carbon cycle

Question 1

What are the 3 types of stores?

Answer 1

Terrestrial, oceanic, atmospheric

Question 2

What are the 6 important fluxes and stores in the geological carbon cycle?

Answer 2

1) terrestrial carbon held within the mantle is released into the atmosphere as CO2- outgassing

2)Co2 within the atmosphere combines with rainfall to produce a weak acid that dizzolves carbon-rich rocks, releasing bicarbonates, this is chemical weathering

3) rivers transport weathered carbon and CA sediments to the oceans where they are deposited.

4)Carbon in organic matter from plants and animal shells and skeletons sink to ocean bed building up strata of coal

5)Carbon rich rocks are subducted along plate boundries and emerge again as volcanoes erupt.

6)presence of intense heating along subduction plate boundries metamorphoses sedimentary rocks by creating metamorphic rock releasing CO2

Question 3

How much CO2 did EFG emit in 2010?

Answer 3

Emitted between 150,000 and 300,000 tonnes of Co2 per day- same a portragal but contributed less than 0.3% of global emissions of GHG in 2010.

Question 4

What is the bio-geochemical carbon cycle?

Answer 4

Involves 4 main processes; photosynthesis, respiration, combustion and decomposition- co2 released into soil or deposited on sea floor.

Question 5

What are the 3 forms of carbon?

Answer 5

inorganic- rocks such as bicarbonate
organic- found in plant material
gaseous- found as co2 and CH4 and CO

Question 6

How much pentagrams of carbon do oceans, earths crust atmosphere and soils store?

Answer 6

Atmosphere- 750pg
earths crust- 100,000,000pg
oceans- 38,000pg
soils-1500pg

Question 7

How much of CO2 produced goes into different stores?

Answer 7

15-20% of co2 goes into biosphere, 55% of co2 goes into the atmosphere, 25% to 30% of Co2 goes into the ocean.

Question 8

What is the biological carbon pump?

Answer 8

transfers 4 to 15 gt of carbon from the atmosphere to the deep ocean as showed. Oceans surface layer contain tiny phytoplankton containing cholorphyll and absrbong sunlight to live. Also have shells and sequester CO2 through photosynthesis creating calcuim carbonate as their shells develop. When die thse carbon rich orgnisms sink to ocean floor accumulating as sediment. Particular proccess known as carbonate pump and is part of the biological carbon pump . Pumps co2 out of atmosphere into the ocean store. Without contributions of phytoplankton, co2 conc in atmosphere would be far higher than it already is.

Question 9

what threats are there to the biological carbon pump?

Answer 9

Naturally efficent system wbut also fragile. Phytoplankton require nutrients in vast quantities and existing ocean temps and currents maintain a constant supply, recycling of particles deep by upwelling i critical. Global movement of water through thermoshaline circulation maintains pump. However, slight changes in water temp can alter the flow. pollution and turbulance also reduce light penetration and slow pump. Each of these factors vulnerable to CC- making risk of pump breaking down real.

Question 10

How does the thermohaline circulation work?

Answer 10

> water in the far north atlantic is cold and very saline making it denser and heavier causing it to sink.

> by sinking it draws warmer water in from the ocean surface above. This, in turn draws water from the tropics

> Eventually, this movement from the tropics draws cold water up from the ocean bottom, ready to be warmed again.

Question 11

Is the gulf stream failing?

Answer 11

During 2004 gluf stream paused for 10 days. Data showed that current slowing with soeed if ocean circ between the gulf of mexico and europe had slowed by 30% since 2000. Hypothesis:

> Melting Arctic ice was increasing the amount of freshwater entering the North Atlantic

> Oceans salinity declining as a result, preventing cold water from sinking

> Meant there was nowhere for the warm waters of the gulf stream to go- north atlantic losing pulling effect.
Slowed by 6million tonnes of water per second over 12 years

Question 12

What is the role of trees in the carbon cycle?

Answer 12

Growth of vegetation depends on water, nutrients and sunlight. 95% of a trees biomass made up of Co2 that it sequesters and converts into cellulose Carbon fixation turns co2 into living organic compounds. Amount of carbon stored within a tree, woodland or forest depends on the balance between photosynthesis and respiration.

Question 13

what is the role of mangroves?

