June 15, 2013
The Precarious Nature Of Global Ocean Chemistry
April Flowers for redOrbit.com - Your Universe Online
The oceans of the past were quite different than the ones we see today. Ocean temperatures are increasing due to global warming, and these increases are harming marine food webs. Coastal dead zones are also being created by the run-off from fertilizers.An international team of researchers, led by McGill University, has completed the first global study of changes that occurred during the nitrogen cycle at the end of the last ice age. The nitrogen cycle was a crucial component of ocean chemistry. The findings of this study, published in Nature Geoscience, confirm oceans are good at balancing the nitrogen cycle on a global scale. However, the results also show this balancing act is a slow process that may take centuries, or even millennia. This raises worries about the effects of the scale and speed of 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,” says Prof. Eric Galbraith from McGill University´s Department of Earth and Oceanic Sciences. ”And what is clear is that there is a strong climate sensitivity in the ocean nitrogen cycle.”
The researchers say the nitrogen cycle is an essential component of the global metabolism, comparable to the proteins that are essential to human health. The nitrogen in the ocean is kept in balance by marine bacteria through a complicated cycle that keeps the ocean healthy, much like proteins are carried by the blood and circulate through the body. Microscopic organisms at the base of the marine food chain, called phytoplankton, fix nitrogen in the shallow, sunlit waters of the ocean. As the phytoplankton die and sink, nitrogen is eliminated in dark, oxygen-poor pockets of the deep oceans, in a process called dentrification.
The research team gathered sediment from the ocean floor in different areas of the world. The samples were used to confirm that as the ice sheets started melting and the climate warmed up at the end of the last ice age — 18,000 years ago — the marine nitrogen cycle started to accelerate. By about 8,000 years ago, the ocean had stabilized itself in a new, warmer state, in which the overall nitrogen cycle was running faster. The team isn´t sure how long it will take for marine ecosystems to adapt given the dramatic rate of change in the current ocean nitrogen cycle.
“We are changing the planet in ways we are not even aware of,” says Galbraith. “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.”