cycles Flashcards
what is meant by a system?
- a set of interrelated events or components working together
- a system has to contain many components to become a system
what are the 2 types of systems?
open system- both energy and matter can enter and leave an open system e.g. in a drainage basin energy from the sun enters and leaves the system, water is the input and output as rive discharge into the sea
closed system- matter cannot enter or leave a closed system- it can only cycle between stores
- energy can enter and leave- it can be input or output e.g. in a carbon cycle energy is input from the sun, from photosynthesis, and output from respiration, but the amount of carbon on earth stays the same because there are no inputs or outputs of matter
isolated systems- these have no interactions with anything outside of the system boundary, there is no input or output of energy or matter
what are the main processes a system is made up of?
inputs- when matter or energy is added to the system
outputs- when matter or energy leaves the system
stores- where matter or energy builds up
flows- when matter or energy moves from one store to another
boundaries- the limits of the system
what are some examples of stores and transfers/flows?
stores- ocean, atmosphere, ice/snow, freshwater, springs, lakes/channels, groundwater/soil, clouds etc.
transfers- surface run-off, transpiration, evaporation, condensation, sublimation, infiltration, precipitation, throughfall etc.
what is a dynamic equilibrium?
- when there is a balance between the inputs and outputs in a system
- however, if one of the elements change e.g. one of the inputs increase without any corresponding change in the outputs then the stores change and the equilibrium is upset, this is called feedback
what is meant by positive feedback?
- this is when mechanisms amplify the change in inputs and outputs meaning the system responds by increasing the effects of the change, moving the system even further from it’s previous state
e.g. (1) temperature rises, (2) ice covering cold parts of earth melts due to higher temperature (3) less ice cover means less of the suns energy is reflected (4) less of suns energy being reflected means more is absorbed by the earth
what is meant by negative feedback?
- this is when mechanisms counteract the change in the inputs or outputs meaning the system responds by decreasing the effects of the change, keeping the system closer to it’s previous state
e.g. (1) large amounts of CO2 emitted (2) CO2 in atmosphere increases (3) extra CO2 causes plants to increase growth (4) plants remove and store more CO2 from atmosphere (5) amount of CO2 in atmosphere reduces
what are the 4 main cascading systems?
- atmosphere- clouds are the most visible stores of water
- lithosphere-
- hydrosphere
- biosphere
what do the 4 cascading systems consist of?
atmosphere- the layer of gas between the Earth’s surface and space held together by gravity e.g. clouds are the most visible store of water
lithosphere- the outermost part of the earth, it includes the crust and the upper parts of the mantle
hydrosphere- includes all of the water on earth e.g. in liquid form such as lakes and rivers, solid form such as ice stored in the cryosphere or gas form such as water vapour stored in the atmosphere, it can also be saline (salty) or fresh
biosphere- part of the earths system where living things are found e.g. plants, animals, birds, fungi, insects, bacteria etc
how are all these subsystems connected?
- matter and energy move between the subsystems meaning the output of one cycle is the input of the next
- changes that occur in one subsystem can affect what happens in the others
e.g. hydrosphere to atmosphere = evaporation, atmosphere to hydrosphere = condensation, hydrosphere to lithosphere = sublimation, hydrosphere provides water for streams to form in lithosphere and provides water for plants and animals in the biosphere
what is the cryosphere?
- the cryosphere are positions of the earths surface where water is in solid form and is cold enough for water to freeze e.g. glacial landscapes
what is cyrospheric water and what are some examples?
- this is the water that is locked up on the earths surface as ice
e.g. sea ice, ice cap, ice sheets (contain 99% of the freshwater ice on Earth is in Antarctica and Greenland), alpine glaciers (thick masses of ice found in deep valleys or upland hollows), permafrost etc
what is meant by permafrost?
- permafrost is defined as ground (soil, rock and induced ice or organic material) that remains at or below 0 degrees for at least 2 consecutive years
- permafrost is found beneath the ice-free regions of the Antarctic continent and also occurs beneath areas in which the ice sheet is frozen to it’s bed
what is terrestrial water and what are the four main categories?
- terrestrial water consists of groundwater, soil, moisture, lakes, wetlands and rivers
- the four main categories are:
1) surface water
2) groundwater
3) soil water
4) biological water
what is meant by surface water and what are some examples?
- surface water is the free-flowing water of rivers as well as the eater of ponds and lakes
- rivers act as both a store and a transfer of water, they are streams of water within a defined channel, they travel from soils and from the atmosphere to a store
- lakes are collections of freshwater (most in the northern hemisphere) found in hollows on the land surface, they are generally deemed a lake if they are greater than 2 hectares in area
- wetlands are an area of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing where there is a dominance by vegetation
what is groundwater and what are some examples?
- groundwater is water that collects underground in the pore spaces of rock
- the depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table
- natural discharge often occurs at springs and seeps, and can form wetlands
- the amount of groundwater is reducing rapidly due to extensive extraction for use in irrigating agricultural land in dry areas
what is soil water and what are some examples?
- soil water is that which is held, together with air, in unsaturated upper weathered layers of the earths
- soil moisture is a key variable in controlling the exchange of water and heat energy between the land surface and the atmosphere through evaporation and plant transpiration
biological water examples
- biological water constitutes the water stored in all the biomass, it varies widely around the glove depending on the vegetation cover and type
- trees take in water via their roots, this is either transported or stored in the trunk and branches of the tree. the water is lose by the process of transpiration through stomata in the leaves, this storage provides a reservoir of water that helps maintain some climatic environments
- many plants are adapted to store water in large quantities e.g. cacti are able to gather water via their extensive root system and then use it very slowly until the next rainstorm
- the baobab tree stores water, but it is thought that this is to strengthen the structure of the tree rather than to be used in tree growth
what factors are driving change in the magnitude of water stores?
- the magnitude of each store depends on the amount of water flowing through them
- some examples of driving changes are:
1) evaporation
2) condensation
3) cloud formation and precipitation
4) cryosphere processes
how does evaporation affect the magnitude of water stores?
- evaporation occurs when liquid water changes state into a gas, becoming water vapour-it gains energy. normally from solar radiation
- evaporation increases the amount of water stored in the atmosphere
- the magnitude of the evaporation flow varies by location and season e.g. if there is lots of solar radiation, a large supply of water and warm, the amount of evaporation will be high
- if there is not much solar radiation, little available liquid water and cool air that is already nearly saturated (unable to absorb any more water vapour), evaporation will be low
how does condensation affect the magnitude of water stores?
