Researchers have found that the plume of cold water released from massive icebergs increases carbon storage in the seas - far more than previously thought. This negative feedback loop significantly slows climate change.
It seems a paradox: giant icebergs, a symbol of climate change, can actually slow down warming of the Earth.
This is possible because the cold, mineral-rich water melting icebergs leave in their wakes nourishes phytoplankton. These tiny marine organisms take up carbon dioxide from the atmosphere, and when they die, sink to the ocean floor to create a literal carbon bank.
"When phytoplankton grow, they give off fecal matter and die, and some of that material sinks deep in the ocean, where it stays for centuries or millennia," explained study author Grant Bigg, an Earth systems professor at the University of Sheffield in England.
Particularly giant icebergs - that is, those at least 18 kilometers long - have this effect, due to the area covered.
Research for the paper, published in "Nature Geoscience," analyzed satellite images of giant icebergs in the Southern Ocean around the Antarctic, measuring the intensity of the color of chlorophyll produced by phytoplankton.
This "plume of productivity extends five to 10 times from the iceberg," Bigg said - meaning "the net carbon storage is much larger than suspected."
"It's essentially slowing the rate at which carbon dioxide is remaining in the atmosphere," Bigg told DW.
The concentration of atmospheric carbon is currently around 400 parts per million, and is increasing by roughly 2 ppm each year. "Giant icebergs have slowed that increase by 5 to 10 percent," Bigg said.
Antarctica is warming faster than other world regions, which is causing the ice sheet to melt and contributing to sea level rise. Warming there is often understood in terms of a positive feedback loop, where warming causes more ice to melt, thus accelerating further warming.
Some research indicates that warming in Antarctica has already reached a tipping point for melting, from which there would be no return.
The finding that melting icebergs can slow global warming was a surprise, as the scale of the phenomenon hadn't before been known.
"We still don't fully understand the climate system - I wouldn't be surprised if there were further both negative and positive feedback that could possibly accelerate or slow down global warming," Bigg concluded.