The carbon cycle

T7 - Carbon

the carbon cycle - components

• closed system - no inputs/outputs

• stores - carbon is held

• fluxes - flows of carbon between different stores

• processes - the ways carbon fluxes happen

how are carbon stores measured

pentagrams of carbon - PgC

carbon stores

• hydrosphere - 38,000PgC - dissolved CO2 in water

• lithosphere - 100,000PgC - rocks like carbonate and FF

• biosphere - 2,000PgC - animals and plants

• atmosphere - 750PgC - gases like CO2

the carbon cycle

the natural process where carbon atoms circulate through the earths atmosphere, land and oceans in a cycle

biochemical carbon stores

• terrestrial

• organisms

• oceans

• atmosphere

biochemical carbon stores - terrestrial

• carbon is in every living organism

• when organisms decay - converted into other stores in soil

• some carbon stored in mantle - converted into atmospheric carbon via out-gassing of volcanos (let out CO2 during eruptions)

biochemical carbon stores - organisms

• phtoosythesis - removes CO2 from atmosphere

• respiration - releases CO2

• decomposition - release CO2 into soil when organisms die

• combustion - burning of biomass/FF releases CO2 into atmosphere

biochemical carbon stores - oceans

• organic matter falls to ocean bed after death

• compressed into sedimentary rock

• can form crude oil and natural gas

biochemical carbon stores - atmosphere

• CO2 stored as gas in atmosphere

• carbon can mix with water vapour - leaves atmosphere (falls in precipitation as carbonic acid)

geological carbon stores

• coal

• limestone

• crude oil

• natural gas

geological carbon stores - natural gas (formation)

• e.g. methane (CH4) - by product of coal/crude oil formation

• trapped within sedimentary layers

geological carbon stores - crude oil (formation)

• fine sediments settle with biological degraded material

• anaerobic reactions turn most pot the organic carbon to liquid

• forms oil - may migrate upwards through permeable rock - trapped by impermeable rock

geological carbon stores - limestone (formation)

• aquatic organism with calcium carbonate shells die

• sink to bottom of ocean, compacted by sediment falling on top

• pressure and chemical reactions cause cementation

• forms limestone

geological carbon stores - coal (formation)

• formed on land

• plants die, enter swamps

• settle and compact

• forms peat and coal

geological processes that release carbon

• chemical weathering

• volcanic out gassing

geological processes that release carbon - out gassing

• extreme heat from tectonic processes - sedimentary rock undergoes changes

• causes CO2 release into atmosphere

• common in geothermal locations e.g. New Zealand

geological processes that release carbon - chemical weathering

• wearing away of rock my chemical reactions

• material dissolves by solution, hydrolysis and oxidation

• carbonic acid rain forms (from co2 and water in the atmosphere)

• can dissolve carbon rich rocks - forms calcium carbonate

• materials transported down rivers, into sea, make sed rock

carbon in the food chain

• primary producers

• respiration

• consumers

• decomposers

carbon in the food chain - decomposers

• consume dead organic matter

• return carbon to atmosphere through respiration

carbon in the food chain - consumers

• eat organisms below them in the food chain

• primary consumers = first to eat producers

• return some carbon to atmosphere through respiration

carbon in the food chain - producers

• make energy through photosynthesis

• plants sequester CO2 to produce energy

biological carbon pump - 1. photosynthesis

• phytoplankton take CO2 from atmosphere by photosynthesis

• sequester CO2 and build calcium carbonate shells - becomes biological carbon

• phytoplankton consumed by other organisms (zooplankton)

• consumers respire and return some carbon to atmosphere

biological carbon pump - 2. carbonate sinks

• phytoplankton/aquatic organisms die and sink

• accumulate as sediment - become sed. rock

• can be decomposed by bacteria - returns carbon to sea as dissolved carbon

carbon pump

the process of carbon entering and moving around the ocean

• oceans act as a store for carbon - reducing atmospheric CO2 levels

• temp changes can change thermohaline circulation - can alter carbon pump

dead organic matter - biological carbon - examples

• tundra soils

• soils

• mangroves

dead organic matter - biological carbon - tundra

• soil contains ancient carbon - permafrost - microbe activity that decays soil is stopped