Answer 13

Biological carbon stored in soils in the form of dead organic matter or returned back to the atmosphere as a result of decomposition. Depending on the nature of the soil this proccess can be relatively quick or in tundra very slow. But deforestation and land use changes release these stores very rapidly as mangroves show;

Mangrove forests are found aling tropical and sub-tropical tidal coasts in africa, australia, asia and the americas. They are vital processors sequestering 1.5 metric tonnes of carbon per hectare each year mangrove soils consist of thick organic layers of litter,humus and peat containing high levels of carbon- over 10%.

Soils are anaeorbic as they can survive without oxygen. Bacteria and microbes dont survive without O2 so decomposition of plant matter is slow. As a result,little of the carbon can be respired back into the atmosphere, and the store remains intact. Any plant matter trapped by the tree roots tend to stay as it decomposes slowly stored for 1000s of years

however if they are cleared carbon released back into the atm. Throughout trop world mangroves cleared for tourism, shrimp farms and aquaculture. If just 2% of mangroves lost carbon released 50x natural sequestration rate.

Question 14

What role to tundra soils play in the carbon cycle?

Answer 14

Much of soil in tundra regions are permanently frozen and contain ancient carbon. Microbe activity is only active in surface layer of soil when it thaws. The rest of the time the roots and dead and decayed organic matter frozen, locking in any carbon into an icy store. Tundra soils contain carbon that has been trapped for hundreds of thousands of years.

Question 15

What is the role of tropical rainforests as carbon stores?

Answer 15

Huge carbon sinks, but fragile. Carbon mainly stored in trees,plant litter and dead wood. Soils are relatively thin and lacking in nutients as litter layer covers them, though very deep, decompose rapidly and nutrients released are rapidly consumed by vegetation.

As litter and dead wood decay, recycled so quickly that a soil store does not develop. Even carbon goven off by decomposers is rapidly recycled. Tropical forests absorb more atm co2 than any other biome, accounting for 30% of net primary production covering just 17% of earths surface. If they died off earth would lose a massive carbon sink.

Question 16

What is the natural greenhouse effect?

Answer 16

sun is the natural driver of almost all the earths atmospheric energy. Energy is recieved as incoming solar radiation for sun. Dark surfaces absorb this radiation and radiate it back as heat. However, insufficent for life on earth and GHG such as CO2 and CH4 into the atmosphere. absorb and refelct beack radiated heat from earths surface retaining heat and keep earth 16C warmer allowing for life on earth.

Question 17

What are the 4 main greenhouse gases?

Answer 17

CO2-89% of GHG increased by 30% since 1850

CH4-7% of GHG, 21x more powerful than CO2 increased by 250 % since 1850

N20- 3% of GHG producesd, 250X more powerful, 16% increase since 1850

Halocarbons- 1% of GHG produced, 300x more powerful and not natural.

Question 18

What is the enhanced greenhouse gas effect?

Answer 18

Concentration of several GHG in the atmosphere have increased by 25% since 1750, when industrialisation began in the UK, and now are increasing faster than ever. Since 1980s 75% of CO2 emissions come from burning of fossil fuels. This had led to the enhanced GHG effect.

Human activities such as burning fossil fuels and deforestation release natural stores of carbon and nitrogen which combine with oxygen to form GHG;
Carbon combines with oxygen to form CO2, nitrogen combines with oxygen to form N20 Increased water vapour caused by more evapotranspiration has lead to increased cloud cover trapping heat in the atmosphere.

Question 19

How does the enhanced GHG effect affect temperature and precipitation?

Answer 19

> the amount of solar energy reaching the earths surface varies at different locations which in turn influences temperature. Angle of the suns rays make solar radiation intense at the equator but dispersed over a wider area at the poles. Different characteristics of earths surface (albedo) affect refelction/absorption. Heat is redistibuted around the globe by air movement caused by pressure differences and ocean currents.

> precipitation heating of earths atmosphere and surface controls temperature,pressure, movement and moisture content of air. Warm air rises and cools, leading to water vapour & clouds

> Because solar radiation is most intense over the equator, convection and low pressure systems dominate there so rainfall is high all year.

> As air pressure rises around 30 degrees N & S of the equator precip decreases

> in mid latitudes air masses of dif characteristics meet and low pressure systems bring rain

> Nearer the poles, precipitation falls as the air cools further and is dense and dry creating polar deserts.

Question 20

What is photosynthesis role in regulating the atmosphere?