- condensation occurs when water vapour changes state to become a liquid, it loses energy to the surroundings and happens when air containing water vapour cools to it’s dew point (the temperature at which it will change from a gas to a liquid) e.g. when temperatures fall at night due to heat being lose to space
- water droplets can stay in the atmosphere or flow to other subsystems e.g. when water vapour condenses, it can form dew on leaves and other surfaces- this decreases the amount of water stored in the atmosphere
- the magnitude of condensation flow depends om the amount of water vapour in the atmosphere and the temperature e.g. if there is lots of water vapour in the air and there a large or rapid drop in temperature, condensation will be high
how does cloud formation and precipitation affect the magnitude of water stores?
- precipitation is the main flow of water from the atmosphere to the ground
- clouds form when warm air cools down, causing the water vapour in it to condense into water droplets which gather as clouds, when the droplets get big enough, they fall as precipitation
- there are several things that can cause warm air to cool, leading to precipitation:
1) other air masses- warm air is less dense than cool air, so as a result, when warm air meets cool air, the warm air is forced up above the cool air and it cools down as it rises. this results in frontal precipitation
2) topography- when warm air meets mountains, its forced to rise, causing it to cool, this results in orographic precipitation
3) convection- when the sun heats up the ground, moisture on the ground evaporates and rises up in a column of warm air, as it gets higher it cools resulting in convective precipitation
how do cryospheric processes affect the magnitude of water stores?
- cryospheric processes such as accumulation and ablation change the amount of water stored as ice in the cryosphere, the balance of accumulation and ablation varies with temperature
- during periods of global cold, inputs into the cryosphere are greater than outputs- water is transferred to it as snow, and less water is transferred away due to melting
- during periods of warmer global temperatures, the magnitude of the cryosphere store reduces as losses due to melting are larger than the inputs of snow
- however, there are still extensive stores of ice on land in Antarctica and Greenland, as well as numerous alpine glaciers and a large volume of sea ice in the Arctic and Antarctica
what factors can affect flow rates?
- interception and shape of leaf
- solar radiation
- soil polarity and capillary action
- gravity and soil type
how does interception and shape of a leaf affect flow rates?
-increased vegetation (vegetation density) and trees results in more interception occurring and then allows slow infiltration into the soil
- however if there is no forest cover, interception rates decreases and more overland flow occurs
- larger leaves will hold more water due to a larger surface area in which interception rates increase and less water flows directly to the river, however, smaller leaves may only hold water for a short amount of time meaning more overland flow can occur and flow rates increase
how does solar radiation affect flow rates?
- if there is lots of solar radiation, a large supply of water and warm, dry air there will be an increased amount of evaporation
- more evaporation leads to more water evaporating from oceans, seas and lakes which form new precipitation
how does soil polarity and capillary action affect flow rates?
- soil porosity is controlled by it’s texture, structure and organic content
- coarse textured soils have larger pores and fissures than fine-grained soils and therefore allow for more water flow
- pores and fissures found in soils can be made larger e.g. the burrowing of worms and other organisms and penetration of plant roots can increase the size and number of macro- and micro-channels within the soil
- capillary action is a natural phenomenon that allows liquid to flow upward against gravity in narrow spaces and helps bring water up into the roots
how does soil type affect the flow of water?
- wide pore spacing at the soil surface increases the rate of water infiltration, so coarse soils have a higher infiltration rate than fine soils
what is the water balance?
- water balance/budget is the balance between inputs (precipitation) and outputs (evapotranspiration, run-off) and it affects how much water is stored in the basin
describe the water balance during wet seasons.
- in wet seasons, precipitation exceeds evapotranspiration so creates a water surplus (supply exceeds demand), the ground stores fill with water so there’s more surface runoff and higher discharge, so river levels rise
describe the water balance during drier seasons.
- in drier seasons, precipitation is lower than evapotranspiration so ground stores are depleted as some water is used e.g. by plants and animals and some flows into the river channels but is not replaced by precipitation
- at the end of the dry season, there a water deficit (shortage) in the ground,
- ground stores are recharged in the next wet season (autumn)
describe the water balance in polar regions.
- in polar regions there is a positive water budget as precipitation exceeds evaporation, therefore producing a water surplus
what is a drainage basin?
- drainage basins are viewed as open (inputs and outputs), local hydrological cycles
- a rivers drainage basin is the area surrounding the river where the rain falling on the land flows into the river, this is also called the river catchment
- the boundary of a drainage basin is the watershed- any precipitation falling beyond the watershed enters a different drainage basin
- water comes in the system as precipitation and leaves via evaporation, transpiration and river discharge
what are the main inputs and outputs in a drainage basin?
inputs- precipitation including all the ways moisture comes out of the atmosphere e.g. rain, snow, hail, dew and frost
outputs- evaporation, transpiration, evapotranspiration and river discharge
what are the main stores and flows in a drainage basin?
stores- interception store, vegetation, surface store, soil store, groundwater storage, channel storage
flows- infiltration, overland flow, throughfall, stemflow, throughflow, percolation, groundwater flow, baseflow, interflow, channel flow, run-off
what is evaporation?
- this is the process by which liquid water changes to a gas
- it requires energy, which is provided by the sun and aided by the wind
what is transpiration?
- this is the loss of water from vegetation through pores (stomata) on their surfaces
what is evapotranspiration?
- the total output of water from the drainage basin directly back into the atmosphere
what is interception storage?
- this is when some precipitation lands on vegetation and creates a significant store of water in woodland area
- it is only temporary as the collected water may evaporate quickly, or fall from the leaves as throughfall
what is vegetation storage?
- this is water that’s been taken up by plants
- it’s all the water contained in plants at any one time
what is surface and soil storage?
soil storage- the amount of water that is stored in the soil
surface storage- the build up of water on the surface usually in the form of puddles
what is groundwater storage?
- this is the water stored in the ground, either in the soil or in the rocks
- the water table is the top surface of the zone of saturation- the zone of soil or rock where all the pores in the soil or rock are full of water
what is channel storage?
- the water that is held in a river or stream channel
what is infiltration?
- the downward movement of water from the surface into the soil
what is overland flow?
- the tendency of water to flow horizontally across land surfaces when rainfall has exceeded the infiltration capacity of the soil and all surface stores are full to overflowing
what is throughfall?
- the proportion of the precipitation that reaches the ground directly through gaps in the vegetation canopy and drips from leaves etc.
- this occurs when the canopy-surface rainwater storage exceeds it’s storage capacity
what is stemflow?
- the portion of precipitation intercepted by the canopy that reaches the ground by flowing down stems, stalks or tree bores
what is throughflow?
- the movement of water downslope through subsoil under the influence of gravity
what is percolation?
