Earth's Life Support Systems Flashcards
(135 cards)
1
Q
What is a systems approach?
A
A model used to help explain phenomena where relationships are examined between a number of components that are linked.
2
Q
What is an open system?
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A type of system whose boundaries are open to both inputs and outputs of energy and matter.
3
Q
What is a closed system?
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A system with inputs and outputs of energy, but without any movement of materials across system boundaries.
4
Q
Define inputs
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An addition of energy and/or materials to a system. E.g light energy from the sun and materials from comets
5
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Define outputs
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The transfer of energy and/or materials out of a system. E.g. astronauts have left materials in space
6
Q
Define stores
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The amount of the total material held within parts of the system.e.g. Fossil fuels are energy stores and crust is a material one
7
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Define flows/transfers
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The transfers of energy or material between the stores. E.g. rivers transfer water and energy
8
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Define flux
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Measurement of rate of flow/transfer between stores. Usually measured in petagrams(Pg)/gigatonnes(Gt) (billion tonnes) per year.
9
Q
Define processes
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The physical mechanisms that drive the flows of energy and material between stores.
10
Q
Define feedback
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The return ‘loop’ where the outputs and consequences have a positive or negative impact on the inputs, altering the subsequent operation of the system.
11
Q
Define negative feedback
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An automatic response to change in a system that restores equilibrium.
12
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Define positive feedback
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An automatic response to change in a system that generates further change
13
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Define dynamic equilibrium
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A system displaying unrepeated average states through time. Even if it is modified by geomorphic processes the general state does not change - it remains in balance. E.g. rivers will always follow essentially the same route every time.
14
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Define mass balance
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Calculation of inputs versus outputs eg water balance would measure rainfall versus evaporation and runoff. Can be +ve or -ve.
15
Q
What is geomorphology?
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the study of the physical features of the Earth’s surface, i.e. the landscape and the different landforms that are contained within it.
16
Q
Which type of systems are water and carbon cycles at a global and local scale?
A
At global scale = closed systems ( only energy crosses boundaries). Time scales vary from days to millions of years.
On smaller scales water and carbon cycle = open systems (material and energy can cross boundaries).
Oceans contain 97% of all water. Other stores include polar ice and glaciers (cryosphere), groundwater, lakes, soils, atmosphere and the biosphere
17
Q
Why is water important for supporting life on the planet?
A
A medium that allows organic molecules to mix/form complex structures. Ubiquity of water due to ‘Goldilocks zone’ from the Sun. more water = more lifeforms. Helps create benign thermal conditions for the earth. Oceans moderate temperatures by absorbing, storing and releasing heat. Clouds containing water particles reflect 1/5th of solar radiation and lower surface temperatures. Water vapour (greenhouse gas) absorbs longwave radiation from the earth to maintain average global temperatures.
18
Q
Why is water important for flora, fauna and people
A
Makes up 65-95% of all living organisms. Crucial for growth, reproduction and metabolic functions. Plants need it for photosynthesis, respiration and transpiration and to maintain rigidity and transport mineral nutrients from the soil. In mammals water is the medium used for all chemical reactions in the body including the circulation of oxygen and nutrients. Sweating and panting cools mammals.
19
Q
Why is water important economically?
A
Used to generate electricity, irrigate crops, provide recreational facilities and satisfy public demand (drinking water, sewage disposal). Used in many industries such as: food manufacturing, brewing, paper and steel making.
20
Q
Describe evaporation, what is net evaporation?
A
The process by which liquid water is converted into a gaseous state. Large proportion of pathway from liquid to vapour. 90% moisture in atmosphere from oceans, seas, lakes and rivers. 10% transpiration. Heat energy breaks bonds. Net evap = rate of evap > rate of condensation. If equal called saturation state. Amount evaporated = amount falling but only 10% falls on land. Used to desalinate water and extract minerals from lakes.
21
Q
Describe sublimation
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The phase change of water from ice to vapour without becoming a liquid. Low humidity and dry winds preferable. Happens more at high altitudes. Needs energy
22
Q
Describe transpiration
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Evaporation of moisture from pores on the leaf surfaces of plants.
23
Q
Describe run-off
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The movement of water across the land surface.
24
Q
Describe evapotranspiration
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Combined loss of water at the surface through evaporation and transpiration by plants. Water evaporated from ground surface and transpiration of groundwater. Varies depending on factors such as temperature, wind, soil, plant and sunlight.
25
Describe infiltration
Vertical movement of rainwater through the soil. Dependent on ground condition, precipitation amount, soil saturation. Some remains in shallow soil layers moving vertically and horizontally, others recharge aquifers deeper underground.
26
Describe condensation
The phase change of water vapour to water. Forms clouds as moisture particles combine with dust and smoke. Happens higher where it is less dense and cooler. Clouds regulate solar energy flow to the earth meaning any changes can have huge impacts. Fog forms when high humidity causes a cooler surface. Occurs at dew point.
