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Climate:

 

“Some form of climate change has probably been involved in all of the mass extinctions.”

                                                                                                http://www.bbc.co.uk

 

At the end of the Triassic and the beginning of the Jurassic, the climatological conditions of the Earth were going through some radical changes.  The carbon dioxide (CO2) content in the atmosphere was at it’s highest ever levels (10 times those of present day).

·        Early Triassic: Carbon dioxide density in atmosphere:rCO2 = 1000 ppm.

·        End Triassic:  Carbon dioxide density in atmosphere:rCO2 = 2500-3000 ppm.

Levels of CO2 in the atmosphere, based on soil carbonate 

(based on Ekart et al. 1999)

The Earth  was coming into full ‘HOT HOUSE’ state.

 

            Humid forests could be seen not only at the equators, but also spreading from mid-latitudes to the poles. Deciduous forests could be seen at high latitudes, tropical forests at mid latitudes and Savanna and deserts at low latitudes. The oceans were becoming warm and often anoxic. The late Triassic is the only interval of the Phanerozoic where there is no evidence of any glacial activity what so ever.

The picture shows the encroachment of the Sahara desert in Tunisia.

It is possible that in the Triassic period there would have been a similar scene. 

 

            One idea is that the increased CO2 content in the atmosphere lead to the global increase in temperatures. Two effects of warming would be, a decline of the equator-to-pole temperature gradient and consequent decrease in oceanic circulation, together with the solubility of oxygen in warmer waters. This may have been responsible for marine anoxia (Wignall and Twitchett, 1996 Illustrated this for the Permian Trassic). This indeed could have been responsible for the huge marine extinctions seen at the end of the Triassic. The terrestrial extinctions could also have been linked to the changes in temperatures.

 

Windward induced circulation is a feature of all seaways.This contributes to poleward heat transport along any coastlines that cross latitude lines. This is due to atmospheric lows which  develop over water bodies in mid to high latitudes in the cooler months and drive circulation in a cyclonic direction. This proves an interesting theory for the increase in temperature of the climate that isn’t linked to CO2 levels produced by volcanism.

 

            It has also been shown that orbital forcing of climate can play a critical role in continental climate with extreme values of orbital parameters reducing the annual temperature range by 74%, resulting in cooler summers and warmer winters (Sloan and Morrill, 1998).

 

As explained earlier, the climate has maybe played a role in every mass extinction. Climate changes do not occur without reason. Something must trigger it whether it be a bolide impact, volcanism, or whatever. In the late Triassic, it is also possible that such an event may have triggered off radical changes that carried out through the Jurassic and can be seen by warmer temperatures, the melting of the poles and a marine transgression (lower sea levels).

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