Historical Global Carbon Cycle Needs A Reexamination

Carbon is an important element in all organisms. 20% of living organisms’ bodies are made up of carbon. Carbon is also the essential element that makes up the organic molecules. Carbon cycle is the process by which carbon is cycled through different parts of the Earth. Since carbon dioxide has a great effect on global warming, scientists pay close attention to the historical global carbon cycle in order to learn how the climate has changed throughout history.

Scientists often use the measurement of carbon isotopes in the fossils from a specific time to predict the carbon dioxide concentration in the atmosphere at that time. Isotopes are atoms with the same chemical behavior but different masses. The two common isotopes of carbon are carbon-12 and carbon-13. CO2 produced by burning plants are different than the CO2 that existed in the atmosphere as plants have a preference with the lighter isotope, carbon-12. Therefore, plants have a lower carbon-13/carbon-12 ratio than the atmosphere does. Once the CO2 produced by the burning of plants enter the atmosphere, it will lower the ratio in the atmosphere. Since the fossils are derived from ancient plants, they have the same ratio of carbon isotopes. Scientists compare fuels from different times to observe the change of carbon-13/carbon-12 ratio, which indicates the change of carbon dioxide concentration in atmosphere.

Recently the University of Miami Rosenstiel School of Marine and Atmospheric Science researchers measured the amount of carbon isotopes in both organic matter and carbonic sediment in a marine sediment core found in the Great Bahama bank. Their analyses showed that several periods of sub-aerial exposure during the Pleistocene ice ages, which took place over the past two million years, lowered the amount of carbon-13 in this sediment. Amanda Oehlert, the lead author of the study, stated that their research showed the importance of understanding the geological context of carbon isotope records.  



Picture: the sub-aerial exposure surface found in the sediment

This study showed that the amount of carbon isotopes in sediment were not the accurate records of changes in the global carbon cycle since post-depositional changes could cause the shift of carbonate values in sediments. Therefore, the predication that scientists made about the change of CO2 in atmosphere through history based on this measurement could not be accurate at all. The study of global carbon cycle is important today as scientists are trying to find the patterns of climate change on the earth in the history. This study is essential to find a solution to the issues of climate change. It is urgent for the scientists to find a more reliable source to make predications about the global carbon cycle. The fact that UM researchers proved the traditional way of studying global wrong makes me wonder if there is any other scientific method that could be wrong.


“How Do We Know That Recent CO2 Increases Are Due to Human Activities?” RealClimate. N.p., n.d. Web. 17 Oct. 2014. <http://www.realclimate.org/index.php/archives/2004/12/how-do-we-know-that-recent-cosub2sub-increases-are-due-to-human-activities-updated/&gt;.

“New Study on Global Carbon Cycle May Require Reappraisal of Climate-Related Events in Earth’ History.” RedOrbit. N.p., 18 Sept. 2014. Web. 17 Oct. 2014. <http://www.redorbit.com/news/science/1113237311/global-carbon-cycle-history-091814/&gt;.

UM Rosenstiel School of Marine and Atmospheric Science. This subaerial exposure surface is observed at 33.782 meters below the mudpit. Science 2.0. N.p., n.d. Web. 17 Oct. 2014. <http://www.science20.com/news_articles/historical_global_carbon_cycle_needs_a_rethink-144995&gt;.