27
Describe precipitation
Moisture (rain, snow, hail) falling from the clouds towards the ground.
28
Describe percolation
The movement of surface and soil water into underlying permeable rock. Primary connection that provides an input to the earth.
29
Describe ablation
The loss of ice and snow, especially from a glacier, through melting, evaporation and sublimation.
30
Describe groundwater flow
The horizontal movement of water within aquifers. Major contributor to flow in streams and rivers. Some infiltrates to aquifers (where spaces between soil and rock particles can be totally filled with water). Flow depends on layers of rock and soil permeability.
31
How do we calculate the global water budget?
INPUTS = OUTPUTS
Precipitation = evaporation & transpiration + surface & sub-surface flows
32
Why does air rise?
convection (surface heated by solar radiation) or orographic uplift.
33
Why does air cool?
if it comes into contact with a cool surface: by moving horizontally across the surface (advection - could form stratiform clouds) or by radiation cooling (ground rapidly loses heat through terrestrial radiation by conduction). When air cannot absorb any more water vapour (at dew point) the water is contains will condense an form clouds. Some do not produce precipitation as small particles are kept buoyant by rising air currents. When particles aggregate reach a critical size they will fall to earth.
34
What is adiabatic expansion?
parcel of air warmed by ground so it is warmer than surrounding air. Rises by convection as it is less dense. Becomes cooler due to the expansion of a parcel of air due to a decrease in pressure which causes cooling. Dew point is reached and at this altitude base of clouds form or will rise further is dew point not reached.
35
What is ELR?
(Environmental Lapse Rate) - vertical temperature profile of the lower atmosphere at any given time. On average temp falls by 6.5 degrees for every km of height gaines. Due to decrease in atmospheric pressure with height and particles get further apart and cooler.
36
What is DALR?
(Dry Adiabatic Lapse Rate) - rate at which a parcel of dry air cools. Cooling caused by adiabatic expansion is 10 degrees/km.
37
What is SALR?
(Saturated Adiabatic Lapse Rate) - the rate at which a saturated parcel of air (condensation is happening) cools as it rises through the atmosphere. Requires latent heat for condensation (7 degrees/km). Lower than DALR. heat released into atmosphere and rate of temperature decrease is less.
38
Describe absolute instability of a parcel of air?
Parcel of air warmer than surroundings so is less dense and rises (unstable). Ability to hold water decreases with altitude so dew point reached and becomes saturated (cloud base). Lapse rate decreases but air is still water so still rises (unstable). Produces cumulonimbus clouds on hot British days.
39
Describe absolute stability of a parcel of air?
Temperature of surroundings higher than more dense air particle. Will not rise and stays close to the surface (stable). Typical summer conditions with cumulus clouds with no rain.
40
Describe conditional instability of a parcel of air?
The temperature of the parcel of air is cooler than the surroundings so will not rise and is stable. eventually it will pass through the dew point and will decrease temperature more slowly. The parcel of air then becomes warmer and less dense and will rise. If the air is forced upwards (e.g. a mountain) high enough it will become warmer than the surroundings and it condenses it will become unstable. This is called conditional instability. Common in Britain.
41
What is a catchment area?
(drainage basin) - an area of land that contributed water to a particular stream or river. Can be large (Thames) or small scale.
42
What is a watershed/drainage divide?
boundary between 2 adjacent drainage basins
43
What 4 factors affect the amount of water in a catchment area?
1. Type of precipitation (rain or snow) - Most rain on reaching the ground flows quickly into streams and rivers. But at high latitudes and mountainous catchments, precipitation often falls as snow and can remain on the ground for months so there may be a lot of time between snowfall and run-off.
2. As intensity increases water moves rapidly overland into streams and rivers.
3. Duration of precipitation - Prolonged events, linked to depressions and frontal systems may deposit exceptional amounts of rain and cause river flooding.
4. Seasonal variation- In some parts of the world (e.g. East Africa) precipitation is concentrated in the rainy season. During this season river discharge is high and flooding is common. In the dry season ricers may cease to flow altogether.
44
Describe interception (store)
Trapping and temporary storage of precipitation on surfaces if plant leaves, stems and branches. Occurs in urban areas on roofs etc.
Loss of water by interception annually = 30-60% grass, 30-35% coniferous forest, 7-15% cereal crops in season.
Factors affecting vegetation type- larger from grasses than crops. Trees (large SA and aerodynamic roughness) higher. Greater from evergreen conifers than deciduous. Have leaves all year and water adheres t spaces between needles = increased evap. Increases with wind speed. Initially as rainfalls onto dry surfaces most is intercepted but as it becomes saturated output through stemflow etc increase. Depends on duration and intensity of a rainfall event.
45
Describe surface stores
Depression storage- water collects in small hollows or depressions on the ground surface.
46
Describe the soil moisture store
Water stored temporarily near to the ground surface in the soil.