- the downward movement of water withing the rock under the soil surface
- rates vary depending on the nature of the rock
what is groundwater flow?
- the slow movement of water through underlying rocks
what is baseflow?
- this is the groundwater flow that feeds into river banks and river beds
what is interflow?
- the water flowing downhill through permeable rock above the water table
what is channel flow?
- the water flowing in the river or stream itself, also known as the river discharge
what is run-off?
- all the water that enters the river channel and eventually flows out of the drainage basin
what is a storm and rainfall event?
- an individual storm is defined as a rainfall period separated by dry intervals of at least 24 hours
- an individual rainfall event is defined as a period separated by dry intervals of at least 4 hours
how do water transfers in a drainage basin vary over time?
- water moves faster along the surface due to slopes making surface run off easier, there are also fewer obstacles slowing the flow down
- the water through soil moves slower and all depends on the infiltration rate e.g. clay retains water, hindering movement
- flow rate through the rock slows down due to permeability of the rock e.g. flow rates through the rock are very slow through the small pores in permeable rocks
what is river discharge?
- river discharge is the volume of water that flows in a river per second
- it is measured in cumecs (m3/s)
how do we calculate river discharge?
- cross sectional area of the river x velocity of the measuring point
1) measure the cross sectional area = width x depth (m/s)
2) measure speed / velocity between 2 points (m/s)
3) work out discharge
why is is helpful to know a rivers discharge over a year?
- it is helpful to know a rivers discharge as patterns in flooding can help manage the river and design water-related structures such as reservoirs, bridges etc. and flood defences and schemes can be put in place
- can also help to develop hydroelectric power and protecting both the ecological health and wetlands
what is a hydrograph and what are it’s features?
- a hydrograph is a graph that measures river discharge over time, it shows how the volume of water flowing at a certain point in a river changes over a period of time
- a flood hydrograph shows river discharge around the time of a storm event
1) peak discharge- this is the highest point on the graph, when the river discharge is as it’s greatest
2) lag time- the delay between peak rainfall and peak discharge - this delay happens because it takes time for the rainwater to flow into the river e.g. a shorter lag time can increase peak discharge because more water reaches the river during a shorter period of time
3) rising limb- this is the part of the graph up to peak discharge - the river discharge increases as rainwater flows into the river
4) falling limb- this is the part of the graph after peak discharge - discharge decreases when less water flows into the river
- a shallow falling limb shows water is flowing in from stores long after it’s stopped raining
what factors affect runoff and shape of a hydrograph?
1) drainage basins with steep sides- tend to have ‘flashier hydrographs then gently sloped river basins, this is because water flows more quickly on the steep slopes and so gets to the river quicker
2) saturated drainage basins- if it is already saturated by antecedent rainfall then overland flow increases as infiltration capacity has been reached, lag time is reduced and peak discharge is higher, resulting in a flashy hydrograph
3) rock type/urbanisation- if rock is impermeable e.g. clay soils or shale rocks, overland flow will be higher and infiltration will be reduced, meaning a flashy hydrograph
4) deforestation- reduces interception rates allowing rainwater to hit the surface directly, the lack of vegetation roots reduces the infiltration rates into the soil, causing rapid overland flow and flashy hydrographs
5) afforestation- has the opposite effect making it a useful flood prevention measure
6) thick vegetation- vegetation intercepts the precipitation, holding the water on it’s leaves; this slows the movement of rainwater to the ground and to river channels
- water is also lost due to evaporation and transpiration from the vegetation surfaces, reducing how much gets to the river
- this subdues the storm hydrograph, increasing lag time and reducing peak discharge
7) agriculture- ploughing breaks up the topsoil and allows greater infiltration, subduing hydrographs, this can be enhanced by contour ploughing where furrows are created that run directly down slope then act as small stream channels and lead to flashy hydrographs
- grass crops increase infiltration and lead to subdues hydrographs
- large numbers of animals on small areas can impact soils leading to overland flows
- terracing on hillsides stops movement of water downhill and subdues hydrographs
- growth of urban areas increases the amount of permeable rock which creates flashy hydrographs
what is a river regime?
- this is the variation in a rivers discharge over the course of a year
what physical factors influence a rivers regime?
1) distance downstream- in humid environments river discharge increases with distance downstream, this is due to the addition of water to the channel as smaller tributaries join the main river
what human factors influence a rivers regime?
1) land use- afforestation tends to reduce discharge as water is taken up by the soil and plants
- urbanisation tend to increase discharge as water can run rapidly (increased overland flow) over impermeable rock, preventing infiltration
2) water abstraction- this happens frequently in areas with low rainfall and high population densities, and in areas with intensive agricultural or industrial activity
- this is the abstraction of water for domestic use and crops which decreases discharge and creates demands for water in summer months
3) channel modifications- constructing a reservoir can regulate discharge or the river can be modified e.g. channel straightening/enlargement which can increase discharge
- however, river restoration and creation of flood storage areas can decrease discharge as they encourage small-scale flooding in a rivers headwater
how climate affects a river regime
1) precipitation patterns- increased rainfall can result in higher amounts of river flows and increased river discharge which is the opposite in terms of prolonged droughts which reduces flow levels
2) warmer temperatures- can spike drastic weather events increasing frequency and intensity, such as heavy rainfall and storms which can lead to sudden peaks in river discharge due to faster lag time
- however, there can also be an increase in drought frequency which can on the other hand significantly reduce the river flows and affect the amount of discharge entering a river
3) colder climates- increased snowfall which can result in time delay as the water is stored until the snow melts again, and when melted there is a surge in discharge into the river, this then can shift the timing of the peak river flows
what is river regime like in summer?
- the river regime is less flashy during summer as there is an increase in vegetation that is in full bloom so there is increased interception for the rainfall so less surface runoff
- due to warm weather the water could evaporate back into the atmosphere so soil moisture depletes and becomes dry, resulting in increased infiltration due to more space for water so when the water is stored soil moisture recharges and less makes it to the river
- eventually when the soil is full it can be released as surface run off
what is recirculation?
- recirculation is the continuous movement of water on earth
- it involves various processes that ensure the constant exchange of water between the earths surface, the atmosphere, and back to the surface again
why does water recirculate between the earths surface and the atmosphere more over land compared to over the ocean?
- water recirculates more overland than over the ocean due to many reasons:
1) evapotranspiration and precipitation- plants and trees on land increase the rate of water vapour after a long period of rain which is released into the atmosphere and recirculating on land
2) land heats up and cools down faster than water so more evaporation occurs, resulting in higher rates of water vapour in the atmosphere
what are the main causes of deforestation?
