4.1 Flashcards
IMPORTANCE OF WATER IN SUPPORTING LIFE ON PLANET
Helps create benign thermal conditions on Earth:
- oceans moderate temperatures by absorbing, storing + releasing heat slowly
water moderates environment in other ways:
- clouds made up of tiny water droplets + ice crystals reflect around 1/5th of incoming solar radiation + lower surface temperatures
- at same time water vapour (potent greenhouse gas) absorbs long-wave radiation from Earth helping to maintain average global temperatures almost 15C higher than they would be otherwise
Oceans occupy how much of Earth’s surface
71%
Water makes up how much % of all living organisms
65-95%
- water crucial to their growth, reproduction, + other metabolic functions
Uses of water for flora, fauna + people
Plants need water for photosynthesis, respiration, transpiration
- photosynthesis takes place in leaves of plants, combining CO2, sunlight, water to make glucose + starches
- respiration in plants + animals converts glucose to energy through its reaction with oxygen, releasing water + CO2
- plants require water to maintain their rigidity (plants wilt when run out of water) + to transport mineral nutrients from soil
- in people + animals, water is medium used for chemical reactions in body (circulation of oxygen + nutrients)
- transpiration of water from leaf surfaces cools plants by evaporation
- sweating is cooling process in humans
- in fur-covered mammals, reptiles + birds, evaporative cooling achieved by panting
How is water essential resource for economic activity
Used to: generate electricity, irrigate crops, provide recreational facilities + satisfy public demand (drinking water + sewage disposal)
- Industries including food manufacturing, brewing, paper + steel making
Biological Importance of carbon to life on Earth
Stored in carbonate rocks (such as limestone), sea floor sediments, ocean water (as dissolved CO2), atmosphere (as CO2 gas) + in biosphere
- life is carbon based: built on large molecules of carbon atoms (proteins, carbohydrates, nucleic acids)
How is carbon used as economic resource?
Fossil fuels (coal, oil, natural gas) power global economy
- oil used as raw material in manufacture of products ranging from plastics to paint + synthetic fabrics
- agricultural crops + forest trees store large amounts of carbon available for human use as food, timber, paper, textiles
Global water cycle
Consists of 3 stores: atmosphere, oceans, land
- oceans - biggest store , atmosphere - smallest store
Water moves between stores through processes of precipitation, evapotranspiration, run-off, groundwater flow
(Evapotranspiration is flow from land to atmosphere)
Global carbon cycle
global carbon cycle is similar in comprising series of stores + flows. Long-term storage in sedimentary rocks holds 99.9% of all carbon on Earth
In contrast, most of carbon in circulation moves rapidly between atmosphere, oceans, soil + biosphere.
- main pathways between stores followed by carbon in this cycle include photosynthesis, respiration, oxidation (decomposition, combustion) + weathering
water and carbon cycles as open + closed systems
On global scale water + carbon cycles are closed systems driven by Sun’s energy (which is external to Earth).
Only energy (+ not matter) cross boundaries of global water + carbon cycles - hence we refer to these systems as ‘closed’
At smaller scales (drainage basin/forest ecosystem), materials as well as Sun’s energy cross system boundaries (so are open systems)
Global stores of water
Oceans (contain 97% of all water on planet)
Polar ice + glaciers
Groundwater (aquifers)
Lakes
Soils
Atmosphere
Rivers
Biosphere
Stores of water explained (fresh water + atmosphere)
- Fresh water comprises only tiny proportion of water in store + 3/4 is frozen in ice caps of Antartica + Greenland
- water stored below ground in permeable rocks amounts to just 1/5th of all fresh water
- only minute fraction of Earth’s water found in atmosphere - explained by rapid flux of water into + out of atmosphere: average residence time of water molecules is 9 days
Inputs + outputs of water
- Inputs of water to atmosphere include water vapour evaporated from oceans, soils, lakes + rivers, + vapour transpired through leaves of plants. Together these processes known as evapotranspiration.
