Question : An increase in 13C over 12C in strata frequently indicates an atmosph

Question

Question:

An increase in 13C over 12C in strata frequently indicates an atmospheric warming event. Yet, in strata spanning the boundary between the Permian and Triassic, a known warm period in earth's history, 13C/12C ratios shift toward negative values. Explain this discrepancy.

Interpretation:

Carbon stable isotopes are fractionated primarily by photosynthesis. The 13C/12C ratio is also an indicator of paleoclimate: a change in the ratio in the remains of plants indicates a change in the amount of photosynthetic activity, and thus in how favorable the environment was for the plants. An increase in 12C shows an increase in burial rates. This is because plants prefer 12C rather than 13C. Seeing an increase in 12C shows there was an abundance of plant life in the burial being examined.

My first impression was an increase in 12C indicates a warming event. The question starts off stating the opposite.

Can someone help explain this to me, and also help me explain the discrepancy in the Permian and Triassic boundary.

Explanation / Answer

The conc. of C12 is more in atmosphere because its not radioactive as C13.

As we know the biological carbon fixation is mainly due to pjotosynthesis. and the plants absorb more co2 ffrom atm. in these periods the sea level rises, because of large production of coral reefs.

They produce caco3 shell from that. Studies shows that the shell of Corals shows that large conc. of C13 , which confrims it. A negative ?13C peak, explained mainly by dissociation of methane

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