- fewer forests result in reduced greenhouse gases, regulating climate change
- removal of trees creates space for crop planting / growing
- urban sprawl, so space is needed for the building of more housing
how does small-scale deforestation impact the water cycle?
- precipitation remains the same but the rate of evapotranspiration decreases due to the vegetation having smaller leaves and roots and therefore less dense
- overland and throughflow then increase due to the lack of interception from trees
- this leads to increased discharge and flashiness, resulting in localised flooding
how does large-scale deforestation impact the water cycle?
- when deforestation is extensive, positive feedback occurs this is because levels of evapotranspiration decrease so water leaves the area in the river channel instead of between the forest and the atmosphere
- this results in less water vapour available in the atmosphere, the air then becomes drier resulting in less precipitation falling
- overland flow and throughflow then majorly decrease so less water reaches the river channel and the flow is reduced
how does urbanisation impact the water cycle?
- urbanisation results in a mass of impermeable rock e.g. concrete, which means water cannot infiltrate into the ground so instead flows overland, reaching the river at a quicker rate
- water on impermeable rock also goes into drains and flows straight to the river channel
- there are also decreased volumes of vegetation which reduces interception and increases surface run off
- road cambers, increase the rate at which surface run off happens to be able to clear roads quicker, however it is quickly taken to the nearest river which can lead to it quickly reaching it’s peak discharge
what is soil drainage?
- this is the subsurface drainage which removes excess water from the soil profile
- it is carried out through a network of tubes commonly known as ‘tiles’
what is the purpose of drain tiles?
- the most common tile is a corrugates plastic tubing with small perforations to allow water to enter
- when the water table in the soil is higher than the tile, water flows into the tubing through small cracks between adjacent tiles, this lowers the water table to the depth of the tile over the course of several days
- drain tiles allow excess water to leave the field, but once the water table has been lowered to the elevation of the tiles, no more water flows through them
what are the advantages of soil drainages?
- it makes the soil easier to work with and makes it easier to achieve greater root penetration, enabling roots to travel faster and further
- increased aeration increases the likelihood of germination and it can make possible sowing of seeds
- heavy machinery can work on the land without danger of compaction which leads to increased overland flow
- large numbers of animals can graze the land without compacting the soil
why is the compaction of soil by machinery seen as a disadvantage?
- as the compaction of soil results in lower infiltration rates as soil particles are compacted closer together
- this results in more surface runoff and flooding is more likely
- compared to if there was reduced compaction, infiltration rates would increase, surface runoff would decreases and flooding is less likely
what are the disadvantages of soil drainage?
- the insertion of drains artificially increases the speed of throughflow in the soil, so much more water reaches watercourses more quickly than before drainages, this can cause likelihood of flooding and increase the range of flows in rivers
- the dry topsoil can be subject to wind erosion if not properly protected as it is easier to pick up and transfer, so there is a loss of nutrients leaving plants less protected. if soil is then blown into the river there will be an increased sediment build-up resulting a smaller volume of water being able to fit into the river
- farmers also use an increase of fertilisers to make up for the lost nutrients, however too much fertiliser can cause eutrophication
what is water abstraction and what are the uses?
- the extraction of water out of rivers or from the ground
- it can be caused due to:
- drinking water usages (domestic use)
- the growth of crops (irrigation)
- in places that suffer from water deficits (when demand exceeds amount available)
- industries
describe the effects of water abstraction from the chalk of southern England.
- water is replenished by rainfall that comes from the aquifer and falls directly on the chalk
- in the summer, evapotranspiration exceeds precipitation so no percolation takes place and soil moisture deficits build up. but water can still be extracted via boreholes
- aquifer is recharged in winter as rainfall can percolate into permeable ground, decreased evapotranspiration
- when water fills up it can come out via springs and some can come out in the summer due to left over water from winter, but in some places it can be intermittent and dry up due to lack of rainfall
- multiple drier winters can deplete the aquifer so chalk stream flows may decrease/dry up all together
what are the impacts of water abstraction in Chilterns compared to London?
Chilterns- chalk streams dry up due to over-abstraction so rare habitats are harmed
- reduces recreational activities such as fishing and river views that attract people
- the water from aquifers is much cleaner than alternate water sources
- decreases industries reliant on waters e.g. salad crops as the water is so clean, so businesses impacted
London- risk of salinisation in East London as groundwater levels near the river are lower than the water level in the river Thames, so saline water can enter the chalk aquifer
- industry is affected as water cannot be extracted
- very expensive to de-salinize the water
- can result in flooding which causes expenses to reconstruct
- when the water dropped, structures were built e.g. London underground but when water rose it would flood
what are unconfined and confined aquifers?
- an unconfined aquifer is where the rock is directly open at the surface of the ground and groundwater is directly recharge e.g. by rain
- a confined aquifer is an aquifer below the land surface that is saturated with water as layers of impermeable rock are below and above it so groundwater cannot be recharge
what is salinisation?
- this is the accumulation of salt water in the soil/ to freshwater flows e.g. from the sea
where is most saline intrusion located?
- the saline intrusion is widespread along the Mediterranean coastlines of Italy, Spain and Türkiye where the demands of tourist resorts are the major cause of over-abstraction
- In Malta, most groundwater can no longer be used for domestic consumption or irrigation due to saline intrusion
what is peatland?
- peat is high carbon soil which is produced in anaerobic conditions due to being waterlogged and highly acidic
what is a drainage ditch?
- these are narrow channels dug out to help carry water away to the river
what are the impacts of drainage ditches on peatland?
- if peat is drained of water, decomposers get to the soil and there is an increased risk of fire due to available oxygen, carbon is then emitted
- these drainage ditches increases the speed of which water is able to reach the main channel
- restoration therefore increases soil moisture and decreases flow to the river
what is meant by a carbon cycle?
- this is the process by which carbon is stored and transferred
- it is a closed system- there are inputs and outputs of energy, but the amount of carbon in the system remains the same
- however, some carbon is locked away in long-term stores e.g. rock and fossil fuels deep underground
- if these are released by e.g. burning fossil fuels, they are inputs
what is an example of positive and negative feedback in the carbon cycle?
positive feedback- temperature rises, plant respiration rate increases, amount of CO2 in the atmosphere increases and greenhouse effect increases
negative feedback- CO2 in atmosphere increases, extra CO2 causes plants to increase growth, plants remove and store more CO3 from atmosphere and the amount of CO2 in the atmosphere reduces
what are the main properties of carbon?
- carbon is one of the most chemically versatile of all the elements
- it is a solid and an element on the periodic table
- it is found in both organic (living things) and inorganic stores (e.g. sedimentary rocks, gases and fossil fuels)
what are the main stores of carbon?
