According to the University of Sheffield, icebergs in the Southern Ocean have a pretty big impact on how much carbon is sequestered in those waters. Runoff from the icebergs is rich in nutrients, and helps phytoplankton grow. Phytoplankton work like plants, and so they breathe in carbon in the air and contribute to keeping that carbon from getting trapped in the atmosphere and contributing to global warming. The Southern Ocean is responsible for about 10% of oceanic carbon sequestration.
The researchers looked at satellite imagery of the oceans color, an easy way to determine phytoplankton activity, taken between 2003 and 2013. They focused on icebergs that were at least 19 kilometers long (about 11 miles, almost as long as Manhattan Island), which could leave trails of fertile water hundreds of kilometers long. All told, it looks like icebergs are responsible for about 20% of the total carbon sequestered in the Southern Ocean.
Now for the bad news—icebergs have been calving or breaking into smaller units, more rapidly in recent years, because global warming has been increasing average ocean temperatures. With more miniature icebergs, there will be fewer phytoplankton blooms, meaning less carbon gets sequestered and more carbon enters the atmosphere. More carbon in the atmosphere means more global warming, higher water temperatures, and fewer icebergs.
While icebergs have contributed to carbon sequestration for much longer than humans have been around, there’s already more carbon in the atmosphere than they handle. That means we’re looking at a downward spiral. This change will happen gradually, of course, but we’re already getting pretty close to the point of no return as far as climate change is concerned. While this new information about icebergs and their relationship with carbon sequestration is fascinating, it also serves to point out another problem we need to fix.