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GEOCHEMICAL CYCLES
-^ Most abundant elements: oxygen (in solid earth!), iron (core),silicon (mantle), hydrogen (oceans), nitrogen, carbon, sulfur… •^ The elemental composition of the Earth has remained essentiallyunchanged over its 4.5 Gyr history^ –^ Extraterrestrial inputs (e.g., from meteorites, cometarymaterial) have been relatively unimportant^ –^ Escape to space has been restricted by gravity •^ Biogeochemical cycling
of these elements between the different THE EARTH: ASSEMBLAGE OF ATOMS OF THE 92 NATURAL ELEMENTSreservoirs of the Earth system determines the composition of theEarth’s atmosphere and oceans, and the evolution of life
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BIOGEOCHEMICAL CYCLING OF ELEMENTS:examples of major processesPhysical exchange, redox chemistry, biochemistry are involved
Surfacereservoirs
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EVOLUTION OF O
AND O^2
IN EARTH’S ATMOSPHERE
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COMPARING THE ATMOSPHERESOF EARTH, VENUS, AND MARS
Venus^ Earth
Mars
Radius (km)^
Surface pressure (atm)
CO(mol/mol)^2
0.96^ 3x
-4^ 0.
N^ (mol/mol)^2
-2^ 3.4x 0.78^ 2.7x
O(mol/mol)^2
-5^ 6.9x 0.21^ 1.3x
H^ O (mol/mol)^2
-3^ 3x10 1x -2^ -4 3x^
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THE NITROGEN CYCLE: MAJOR PROCESSESATMOSPHERE^
N^2
NO HNO^3
+^ NH /NH 34
orgNBIOSPHERE LITHOSPHERE
combustionlightning
oxidation deposition
decayassimilation
denitri-fication nitrification biofixation burial^
weathering docsity.com
BOX MODEL OF THE NITROGEN CYCLEInventories in Tg N-1Flows in Tg N yr
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PRESENT-DAY GLOBAL BUDGETOF ATMOSPHERIC N
O 2
SOURCES (Tg N yr
-1^ )^
18 (7 – 37) Natural^
10 (5 – 16) Ocean^
3 (1 - 5) Tropical soils^
4 (3 – 6) Temperate soils
2 (1 – 4) Anthropogenic
8 (2 – 21) Agricultural soils
4 (1 – 15) Livestock^
2 (1 – 3) Industrial^
1 (1 – 2) -1SINK (Tg N yr ) Photolysis and oxidation instratosphere
12 (9 – 16) ACCUMULATION (Tg N yr
-1^ )^ 4 (3 – 5)
Although a closed budget can be constructed, uncertainties in sources are large!(N^ O atm mass = 5.13 10^2
18 kg x 3.1 10
-7^ x28/29 = 1535 Tg )
IPCC[2001] docsity.com
FAST OXYGEN CYCLE: ATMOSPHERE-BIOSPHERE • Source of O
: photosynthesis 2 nCO+ nH^ O^2
(CH^ O)^2
+ nOn 2
-^ Sink: respiration/decay
(CH^ O)+ nO^2 n^
nCO 2
+ nH^ O 2 2 O 2
CO^2 orgC
orgClitter
Photosynthesisless respiration
Olifetime: 6000 years^2 decay
vs Photosynthesis ~200 PgO/yr (^6) 1.2x10 Pg (^3) 4x10 Pg (^2) 8x10 Pg
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SLOW OXYGEN CYCLE: ATMOSPHERE-LITHOSPHERE
COO 2
2 Compressionsubduction
CONTINENTUplift
OCEAN
weatheringorgCFeS^2
runoffFeO 23 H SO 24
O^2
PhotosynthesisdecayCO^2 orgC
burial SEDIMENTS
CO^2 microbesFeS^ orgC^2
(^7) orgC: 1x10 Pg C (^6) FeS: 5x10 Pg S 2
(^6) O: 1.2x10 Pg O 2
Olifetime: 3 million years^2
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ANTARCTIC ICE CORE RECORD OF TEMPERATURE AND CO
2 docsity.com
Arrows indicateEl Nino events
Atmospheric increase is ~50% of fossil fuel emissions but with largeinterannual variability
INTERANNUAL TREND IN CO
INCREASE 2 1 ppm = 2.1 Pg C
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The heavier temperature lines 160,000 BP to present reflect more data points, not necessarily greater variability. Source: Climate and Atmospheric History of the past 420,000 years from the Vostok Ice Core, Antarctica
, by Petit
J.R., Jouzel J., Raynaud D., Barkov N.I., Barnola J.M., Basile I., Bender M., Chappellaz J., Davis J. Delaygue G.,Delmotte M. Kotlyakov V.M., Legrand M., Lipenkov V.M., Lorius C., Pépin L., Ritz C., Saltzman E., Stievenard M.,Nature, 3 June 1999.
Antarctic Ice Core Data
COvaries over geologic time, within the range 190 – 280 ppm for the last^2 420,000 years. The variations correlate with climate: cold
^ low CO^2
.^ Is
COdriving climate or vice versa?^2
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GLOBAL PREINDUSTRIAL CARBON CYCLE
Inventories in Pg CFlows in Pg C a
-
6 8 PgC/yr
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