1) carbon dioxide, a gas found in the atmosphere, soils and oceans
2) methane, a gas found in the atmosphere, soils, oceans and sedimentary rocks
3) calcium carbonate, a solid compound found in calcareous rocks, oceans and in the skeletons and shells of ocean creatures
4) hydrocarbons, solids, liquids or gases usually found in sedimentary rocks
5) bio-molecules, complex carbon compounds produces in living things e.g. proteins, carbohydrates, fats and oils and DNA
how is carbon found in each of the Earth’s systems?
lithosphere- over 99.9% of the carbon on Earth is stored in sedimentary rocks such as limestone and around 0.004% of the carbon on Earth is stored in fossil fuels, such as coal and oil in the lithosphere as well as in peat
hydrosphere- carbon dioxide is dissolved in rivers, lakes and oceans
- the oceans are the second-largest carbon store on earth, containing approximately 0.04%, the majority found deep in the ocean in the form of dissolved inorganic carbon
- a small amount is found at the ocean surface where it is exchange with the atmosphere when photosynthesis occurs
atmosphere- carbon is stored as carbon dioxide and in smaller quantities as methane in the atmosphere
- the atmosphere contains about 0.001% of the earths carbon
biosphere- carbon is stored in the tissues of living organisms, it is transferred to the soil when living organisms die and decay. it contains approx. 0.004% of the earths total carbon
- the highest percentage of carbon is found in tropical rainforests and boreal forests
cryosphere- contains less than 0.01% of the earths carbon, most in the soil in areas of permafrost where decomposing plants and animals have frozen into the ground
what are the major differences between the fast and slow carbon cycle?
slow carbon cycle- this involves the long-term storage of carbon e.g. when marine organisms die their shells build up by combining calcium with carbon and when they die they accumulate on the ocean floor in which they compress and become carbon-rich sedimentary rock
- this carbon is usually stored in rocks for around 150 million years
- the main example of a slow carbon cycle is the lithosphere
fast carbon cycle- the transfer between the oceans, atmosphere, soils and living organisms is ten to one thousand times faster than the slow carbon cycle e.g. CO2 is absorbed by phytoplankton by photosynthesis and stored in tissues, respiration by living organisms releases CO2 to the atmosphere and this CO2 is exchanged between the atmosphere and oceans and returned to the surface of the earth as acid rain where the cycle starts again
what stores are the ocean divided into?
1) the surface layer (euphotic zone), where sunlight penetrates so that photosynthesis can take place (contains approx. 900GtC)
2) the intermediate (twilight zone) and the deep layer water contain approx. 37,100GtC
3) living organic matter (fish, plankton, bacteria etc) amounts to approx. 30GtC and dissolved organic matter 700GtC giving the total for oceanic carbon between 37,000-40,000Gtc
how is carbon stored in sedimentary layers in the ocean?
- when organisms die, their dead cells, shells and other parts sink into deep water
- decay releases carbon dioxide into this deep water, some material sinks right to the bottom, where it forms layers of carbon-rich sediments
- over millions of years, chemical and physical processes may turn these sediments into rocks and this part of the carbon cycle can lock up carbon for millions of years (estimated 100million GtC-gigatonnes)
where are the main stores of carbon in the terrestrial biosphere?
1) living vegetation- 19% of the carbon in the earths biosphere is stored in plants, mostly directly in the tissues of the plants
- the amount of carbon in the biomass varies from between 35-65% of the dry weight, depending on the location and vegetation type
- it is estimated that half of the carbon in forests occurs in high-latitude forests, and a little more than one-third occurs in low-latitude forests, with the 2 largest forest reservoirs of carbon being a boreal forest in Russia (25%) and the Amazon basin (20%)
2) plant litter- fresh, decomposed and easily recognisable plant debris e.g. leaves, cones, needles, twigs, barks etc
- leaf tissues account for about 70% of the litter in forests, but woody litter tends to increase with forest age
3) soil humus- originates from litter decomposition and is a thick brown or black substance that remains after most of the organic litter has decomposed
- it gets dispersed throughout the soil by soil organisms such as earthworms
- in tropical, temperate and boreal forests together approx. 31% is stored in the biomass and 69% in the soil, in tropical forests 50% is in biomass and 50% in soil
4) peat- partially decayed vegetation or organic matter that is unique to natural areas called peatland, they form in wetland conditions with low oxygen (anaerobic conditions) store approx. 250GtC worldwide
what reasons help explain why carbon dioxide taken up by plants has increases since 1960?
1) increased temperatures have led to an increase in the length of the growing season so there are more plants and higher evapotranspiration rates
2) more CO2 in the atmosphere results in more photosynthesis and plant growth
3) farmland in mid-latitudes abandoned in the early 20th century were replaced by trees which store much more carbon than crops
4) more wildfires are being extinguished which leads to the build-up of woody material that stores carbon, as well as fires and deforestation elsewhere have led to increased atmospheric CO2
5) increased temperatures have warmed up the land e.g. in tundra areas warming of the land increases the rate of decay of accumulated dead organic matter leading to the release of CO2
what is meant by a greenhouse gas?
- a gas that absorbs and traps heat in the atmosphere
what happens to solar radiation when it passes through the atmosphere?
- solar radiation enters the earth’s atmosphere and is absorbed by the earths surface and warms it
- some solar radiation is reflected by the atmosphere and earths surface and some of the infrared radiation passes through the atmosphere and is lost in space
- some of the infrared radiation is absorbed and re-emitted by the greenhouse gas molecules, the direct effect is the warming of the earths surface and the troposphere
what is meant by radiative forcing?
- this is the amount that the Earth’s energy budget is out of balance
- it is the difference between incoming energy from the sun and the outgoing energy to the atmosphere, measured in watts/m2
- radiative forcing has increased since 1750 and has changed due to human emissions that emit greenhouse gases and the changing albedo effect due to land use changes
what is the most common greenhouse gas?
most common= carbon dioxide as even though a molecule of methane absorbs 30 times more infrared radiation than one of CO2, carbon dioxide remains in the atmosphere for over 100 years
what factors does the warming effect of different greenhouse gases depend on?
1) their concentration in the atmosphere
2) the wavelengths of light they can absorb
3) how long they stay in the atmosphere
how is coal and fossil fuels formed?
- trees and plants die and fall into swamps which turn into peat
- layers build up and are heated by the earth
- after years of layering the coal is pushed further into the ground so has to be extracted
why do we burn hydrocarbons?
- as they have been extracted and burnt for energy e.g. petrol in cars or coal for heat
what is a carbon sequestration?