Answer 20

Phytoplankton in oceans sequester CO2 through the process of photosynthesis- form atm to ocean- biological carbon pump and proccesses transfer 5-15 Gt of carbon from atm to ocean.

Terrestrail photosynthesis enables plants to sequester 100-120Gt of CO2 per year. Then released back into atm through respiration and decomposition.

Anything that affects lvl of phytoplankton in oceans or area of land covered by forest will have an impact of lvl of carbon sequestration. In turn affecting comp of atmosphere.

Tropical rainforests ideal for plant growth promoting photosynthesis.

Marin equivalents of rainforests in terms of plant growth are coral reefs and mangroves. Warm tropical shallow wwaters are ideal for both

Deserts meanwhile are areas of sparse vegetation hence relatively little CO2 absorbed there.

Increased melting of Arctic sea means hreater expenses of ocean exposed to direct sun as seasonal thaws last longer increasing photosynthesis by phytoplankton resulting in agal blooms as more CO2 is absorbed.

Question 21

Soils role in the carbon cycle?

Answer 21

Carbon is vital is soils, organic material is meduim by which C passes through system, supports micro-organisms that maintain the carbon cycle, breaks down organic matter, provides pore spaces for infiltration and storage of water enhancing plant growth. Withou carbon, nutrient and water cycles cannot operate properly. Amount of carbon stored depends on system;

> amount of organic carbon stored within soil= inputs (plant litter/animal waste) minus outputs (erosion, decomposition and plant growth)
size of store depnds on biome

Question 22

What are the characteristics of healthy soils?

Answer 22

> dark,crumbly and porous
contain many worm and other organisms
provide air, water and nutrients for microorganisms and plants to thrive
contain more carbon or organic matter
sequester carbon
improve resilience to wetter weather because they enable infiltration and percolation of water
retain moisture regulatinf soil temp reducin effect of drought

In winter more organic deacy increases co2 levels whilst in the spring plant growth reduces levels, if winters shorten possible less CO2 released.

Question 23

How has increased fossil fuel usage affected the balance of the carbon cycle?

Answer 23

Earths reservoirs act as sinks and sources if stable equilibruim, maintaining a steady amount of CO2 helps to stablise global temps. However, human activities have increased CO2 inputs into atm without any correspondaning increases in the natural sinks. Hence atm stores of C have increased to 421 PPM , which is widely believed to be main cause of rising global temps.

Process of fossil fuel combustion has altered the balance of C pathways and stores with C released in large amounts from stores, flows have greatly increased. Since the late 1950s, the most abundant flow- inputs of atmospheric CO2 measured mauna loa observatory.

Question 24

What implications do the atmosphere going into disequilibrium hold?

Answer 24

> across europe average tmep projected to increase by more than the global average with largest increases expected to be over Eastern and Northern Europe in winter and over southern europe in summer.

> Annual precipitation projected to increase in Northern Europe and decrease in southern europe increasing differences between regions that are currently wet and those that are dry.

> extreme weather events also likely to increase in inten and freq

Question 25

How is disequilibruim of atm expected to cause arctic amplification and what changes have occured as a result?

Answer 25

Artic rwgion heatinf 2x as fast as global average known as arctic amp as melting permafrost releases CO2 and CH4. Increasing the concetration of these GHG in atm and leading to increased global temps and further melting.

Climate change is altering the Artic tundra ecosystem with warming leading to extensive meltinh of sea ice is summer and recution in permafrost meaning vegetation started to establish themselves some studies siggest that carbon remains in soils and used by new veg with warmer temps increasing decomposition releasing C and nutrients encouraging plant growth increasing photosynthesis.

+ feedback loop as INCREASES GHG > More melting of tundra so more methane and CO2 released>increased GHG

Question 26

What is disequilibrium implications for the hydrological cycle?

Answer 26

Projected changes in temp and prec patterns across Europe would also impact of hydrological cycle. In summer months much of water comes form the melting of apline glaciers but according to scientists the eastern alps could be completly ice free by 2100 affecting hydrological cycle;

> prec om form of snow could diminish and rainfall patterns change

> River discharge patterns may also change with greater flooding in the winter and drought in the summer
.
as apline glaciers melt water flows lead to increased sediment yield once glaciers retreated sicharge & sed yeilds and water qual decline.

Question 27

What is the debate about carbon pathways?

