Climate Change and Ice Age: Influx of Freshwater Increases Methane Gas Production

During the last Ice Age, massive slabs of ice covered much of North America, but new research now shows that calving icebergs resulted in a huge influx of freshwater that increased the production of the greenhouse gas, methane, in tropical wetlands.

You would think that rising methane levels would be linked to warming in the Northern Hemisphere; however, scientists reveal that this actually took place during cold intervals, changing their perception of climate change on Earth.

"Essentially what happened was that the cold water influx altered the rainfall patterns at the middle of the globe," lead author Rachael Rhodes, from the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University, explained in a news release. "The band of tropical rainfall, which includes the monsoons, shifts to the north and south through the year."

"Our data suggest that when the icebergs entered the North Atlantic causing exceptional cooling, the rainfall belt was condensed into the Southern Hemisphere, causing tropical wetland expansion and abrupt spikes in atmospheric methane," she added.

While it has long been known that Ice Age icebergs underwent catastrophic collapses, sending freshwater into the North Atlantic - phenomena known as Heinrich events - exactly when they took place and how long they lasted remained a mystery.

That is, until Rhodes and her colleagues examined evidence from the highly detailed West Antarctic Ice Sheet Divide ice core. Using a new analytical method, the team was able to create detailed measurements of the air trapped in the ice.

What they found was that the influx of freshwater into the North Atlantic Ocean from icebergs created climate effects that lasted between 740 and 1,520 years.

"The cooling caused by the iceberg influx was regional but the impact on climate was much broader," said co-author Edward Brook. "The iceberg surges push the rain belts, or the tropical climate system, to the south and the impact on climate can be rather significant."

Specifically, by pushing monsoon seasons into a smaller geographic area, rainfall events became more intense and the wet season lasted longer.

"It is a great example of how inter-connected things are when it comes to climate," Rhodes concluded. "This shows the link between polar areas and the tropics, and these changes can happen very rapidly. Climate models suggest only a decade passed between the iceberg intrusion and a resulting impact in the tropics."

The results were published in the journal Science.

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