Melting icebergs may be fighting against the very forces that cause them to melt, a new study suggests.
Water dripping off icebergs and into the Antarctic Ocean, also known as the Southern Ocean, contains iron and other nutrients, according to research published Monday in the journal Nature Geoscience. These nutrients fertilize phytoplankton, the microscopic marine life that plays a key role in oceanic ecosystems, and help the tiny plants absorb carbon dioxide in the atmosphere as they grow into plumes.
In other words, there might be even more carbon dioxide in our atmosphere if it weren’t for the help of phytoplankton, said Dr. Grant Bigg, professor of earth system science at the University of Sheffield in England and lead author of the study.
“Previous research had shown that there was a fertilizing effect from iceberg meltwater but no one had looked at the giant icebergs in a systematic way before,” he said. “The extent, and strength, of the fertilized phytoplankton plume was the big surprise.”
For the study, Bigg and his colleagues analyzed 175 satellite images taken between 2003 and 2013 that show ocean water and at least 18-kilometer-long icebergs in the remote Antarctic Ocean. A greenish color of the water indicated high levels of phytoplankton productivity.
They noticed the colorful phytoplankton plumes in the photos extended hundreds of kilometers from giant icebergs and persisted for at least a month after the iceberg passed by. The researchers concluded that this biological process involving meltwater and phytoplankton may be responsible for up to 20 percent of the carbon that’s stored in the deep Antarctic Ocean.
“The research is important as it has shown that there is more carbon stored in the Southern Ocean than previously calculated, which will have knock-on consequences for the global carbon budget,” Bigg said. “It also demonstrates an unusual negative feedback on climate — even if it is a secondary one and merely slowing climate change.”
But this does not mean that meltwater and phytoplankton will save us from climate change, many scientists caution.
“I would hate for somebody to look at this and say, see it’s a negative feedback, we can do whatever we want and it’s not going to have an effect,” Dr. Ronald Kaufmann, a marine and environmental scientist at the University of San Diego who was not involved in the study, told The Christian Science Monitor.
“This is moving the needle back in the other direction, there’s no question about that,” he said. “But…I don’t think this is going to offset the burning of coal, for example.”
After all, the relationship between the ocean and atmosphere remains complicated. Carbon dioxide may be absorbed by meltwater, but it can be released by seasonal warming of the water as well.
A separate team of scientists led by the National Center for Atmospheric Research in Boulder, Colorado, plans to further investigate this month just how much excess carbon dioxide the Antarctic Ocean’s icy waters are able to absorb.
“If we want to better predict the temperature in 50 years, we have to know how much carbon dioxide the oceans and terrestrial ecosystems are going to take up,” Dr. Britton Stephens, a scientist at the center, said in a statement. “Understanding the Southern Ocean’s role is important because ocean circulation there provides a major opportunity for the exchange of carbon between the atmosphere and the vast reservoir of the deep ocean.”
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