47
Describe groundwater stores
Water stored underground in permeable and porous rocks known as aquifers. A saturated zone below the water table. Varies seasonally, falls in summer with increased evaptran.
48
Describe groundwater flow
The horizontal movement of water within aquifers.
The slow lateral transfer of water through saturated soil or rock (below the water table).
This is very slow as water usually flows through solid rock (few pores). It can be rapid in highly permeable rocks. Water enters river channels through banks and begs. Mountains channel flow during droughts
49
Describe throughfall (flow)
Water drips from leaves and branches onto the ground.
50
Describe stemflow
Water flows down the trunk or stem of a plant.
51
Describe overland flow
what are the two different types?
Rainfall that runs off the ground surface either because the soil is saturated or the intensity of rainfall exceeds the soil’s infiltration capacity. Movement of water over the land surface as sheet flows or in small channels (rills). This is a very rapid transfer and uncommon in the UK. It will cause flooding.
Saturated overland flow- if the soil is saturated or frozen meaning water can’t infiltrate the soil and so flows over the surface. There is a link to antecedent precipitation (rainfall over previous days).
Infiltration excess overland flow - Happens when the intensity of precipitation is greater than the infiltration capacity of the soil. This is rare but could occur in thunderstorms or if the ground is bare and compacted.
52
Describe infiltration (flow)
What factors affect the rate of infiltration?
The vertical movement of rainwater through the soil. Infiltration capacity- the maximum rate at which water can enter the soil (mm/hour).
Factors affecting: soil type, land use - sandy soil has higher infiltration than clay as macropores allow faster transfer than micropores. Crop use for land will increase as roots act as channels. Saturates land will reduce infiltration and can cause flooding. Antecedent precipitation- lots of rain will reduce it as saturated soil cannot absorb any more. Dry soil is better. Start of rain will infiltrate better before saturation.
53
Describe throughflow
Water flowing horizontally (lateral transfer) through the soil to stream and river channels. This occurs in a downslope direction parallel to the ground surface and above the water table. This is slow compared to overland flow and accounts for the majority of transfer to river channels. It may flow through pore spaces or more quickly as pipe flow along routeways formed by roots, burrows or cracks
54
Describe percolation (flow)
The movement of surface and soil water into underlying permeable rocks.
55
Describe evaporation
The process by which liquid water is converted into a gaseous state. This is most rapid when the air is warm and dry. Latent heat energy is stored in vapour and is released as condensation. Allows lots of heat to be transferred around the planet.
56
Describe transpiration
what factors affect the rate of transpiration?
The evaporation of moisture from pores on the leaf surfaces of plants. Water is released through the stomata. Gets there through the roots from groundwater/soil stores and transferred up plants.
Factors affecting - increased temperature increases it as more heat energy to evap. High wind speeds increase ad moving air will remove water vapour increase diffusion from leaf. High water availability increases it as more taken up.
57
Describe evapotranspiration
The combined loss of water at the surface through evaporation and transpiration by plants.
58
Describe channel run-off
All water that enters a river channel and flows out of the drainage basin.
59
What are the 2 effects of cryospheric processes?
1. Ablation- causes rapid loss of snow in upland areas and flooding in lowland areas. More ablation = more water running into catchment areas and more in rivers and soil.
2. Meltwater - important components of river flow in high latitudes and mountain catchments in summer. Melted snow = more water in catchment area as more flowing down from high altitudes.
60
Describe short-term diurnal changes to the water cycle
significant changes within a 24 hr period. Lower temperatures at night reduce evaporation and transpiration. Convectional precipitation, dependent on direct heating of the ground surface by the Sun, is a daytime phenomenon that falls in afternoon. Common in tropics where most precipitation is from convectional precipitation. Changes in weather will affect stores and flows. Snow and ice will melt at higher temperatures in the day and increase stores and flows.
61
Describe seasonal changes to the water cycle
seasons are controlled by variation in the intensity of solar radiation. Small scale changes. Highest radiation in summer (800W/m2) and lowest in winter (150). Evapotrans. greatest in summer where 80% precipitation lost and soil moisture loss will cause low river levels. In winter there is likely to be more snow.
62
How do landforms give evidence for climate change?
Features such as U-shaped valleys, roche moutonnees, erratic boulders and moraines show glaciers have been present. Some periglacial landforms e.g. deep ice wedges can give numerical estimates as they were only formed at temperatures below -6 degrees. Valley glaciers are used with accumulation area ratio technique to show the area above the summer snowline is 2/3rds of the glacier surface area. This correlates with average temperature for present day glaciers. Mapping the surface area of a former glacier from the field evidence for moraines and glacial erosion means that the likely altitude of the glacier’s summer snowline can be estimated. This allows the size and shape of the glacier to be estimated.
63
What are the limitations of using landforms as evidence for climate change?
It is difficult to use landforms to provide quantitative evidence for the magnitude of climate change. Humans can obscure landforms by building on them etc.
64
How do ice cores provide evidence for climate change?