Answer 27

As increased thawing occurs constant release of carbon occurinhg as a result a faer pathway is emerging. In theory if Photosynethesis= release of GHG.

However, increased thawing means water and methane are released as ancient veg decomposes and trapped gases seep to the surface. Plants and microorganisms grow fater than before and respire CO2. 2 pathways;

pathway 1 - shrubs and tress invade arctic and sotre more carbon than is released reaching a short term balance - negative feedback

Pathway 2 - decomposition of plant material in wet soils reduces C stores by releasing more CO2 and CH4 into the atmosphere. Increased GHG reiforce global warming in long term- positive feedback. WIth scientists believing that this will add as mich carbon to atmosphere than all over land use changes in the rest of the world combined.

Question 28

WHat factors do energy consumption depend on?

Answer 28

lifestyle, climate, technology, availability and need. Global consumption continues to rise as countries develop economically. direct correlation between energy use and GDP per capita.

Question 29

WHen were the UK net exporters and WHy do we now import and what does this mean?

Answer 29

in 1981 to 2004 we were net exporters due to North Sea oil and gas development however production peaked in 1999 and thus reliance on imported energy has growth with the UK said to be energy insecure.

Question 30

How much were renewables a part of our energy mix in 2022?

Answer 30

56% from low-carbon sources - including 41.4% from renewables and 14.6% from nuclear

Question 31

Where do most of our crude oil imports come from?

Answer 31

In 2015 1/3 of the UK’s fuel imports consisted of crude oil with 50% of it coming from norway. But Norway now provides less than it used to, OPEC suppliers make much of the shortfall.
>Natural gas made up 29% of the UKs fuel imports. WIth norway main provider coming through piplines in the North Sea. ALso imports liquid gas 98% from Quatar.

Question 32

Who are the main energy players?

Answer 32

Energy TNCs- Tncs explore,ecploit and distribute energy resources

> They own supply lines and invest in distribution and processing of raw materials as well as electricity production and transmission.

> respond to market conditions to secure profits for their shareholders.

Question 33

What is OPECs role in the global energy market?

Answer 33

OPEC - organisation of petroleum exporting countries is a IGO- members are oil-producing countries like saudi arabia where oil is their main/ only export and is therefore vital.
Between them, OPEC producers control 81% of proven world oil reserves.

Mission is to untify and ccordinate petroleum policies of its members to sensure stabalisation of oil markets in order to secure:
>efficent economic and regular supply of petroleum to consumers
>steady income for producers
> a fair return for those investing in industry.

Opec have set oil production quotas in ast bossting supplied when demand rises and reducing them when demand falls. Yet, in 2012-16 maintaing output at high levels kept oil prices low, possibily to compete with the USAs increased oil production from fracking cuasing collapse in oil prices.

Question 34

What is the national governements role as energy players?

Answer 34

> to meet intetnational obligations as well as securing energy supplies for the nations present and future as well as supporting the countries economic growth

> regulating the role of private companies and setting enviromental priorities. Examples PPP between EDF and china general nuclear in hinkley C.

Question 35

what are consumers roles as energy players?

Answer 35

Create demand purchasing choices based on price, consumers have some power over oil companies as by purchasing electricc cars or installing solar panels. Bt only installed due to governemtn subsidies. Expansion of nuclear energy as well as the extraction of oil and gas through fracking both very controversial with widespread protests.

Question 36

How are coal, natural gas and oil formed?

Answer 36

Coal,oil and natural gas all formed under past geological conditions whcih determine where in the world they were formed in western europe and northern america caol was formed as when formed part of land mass was located in the tropics formeing rainforest and swamp forests which when they fell they transformed under the pressure of overlying strata into the seams of the coal.

Oil and natural gas are younger than coal formed in mesozoic era formed as remains of plants and animals buried under alternate layers of mud and sand on ocean floors. Heat and pressure then converted these fossil remains into oil ehich accumulated in porous sandstone then subsequent movements trapped pockets of oil and natural gas in sandstone caapped by non-porous shale trapping reservoirs.

Question 37

How is fossil fuel demand varying globally?

