Yes, I gave you a bum steer referring to grasses. What I should have
said was that the evolution of the C4 pathway could have been the
cause or a contributing factor leading to the current Pliestocene ice
age.
http://en.wikipedia.org/wiki/C4_carbon_fixation
But the from what it says in Wikipedia, C4 fixation did not start
until the Oligocene, and so could not be responsible for its
initiation.
So you are probably correct. The opening of Drakes Passage caused a
change in both oceanic and atmospheric circulation allowing ice to
form on Antarctica. The cooling there from the ice albedo effect would
result in the formation of sea ice around its coast. The sea ice
extracts fresher water from the ocean and the remaining cold saltier
water is denser and sinks. Being colder it dissolves more CO2 removing
it from the atmosphere.
It was only later when the C$ plants had really developed and the
Isthmus of Panama closed 3 Ma ago, that the ice sheets could form in
the northern hemisphere, and the real ice age began.
Cheers, Alastair.
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