Carbon Cycle Was Already Disrupted Millions Of Years Ago
- Carbon Cycle Was Already Disrupted Millions Of Years Ago
by Staff Writers
Amsterdam, The Netherlands (SPX) Apr 19, 2006
Dutch researcher Yvonne van Breugel analysed rocks from seabeds
millions of years old. Carbon occurs naturally in two stable forms;
atomic mass 12 (99 percent) and atomic mass 13 (1 percent). Episodes
in the Jurassic and Cretaceous periods were characterised by a
relatively strong increase in 12C.
The analyses have shown that this was caused by a sudden large-scale
release of carbon from stocks stored in the ocean floor or peats and
The atmospheric carbon dioxide concentration is increasing as a
consequence of the large-scale use of fossil fuels in the industrial
era. This has apparently brought about a stronger relative increase
in the light carbon isotope 12C. Due to this the ratio of the stable
carbon isotopes 13C/12C has show a clearly measurable decrease of
0.1%. However in the Jurassic and Cretaceous periods, 180 and 120
million years ago, there were periods with a shift four times as
large in a period of just several tens of thousands of years. Where
did all of that light carbon suddenly come from?
Van Breugel investigated chemical fossils of marine algae and land
plants from sediments deposited in the aforementioned periods.
Plants and algae assimilate CO2 from the air and water. Consequently
changes in the isotope ratio are recorded in organic material. These
chemical fossils have been well preserved because large parts of the
oceans in the Jurassic and Cretaceous periods contained little (if
In sediment cores from various widely-separated areas Van Breugel
found a 0.4% decrease in the 13C/12C ratio. This means that there
were large-scale changes in the carbon cycle over a short geological
timescale of several tens of thousands of years. From the results
Van Breugel deduced that large quantities of 12C in the form of CO2
or methane were suddenly released into the atmosphere.
This could have been the result of methane being released from gas
hydrates which were buried in the ocean floor. It is not clear which
mechanism was responsible for this. Methane could also have been
formed under high pressure in coal seams and then subsequently
released upon coming into contact with magma. A third option is that
carbon from organically-rich sediment came into contact with hot
magma. As a result of this the organic molecules combusted into CO2
File photo: Plant fossils preserved for millions of years.
Yvonne van Breugel's research was funded by NWO