- Moisture leaves atmosphere as precipitation (rain, snow, hail) + condensation (e.g fog)
~ Ice sheets, glaciers + snowfields release water by ablation (melting + sublimation). - Precipitation + meltwater drain from land surface as run-off into rivers. Most rivers flow to oceans though some, in continental drylands like southwest USA, drain to inland basins.
~ large part of water falling as precipitation on land reaches rivers only after infiltrating + flowing through soil. - after infiltrating soil, water under gravity may percolate into permeable rocks/aquifers
~ this groundwater eventually reaches surface as springs/seepages + contributes to run-off
Global carbon cycle stores
Sedimentary (carbonate) rocks
Oceans
Sea floor sediments
Fossil fuels
Soils + plants
Atmosphere
Biggest carbon store
Carbonate rocks
- most of carbon that is not stored in rocks + sediments is found in oceans as dissolved CO2
- relatively small carbon storage in atmosphere, plants, soils (but play crucial part in cycle + represent most of carbon in circulation at any 1 time
SLOW CARBON CYCLE
- carbon stored in rocks, sea-floor sediments + fossil fuels locked away for millions of years
Typical residence times for carbon held in rocks in SLOW CARBON CYCLE
around 150 million years
total amount of carbon circulated by SLOW CYCLE
between 10 + 100 million tonnes a year
- IN SLOW CARBON CYCLE CO2 diffuses from atmosphere into oceans where…
- where marine organisms (e.g. clams + corals) make their shells + skeletons by fixing dissolved carbon together with calcium to form calcium carbonate
- on death, remains of these organisms sink to ocean floor
- there they accumulate + over millions of years, heat + pressure convert them to carbon-rich sedimentary rocks
- CARBON-RICH SEDIMENTARY ROCKS
- Some carbon-rich sedimentary rocks (subducted into upper mantle at tectonic plate boundaries) are vented to atmosphere in volcanic eruptions
~ Others exposed at/near surface by erosion + tectonic movements attacked by chemical weathering
- CHEMICAL WEATHERING PROCESSES SUCH AS CARBONATION…
- are result of precipitation charged with CO2 from atmosphere, which forms weak acid.
~ acid attacks carbonate minerals in rocks, releasing CO2 to atmosphere, + in dissolved form to streams, rivers + oceans.
- ON LAND, PARTLY DECOMPOSED ORGANIC MATERIAL MAY BE…
- buried beneath younger sediments to form carbonaceous rocks (coal, oil + natural gas)
~ Like deep-ocean sediments, these fossil fuels act as carbon sinks that endure for millions of years
FAST CARBON CYCLE
Carbon circulates most rapidly between atmosphere, oceans, living organisms (biosphere) + soils. These transfers are between 10 + 1000 times faster than those in slow carbon cycle.
- LAND PLANTS + MICROSCOPIC PHYTOPLANKTON IN OCEANS = KEY COMPONENTS OF FAST CYCLE
- through photosynthesis they absorb CO2 from atmosphere + combine it with water to make carbohydrates (sugars/glucose)
- respiration by plants + animals is opposite process + results in release of CO2
- decomposition of dead organic material by microbial activity also returns CO2 to atmosphere
- IN FAST CYCLE, CARBON EXCHANGE ALSO OCCURS BETWEEN ATMOSPHERE + OCEANS
- atmospheric CO2 dissolves in ocean surface waters while oceans ventilate CO2 back to atmosphere
- through this exchange, individual carbon atoms stored (by natural sequestration) in oceans for 350 years on average
Processes of water cycle: Water balance equation
summarises flows of water in drainage basin over time
- states that precipitation = evapotranspiration + streamflow +/- water entering/leaving storage:
Precipitation (P) = Evapotranspiration (E) + Streamflow (Q) +/- storage
Flows in water cycle
Precipitation, evaporation, transpiration, run-off, infiltration, percolation(movement of surface + soil water into underlying permeable rocks), throughflow (water flowing horizontally through soil to stream + river channels)
What is Precipitation
water + ice that falls from clouds towards ground. It takes several forms: most commonly rain + snow, but also hail, sleet + drizzle.
