MET 112 Global Climate Change - Lecture 9 The Carbon Cycle Dr. Craig Clements San José State University

Goals  We want to understand the difference between short term and long term carbon cycle  We want to understand the main components of the long term carbon cycle

The Earth’s history can be characterized by different geologic events or eras.

An Earth System Perspective  Earth composed of: –Atmosphere –Hydrosphere –Cryosphere –Land Surfaces –Biosphere  These ‘Machines’ run the Earth

Hydrosphere  Component comprising all liquid water – Surface and subterranean (ground water)  Fresh/Salt water  Thus…lakes, streams, rivers, oceans…  Oceans: –Oceans currently cover ~ 70% of earth –Average depth of oceans: 3.5 km –Oceans store large amount of energy –Oceans dissolve carbon dioxide (more later) –Circulation driven by wind systems –Sea Level has varied significantly over Earth’s history –Slow to heat up and cool down

Land Surfaces  Continents  Soils surfaces and vegetation  Volcanoes  Climate: –Location of continents controls ocean/atmosphere circulations –Volcanoes return CO 2 to atmosphere –Volcanic aerosols affect climate

Biosphere  All living organisms; (Biota)  Biota- "The living plants and animals of a region.“ or "The sum total of all organisms alive today” –Marine –Terrestrial  Climate:  Photosynthetic process store significant amount of carbon (from CO 2 )

The Earth’s history can be characterized by different geologic events or eras.

Interactions  Components of the Earth System are linked by various exchanges including  Energy  Water (previous example)  Carbon  In this lecture, we are going to focus on the exchange of Carbon within the Earth System

Carbon: what is it?  Carbon (C), the fourth most abundant element in the Universe,  Building block of life. –from fossil fuels and DNA –Carbon cycles through the land (bioshpere), ocean, atmosphere, and the Earth’s interior  Carbon found –in all living things –in the atmosphere –in the layers of limestone sediment on the ocean floor –in fossil fuels like coal

Carbon: where is it?  Exists: – Atmosphere: –CO 2 and CH 4 (to lesser extent) –Living biota (plants/animals) –Carbon –Soils and Detritus –Carbon –Methane –Oceans –Dissolved CO 2 –Most carbon in the deep ocean

Carbon conservation  Initial carbon present during Earth’s formation  Carbon doesn’t increase or decrease globally  Carbon is exchanged between different components of Earth System.

The Carbon Cycle  The complex series of reactions by which carbon passes through the Earth's –Atmosphere –Land (biosphere and Earth’s crust) –Oceans  Carbon is exchanged in the earth system at all time scales -Long term cycle (hundreds to millions of years) -Short term cycle (from seconds to a few years)

The carbon cycle has different speeds Short Term Carbon Cycle Long Term Carbon Cycle

Short Term Carbon Cycle  One example of the short term carbon cycle involves plants  Photosynthesis: is the conversion of carbon dioxide and water into a sugar called glucose (carbohydrate) using sunlight energy. Oxygen is produced as a waste product.  Plants require  Sunlight, water and carbon, (from CO 2 in atmosphere or ocean) to produce carbohydrates (food) to grow.  When plants decay, carbon is mostly returned to the atmosphere (respiration)  Global CO2

Short Term Carbon Cycle  One example of the short term carbon cycle involves plants  Photosynthesis: is the conversion of carbon dioxide and water into a sugar called glucose (carbohydrate) using sunlight energy. Oxygen is produced as a waste product.  Plants require  Sunlight, water and carbon, (from CO 2 in atmosphere or ocean) to produce carbohydrates (food) to grow.  When plants decay, carbon is mostly returned to the atmosphere (respiration)  During spring: (more photosynthesis)  atmospheric CO 2 levels go down (slightly)  During fall: (more respiration)  atmospheric CO 2 levels go up (slightly)

Carbon exchange (short term)  Other examples of short term carbon exchanges include:  Soils and Detritus: -organic matter decays and releases carbon  Surface Oceans –absorb CO2 via photosynthesis –also release CO2

Short Term Carbon Exchanges

How do we measure the short-term CO 2 cycle? –To determine the ecosystem exchange of CO2 we must measure the flux of CO2 between the biosphere and atmosphere. –These measurements are routine and there is a network of stations that measure CO2 fluxes around the world.

How do we measure the short-term CO 2 cycle? –Ecosystems ‘breathe’ CO2 in and out. –To determine the ecosystem exchange of CO2 we must measure the flux of CO2 between the biosphere and atmosphere. –These measurements are routine and there is a network of stations that measure CO2 fluxes around the world.

