At the end of the last glaciation, atmospheric levels of carbon dioxide has increased rapidly as the planet warms, scientists have long assumed that the source was released CO2 in the deep ocean.
But a new study using detailed dating of foraminifera found in a sediment core from the Gorda Ridge off Oregon indicate that the North Pacific was not an important reservoir of carbon during glacial periods. This discovery could send scientists back to the proverbial drawing board in search of other potential sources of CO2 during glacial periods.
The study, which was supported by the National Science Foundation and the University of Michigan, published online this week in Nature Geoscience.
"Frankly, we're a bit confused by all this," said Alan Mix, a professor of oceanography at Oregon State University and author of the study. "The depth of the North Pacific was such a clear source of carbon, but it just does not mix at least we have shown how the carbon was not;. Now we just need to know where he was. "
During periods of glaciation, global climate was CO2 in the atmosphere was cooler and lower. Humans did not cause this change in CO2, this means that the carbon absorbed by another tank. An obvious place to look for the missing carbon is the sea, which stores more than 90 percent carbon readily tradable on Earth.
The Pacific Ocean is the largest ocean in the volume. The longest deep water masses isolated from the atmosphere and the most enriched carbon are now in the Pacific Ocean, northeast, so the researchers concentrated their efforts there. They assume that the age of ventilation in the pool - or the time since the deep water was put in contact with the atmosphere - would be older during the glacial periods, CO2 to accumulate in the abyss.
"We were surprised to learn that the last ice age, the far north-east Pacific Ocean was similar to that age today shows that ventilation was unlikely place to hide the missing carbon," said David Lund, at the paleoceanographer ' University of Michigan, formerly of Oregon State, and the author of the paper to Nature Geosciences.
"This indicates that the depth of the Pacific was not an important carbon sink during the ice ages," Lund said. "Even more interesting is that we found that the age of increased ventilation during deglaciation, exactly when atmospheric CO2 levels were rising."
The researchers reconstructed the history of deep ventilation in the North Pacific through the study of sediments in the site about 75 miles from the coast in southwestern Oregon. Here, water is more than a mile and a half deep and the water mass known as the oldest modern oceans, Mix said. With radiocarbon dating of planktonic or surface-dwelling, and benthic animals (the sea-dwelling) foraminifera, researchers can determine isotopic signatures of foraminifera match "the values provided by default Oceanic Control the atmosphere."
Organisms living on the sea floor are the parents of "apparent" age of radiocarbon measurements of organisms lived on the sea surface, Mix said, though both come from the same sediments, and are actually the same age. Radiocarbon dating was performed using a particle accelerator in advance connects the authors', John Southon of the University of California at Irvine.
"The various sources of CO2 have apparently different ages, depending on how long they have been isolated from the atmosphere," said Mix. "We use these dates as a kind of label of` the return address "instead of providing for certain ages of events. The key is that the depth of the North Pacific was not the source of CO2 are increasing at the end of the last ice age. "
The study is important not only to trace the history of climate scientists say, but to predict how a country can respond to future climate change. To "breathe in and out of coal," Mix said, inhaling the carbon in sediments and soils, while exhaling through volcanism, and slow between the oceans, soil and vegetation with the atmosphere.
When everything is in balance, the Earth is said to be in a "stable". But many times in the past, the carbon footprint has grown out of control.
"As the sea is a huge stock of coal, a relatively small change in the oceans can have a big impact," Mix said. "We know that ocean currents changed, and why ice ages, many scientists assumed in depth in the Pacific was a source of increased levels of CO2 during the last deglaciation."
Lund said that "it is possible that we have a misunderstanding of the radiocarbon measurements by assuming the signal that controls the ocean mixing."
"These are areas of volcanic activity, so that the contribution of carbon from volcanoes, which has not been radiocarbon measurements because of its great age, should be considered," said Lund. "But it is too early to draw conclusions."
The researchers next step is to look for chemical traces of volcanic activity.
Another source of carbon might be from the earth, but the authors say it would be difficult to explain the magnitude of the increase of carbon in the atmosphere and the apparent age of carbon released carbon pre- industrial sources on land alone.
"If we can better understand how carbon passes through the Earth system in the past, and how this relates to climate change, it is best that you can predict how the carbon being added to the atmosphere moves in the future" said Mix.
About the OSU College of Oceanic and Atmospheric Sciences: COAS is internationally recognized for its faculty, research and facilities, including the state of the infrastructure to support real-time ocean / atmosphere observation and prediction. The university is a leader in the study of Earth as an integrated system, providing scientific understanding to address complex environmental problems
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