It turns out that icebergs may be a natural sponge for excessive carbon dioxide in the atmosphere, a new study explains. Giant Manhattan-sized Antarctic icebergs are fertilizing the Southern Ocean, leaving expansive algae blooms in their wake. These blooms then absorb vast amounts of carbon dioxide. Known as calving, icebergs break off from Antarctica (mostly during that continent's summer) and are chock full of inorganic and organic matter. Part of Earth's carbon cycle, this study is the first time scientists have quantified the effects of iceberg fertilization in the Southern Ocean.

Once adrift in the Southern Ocean, they begin to melt and release a "vast trail of iron and other nutrients that act as fertilizers for algae and other tiny plant-like organisms in the ocean." Because algae is a plant, it absorbs the "fertilizer" left in the iceberg's wake. Couple that with carbon dioxide and sunlight, and the algae grow, typically "over a radius of at least 4–10 times the iceberg’s length." 

As the algae blooms, it can become so vast that its chlorophyll is visible from space (as algae live in the first 200 to 300 feet of ocean). As the algae and other organisms grow, they feed on sunlight, nutrients, and carbon dioxide, releasing oxygen as a byproduct. In fact, it's estimated that 70 percent of the oxygen in our atmosphere comes from this tiniest of organisms.

The study, published this week in the journal Nature Geoscience, looked at the "satellite images of 17 giant icebergs off Antarctica from 2003 to 2013 and found that algae could turn the water greener for hundreds of kms (miles) around the icebergs, with nutrients spread by winds and currents." Prior to the study, most scientists believed that the "impact of ocean fertilization from the demise of giant icebergs" was "small and localized."

The study's lead author, Professor Grant Bigg of the University of Sheffield, told the Associated Press they were "very surprised to find that the impact can extend up to 1,000 kms,” (625 miles) from the icebergs." The ocean blooms that formed in the wake of these giant icebergs can "absorb 10 to 40 million tonnes of carbon dioxide a year." The authors defined a giant iceberg as being longer than 10 nautical miles (18 kms), about the size of Manhattan.

At any given time, there are roughly 30 giant icebergs floating off Antarctica and they can persist for years. The study also showed that the giant icebergs had an "out-sized impact in promoting ocean fertilization when compared with small icebergs." Biggs believes that carbon dioxide (CO2) levels would have increased an additional 0.2 percent a year without these giant icebergs promoting large algae blooms. Less CO2 should equate to less global warming.

The study's authors note the amount of ice breaking off has gained an estimated "five percent in the past two decades." But in October, NASA reported that satellite imagery showed Antarctica added more ice than it had been losing, adding enough to the "continent to outweigh the increased losses from its thinning glaciers." This would likely explain the increase in ice calving.

Another benefit to the increased ice cover over Antarctica is a much slower sea level rise as predicted by the UN's Intergovernmental Panel on #Climate Change (IPCC). Studies show that both Arctic and Greenland ice is also freezing at historical levels, as reported by other agencies around the world.

And in 2014, NASA reported that "sea ice surrounding Antarctica reached a new record high extent this year, covering more of the southern oceans than it has since scientists began a long-term satellite record to map sea ice extent in the late 1970s." During Antarctica's summer, that sea ice breaks off, which results in an increase in icebergs. #Science