CO 2 Flux: Ecosystem ‘Breathing’ CO 2 Exchange

CO 2 Flux: Ecosystem ‘Breathing’ Fast, 3-D Anemometer Fast, CO 2 sensor (ms -1 ) (mg m -3 )

CO 2 Flux: Ecosystem ‘Breathing’ CO 2 Flux: CO 2 ( ρ ) concentration Vertical Velocity perturbation (w’) Flux = Eddy Covariance To measure: Need fast velocity and CO2 measurements! =(ms -1 ) x (mg m -3 ) =mg m -2 s -1

CO 2 Flux: Ecosystem ‘Breathing’ H.P. Schmid (2000)

Long Term Carbon Cycle  Carbon is slowly and continuously being transported around our earth system. –Between atmosphere/ocean/biosphere –And the Earth’s crust (rocks like limestone)  The main components to the long term carbon cycle:

Where is most of the carbon today?  Most Carbon is ‘locked’ away in the earth’s crust (i.e. rocks) as –Carbonates (containing carbon)  Limestone is mainly made of calcium carbonate (CaCO 3 )  Carbonates are formed by a complex geochemical process called: –Silicate-to-Carbonate Conversion (long term carbon cycle)

Silicate to carbonate conversion – chemical weathering One component of the long term carbon cycle

Granite (A Silicate Rock)

Limestone (A Carbonate Rock)

Silicate-to-Carbonate Conversion 1.Chemical Weathering Phase CO 2 + rainwater  carbonic acid Carbonic acid dissolves silicate rock 2.Transport Phase Solution products transported to ocean by rivers 3.Formation Phase In oceans, calcium carbonate precipitates out of solution and settles to the bottom

Silicate-to-Carbonate Conversion Rain 1. CO 2 Dissolves in Rainwater 2. Acid Dissolves Silicates ( carbonic acid) 3. Dissolved Material Transported to Oceans 4. CaCO 3 Forms in Ocean and Settles to the Bottom Calcium carbonate Land

Changes in chemical weathering  The process is temperature dependant: –rate of evaporation of water is temperature dependant –so, increasing temperature increases weathering (more water vapor, more clouds, more rain)  Thus as CO 2 in the atmosphere rises, the planet warms. Evaporation increases, thus the flow of carbon into the rock cycle increases removing CO 2 from the atmosphere and lowering the planet’s temperature –Negative feedback

Earth vs. Venus  The amount of carbon in carbonate minerals (e.g., limestone) is approximately – the same as the amount of carbon in Venus’ atmosphere  On Earth, most of the CO 2 produced is –now “locked up” in the carbonates  On Venus, the silicate-to-carbonate conversion process apparently never took place

Subjuction/Volcanism Another Component of the Long-Term Carbon Cycle

Subduction Definition: The process of the ocean plate descending beneath the continental plate. During this processes, extreme heat and pressure convert carbonate rocks eventually into CO 2

Volcanic Eruption Mt. Pinatubo (June 15, 1991) Eruption injected (Mt – megatons) 17 Mt SO 2, 42 Mt CO 2, 3 Mt Cl, 491 Mt H 2 O Can inject large amounts of CO 2 into the atmosphere

Organic Carbon Burial/Oxidation of Buried Carbon Another Component of the Long-Term Carbon Cycle

Buried organic carbon (1)  Living plants remove CO 2 from the atmosphere by the process of –photosynthesis  When dead plants decay, the CO 2 is put back into the atmosphere –fairly quickly when the carbon in the plants is oxidized  However, some carbon escapes oxidation when it is covered up by sediments

Organic Carbon Burial Process CO 2 Removed by Photo- Synthesis CO 2 Put Into Atmosphere by Decay C C O2O2 Some Carbon escapes oxidation C Result: Carbon into land

Oxidation of Buried Organic Carbon  Eventually, buried organic carbon may be exposed by erosion  The carbon is then oxidized to CO 2

Oxidation of Buried Organic Carbon Atmosphere Buried Carbon (e.g., coal)

Oxidation of Buried Organic Carbon Atmosphere Buried Carbon (e.g., coal) Erosion

Oxidation of Buried Organic Carbon Atmosphere Buried Carbon O2O2 CO 2 C Result: Carbon into atmosphere (CO 2 )

The (Almost) Complete Long-Term Carbon Cycle  Inorganic Component –Silicate-to-Carbonate Conversion –Subduction/Volcanism  Organic Component –Organic Carbon Burial –Oxidation of Buried Organic Carbon