“It’s another component of the climate change story,” Grant R. Bigg, a professor in Earth systems science at the University of Sheffield and the author of the new study, tells The Christian Science Monitor in an interview. “If giant icebergs hadn’t existed, then the carbon dioxide in the atmosphere would have gone up even more than it currently has. It’s been something which has helped to slow down the rate of increase of carbon dioxide and therefore climate change.”
Dr. Bigg and his colleagues tested the impact of this phenomenon by analyzing satellite images of 17 giant icebergs and the colorful plume surrounding them. The plume, colored by the elevated chlorophyll levels of the phytoplankton blooms, stretched out some four to 10 times the iceberg’s length and could last for over a month after the iceberg passed by. Their findings are described in an article published Monday in the journal Nature Geoscience.
Icebergs aren’t just giant ice cubes floating around in the ocean, Kaufmann says. They’re more complex. The humongous frozen masses start as snow falling on the Antarctic continent. Over thousands of years that snow amasses into a gigantic glacier.
Glaciers flow, like molasses, over the continent. As they travel, glaciers rub and churn against the ground, actually incorporating some of the rock and soil into the ice crystals. That’s how a glacier picks up nutrients, like iron.
Eventually, a glacier will reach the coast and stretch out over the water in an ice shelf. Icebergs are created when pieces of that shelf break off and float away into the ocean.
Out in the open ocean, wind, current and warmer temperatures erode the iceberg. As it bobs around in the Southern Ocean, the iceberg ends up leaving a trail of iron-rich meltwater.
In the Southern Ocean, iron is thought to be a limiting nutrient for phytoplankton productivity. So such a large influx of iron stimulates a bloom of the tiny plants.
As phytoplankton grow, they extract carbon dioxide from the atmosphere and incorporate it into their own cellular material. That carbon might get sequestered when the plant dies and sinks down to the depths of the ocean, or might be carried into the deep by the excrement of an animal that consumes the tiny plants. With the carbon buried in the ocean sediments, it’s out of the global carbon cycle indefinitely.