Lesson 1 Topic - 5

Carbon in the System

Carbon reservoirs

Atmosphere

Solid Earth

Ocean Land Surface

750 Gton C(CO2)

How does the size of each carbon reservoir respond to perturbations?

Soils: 1580 GtonVegetation: 610 GTon39,800 Gton

99.9% of all C!!!20% of this is Organic80% is CaCO3

CaSiO3 (s)+ CO2 (g) = CaCO3 (s) + SiO2 (aq)

Net result of silicate weathering

CaSiO3 (s)+ 2H2CO3(aq) = Ca+2 + 2HCO3(aq)

+ SiO2 (aq) +H2O

Ca+2 + 2HCO3(aq) = CaCO3 (s)+ H2CO3(aq)

CO2 (g)+ H2O(l) = H2CO3(aq)

Carbonate metamorphism (reverse of silicate weathering)

CaCO3 (s)+ SiO2 (s) = CaSiO3 (s)(wollastonite) + CO2 (g)

Carbonate-silicate cycle

Urey Reaction

CaSiO3+ CO2 = CaCO3 + SiO2 Igneous Rock Frozen lava/magma At high temperature Deep earth CO2 goes to gas

form Wants all the CO2 in

atmosphere

Sedimentary Rock Limestone & sand Prefers the low

temperatures at surface

Wants low concentrations of CO2 (PCO2 10 ppm)

Natural atmosphere = 280 ppm

Rate of CO2 going into atmosphere is a driver of the Carbon Cycle

Rate of weathering dependent on the rainfall as it dissolves Rock + CO2 into water.

Therefore depends on Temperature which depends on CO2 concentration

Organic Carbon

CO2 + H2O + Energy CH2O + O2Photosynthesis

Organic Carbon

Reverse of this is Respiration

Diatom with sliceous test (50mm diameter)

Coccolithoforid with calcite test(10mm diameter)

Primary producers in the seaphytoplankton (upper 100m in photic zone)

Foraminifera with calcite test (600mm diameter)

Radiolarian with siliceous test (50mm diameter)

Planktonic consumers in the seazooplankton

Organic Carbon in the Ocean

Primary production of organic C in surface waters oxidation of organic C in deeper waters

Settling organic particles by-pass fluid advection

Balanced by upwelling

Buffer Reaction

32232

233

332

3222

2HCOOHCOCO

COHHCOHCOHCOHCOHOHCO

Le Chateliers Principle

Overall Reaction

CO2 in the air sees [CO2] in the water. When CO2 in the air increases, some of

the CO2 in the water is taken away as is CO32- hiding it as HCO3- allowing more CO2 to dissolve.

What happens when CO32- is depleted? Low CO32- causes CaCO3 to dissolve so

CaCO3 Ca2+ + CO32- Where is the CaCO3 coming from?

32232 2HCOOHCOCO

So how much CO2 can the Oceans take up?

Current(?) CO2 budget (in 2007) Volcanoes: 0.1 Gton C per year Deforestation: 2 Gton C per year Fossil Fuel: 7 Gton C per year What is it now?

Atmospheric CO2 changing at ~2ppm per year = 4 Gton C per year

Where is the rest of the 5 Gton C per year? Oceans are taking up 2.5 Gton C per year By default the remaining 2.5 Gton C must be

going into the Land!

Observed CO2 Changes

Source: Scripps CO2 Program

CO2 Annual Cycle

CO2 Anomalies

Seasonal fluctuation in mospheric CO2 at Mauna Loa

OrganicCcycle(LongTerm)

GeologicalprocessescontrolatmosphericCO2 onlongertimescales0.1%ofmarineproductivityleaksintolongtermgeologicstorageThisleakcontrolstheO2 contentoftheatmosphere

CO2 +H2O= CH2O+ O2OrganicCinsedimentaryrocksisthelargestreservoironearth(108 Gtons)Residencetimeis200Ma

Carbon Cycle

Processes & Time-scales