Carbon Cycle

http://earthobservatory.nasa.gov/Features/CarbonCycle/?src=eoa-features

The Carbon Cycle

A previous version of this article, written in 2001, is now archived as a PDF file.

By Holli RiebeekDesign by Robert SimmonJune 16, 2011

Carbon is the backbone of life on Earth. We are made of carbon, we eat carbon, and our civilizations—our economies, our homes, our means of transport—are built on carbon. We need carbon, but that need is also entwined with one of the most serious problems facing us today: global climate change.

Carbon is both the foundation of all life on Earth, and the source of the majority of energy consumed by human civilization. [Photographs ©2007MorBCN (top) and ©2009sarahluv (lower).]

Forged in the heart of aging stars, carbon is the fourth most abundant element in the Universe. Most of Earth’s carbon—about 65,500 billion metric tons—is stored in rocks. The rest is in the ocean, atmosphere, plants, soil, and fossil fuels.

Carbon flows between each reservoir in an exchange called the carbon cycle, which has slow and fast components. Any change in the cycle that shifts carbon out of one reservoir puts more carbon in the other reservoirs. Changes that put carbon gases into the atmosphere result in warmer temperatures on Earth.

This diagram of the fast carbon cycle shows the movement of carbon between land, atmosphere, and oceans. Yellow numbers are natural fluxes, and red are human contributions in gigatons of carbon per year. White numbers indicate stored carbon. (Diagram adapted from U.S. DOE, Biological and Environmental Research Information System.)

Over the long term, the carbon cycle seems to maintain a balance that prevents all of Earth’s carbon from entering the atmosphere (as is the case on Venus) or from being stored entirely in rocks. This balance helps keep Earth’s temperature relatively stable, like a thermostat.

This thermostat works over a few hundred thousand years, as part of the slow carbon cycle. This means that for shorter time periods—tens to a hundred thousand years—the temperature of Earth can vary. And, in fact, Earth swings between ice ages and warmer interglacial periods on these time scales. Parts of the carbon cycle may even amplify these short-term temperature changes.

The uplift of the Himalaya, beginning 50 million years ago, reset Earth’s thermostat by providing a large source of fresh rock to pull more carbon into the slow carbon cycle through chemical weathering. The resulting drop in temperatures and the formation of ice sheets changed the ratio between heavy and light oxygen in the deep ocean, as shown in this graph. (Graph based on data from Zachos at al., 2001.)

On very long time scales (millions to tens of millions of years), the movement of tectonic plates and changes in the rate at which carbon seeps from the Earth’s interior may change the temperature on the thermostat. Earth has undergone such a change over the last 50 million years, from the extremely warm climates of the Cretaceous (roughly 145 to 65 million years ago) to the glacial climates of the Pleistocene (roughly 1.8 million to 11,500 years ago). [See Divisions of Geologic Time—Major Chronostratigraphic and Geochronologic Units for more information about geological eras.]

Glacial / interglacial variations in atmospheric carbon dioxide

http://www.up.ethz.ch/education/biogeochem_cycles/reading_list/sigman_nat_00.pdf

Glacial/interglacial variations in atmospheric carbon dioxide

Daniel M. Sigman* & Edward A. Boyle²

* Department of Geosciences, Guyot Hall, Princeton University, Princeton, New Jersey 08544, USA

² Department of Earth, Atmospheric, and Planetary Sciences, Room E34-258, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Massachusetts 02139,
USA

Twenty years ago, measurements on ice cores showed that the concentration of carbon dioxide in the atmosphere was lower during ice ages than it is today. As yet, there is no broadly accepted explanation for this difference. Current investigations focus on the ocean's `biological pump', the sequestration of carbon in the ocean interior by the rain of organic carbon out of the surface ocean, and its effect on the burial of calcium carbonate in marine sediments. Some researchers surmise that the whole-ocean reservoir of algal nutrients was larger during glacial times, strengthening the biological pump at low latitudes, where these nutrients are currently limiting. Others propose that the biological pump was more efficient during glacial times because of more complete utilization of nutrients at high latitudes, where much of the nutrient supply currently goes unused. We present a version of the latter hypothesis that focuses on the open ocean surrounding Antarctica, involving both the biology and physics of that region.

Pg 8 -
In the subantarctic, planktonic foraminiferal Cd/Ca and the 13C/12C of diatom-bound organic matter both show changes that are consistent with an ice age state of higher nutrient utilization62,82.