Answer 37

As countries develop, the global demand for different soirces of energy is increasing. Primary energy sources used by different countries change over time, but fossil fuels still make up 86% of global enrgy mix. Global consu of fossil fuels increased by 50% since 1990 and chines oil consu doubled from 2000-2010 expected that by 2035 china will be the worlds largest energy importer however china has 1 of the the 14 th biggest oil reserves but only 10% size of canadas so still imports lost 2nd biggest importer behinf USA.

Question 38

EXamples of energy pathways?

Answer 38

4188km long ESPO pipeline exports crude oil from Russia to china, SK and japan build by russias TRansneft and completed in 2012. Operates pathline. Transporting via pipeline is increasingly efficent and international. Some of the worlds biggest pipelines carry billions of cubic metres of gas thousands of kilometres. Pathways depend on multilateral and bilteral agreements. When russias Gazprom export 80% of their gas to europe avoid transit states ie nord stream runs 1200km along bed of the baltic sea.

other pipelines include yamal-europe pipeline a 4107km gas pipeline that runs from russia through belarus poland and germany.

Question 39

WHat are chokepoints?

Answer 39

Half of the worlds oil moved by tankers on fixed shipping routes. There are 8 major chokepoints with over half of the worlds going going through these- a narrow sea channel or convergence where key transport routes can easily be disrupted eg 20% of world’s oil passes through thr Strait of Hormuz a 39km wide stretch of water between gulf of oman and persian gulf if blocked or threatened energy prices can rise quickly. OIl transits chokepoints are crucial elements in gloabl energy security.

Question 40

How can energy pathways be disrupted?

Answer 40

Securing energy resources involves geopolitical factors about control and ownership any isruption to energy oathways incvoving piracy, natural hazards and political conflict threaten to un dermine energy security.

> in december 2015, piracy attacks occured along the strait of mallacca between indeonesia and malysia. Worlds 2nd largest chokepoint by oil. Criminal gangs frequently seized ships for hostage payments- over 500 attacks occured from 2009-15

> The Trans Forcados pipeline was bombed by nigerian militants in 2016 resulting in loss of 300,000 barrels of crude oil a day.

> During a stormy winter in 2013, Uk gas reserves fell to 6 hours worth as storm damage paralysed an import pipeline.

Question 41

How have proxy wars been created as a result of energy pipe-lines?

Answer 41

2 sides are involved in the battle for control over syrian territory. Russia and iran support assad as russia wants cintrol over the european market and to set up a pipeline than runs through syria with iran also wanting a share.

Sunni quatar and saudi arabia also want to become uropes main suppliers of gas and oil so also needed to be pipelined they are US allies so as a result of this USa happy to suppor al q’aeda and for US companies to build up pipelines allowing for Exonn to market middle eastern energy to europe.

Question 42

What are the 4 main unconventional fossil fuels?

Answer 42

Deep water oil- as accessible reserves run out, prospecting companies have to look into deeper ocean waters with greater risks and costs e.g. gulf of mexico anf brazils off-shore reserves.

Tar sands- bitimpis sands or extra heavy oil are naturally occuring mixture of sand,clay and bitumen- form of petroleum canada has 73% of global stocks.

Shale gas- usually methane in coal seams or natural gas trapped in fractures and pores of sandstone and shale.

Oil shale- depsiots of organic compounds called kerogen in sedi rocks that havent undergone suffcient pressure, heat or tuime to become normal oil. USA 77% of stocks.

Question 43

What impact does deforestation have on the water cycle?

Answer 43

> reduced infiltration
runoff and erosion are increased
Flood peaks are higher and lag time is shorter
increased discharge leads to flooding
more eroded material is carried in the river, both as bed load and as silt and clay in suspension
Annual rainfall is reduces and seasonality of rainfall increases.

Question 44

WHat impacts do deforestation have on soil health?

Answer 44

> rainfall impact washes finer particles of clay and humus away
coarser and heavier sand left behind.
CO2 released from decaying wood material
biomass is lost due to reduced plant growth/ phototsyenthesis
Rapid soil erosion lead to a loss in nutrients
increased leaching ( loss of nutrients) means minerals are lost.

Question 45

WHat impacts do deforestation have on soil health?

Answer 45

> rainfall impact washes finer particles of clay and humus away
coarser and heavier sand left behind.
CO2 released from decaying wood material
biomass is lost due to reduced plant growth/ phototsyenthesis
Rapid soil erosion lead to a loss in nutrients
increased leaching ( loss of nutrients) means minerals are lost.

Question 46

WHat is deforestations impact on the enviroment?