- the capture of carbon dioxide from the atmosphere and held in a solid or liquid form
- it is a slow carbon flow as it takes millions of years for carbon to be sequestered in sedimentary rocks
what is a carbon sink and a carbon store?
carbon sink- a store of carbon that absorbs more than releases it
carbon store- when more carbon leaves a store than enters it
how does carbon flow between stores?
1) photosynthesis- tiny marine plants (phytoplankton) use energy from the sunlight to combine carbon dioxide from the atmosphere with water to form glucose and oxygen which enables plants to grow
- carbon is passed through the food chain and releases through respiration and decomposition
2) combustion- transfers carbon stored in living, dead or decomposed biomass to the atmosphere by burning e.g. wildfires cause carbon flows
3) ocean uptake and loss- carbon dioxide is dissolved from the atmosphere into the ocean and is transferred to the oceans when it is taken up by the organisms that live in them
- carbon is also transferred from the ocean to the atmosphere when carbon-rich water from deep in the oceans rises to the surface and releases carbon dioxide
4) sequestration- carbon from the atmosphere can be sequestered (captured) and held in sedimentary rocks or as fossil fuels in which they form over millions of years when dead animals and plant material in the ocean falls to the floor and is compacted in layers
- carbon in fossil fuels is sequestered until we can burn them
5) respiration- transfers carbon from living organisms to the atmosphere
- plants and animals break down glucose for energy, releasing carbon dioxide and methane
6) decomposition- transfers carbon from living organisms to the atmosphere and the soil, after death bacteria and fungi break organism down and carbon dioxide and methane are released
- some carbon is transferred to the soil in the form of humus
7) weathering- chemical weathering transfers carbon from the atmosphere to the hydrosphere and biosphere, atmospheric carbon reacts with water vapour to form acid rain and when it falls onto rocks a chemical reaction occurs which dissolves the rocks
- the molecules resulting from this reaction may be washed into the sea and here they react with carbon dioxide dissolved in the water to form calcium carbonate which is used by sea creatures e.g. to make shells
how is decomposition carried out and why is it important?
- the process is carried out by decomposers whose special role is to break down the cells and tissues in dead organisms into large bio molecules and then break those bio molecules down into smaller molecules and individual atoms
- decomposition ensures that the important elements of life e.g. carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur and magnesium, can be continually recycles into the soil and made available for life
how can plant growth be limited by the amount of decomposition and what impact does this have on the carbon cycle?
- a plant cannot make it’s DNA molecules unless it has a supply of nitrogen, phosphorus and sulphur atoms from the soil in addition to carbon, hydrogen and oxygen atoms it obtains through photosynthesis
- for this reason, plant growth is limited by the availability of nitrogen, phosphorus, magnesium and sulphur atoms in addition to the availability of carbon dioxide, water and light energy
- therefore, less plants can limit the carbon cycle as less carbon is stored in the biosphere due to less uptake from the atmosphere
what is the geological component of the carbon cycle and what happens during it?
1) in the atmosphere, carbon dioxide is removed by dissolving in water and forming carbonic acid
2) as this weakly acidic water reaches the surface as rain, it reacts with minerals at the Earths surface slowly dissolving them into their component ions through chemical weathering, and the components are then carried in surface waters like streams and rivers and eventually to oceans
3) calcium carbonate is also precipitated from calcium and bicarbonate ions in seawater by marine organisms and when these creatures die, their skeletons sink to the bottom of the oceans where they collect as sediment
4) burial by overlying layers of sediment can eventually turn these sediments into sedimentary limestone, this also happens with coral
5) the carbon is now stored below the sea floor in layers of limestone
6) tectonic uplift can then expose this buried limestone e.g. the Himalayas, tectonic forces cause plate movement to push the sea floor under continental margins in the process of subduction and the carbonaceous sea-floor deposits are pushed deep into the Earth where they heat up, eventually melt and can rise back up to the surface through volcanic eruptions
what is an oceanic carbon pump?
- this is where water is able to dissolve carbon dioxide
- at lower temperatures more carbon dioxide can be dissolved and leads to vertical deep mixing which the most important movement of carbon dioxide in the oceans
- this occurs when warm water in oceanic surface current is carried from the warm tropics to the cold polar regions, here the water is cooled, making it dense enough to sink below the surface layer
- when cold water returns to the surface and warms up again, it loses carbon dioxide to the atmosphere, this cycle carbon between the ocean and atmosphere and this vertical circulation means the ocean stores a lot more carbon
what is a biological pump (how do plants and animals move carbon from the atmosphere to the deep ocean?
- living things in the ocean move carbon from the atmosphere into surface waters when down unto the deeper ocean and eventually into rocks
- this actions of organisms moving carbon in one direction is called a biological pump
- carbon gets incorporated into marine organisms as organic matter or calcium carbonate, being eating plants e.g. phytoplankton
- when organisms die, their dead cells, shells and other parts sink into deep water where they decompose
- decay releases carbon dioxide into the deep water where some dense materials of carbon-rich sediments
- over millions of years processes turn these sediments into rocks where carbon can be stored over a long period of time
how does the biological marine pump become affected by warmer oceans?
- warmer oceans can reduce the effectiveness of the biological pump as it can decrease the abundance of the phytoplankton as they grow better in cool, nutrient-rich waters
- therefore, this could limit the oceans ability to take carbon from the atmosphere through the biological pump and lessens the effectiveness of the ocean as a carbon sink
what is biomass combustion?
- this is the burning of living and dead vegetation, it included human-included burning as well as naturally occurring fires, it happens most in:
- the boreal (northern) forests in Alaska, Canada, Russia etc
- savanna grasslands and forests in Africa, Brazil and norther Australia
- tropical forests in Brazil, Indonesia, Columbia etc
what happens during combustion?
- occurs when any organic material is reacted (burned) in the presence of oxygen to give off the products of carbon dioxide, water and energy
- the organic material can be any vegetation or fossil fuel such as natural gas (methane), oil or coal
what and how do natural processes change the carbon cycle?
1) wildfires- wildfires rapidly transfer large quantities of carbon from biomass (or soil) to the atmosphere
- a loss of vegetation decreases photosynthesis, so less carbon is removed from the atmosphere
- in the longer term, fires can encourage the growth of new plants, which take in carbon from the atmosphere for photosynthesis
- depending on the amount of regrowth, fires can have a neutral effect on the amount of atmospheric carbon
2) volcanic activity- carbon stored within the Earth in magma is releases during volcanic eruptions, the majority enters as CO2
- recent volcanic eruptions have released much less CO2, than human activities, however there is the potential for a very large eruption to disrupt the carbon cycle significantly
what and how can humans impact the carbon cycle?
