Time scale of climate change

Rates of forcing vs. response

Zachos et al., )Benthic foram  18 O tracks deep ocean T and ice volume…. 2)Uses “global” benthic foram  18 O data set from >40 odp sites 3)Total  18 O since 65 Ma = 5.4 o / oo (if T alone = 22°C) 4)  18 O from 51Ma to 34 Ma = 3 o / oo (T drop of up to 12°C through 34 Ma) then a precipitous 1 o / oo increase in  18 O at 34 Ma that is about 60 to 90% ice build-up with the remainder a further decrease in bottom water T. 5)This event appears to correspond to the sudden buildup of a permanent Antarctic ice sheet……probably temperate in nature. The trigger appears to have been the opening of the Tasman/Antarctic gateway. 6)Antarctica ~50% modern ice volume until 26 Ma 7)“Warmer” from 26 Ma until about 15 Ma when “cooling” and Antarctic ice growth began again. Trigger? Not obvious….perhaps pCO 2 ? 8)General cooling through Mio/Plio boundary, when West Antarctic ice growth was inferred – triggered by Panama seaway closure? 9)“Subtle warming” at about 3.2 Ma in the Pliocene, then continued cooling and  18 O increase associated with growth of the northern hemisphere ice sheets.

Soft collision of India w/ S. Tibet----- Hard collision of India w/ Eurasia----- Opening of Antarctic gateways Closure of SE Asia deep passage----- Closure of Panama deep passage----- Africa moving northward

(2001)

Naish et al., 2001

Pearson and Palmer, 2000