High resolution over 1000s of years. Cores several km in length can be extracted from the Greenland ice sheet from over 100,000 years ago. The Antarctic ice records even longer periods. Layer counting makes this very accurate. Measures of snowfall totals, atmospheric gas in bubbles and dust concentration and temperatures can be taken. 16O and 18O isotopes are used. They form water molecules which condense at different temperatures. (18O condenses first when air is cooled). The ratio between the isotopes can be used to reconstruct the temperature at the time.
65
What are the limitations of using ice cores as evidence for climate change?
Proxy evidence- limited accuracy of temperatures estimated from those oxygen isotope records. As global ice sheets grew during the ice age a huge volume of water stored as ice altered the oxygen isotope composition of seawater. The increasing elevation of the surface of a growing ice cap would be expected to lead to a decrease in temperatures. Difficult to get evidence- equipment/funding/storage needed.
66
How do fossil records provide evidence for climate change?
Temperature and precipitation are controls on the distribution of plant and animal species. Comparison between species’ fossil and present-day distributions can be used to estimate past conditions. Beetle species can be compared to the environment at the time in a ‘mutual climatic range’.
67
What are the limitations of using fossil records as evidence for climate change?
Proxy data relies on us finding the fossils. Fossils may have been moved by glaciers, oceans etc.
68
How is pollen used as evidence as climate change?
Plant pollen is produced in large quantities by flowering plants and long distance wind dispersal means that a single site can give a broad picture of the surrounding vegetation diversity. The durable exine (outer wall) of pollen grains can survive for thousands of years in suitable conditions such as bogs. Other organic remains such as fossils, seeds, bones and snail-shells. Can be extracted from peat bogs or sediments.
69
What are the limitations of using pollen as evidence for climate change?
There may be a time lag between climatic change and the organism’s response (e.g. seed dispersal from its original place to other sites).
70
What is eustatic sea level change and what is it caused by?
global changes in sea-level due to changes in the atmosphere. Caused by melting glaciers and ice sheets and increases in ocean temperatures.
71
What is isostatic change to the water cycle and what are the three main changes that occur?
crust rising and falling may cause ice sheets to melt if its weight causes a depression of the crust.
1. The net transfer of water from the ocean reservoir to storage in ice sheets, glaciers and permafrost. In glaciers the sea level worldwide falls by 100-130m and ice sheets and glaciers expand to cover ⅓rd of the continental land mass. As ice sheets advance towards the Equator they destroy forests and grasslands.
2. The area covered by vegetation and water stored in the biosphere shrinks. In the tropics the climate becomes drier and deserts and grasslands displace large areas of rainforest.
3.There are lower rates of evapotranspiration during glacial phases that reduce the exchange of water between the atmosphere and the oceans, biosphere and soils. This together with so much freshwater stored as snow and ice, slows the water cycle.
72
How has sea level changed over time?
Generally over time, the sea level has risen steadily until a period of plateau from approximately 4AD. 16BC was when the sea level was at its lowest due to most water being stored as Devensian ice. Since then, as temperatures rise the sea level has increased especially during the Flandrian Transgression. Since 4AD sea level has changed minimally with only tiny fluctuations in height.
73
How does deforestation affect the water cycle (human factor)?
Stores - greater soil store and lower biomass store
Flows - Less interception by vegetation so more reaches the groundwater stores and erodes soil.
74
How does ploughing affect the water cycle (human factor?
Stores - Soil moisture is brought up to surface stores. Soil moisture store is decreased.
Flows - Crop harvesting means little organic matter is returned to the soil.
Increased evaporation and soil moisture loss. Furrows ploughed downslope act as drainage channels, accelerating run-off and soil erosion. Infiltration is greater. Increase in overland flow.
75
How has irrigation affected the water cycle (human factor)?
Stores - Increase of water in soil storage.
Flows - Diverts surface water from rivers and groundwater to land. Some water is extracted by crops from soil storage and released by transpiration but most is lost to evaporation and soil drainage. Surface runoff increases
76
How does the underground drainage of soils affect the water cycle (human factor)?
Stores - The drainage of soil will decrease the groundwater and soil stores.
Flows - Artificial underdrainage increases the rate of water transfer to streams and rivers.
77
How does the compaction of soils affect the water cycle (human factor)?
Stores - Erosion by wind and water especially when crops are lifted and little protective cover. Soil moisture store will decrease.
Flows - Infiltration will decrease. There is less interception increasing soil erosion and may cause flooding. More evaporation and overland flow.
78
How does the replacement of vegetation and soil with impermeable surfaces affect the water cycle (human factor)?
Stores - Provide minimal water storage capacity. Less water is stored in groundwater stores.
Flows - Allow little or no infiltration.
More run-off therefore there is more water on the surface and there will be more evapotranspiration from the surface.
79
How does the construction of drainage systems affect the water cycle (human factor)?
Stores - Rising water level as surface water is removed. Reduces groundwater/surface storage.