1) hydrocarbon (fossil fuel) extraction and burning (cement manufacture)- dead plants and animals turn into fossil fuels following burial and the pressure from layers of sediment leads to an anoxic (oxygen free) environment that allows for decomposition to take place without oxygen
- animal remains tend to form petroleum (crude oil) while plant matter is more likely to form coal and natural gas, and when these fossil fuels are extracted from the ground and then burnt, CO2 and water are released into the atmosphere
- cement manufacture contributes CO2 to the atmosphere when calcium carbonate is heated, producing lime and CO2 and CO2 is also produced by burning the fossil fuels that provide the heat for the cement manufacture process
2) deforestation- forests may be cleared for agriculture, logging or to make way for development but clearance reduces the size of the carbon store and if the cleared forest is burned there is a rapid flow of carbon from the biosphere to the atmosphere
3) farming practices- when soil is ploughed, the soil layers invert, and it releases in soil organic matter being broken down much more rapidly and carbon being lost from the soil into the atmosphere
- animals release CO2 and methane when they respire and digest food
4) land use changes- as well as deforestation, logging operations also remove forests which leads to which means vegetation is removed to make way for buildings- this reduces carbon storages in the biosphere
- concrete production also releases lots of CO2 and lots of concrete is used when urban areas expand
5) urban growth- as cities grow, the land use changes from either natural vegetation or agriculture to one which is built up, the CO2 emissions resulting from energy consumption for transport, industry and domestic use, added to the CO2 emitted in the cement manufacture required for all buildings and infrastructure, have increases
how do changes in the carbon cycle affect the land, ocean and atmosphere?
atmosphere and climate- greenhouse gases trap some of the suns energy, keeping some of the heat in and keeping the planet warm
- as the concentrations of greenhouse gases in the atmosphere increase e.g. due to changes in the carbon cycle cause by deforestation, temperatures are expected to rise (global warming)
- changes in temperature across the globe will affect other aspects of the climate e.g. more intense storms predicted
land- the carbon cycle allows plants to grow- if there was no carbon in the atmosphere, plants could not photosynthesise, if there was no decomposition dead plants would remain where they fell and their nutrients would never be recycled
- changes in the cycle can reduce the amount of carbon stored in the land e.g. warmer temperatures caused by global warming are causing permafrost to melt which releases carbon previously stored in the permafrost into the atmosphere
- an increase in global temperatures could also increase the frequency of wildfires
oceans- CO2 is dissolved directly into the oceans from the atmosphere and it is used by organisms such as phytoplankton and seaweed during photosynthesis and by other marine organisms to form calcium carbonate shells and skeletons
- increased levels of CO2 in the atmosphere can increase the acidity of the oceans as the oceans initially absorb more CO2
- global warming can also affect oceans e.g. organisms that are sensitive to temperature e.g. phytoplankton, may not be able to survive at higher temperatures, so their numbers decrease leading to less CO2 used for photosynthesis and therefore less carbon is removed from the atmosphere
- warmer water also means it is less able to absorb CO2, so as temperatures rise the amount of CO2 that could potentially be dissolved in the sea decreases
how are humans trying to influence the carbon cycle?
individual- people can choose to use their cars less and buy more fuel efficient cars, they can also make their homes more energy efficient, e.g. with double glazing, insulation and more efficient appliances
regional and national- governments can reduce reliance on fossil fuels for heating and powering homes by increasing the availability and reducing the cost of renewable energy sources e.g. wind, tidal and solar
- afforestation and restoring degraded forests can increase carbon uptake by the biosphere
- planners can increase the sustainability of developments by improving public transport (to reduce car use) and creating more green spaces
- governments can also invest in carbon captures and storage so CO2 emitted from burning fossil fuels is captured and stored underground e.g. in depleted oil and gas reservoirs
global- countries can work together to reduce emissions e.g. the Paris agreement and more are international treaties that help to control the amount of greenhouse gases releases
- international carbon trading schemes help to give countries and businesses a limit on the emissions they can produce- if they produce less they can sell the extra credits, if they produce more they need to buy more credits
what case study is representative of the carbon cycle and why is it important?
- the Amazon rainforest in South America and it covers 40% of the South American landmass with a hot, very wet climate and very dense vegetation
- it is home to up to 1 million plant species, over 500 species of mammals and over 2000 species of fish
- it is also home to many endangered species including the Amazonian manatee etc
- today, the Amazon rainforest is home to 34 million people who depend on the resources it provides as it covers 9 countries
how is the water cycle important to the Amazon environment?
water cycle- this cycle causes the Amazon to be very wet as there is a lot of evaporation over the Atlantic Ocean, and the wet air is blown towards the Amazon which contributes to the Amazons very high rainfall
- warm temperatures mean that evaporation is high in the rainforest itself, which increases the amount of precipitation and increase growth of vegetation
- the rainforest has a dense canopy meaning that interception is high and as a result of this less water flows into rivers and does so more slowly
- the water cycle also helps maintain high humidity and infrequent rainfall for the species that are adapted there
how is the carbon cycle important to the Amazon environment?
carbon cycle- the amazon rainforest acts as a carbon soil due to the large storage of carbon in it’s vegetation and soil
- the increasing concentration of CO2 in the atmosphere has led to increased productivity in the rainforest as the vegetation is able to access more CO2 for photosynthesis this results in the amount of biomass increasing
- as a result, the amount of CO2 sequestered by the rainforest has increases, making it an even more important carbon store, however it is suggested that although trees are growing more quickly, they’re also dying young
- a s result, we may not be able to rely on the Amazon rainforest to continue to be such an effective carbon sink in the future
how is the human activity of deforestation effecting the water cycle and the carbon cycle?
water cycle- in deforested areas there is no tree canopy to intercept rainfall, so more water reaches the ground surface but there is too much rainfall to intercept into the soil so instead the water moves to rivers as surface runoff, which increase the risk of flooding
- deforestation also reduces the rate of evapotranspiration, this means less water vapour reaches the atmosphere, fewer clouds form and rainfall is reduced, increasing the risk of drought
carbon cycle- without roots to hold the soil together, heavy rain washes away and the nutrient-rich top layer of soil, transferring carbon stored in the soil to the hydrosphere
- deforestation also means that there is less leaf litter, so humus is not formed and the soil cannot support much new growth which limits the amount of carbon that is absorbed
- trees remove CO2 from the atmosphere and store it, so fewer trees means more atmospheric CO2, which enhances the greenhouse effect and global warming
how are certain factors different between areas of forest and pasture land?
forest- there is an increase in trees present so stores more carbon
- there is more evapotranspiration, precipitation, vegetation and air humidity
- stores more soil carbon (4-9gkm2) and has a temperature of 21.4 degrees
pasture- has less trees and vegetation (mainly grassland) so stores less carbon
- evapotranspiration decreases and there is increase moisture
- stores less soil carbon (less than 1 kg/m2) and has a temperature of 33 degrees
what are some of the attempts that limit human impacts on the Amazon?
