climb until they peaked some 26 miles in from the ice edge. There, the phytoplankton abundance was four time higher than in the open ocean. The layer was about as thick as a five-year-old is tall, Arrigo said, and the waters were as green as pea soup.Skip to next paragraph
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The right nutrients had been there all along. What was missing was sufficient light, Dr. Perovich says.
Since satellites first began keeping track of the ice in 1979, the extent of summer ice has declined by about 45 percent due to global warming, wind patterns, and pollution that increase melting. These days, much of the sea ice heading into the melt season tends to be no more than about six feet thick, with little or no snow cover. As the ice melts, ponds of meltwater readily form on the surface and act as skylights, Dr. Perovich says.
Now, 43 percent of sunlight reaches the ocean surface, he adds. Plenty of food and light 24/7 is the perfect recipe for megablooms, he says.
The quantities of plankton are "truly exceptional," says Walker Smith, a marine biologist at the College of William and Mary in Williamsburg, Va., who was not part of the team conducting the research.
If these blooms are widespread under the ice along continental shelves, the primary productivity in these regions could be up to 10 times greater than open-water productivity, the team estimates.
Indeed, the find helps explain why phytoplankton is less abundant in open water: The blooms snag nearly all of the nutrients moving into the basin from the Pacific via the Bering Strait before the ice melts significantly, Arrigo says.
Researchers had interpreted the relative dearth of open-water plankton as a sign of low primary productivity in the Arctic Ocean, but "the real action was going on under the ice," he says. "And where we thought the bloom was beginning when the ice melted, actually the bloom was ending."
In addition, researchers have noted that the Arctic ocean is becoming an enormous sink for atmospheric CO2 as the waters open up in the summer. Yet the open waters in the Chukchi Sea don't show the levels of dissolved CO2 they should if that's the case. Now, it looks as though the answer lies with the under-ice phytoplankton blooms, because they consume the CO2 via photosynthesis, just as land plants do.
More work needs to be done to determine the basinwide extent of the blooms and their timing. Yet the steady retreat of summer sea ice and the increasingly early onset of the melt period raises some troubling prospects, the researchers add.
If the bloom comes earlier, it might occur before the marine creatures who come to feed on it have arrived there to eat. The biggest effect could be on the fish the feed on plankton throughout the water column, rather than on bottom feeders such as whales and walruses, Arrigo says.
Despite the concerns, the thrill of discovery remains an undercurrent as the researchers talk about their results.
"This is what you live for as a scientist," uncovering something "beyond unexpected," Perovich says. "This is a new Arctic Ocean, full of surprises."