Answer 46

> turbulence increased as the heated ground induces convectional air currents.
Ocygen content is reduced and transpiration rates are lower
Reduced shading leads to more direct sunlight reaching the forest floor
Reduced evaportranspiration makes it less humid.
Air is dryer
Evaportranspiration rates from the resultant grasslands are about 1/3rd of the tropoical rainforest.

Question 47

What is deforestations impact on the biosphere?

Answer 47

> evapourtion of vegetation is reduced
less absorption of co2 means a reduced carbon store
species diveristy is reduced
ecosystem services are reduced
Decrease in habitiats so fewer species survive
bio mass reduced less plant growth.

Question 48

How much grassland was lost in american midwest in an attempt to grow rapeseed for biofeul?

Answer 48

5.5 mil hectares lost in aim to increase amount of biofeul and ethanol used in petrol, boost economies of rural US states, reduce US dependance on overseas oil imports and reduce co2 emissions from transport.

Question 49

What are the benefits of natural grasslands?

Answer 49

Trap moisture and foodwater
Absorb toxins from soils
maintain healthy soils
provide cover for dry soils
maintain natural habitats
act as a carbon sink- absorbing CO2 and releasing O2 all year round.
act as a terrestrail carbon store

Question 50

What are the disadvantages of converting grasslands to grow biofeul crops?

Answer 50

< intial rmoval released CO2 from soils
>Annual ploughing allows bacteria to release CO2
>biofeul crops are heavy consumers of water, so need irrigation which has a significant impact on aquifers
> cultivated soils are liable to erosion by runoff and wind
> Natural habitats are reduced
> Lung affect reduced

Question 51

what is ocean acidification?

Answer 51

The world’s oceans are a major carbon sink- absorbed about 30% of the co2 produced as a result of human activities since 1800, and about 50% of that produced by burning fossil fuels. as co2 increases combines with water to form carbonic acid this causes corals to not be able to aborb the alkaline calcium carbonate that they need to mauntain their skeletons and reefs to dissolve. Ocean acidfication has lowered the pH of the ocean by about 0.1. This means that its now about 30% more acidic.

Question 52

Why are coral reefs important?

Answer 52

Corals which are marine invertebrates get their colour from algae that live in their tissues.
The most important role of algae is to provide food to the coral.
narrow temp range within which it can live;never below 18C and ideally in the range of 23-29c, water becomes too warm, the algea are ejected and the coral turns white- known as coral bleeching.
PH could be lowered to 7.8Ph by 2100
Increased acidifcation risks crossing the critical threshold, If reefs are destroyed we will lose vital ecosystem services that they provide.They;
>shelter 25% of marine resources
>protect shorelines
>support fishing industries
> provide income from tourism

Question 53

What are ecosystem services?

Answer 53

supporting services- keep healthy ecosystem with nutrient/water cycling

Provisioning services- Products obtained from ecosystems, including food and medicine.

Regulating services- benefits obtained from reg of ecosystem procceses including reg of air quality

Cultural services- non-material benefits that people obtain from ecosystems like spiritual well being.

Question 54

How climate change led to drought increasing?

Answer 54

> increase in freq and intensity of storms and hurricanes
rising SL
more frequent floods, droughts and heatwaves

Any change in ocean currents and atmospheric circ could also affect patterns of precipitation, evaportranspiration and temperature as climate belts move in response to climate change.

As planet warms, not only have the earth climate zones began to shift but doing it at an accelerated rate. They found that for an initial 2oC warming an additional 10% of land area shifting to a new climate zone. Pace of change then quickens for the next 2 degrees of warming with an additional 10% of land area shifting to a new climate zone.

Certain regions such as north america, europe and other mid & high latitude regions will undergo more changes than tropical regions. In addition, the coldest zones on the planet are decreasing in extent and dry areas are increasing, likely that todays arid and semi-arid areas will expand into continental areas of asia as well as parts of N and sub-suharan africa.

Question 55

Whats causing drought in the amazon?

Answer 55

Suffered sever droughts in 2005 and 2010 with 2014-15 drought worst to hit Brazil for 80years. Amazon basin plays a key role in Earths carbon cycle, holding 17% of terrestrial vegetation carbon store. Drough caused function of amazon as a carbon sink to decrease as forest fires broke out worries that amazon could turn into a carbon source.