Fig 6 on page 9 gives a very clear depiction of the Dissolved Oxygen levels of surface water in present day oceans and during the last glacial period.

Earth's Biogeochemical Cycles

http://www.earth-stream.com/outpage.php?s=18&id=188819

Earth's Biogeochemical Cycles, Once In Concert, Falling Out Of Sync

ScienceDaily (Aug. 4, 2009) — What do the Gulf of Mexico's "dead zone," global climate change, and acid rain have in common? They're all a result of human impacts to Earth's biology, chemistry and geology, and the natural cycles that involve all three.

On August 4-5, 2009, scientists who study such cycles--biogeochemists--will convene at a special series of sessions at the Ecological Society of America (ESA)'s 94th annual meeting in Albuquerque, N.M.

They will present results of research supported through various National Science Foundation (NSF) efforts, including coupled biogeochemical cycles (CBC) funding. CBC is an emerging scientific discipline that looks at how Earth's biogeochemical cycles interact.

"Advancing our understanding of Earth's systems increasingly depends on collaborations between bioscientists and geoscientists," said James Collins, NSF assistant director for biological sciences. "The interdisciplinary science of biogeochemistry is a way of connecting processes happening in local ecosystems with phenomena occurring on a global scale, like climate change."

A biogeochemical cycle is a pathway by which a chemical element, such as carbon, or compound, like water, moves through Earth's biosphere, atmosphere, hydrosphere and lithosphere.

In effect, the element is "recycled," although in some cycles the element is accumulated or held for long periods of time.

Chemical compounds are passed from one organism to another, and from one part of the biosphere to another, through biogeochemical cycles.

Water, for example, can go through three phases (liquid, solid, gas) as it cycles through the Earth system. It evaporates from plants as well as land and ocean surfaces into the atmosphere and, after condensing in clouds, returns to Earth as rain and snow.

Researchers are discovering that biogeochemical cycles--whether the water cycle, the nitrogen cycle, the carbon cycle, or others--happen in concert with one another. Biogeochemical cycles are "coupled" to each other and to Earth's physical features.

"Historically, biogeochemists have focused on specific cycles, such as the carbon cycle or the nitrogen cycle," said Tim Killeen, NSF assistant director for geosciences. "Biogeochemical cycles don't exist in isolation, however. There is no nitrogen cycle without a carbon cycle, a hydrogen cycle, an oxygen cycle, and even cycles of trace metals such as iron."

Now, with global warming and other planet-wide impacts, biogeochemical cycles are being drastically altered. Like broken gears in machinery that was once finely-tuned, these cycles are falling out of sync.

Knowledge about coupled biogeochemical cycles is "essential to addressing a range of human impacts," said Jon Cole, a biogeochemist at the Cary Institute of Ecosystem Studies in Millbrook, N.Y., and co-organizer of the CBC symposium at ESA.

"It will shed light on questions such as the success of wetland restoration and the status of aquatic food webs. The special CBC conference sessions at ESA will explore future research needs in environmental chemistry, with a focus on how global climate change may impact various habitats."

Earth's habitats have different chemical compositions. Oceans are wet and salty; forest soils are rich in organic forms of nitrogen and carbon that retain moisture.

The atmosphere has a fairly constant chemical composition--roughly 79 percent nitrogen, 20 percent oxygen, and a 1 percent mix of other gases like water, carbon dioxide, and methane.

"Seemingly subtle chemical changes may have large effects," said Cole.

"Consider that global climate change is caused by increases in carbon dioxide and methane, gases which occupy less than ½ of one percent of the atmosphere. Now more than ever, we need a comprehensive view of Earth's biogeochemical cycles."

The study of coupled biogeochemical cycles has direct management applications.

The "dead zone" in the Gulf of Mexico is one example. Nitrogen-based fertilizers make their way from Iowa cornfields to the Mississippi River, where they are transported to the Gulf of Mexico. Once deposited in the Gulf, nitrogen stimulates algal blooms.

When the algae die, their decomposition consumes oxygen, creating an area of water roughly the size of New Jersey that is inhospitable to aquatic life. Protecting the Gulf's fisheries--with an estimated annual value of half-a-billion dollars--relies on understanding how coupled biogeochemical cycles interact.

A better understanding of the relationship between nitrogen and oxygen cycles may help determine how best to use nitrogen fertilizers, for example, to avoid dead zones.