Finishing Ruddiman s Chapter 5. Tectonics and Long-Term Climate Change
A 2cnd hypothesis that tries to explain how plate tectonics controls Earth s climate: Uplift-Weathering Hypothesis Maureen Raymo built on earlier ideas proposed by T.C. Chamberlain
Remember this? Vegetation enhances silicate weathering rates. (warmer temp., more water yields more veg. and more carbonic acid)
Geological disturbance enhances silicate weathering rates by disrupting the equilibrated soil carapace.
Uplift-Weathering Hypothesis Enhanced chemical weathering caused by increased mountain building is an active driver of climate change. The BLAG H asserts changing rates of sea-floor spreading change in CO 2 levels in the atmosphere. The Uplift-Weathering H asserts that mountainbuilding does it too.
Increase sea-floor spreading rate Increase subduction rate Increase CO 2 input into atmosphere
Increase sea-floor spreading rate Increase subduction rate Increase CO 2 input into atmosphere spins-up the silicateweathering drawdown of CO 2
rem: Hydrolysis of silicate minerals and precipitation of CaCO 3 in oceans accounts for 80% of ~2 Gt of C sequestered each year. Sicarbonic acid hydrolysis hydrogen ion bicarbonate CaCO 3, H+ HCO3- H 2 CO HCO3- SiO 2 3 HCO3-H+ Ca+ Wollastonite, a Ca-plagioclase silicate mineral sediment
decrease sea-floor spreading rate decline in subduction rate decline in CO 2 input into atmosphere spins-down the silicateweathering drawdown of ie, warming CO 2
Uplift-Weathering Hypothesis: add mountain building to plate-tectonic effects and the Si-mineral weathering process mountain building controls the supply of unweathered silicate minerals.
Uplift Weathering Hypothesis: global rate of chemical weathering (hence CO 2 levels) influenced by availability of fresh mineral surfaces for hydrolysis to attack.
Mountain ranges have always been with us, but great plateaus are anomalous events in geological time. The collision between India and Asia began ca. 55 mya Tibet This 1000 x 2500 km plateau is an oddity in geological time and probably greatly enhanced global, silicate mineral weathering rates.
Shigatse, Tibet Cretaceous Earth 145 65 mya By Pierre Dèzes 1999, "Tectonic and metamorphic Evolution of the Central Himalayan Domain in Southeast Zanskar (Kashmir, India)". Mémoires de Géologie (Lausanne) No. 32, ISSN 1015-3578
By Pierre Dèzes 1999, "Tectonic and metamorphic Evolution of the Central Himalayan Domain in Southeast Zanskar (Kashmir, India)". Mémoires de Géologie (Lausanne) No. 32, ISSN 1015-3578,
Much of eastern Asia affected by Himalayan orogeny
Laramide???? post- 50 mya Altiplano: mainly post-20 mya? thickness of the Earth's crust (km)
The power of comminution
Tectonic uplift enhances comminution and hence hydrolysis and CO 2 draw-down Increased mass movements Increased glaciation Increased corrasion of sediment
Chemical weathering rapidly (100 s yr) strips cations like Ca and Mg from minerals exposed by physical weathering inceptisol ultisol
Freshly shattered rocks produce most of the Ca+ needed for sequestering CO 2 within CaCO 3.
Most of the dissolved chemical load in Amazon originates in actively uplifting Andes, not in the vast, ancient, lowlands. Stallard and Edmond, 1983. Geochemistry of the Amazon.
Silicate-mineral weathering is both a climate forcing and a feedback.
Summary So far we have 3 interrelated hypotheses about processes that determine Earth s climate over time scales of millions to billions of years: 1)Polar Position 2)BLAG (seafloor-spreading rate) 3)Uplift Weathering
In the background of all 3 processes, the silicate-mineral-weathering mechanism acts as a thermostat.
Earth s Interior physics plate tectonics polar position polar ice sheets polar position hypothesis Earth s Climate
Earth s Interior physics plate tectonics, volcanism atmosphere s CO 2 conc. silicate-mineral weathering biological activity Earth s Climate
Earth s Interior physics plate tectonics, volcanism atmosphere s CO 2 conc. BLAG + Polar Position + Uplift-weathering mountain building silicate mineral weathering biological activity Earth s Climate
Finishing up Ruddiman s Chapter 5. Tectonics and Long-Term Climate Change
Thinking critically about geological controls over CO2 concentration in Earth s atmosphere: Si-Ca mineral metamorphism hydrolysis (chemical weathering) CaCO 3 sediment CO 2
metamorphism of carbonate sediment releases CO 2 CO 2 Si-Ca mineral metamorphism hydrolysis (chemical weathering) CaCO 3 sediment CO 2
CO 2 Si-Ca mineral metamorphism hydrolysis (chemical weathering) subduction orogeny CaCO 3 sediment CO 2
How do these compare? CO 2 Si-Ca mineral metamorphism hydrolysis (chemical weathering) subduction orogeny CaCO 3 sediment CO 2
Question #2. Aren t rates of sea-floor spreading and rates of mountain uplift intimately connected?