Flows - A high proportion of precipitation flows quickly into streams and rivers.
80
How does encroachment on floodplains affect the water cycle (human factors)?
Stores - Reduces water storage capacity. Permeable surfaces are replaced with impermeable.
Flows - River flow increased and flood risks occur.
81
How does planting new trees affect with examples:
a) Interception
b) Evaporation
c) Run-off and channel flow
d) transpiration
a) Higher rates - interception rates for Sitka spruce are as high as 60%. In upland Britain, where temperatures and evaporation are lower, interception is half this. Needle-like structures of conifer leaves, their evergreen habit and high density all cause high rates of intersection.
b) Increased - A large proportion of intercepted rainfall is stored on leaf surfaces and is evaporated directly to the atmosphere.
c) reduced - High interception and evaporation rates and the absorption of water by tree roots, drainage basin hydrology is altered. Streams draining plantations have long lag times, low peak flows and low discharge. Conifer plantations reduce water yield.
d) increased - typical values for Sitka spruce in Pennines are around 350mm/year of rainfall equivalent.
82
What is a glacial period?
A prolonged cold climatic phase lasting for tens of thousands of years and causing continental glaciation in middle and high latitudes. More water stored on land in ice and snow so sea levels drop.
83
What is an interglacial period?
A period of climatic warming (lasting c.10,000 years) between glaciers. More rain and melting.
84
What changes have occured in the water cycle in the last 400,000 years?
4 major glacial cycles with cold glacial periods followed by warmer interglacials. Each lasted around 100,000 years with temperatures fluctuating between 2 to -8 degrees. 20,000 years ago average temperatures in UK was 5 degrees lower in glacial period. In interglacial periods the temperatures were similar to today. Climatic shifts have major impacts.
85
What changes have occured in the water cycle in the last 21,000 years?
peak of last ice age to deglaciation and current interglacial period (Holocene). 21,000 years ago UK covered in 300m thick ice. 15,000 years ago sudden and dramatic warming. Temp rose to close to today's (called lateglaical interstadial). 13,000 glaciers melted. Orbital variations in solar radiation inputs crease ice ages but warming period so fast it was amplified by small changes in day length and solar intensity. Ocean currents important. Between 12,900 and 11,5000 years ago there was a dramatic cold episode. Glacial features and moraines are from then (called Younger Dryas stadial). 400km thick glaciers. Spring snowmelt floods deposited coarse gravel in lowland areas and permafrost/solifluction happened. Tundra vegetation returned. May have been caused by ocean currents as deep water circulation ceased before this occurred as meltwater inputs reduced the density of surface sea waters causing temp to fall. 10,000 climate becomes like today and temperate species spread. 100m sea level rise. Period of climatic stability. 8200 years ago most significant fluctuation with a dip. Some subtle trends - may have been 2 degrees warmer 5000 years ago in ‘climatic optimum’. Most recent was medieval warm period from 750AD to 1300. 1600 to 1850 ‘Little Ice Age’ and Alps extended. Bond cycles show abrupt climate shifts every 1470 years.
86
What is surface water extraction?
From rivers and lakes; may be temporarily stored in reservoirs before use
87
What is an aquifer?
a water-bearing band of porous or permeable rock.
88
How is groundwater extracted?
extracted from wells and boreholes.
89
How does groundwater extraction contribute to base flow in rivers?
emerging in springs and seepages, groundwater feeds rivers and makes a major contribution to their base flow.
90
What is the water table?
the upper surface of the zone of saturation in permeable rocks and the soil.
91
What causes fluctuation in the water table?
periods of exceptional rainfall, drought and abstraction.
92
What is the role of a syncline in an artesian basin?
a downfolded, basin-like geographical structure that contains groundwater.
93
Define artesian pressure
the hydrostatic pressure exerted on groundwater in a confined aquifer occupying a synclinal structure.
94
Define artesian aquifer
a confined aquifer containing groundwater that when tapped will rise to the surface under its own pressure.
95
Define a potentiometric surface
an imaginary surface that defines the theoretical level to which water would rise in a confined aquifer.
96
Why is the carbon cycle important?
Makes up many life forms - life is built on large molecules of carbon atoms such as proteins, carbohydrates and nucleic acids.
We use it in many different ways (economic reserve) - fossil fuels power the global economy. Oil is used to make products such as plastics and synthetic fabrics. Agricultural crops and forest trees also store large amounts of carbon available for human use as food, timber, paper etc.
97
What is the largest carbon store and its residence time?
Sedimentary rocks/lithosphere - (60,000,000 - 100,000,000 Gt. 99.9%.
Residence time (average length of time carbon remains in stores)- 150 million years
98
Describe respiration
The process of living organisms where the intake of oxygen oxidises organic substances to produce energy and release carbon dioxide.
99
Describe decomposition
the breakdown of animal and plant structures by bacteria and the release of carbon compounds into the atmosphere, soil and to the ocean floor.
