plan 1.fluxes and why the mantle matters 2.earth’s buffer – ocean 3.earth’s buffer –...
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Plan
1. Fluxes and why the mantle matters
2. Earth’s buffer – ocean
3. Earth’s buffer – weathering
4. A question
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Mantle = 2.2 to 10 X 1023 moles C
Crust = 8.5 X 1021 moles C
2.2 X 1012 moles C/yr
Total mantle flux
Mid- ocean ridges ArcsPlumes/Oceanic Islands
1 X 1012 moles C/yr 0.2 X 1012 moles C/yr1 X 1012 moles C/yr
Total flux is1.6 X1012 but only 2020% is from mantle
Estimates summarized in Hayes and Waldbauer (2006) and Dasgupta and Hirschmann (2010)
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Crust = 8.5 X 1021 moles C
2.2 X 1012 moles C/yr
Total mantle flux
atmosphere = 7.2 X 1016 moles C
Fossil fuel and cement flux = 1016 to 1017
moles C/yr
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Crust = 8.5 X 1021 moles C
2.2 X 1012 moles C/yr
Total mantle flux
Arcs
1 X 1012 moles C/yr 0.2 X 1012 moles C/yr1 X 1012 moles C/yr
Total flux is1.6 X1012 but only 2020% is from mantle
Flux = 2.2 X 1012 moles C/yr
Crust = 8.5 X 1021 moles C
= 3.86 byr
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Crust = 8.5 X 1021 moles C
Age (byr)
4.0 0
0
8.5 X 1021 moles C
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Hayes and Waldbauer (2006)
Assumes higher early flux
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Current crustal inventory
Assumes higher early flux
Hayes and Waldbauer (2006)
1. High return flux
2. 3. Crustal inventory in 1 byr
3. Only takes 30,000 yrs to400 ppm in atm with current mantleflux (1012). Thus, crustal systemmust modulate perturbations
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Berner, 1999
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1) Open ocean carbonate: Ca2+ + 2HCO3- = CaCO3 + CO2 + H2O (Coccolithophores, forams) - mid Mesozoic revolution3) Shallow water – reefs – formation returns CO2 to atmosphere2) CCD buffer CO2 increase shallows – Ca increase deepens – e folding 10kyr
Ridgewell and Zeebe 2005 EPSL
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All ocean inorganic carbonate precipitation
Pre-biogenic carbonate - >500 myr
Higher saturation state
Ca++
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Shallow water biogenic carbonate Open ocean carbonate
CCD
Shallow water biogenic carbonate – 500 to mid Mesozoic
Ca++
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Shallow water biogenic carbonateOpen ocean biogenic carbonate
CCD
Open ocean biogenic carbonate – Mid Mesozoic to Recent
Ca++ Lower saturation state
CCD buffer
Ca++ + 2HCO3 = CaCO3 + CO2 + H2O.Reaction 1:
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StrangeloveNeritanCretan
Strangelove – supersaturation, abiotic,highly sensitive to perturbations
Neritan – biotic, less sensitive to perturbations, shallow environments
Cretan – Mid-Mesozoic revolution,Much less sensitive to perturbations,Full ocean deposition. Lower saturation
Ridgewell and Zeebe, 2005;Zeebe and Zeebe and Westbroek, 2003
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CO2 + H2O = CH2O + O2
Organic Burial
47% in ocean
53% land
P and N (nutrients)
sunlight
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Total carbon should be fixed and isotopiccomposition should vary dependent upon howmuch of each component through time
Increasein burial oforganic matter
Increasein inorganiccarbonate deposition
Mantle
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Compiled in Hayes and Waldbauer 2006
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Sageman et al., 2006, Geology
Ocean Anoxic Even 2
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Berner, 1999
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2 CO2 + H2O + CaSiO3 = 2 HCO3- + SiO2
Ca++ + 2 HCO3- = CaCO3 + 1 CO2 + H2O
Urey Reaction CO2 + CaSiO3 = CaCO3 + SiO2
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3. CO2 + H2O = CH2O + O2
Massive Organic Burial
P (nutrients)
0. LIP
Release CO2
1. Increased temp and hydrologic cycle2. Increased weathering
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Sageman et al., 2006, Geology
Ocean Anoxic Even 2
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Starts to collide at~40 myr
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Some of the worlds largest rivers drain theworlds largest mountain belt
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Steady State chemical
weathering
Waldbauer and Chamberlain, 2005
Hilley et al., 2010
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Chemical Weathering Model
Rate of mineral concentration (qi) change due to chemical weathering:
In steady state, composition of the weathering profile is constant:
In a state of steady uplift at a velocity u, z=ut where z=t=0 at the bottom of the weathering zone. Thus dz/dt=u and :
iiii qAkdt
dq−=
tz
q
dt
dzqAk
zt
q iiii
i ⎟⎠
⎞⎜⎝
⎛∂∂
−−==⎟⎠
⎞⎜⎝
⎛∂∂
0
⎥⎦
⎤⎢⎣
⎡−=u
zAkqzq iiii exp)( 0
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τ=Zu
⎥⎦
⎤⎢⎣
⎡⎟⎠
⎞⎜⎝
⎛−−==−= ∫ u
ZAkuqdzzqAk
dt
dqR iii
Z
iiii
i exp1)( 0
0
'
[ ])exp(10
ττ iii
i Akq
R −−=
Uplift and Effective Surface Age
The total chemical weathering rate is found by integrating over the depth of the weathering profile Z:
This result can be parameterized in terms of the ‘effective surface age’ t:
We define Ri=Ri’/Z (normalize to volume of weathering profile) and express the weathering rate as a function of effective surface age:
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10 mm/yr
5 m
.01 mm/yr
30 m
Active Collisional Orogene.g. New Zealand, Himalayas, Andes
u=10mm/yr Z=5mt=Z/u=500 years
Stable Tropical Cratone.g. Amazon, Congo Basins
u=.01mm/yr Z=30mt=Z/u=3,000,000 years
Effective Surface Age
Equivalent to residence time defined byAnderson et al., 2002
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Chemical Weathering Rate of Granitic Minerals
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Eastern SyntaxisHimalaya
Western SyntaxisHimalaya
New Zealand
Exposure of freshrock throughtectonic processesdominant control onchemical weathering
See also Riebe et al. 2001
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Hren et al., 2007
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Hren et al., 2009
Precipitation in Himalaya/Tibet
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Precip and erosion gradients
Zone 3 is Yarlung
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Problems in Approach
1. No hydrology
2. Little thermodynamics
3. Can runaway
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Uplift
Reactive flow paths
Two equations
1. Reactive transport
2. Erosion soil model
Maher and Chamberlain, 2014, Science
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Solute Production
Higher Dw higher solutes
Reactive flowpath length
Reaction rate andMaximum concentration
Fraction on freshMinerals in soil
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Mountains matter the most in climate regulation
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What is the optimal size ?