• only decayed when surface thaws

• large carbon stores

dead organic matter - biological carbon - mangroves

• sequester 1.5 tonnes of carbon per hectare annually

• layers of litter, humus and peat - over 10% carbon

• submerged by tidal water - soils are anaerobic

• biological decomposers cant survive without oxygen

• breakdown of material takes much longer

dead organic matter - biological carbon - soils

• dead organic matter in soils contains biological carbon

• can be returned when decomposed by decomposers

• rate of return dependent on temp and climate

• deforestation, land sue change = speeds process

natural greenhouse effect - purpose

keeps the earth at the optimum temperature to support life

greenhouse gases

gases that lead to the greenhouse effect

• methane (MH4) and CO2

• naturally emitted through respiration

natural greenhouse effect - process

• solar radiation enters atmosphere, passes through GG layer

• radiation mostly absorbed by surface, some is reflected

• reflected radiation reenters space

• GG layer blankets earth - stops too much radiation leaving atmosphere

• allows earth to be high enough temp for life

enhanced greenhouse effect

• humans inc. amount of GG in atmosphere

• adds to the blanket layer in the atmosphere

• more radiation reflected that leaving atmosphere

• warmer temperatures occur

impacts of the greenhouse effect

• temperature distribution

• precipitation distribution

• the albedo effect

the albedo effect

the effect where the colour of the earths surface impacts how much radiation is absorbed

impacts of greenhouse effect - albedo effect

• glaciers/ice caps = white snow, reflects the majority of heat

• oceans/forests = dark, absorb heat

• heat is redistributed by air circulation and ocean currents

impacts of greenhouse effect - precipitation distribution

• heating of earth leads to warm air rising, condensing into clouds

• equator = intense radiation - lot of air rises, high rainfall

• 30N/S = air cools and sinks, high pressure, rainfall rare

• 60N/S = different air masses meet, frontal rainfall

• poles = cold, air sinks, little rainfall

impacts of greenhouse effect - temperature distribution

• different amount of solar energy around world

• angle of sun rays = equator receives most conc. radiation

• poles = radiation dispersed over larger distance

atmospheric regualtion - role of photosythesis

• phytoplankton seq. 5-15Gt carbon annually

• primary producers seq. 100-120Gt

• tropical rainforests seq. 2200Gt per m³

• arctic sea melt - increasing - ocean exposed to sun longer = algal bloom

• algae seq. CO2 but alters ecosystems

atmospheric regulation - seasonal change

• winter = cooler, less sun - less photosynthesis - less CO2 seq. by plants

• so higher carbon storage in summer

• CC = shorter winters - less CO2 release

atmospheric regulation - soil health

• amount stored in soil varies = size of store, total input (litter/waste), total output (uptake by plants, erosion)

• healthy soil = more carbon, dark colour

when are FF combusted

• oil - in petrol, by cars

• natural gas - heats stoves to cook

• releases CO2 when combusted

carbon cycle - balance

• in equilibrium between stores and sinks

• since industrialisations (1800s in uk) FF combustion has inc.

• conc. of atmospheric CO2 has increased

• linked to inc. in global temps - due to G effect

higher atmospheric CO2 - impact on climate

• inc. temps

• E/N Europe - warmer winter, inc. precip

• S Europe - warmer summer, dec. precipitation- less water availability, inc. drought/forest fire risk

higher atmospheric CO2 - extreme weather

• more extreme events

• surface of sea - likely to reach 27"‘C for 3 weeks = more chance

• more likely tropical storms - more intense, over larger area

arctic amplification

the artic is warming at twice the rate than other areas

artic amplification - snow changes

• cover reducing - more melting

• reduced albedo effect - more solar absorption - worsens temp inc.

• devastates the ecosystem

artic amplification - permafrost

• warm temps thaws permafrost - releases stored GGs

• leads to more GHGs, impacts greenhouse effect

• this rises temps. causes more melting

• possibility of vegetation growing - can store carbon by photosynthesis

global warming - effects on hydrological cycle - precipitation

• if precipitation fall as rain, not winter snow = winter floods

• summer drought/forest fires - inc. in chance

global warming - effects on hydrological cycle - glaciers

• glaciers retreat as they melt - inc. in river discharge and sediment, until glaciers are gone

• European countries recover glacier meltwater in summer (from alpine glaciers)

• may be no ice in eastern alps by 2100

• will effect river discharge

geological carbon

stored in sedimentary carbonate rocks

• limestone and chalk

• in the oceans

biological carbon

• shale, coal

• other sedimentary rocks

forms of carbon

• inorganic - in rocks as bicabonates/carbonates

• organic - in plant material

• gaseous - as CO2, methane and CO (carbon monoxide)

carbon fluxes - time variations

• some are fast - photosynthesis and respiration release

• controlled by sunlight, respiration and moisture

• organic material in soil - may take years to be broken down

• some organic material - not decayed - transformed into sedimentary rock

radiative forcing effect

measure of energy balance

• the results of change to an agent e.g. GHGs and its ability to effect global energy balance and contribute to CC

primary productivity

the rate at which plants produce biomass from photosynthesis

• high in tropical rainforests (high humidity and temp)

• low in cold/dry - slower growth

net primary productivity

the amount of biomass produced by plants minus the energy lost through respiration

2 possible carbon pathways

negative feedback

• shrubs invade arctic, store more carbon that is being released

• short term balance

positive feedback

• decomposition of plants in wet soil releases more GHGs

• increases global warming, more melting - more decomposition