100
Describe photosynthesis
Process by which green plants convert water and carbon dioxide into starch and sugar in the presence of sunlight.
101
Describe combustion
The burning of organic material.
102
Describe oxidation
A chemical process that weathers certain types of rock and involves the absorption of oxygen from either the atmosphere or water by rock minerals.
103
Describe weathering
The in situ breakdown of rocks exposed at, or near, the land surface by physical, chemical and biological processes.
104
Define volcanic activity
An opening in the Earth’s crust from which lava, ash and hot gases (include carbon) flow or are thrown out during an eruption.
105
What is a carbon sink?
long-term store of carbon in ocean sediments, carbonate rocks, forests etc.
106
Why is carbon stored in biosphere important despite its small quantities?
important because it is used for plant growth and therefore food sources. It is the basis for all new living things. Carbon cycles more quickly between these stores.
107
Describe the slow carbon cycle
Carbon stored in rocks, sea-floor sediments and fossil fuels is locked away for millions of years.
Between 10 and 100 million tonnes a year is cycled.
Residency time for carbon held in rocks is about 150 million years.
Diffuses from the atmosphere into the oceans where marine organisms make their shells and skeletons by fixing dissolved carbon together with calcium to form calcium carbonate. On death, the remains of these organisms sink to the ocean floor. There they accumulate and over millions of tears, heat and pressure convert them to carbon-rich sedimentary rock.
Returned to atmosphere by:
Subduction - Some carbon-rich sedimentary rocks, subducted into the upper mantle at tectonic plate boundaries, are vented to the atmosphere in volcanic eruptions.
Chemical weathering - Other rocks exposed at or near the surface by erosion and tectonic movements are attacked by chemical weathering. E.g. carbonation - the result of precipitation charged with carbon dioxide from the atmosphere which causes a weak acid that attacks carbonate minerals in rocks, releasing carbon dioxide to the atmosphere.
Carbon becomes stored in carbonaceous rocks when partly decomposed organic material may be buried beneath younger sediments to form rocks such as coal, oil, gas - acts as carbon sink. Formed from plant matter on land whereas others are formed in oceans.
108
Describe the fast carbon cycle
Between 10 and 1000 times faster than the slow carbon cycle.
Phytoplankton - Tiny photosynthesising marine organisms in the surface waters of the ocean. They absorb carbon dioxide from the atmosphere and combine it with water to make carbohydrates.
Atmosphere to oceans - Atmospheric carbon dioxide dissolved in ocean surface waters while the oceans ventilate carbon dioxide back to the atmosphere.
Natural sequestration - The process of storing carbon dioxide in underground geologic formations. Individual carbon atoms are stored in the oceans for 350 years.
109
Describe precipitation
moisture (rain, snow, hail) falling from clouds to the ground. Atmospheric carbon dioxide dissolves in rainwater to form weak carbonic acid (this is a natural process). rising concentrations of carbon dioxide due to anthropogenic emissions have increased the acidity of rainfall. contributed to increased acidity of ocean surface waters with potentially harmful effects on marine life.
110
Describe photosynthesis
Process by which green plants convert water and carbon dioxide into starch and sugar in the presence of sunlight. 120 GT a year. Sun’s energy is used with carbon dioxide from the atmosphere and water, green plants and marine phytoplankton through the process of photosynthesis. plants use energy in the form of glucose to maintain growth, reproduction and other processes and release carbon dioxide back into the atmosphere.
6CO2 + 6H2O → C6H12O6 + 6O2
111
Describe respiration
The process of living organisms where the intake of oxygen oxidises organic substances to produce energy and release carbon dioxide. carbohydrates fixed in photosynthesis are converted to carbon dioxide and water
CH2O + O2 → CO2 + H2O + energy
plants and animals absorb oxygen which burns carbohydrates and provides energy needed for metabolism and growth. This process absorbs O2 and emits CO2. One of the two most important processes in the fast carbon cycle. The volume of carbon exchanged by respiration and photosynthesis each year is one thousand times greater than that moving through the slow carbon cycle.
112
Describe decomposition
The breakdown of animal and plant structures by bacteria and the release of carbon compounds into the atmosphere, soil and to the ocean floor. decomposer organisms such as bacteria and fungi break down dead organic material, extracting energy and releasing carbon dioxide to the atmosphere and mineral nutrients to the soil. rates depend on climatic conditions. fastest rates occur in warm, humid environments such as the tropical rainforest. slow in cold areas (tundra).
113
Describe combustion (natural and fossil fuels)
The burning of organic material. organic material reacts or burns in the presence of oxygen. releases carbon dioxide and other gases such as sulphur dioxide and nitrogen oxides. combustion is a natural fuel used in many ecosystems. Wildfires from lightning strikes are essential to the health of some ecosystems such as the coniferous forests. Long, cold winters slow the decomposition of forest litter which builds up on the floor. Fire shifts this jam, freeing carbon and nutrients previously inaccessible to forest trees. opens up the forest canopy creating new habitats and increasing biodiversity. human activities for clearing land for cultivation or improving the quality of grazing. fossil fuel combustion is growing despite efforts to curb the issue (nearly 10GT a year of carbon dioxide) from geological stores to the atmosphere, oceans and biosphere.
