Global warming: ‘Changing the planet’

‘It is important to realize just how interconnected everything is.’

A shift in the ocean nitrogen cycle would affect the entire food chain, from plankton to penguins. Bob Berwyn photo.

By Summit Voice

FRISCO — The nitrogen cycle in the world’s oceans could be thrown out of whack for centuries or longer due to the rapid climate change caused by the emission of greenhouse gases.

“We are changing the planet in ways we are not even aware of,” said Prof. Eric Galbraith, of McGill University’s Department of Earth and Oceanic Sciences. “You wouldn’t think that putting carbon dioxide into the atmosphere would change the amount of nitrogen available to fish in the ocean, but it clearly does. It is important to realize just how interconnected everything is.”

In a study funded by the National Science Foundation, the international research team led by Galbraith studied sediments from the ocean floor to see how ocean chemistry changed at the end of the last ice age, about 18,000 years ago. They were able to confirm that, as the ice sheets started melting and the climate warmed up, the marine nitrogen cycle started to accelerate.

The ocean stabilized in a new, warmer state, in which the overall nitrogen cycle was running faster, but it took about 8,000 years ago. Given the current dramatic rate of change in the ocean nitrogen cycle the researchers are not sure how long it will take for marine ecosystems to adapt.

The study confirms that oceans are good at balancing the nitrogen cycle on a global scale, but it’s a slow process that may take many centuries, or even millennia, raising worries about the effects of the scale and speed of current changes in the ocean.

“For the first time we can quantify how oceans responded to slow, natural climate warming as the world emerged from the last ice age,” Galbraith said. ”And what is clear is that there is a strong climate sensitivity in the ocean nitrogen cycle.”

The nitrogen cycle is a key component of the global ocean metabolism. Like the proteins that are essential to human health, nitrogen is crucial to the health of oceans. And just as proteins are carried by the blood and circulate through the body, the nitrogen in the ocean is kept in balance by marine bacteria through a complicated cycle that keeps the ocean healthy.

The phytoplankton (microscopic organisms at the base of the food chain) ‘fix’ nitrogen in the shallow, sunlit waters of the ocean, and then as they die and sink, nitrogen is eliminated (a process known as ‘denitrification’) in dark, oxygen-poor pockets of the ocean depths.

To read the full study in Nature Geoscience:

This research was funded by: the Canadian Institute for Advanced Research (CIFAR) through the Earth System Evolution Program.


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