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Mon December 9, 2013
Dr. Eric Galbraith, McGill University – The Ocean’s Nitrogen Cycle
In today’s Academic Minute, Dr. Erick Galbraith of McGill University explains how climate change could alter ocean currents and the marine nitrogen cycle.
Eric Galbraith is an assistant professor in the Department of Earth and Planetary Sciences at McGill University in Montreal, Canada. As a marine biochemist, his research uses observations of the modern ocean, computer simulations of ocean biogeochemistry, and sedimentary records of past climate change to examine the connections between climate and marine ecosystems. He earned his Ph.D. at the University of British Columbia.
Dr. Eric Galbraith– The Ocean’s Nitrogen Cycle
As the philosopher-scientist James Lovelock pointed out, the Earth’s biosphere is a lot like a single organism. The organism's largest and most ancient part is the ocean ecosystem. Its basic life support system depends on having a constant supply of nitrogen. The circulation of ocean currents carries nitrogen from its source to its demise, just like our blood circulation carries nutrients from our stomachs to our kidneys. Along the way it supports all life within the ocean, from sardines to penguins to whales, as it has done for millions of years. New nitrogen is constantly produced by a special breed of bacteria, that evolved far back in the early days of life on Earth, and grows in the sunny surface ocean. While a very different type of bacteria that lives in deep, dark pockets of the ocean interior, eliminates excess nitrogen, maintaining an ancient balance.
Now, as climate change warms the ocean, it is redirecting the circulation of its currents and altering the habitats of the bacteria that supply and eliminate nitrogen. But it has been hard to gauge the effect this will have on the nitrogen cycle.
In order to find out, my colleagues and I pieced together clues from the slow natural climate warming at the end of the last ice age. We used a collection of mud samples carefully extracted from the deep sea floor in different parts of the world, and measured the isotopes of nitrogen fossilized within the mud. We found that the nitrogen balance was, indeed, thrown out of whack by the slow natural climate warming, and shifted into a higher speed. But also that it stabilized again after a few thousand years. This would have had repercussions throughout the marine ecosystem, and would have forced the habitats of many fish and invertebrates to shift.
We expect the warming now being caused by humans will cause an even larger destabilization of the ocean’s basic life support system, as it is happening about a hundred times faster than our fossilized example. It seems likely that the system will eventually re-stabilize itself, but it may take many centuries to do so, and will make life more difficult for many marine animals in the meantime.