1) replanting (afforestation)- new plants are planted to replace the ones that are cut down and it is important that the same type of trees are planted that were cut down, so that the variety of trees is kept for future and the local carbon and water cycles return to their initial state
2) forest protection- many countries have set up national parks and nature reserves to protect rainforests e.g. the central amazon conservation complex in Brazil was set up in 2003 and protects biodiversity in an area of 49000km2 while allowing local people to use the forest in a sustainable way
- within national parks and nature reserves, damaging activities such as logging can be monitored and prevented
3) reforestation- this is the conversion of previously forested land back to forest so helps restore habitats for wildlife
4) environmental laws- e.g. laws that ban the use of wood from forests that are not manages suitably, laws that ban excessive logging, laws that control land use e.g. the Brazilian Forests code says that landowners have to keep 50-80% of their land as forest
5) selective logging- only some trees (older ones) are felled, this is less damaging to the forests than felling all the trees in the area, if only a few trees are taken from each area then the structure of the forest is kept
- the canopy is still there and the soil is not exposed meaning the forest is able to regenerate, so the impact on the carbon and water cycle is small
what are the advantages and disadvantages of using these methods?
advantages- protection of existing forests will preserve current soil carbon stocks and forests will remain as a carbon sink
- there will be increased carbon density above and below ground
- trees in croplands can be economically sustainable as they produce products e.g. apples from orchids without removing vegetation
- they can provide oxygen and increase air quality
disadvantages- albedo effect reflects sunlight due to darker colour of land so increases global temperatures
- if planted in the wrong places they can dry up streams and rivers as well as peat so they release carbon
- non-native trees can take over and decrease surrounding biodiversity so money is then spent to clear them
- billions of trees are lost every year due to fires so the act of reforestation and protection is increased
monoculture trees can result in the spread of disease
- payment systems do not prioritise protection of trees yet they prioritise planting so intern they need to prioritise both
what are the problems with planting trees?
- costly to buy the seeds
- no space to plant, however farmland could be used but the risk of having no room for the growth of food is possible
- they can respire and release carbon back into the atmosphere
- risk of being burnt from wildfires so CO2 is released into the atmosphere and carbon is never fully removed
- plantations are slow growing ad require active monitoring and managing for a lifetime
- certain plantation of trees can result in the disruption of the whole ecosystem
what is a natural / terrestrial carbon sequestration?
-this involves the use of plants to capture CO2 from the atmosphere and then to store it as carbon in the stems and roots of the plants as well as in the sol
- the aim is to develop a set of land management practices that maximises the amount of carbon that remains stored in the soil and in plant material for the long term
- it can also help to enrich wildlife
what are the disadvantages to terrestrial sequestration?
- a forest planted to capture carbon might lose that carbon back to the atmosphere e.g. in a forest fire or if the forest suffers disease
- land-based sequestration plantations are slow growing and require active monitoring and management for the lifetime of the plantation usually many decades
how do we reduce soil carbon when using farming techniques?
- avoid overstocking of grazing animals as they reduce the amount of carbo stored in the soil
- adding manure instead of fertiliser increases plant growth and therefore increases carbon store
- reduce ploughing which prevents fast decomposition
- mulching adds organic matter and prevents carbon loss
- rotate cash crops to increases plant growth and carbon storage
what is a carbon budget?
- the amount of carbon stored and transferred within the carbon cycle on global or local scales
what is a carbon footprint?
- the total amount of greenhouse gases produced (directly and indirectly) to support human activities, and expressed in gigatonnes of carbon dioxide equivalent per year (Gtc/yr)
how do scientists measure CO2 in the air?
- a glass flask air sample is taken as air rushes in and CO2 is measured in a lab
- the air is sent through an analyser and a monometer distinguishes where it came from e.g. cars or oceans, and also analyses the isotopic concentration
- the air is measured in the same place to keep the variable the same and increase consistency
what is happening to the ocean sink and amount of CO2 store on land as CO2 emissions and atmospheric concentrations increase?
- as carbon emissions increase the ocean sink also steadily increases overtime
- as atmospheric concentrations increase the amount of CO2 absorbed by the ocean and land levels off as it has a limit to how much CO2 it can dissolve so more is emitted back into the atmosphere
what is meant by ocean acidification and how does it occur?
- about 30% of the CO2 that has been released into the atmosphere ha diffused into the ocean through direct chemical exchange
- dissolving carbon dioxide in the ocean creates carbonic acid, which slightly changes the pH of the ocean to become more acidic
how does ocean acidification affect marine organisms and coral reefs?
- carbonic acid reacts with carbonate ions in the water to form bicarbonate, however those same ions are what marine organisms e.g. planktonic species and coral need to create their calcium carbonate shells
- with less carbonate available, the animals need to expand more energy to build their shells and as a result the shells end up being thinner and more fragile
- coral reefs provide food and livelihood security for some 500 million people worldwide, but there is significant reef loss due to the loss of carbonate ions and the consequent fall in marine biodiversity threatens the survival of coastal communities through reduced food availability and a reduced capacity of coastlines to buffer the impact of seal level rise (increasing storm surges)
how is warmer temperatures impacting the oceans salinity?
- if there is less sea ice then there will be an increase in the absorption of the earths energy due to the dark ocean surfaces (albedo effect)
- melting of freshwater ice will decrease the oceans salinity as the water will warm and then less cold-carbon water will sink which impacts the ocean currents (conveyor)
what are the main reasons for sea levels rising?
- sea ice melting
- thermal expansion
what are the negative impacts of melting sea ice?
- in the last 35 years satellites monitoring sea ice in the Arctic have measured a retreat of 12,8% per decade
- when the sea ice melts, it is not just an indicator of a warming climate but also part of a feedback loop as the reflective ice is replaced by more heat absorbent water so when it starts to melt the ocean is able to absorb more sunlight, which in turn amplifies the warming that caused the ice melting in the first place
- sea ice also provides a unique habitat for algae that appears in more concentrated forms so the loss of ice-bound algae affects marine life all the way up the food chain, from krill and fish to seals, walruses and polar bears
- animals like polar bears, that rely on sea ice to get their main food source of seals, can no longer travel upon it
what is meant by thermal expansion and how is it affecting the ocean?
- as the ocean absorbs the trapped heat, it’s temperature rises and water expands contributing to an increase in global sea levels