114
Describe weathering and what are the different types?
The in situ breakdown of rocks exposed at, or near, the land surface by physical, chemical and biological processes. Most involve rainwater which contains dissolved CO2 derived from the soil and atmosphere. it will dissolve limestone and chalk in the process of carbonation.
CaCO3 + H2CO6 →Ca(HCO3)2
It releases carbon from limestone to streams, rivers, oceans and atmosphere. the process is better beneath the soil cover as the higher concentration of carbon dioxide in the soil makes it highly acidic.
chemical weathering transfers 0.3 billion tonnes of carbon to the atmosphere and oceans every year.
physical weathering by freeze-thaw breaks rock down into smaller particles but involves no chemical changes. increases the surface area exposed to chemical attack.
biological weathering processes such as chelation also contribute to rock breakdown. rainwater mixed with dead and decaying organic material in the soil forms humid acids which attack rock minerals. important in humid tropical environments.
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Carbon sequestration, describe the physical carbon pump
The surface and deep ocean waters mix by vertical currents, creating a more even distribution of carbon (geographically and vertically) in the oceans. initially CO2 enters the oceans from the atmosphere by diffusion. surface currents then transport the water and its dissolved CO2 polewards where it cools becomes more dense and sinks. downwelling occurs in only a handful of places (e.g. North Atlantic between Greenland and Iceland). Downwelling carries dissolved carbon to ocean depths where molecules may remain for centuries. deep currents transport carbon to areas of upwelling. cold, carbon rich water rises to the surface and CO2 diffuses back into the atmosphere.
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Carbon sequestration, describe the biological carbon pump
marine organisms drive the biological pump that also causes carbon to be exchanged between the oceans and atmosphere. half of all carbon fixation by photosynthesis takes place in the oceans. around 50 GT of carbon is drawn from the atmosphere by this process. phytoplankton, floating under the ocean surface, combines sunlight, water and dissolved CO2 to produce organic material. Whether consumed by animals through the food chain, or through natural death, carbon locked in the phytoplankton either accumulates in sediments on the ocean floor or is decomposed and released into the ocean. Other organisms such as tiny coccolithophores, molluscs and crustaceans extract carbonate and calcium ions from sea water to manufacture plates, shells and skeletons of calcium carbonates. most eventually ends up in ocean sediments and is lithified to form chalk and limestone.
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How does the replacement of veg and soil with impermeable surfaces affect the carbon cycle (human)
Stores - Decreases sequestration of carbon. Store of carbon in biosphere and soil decreases. Atmospheric store increases
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How does the combustion of fossil fuels affect the carbon cycle (human)
Stores - Urban areas account for 2% land area but are the source of 97% of anthropogenic carbon emissions. Decreasing lithosphere, atmosphere increase.
Flows - Increased combustion.
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How does the construction of industry affect the carbon cycle (human)
Stores - CO2 released to atmosphere when limestone (CaCO3) converted to lime (CaO). 2.4% of global emission, highly localised. Atmosphere store will increase, lithosphere decreased.
Flows - Chemical reaction used to form cement. (Industrial process releases carbon dioxide).
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How does deforestation affect the carbon cycle? (human)
Stores - Reduces carbon storage in the above and below ground biomass. Atmosphere store increases. Use of land for a different process will reduce the system’s ability to absorb carbon.
Flows - Reduced photosynthesis. Decomposition processes decreased. If forest is burnt = combustion = more carbon dioxide in atmosphere. Ash may increase soil store but only short term.
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How does the conversion of natural grassland to pasture affect the carbon cycle (human)?
Stores - Lack of biodiversity - lower biomass. Growth cycle of crops is reduced to 4 or 5 months.
Flows - Less carbon exchanges through photosynthesis. Crops don’t grow all year round - reduced photosynthesis compared to all year natural land. Less decomposition.
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How does ploughing affect the carbon cycle (human)?
Stores - Soil carbon storage is reduced by ploughing and the exposure of soil organic matter to oxidation. Atmospheric store increases as carbon dioxide is released from oxidation.
Flows - Soil erosion - wind and water erosion most severe when crops have been listed and soils have little protective cover.
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How does harvesting affect the carbon cycle (human)?
Stores - Loss in biomass as only small amounts of organic matter are returned to the soil.
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How does a growth in forestry affect carbon stores (human)?
Increased carbon stores
170-200 tonnes - UK, mature forest trees contain on average 170-200 tonnes of carbon per hectare. This is 10 times higher than grassland and 20 times higher than heathland.
500 tonnes C/ha - Soil represents a huge forest carbon pool. Forest soil carbon is 500 tonnes per hectare.
