Plate Tectonic and climate
Summary
We have now finished the first part of the course on Plate Tectonics and their effect on
Climate. To summarize:
We have first discussed the Snowball Earth which we believed has occurred episodically
around 500 Ma ago. The first hypothesis that was believed to be responsible for the
snowball earth was the relative (latitudinal) position of the continent on earth during this
period – i.e. if land masses are mainly present at high latitude, then the potential for ice
sheet growth is high; the ice-albedo feedback can then take over. Evidence shows that
snowball earth may have occurred during times when the continents were not at high
latitude. Conversely snowball earth was not present at times when continents were near
the poles.
Climate records (e.g. delta 018) show a gradual cooling of the climate in the last 50 Ma
with sharper cooling trend at 46, 16 and 3 Ma. We discussed the effects of Plateau uplift
(Colorado and Tibetan) as a potential culprit for the gradual cooling/drying of the climate
during this period. These occurred in the last 40 Ma years and have led to more
meridionality in the atmospheric circulation and consequently sharper land ocean contrast
(colder/drier continental climates) in line with several proxies of fauna/flora. Around 3
Ma ago, several plate tectonic related events had an effect on the ocean circulation. These
include the Opening of the Drake Passage, the Partial Closing of the Indonesian
Throughflow, and the Closing of the Isthmus of Panama. Scher and Martin argued that
around 2-3 Ma ago, the Drake Passage opened. This led to more mixing in the Southern
Ocean, a more vigorous biological pump, less CO2 in the atmosphere and the beginning
of ice ages. Cane and Molnar on the other hand, argues for a partial closing of the
Indonesian throughflow, the subsequent cooling of the Indian Ocean, the drying of
African Climate; as well as a permanent El-Nino state, less heat transport to northern
Canada which would be responsible for the beginning of NH ice ages. Finally Haug and
Tiedemann argued that the closing of the Panama canal, would have strengthened the
Gulf Stream, warm up the northern North Atlantic, providing moisture to the high North
– a necessary conditions for glacial inception – the gradual change in obliquity would
have provided the necessary final ingredient for glacial inception.
In the second part of the course, we will talk about higher frequency climate change.
Those associated with changes in solar insolation (Milankovih forcing). This does not
mean that such high frequency changes in climate were not present earlier in the Earth’s
history – they were most likely present -, it is just that the temporal resolution of climate
record going far back in time does not allow us to resolve such climate changes. Also the
amount of records from that period is not as large.