100 years - Forest trees extract carbon dioxide from the atmosphere and sequester it for hundreds of years. Most of it is stored in the wood of the tree stem. However, forest trees only become an active carbon sink (absorbing more than they are releasing) for the first 100 years after planting. After this the amount of carbon captured levels off and is balanced by inputs of letter to the soil, the release of carbon dioxide by respiration and activities of soil decomposers. Forestry plantations therefore usually have a rotation period of 80-100 years. After this trees are felled and reforestation begins again.
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Why do we extract water from peatlands?
Peat is drained to lower the water table and improve agricultural land. Moorland drainage ditches are partly responsible for increased flood risk in York. Lowering of the water table - increased infiltration, decreased evaporation.
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What effect does water extraction have on peatlands?
As peat dries out it becomes friable and vulnerable to erosion. ‘Fen blows’ - dust clouds created by excessive drainage of peatlands in East Anglia.
Drainage allows air to penetrate peat - increased decomposition and release of CO2 to the atmosphere. Dry peat can burn - combustion also releases CO2. if all England’s peatlands were destroyed CO2 released would be equivalent to 5 years of the current total annual CO2 emissions for the country.
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Why are peatlands so important for the carbon cycle?
important store 584 million tonnes England. Vegetation sequesters carbon.
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How does the combustion of oil and gas affect the carbon cycle?
Formed from the remains of tiny aquatic animals and plants.
Gas and oil occur in ‘pockets’ in rocks, migrating up through the crust until meeting caprocks.
Natural gas, such as methane, is made up of fractions of oil molecules, so small they are in gas form not liquid, and usually found with crude oil.
Other hydrocarbon deposits include oil shales, tar sands and gas hydrates.
66.6% of carbon dioxide emsissions come from burning fossil fuels
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How does the combustion of coal affect the carbon cycle?
Formed from the remains of trees, ferns and other plants.
There are four main types of coal:
anthracite is the hardest coal;it has most carbon and, hence, a higher energy content
bituminous coals are next in hardness and carbon content
soft coals such as lignite and brown coal are lower in carbon (25-35%) and energy potential; these are the major global source of energy supplies but emit more C02 than hard coals
peat is the stage before coal; it is an important carbon and energy source
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What is CCS?
Carbon capture and storage - carbon is captured and stored over a long period of time. The carbon released by the chimneys will be trapped and pumped underground to fill in pore spaces in rocks that used to be filled with natural gas.
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Advantages and limitations of CCS?
Adv - Can help provide a carbon neutral system or even take in more carbon than is produced.
Returns carbon into ground sources for sources
Disadvantages - not widely used
currently don’t have the technology to do this on a large scale.
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Overall changes to the carbon cycle over time?
Variations in atmospheric CO2 levels vary
Variations in amounts of CO2 sequestered in plants (photosynthesis), oceans etc
Changes in the biosphere: deforestation, changes in primary production on land and in oceans
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What are the short term diurnal changes to the carbon cycle?
Significant changes occur within a 24-hour period. During the daytime CO2 flows from the atmosphere to vegetation. At night the flux is reversed. Without sunlight, photosynthesis switches off, and vegetation loses CO2 to the atmosphere. The same pattern occurs with phytoplankton in the oceans.
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What are the short term seasonal changes to the carbon cycle?
driven by changes in photoperiod (day length) and temperature in the mid and high latitudes. In the low (tropical) latitudes, they are driven by water availability.
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What are the 5 long term changes to the carbon cycles and their effect
Reduction in CO2 in the atmosphere - At times of glacial maxima concentrations fall to 180ppm while in warmer times they are 100ppm higher. No clear explanation although it is possible that excess CO2 finds its way from the atmosphere to the deep ocean. One mechanism is changes in ocean circulation during glacials that bring nutrients to the surface and stimulate phytoplankton growth. These fix large amounts of CO2 by photosynthesis before dying and sinking to the deep ocean where the carbon is stored. Lower ocean temperatures also make CO2 more soluble in surface waters.
Reduction in pool of carbon in vegetation
Carbon pool in vegetation shrinks during glacials as ice sheets advance and occupy large areas of the continents. Deserts expand, tundra replaces temperate forests and grasslands encroach on tropical rainforests.
Carbon stored in soils no longer exchanged with the atmosphere & carbon sequestered by tundra
With much of the land surface covered by ice, carbon stored in the soil will no longer be exchanged with the atmosphere. Expanses of tundra beyond the ice-limit sequester huge amounts of carbon in permafrost.
Total volume of carbon fixed by photosynthesis declines
With less vegetation cover, fewer forests, lower temperatures and lower precipitation, NNP and the total volume of carbon fixed in photosynthesis will decline.
Amounts of carbon released by decomposition reduced
Reduced photosynthesis will cause a slowing of the carbon flux and smaller amounts of CO2 returned to the atmosphere through decomposition.