When does precipitation form
forms when vapour in atmosphere cools to its dew point + condenses into tiny water droplets/ice particles to form clouds. Eventually these droplets/ice particles aggregate, reach critical size + leave cloud as precipitation.
Precipitation also varies in character + this impacts water cycle at drainage basin scale
- Most rain on reaching ground flows quickly into streams + rivers
~ But in high latitudes + mountainous catchments, precipitation often falls as snow + may remain on ground for several months. So there may be time lag between snowfall + run-off. - Intensity: amount of precipitation falling in given time. High-intensity precipitation (e.g. 10-15 mm/hour) moves rapidly overland into streams + rivers, as it is falling at rate that exceeds infiltration capacity of soil.
- Duration: length of time that precipitation event lasts. Prolonged events, linked to depressions + frontal systems, may deposit large amounts of precipitation + cause saturation of soil which leads to overland flow + river flooding.
- In some parts of world (e.g. East Africa, Mediterranean) precipitation concentrated in rainy season. During this season river discharge is high + flooding common. In dry season rivers may cease to flow altogether.
Transpiration
diffusion of water vapour to atmosphere from leaf pores (stomata) of plants.
- responsible for around 10% of moisture in atmosphere
- Like evaporation, transpiration influenced by temperature + wind speed. - also influenced by water availability to plants
~ E.g, deciduous trees shed their leaves in climates with either dry/cold seasons to reduce moisture loss through transpiration.
Condensation
phase change of vapour to liquid water
- occurs when air is cooled to its dew point.
- At this critical temperature air becomes saturated with vapour resulting in condensation.
- Clouds form through condensation in atmosphere
- condensation at/near ground produces dew + fog
~ both types of condensation deposit large amounts of moisture on vegetation + other surfaces
Cumuliform clouds
Have flat bases + considerable vertical development
- most often form when air heated locally through contact with Earth’s surface
- this causes heated air parcels to rise freely through atmosphere (convection), expand (due to fall in pressure with altitude) + cool.
- As cooling reaches dew point, condensation begins + clouds form.
Stratiform/layer clouds
develop where air mass moves horizontally across cooler surface (often ocean)
- this process, together with mixing + turbulence is known as advection
cirrus clouds
Wispy, consist of tiny ice crystals
- form at high altitude
do not produce precipitation + so have little influence on water cycle
Formation of clouds
Clouds: visible aggregates of water/ice/both that float in free air
Form when water vapour cooled to its dew point
Cooling occurs when…
- Air, warmed by contact with ground/sea surface, rises freely through atmosphere. As air rises + pressure falls it cools by expansion (adiabatic expansion). This vertical movement of air is convection.
- Air masses move horizontally across relatively cooler surface (advection)
- Air masses rise as they cross mountain barrier/as turbulence forces their ascent.
- relatively warm air mass mixes with cooler one.
Adiabatic expansion
Expansion of parcel of air due to decrease in pressure
- Expansion causes cooling
Advection
Horizontal movement of air mass which often results in heating/cooling
Convection
Motion of gas/liquid which when warmed rises until eventually cools + sinks in continuous circulation
Lapse rates
Describes vertical distribution of temp in lower atmosphere + temp changes that occur within air parcel as it rises vertically away from ground
3 types: ELR, DALR, SALR
ENVIRONMENTAL LAPSE RATE (ELR)
Vertical temperature profile of lower atmosphere at any given time
- on average, temp falls by 6.5C for every km of height gained
DRY ADIABATIC LAPSE RATE (DALR)
Rate at which parcel of dry air (less than 100% humidity so condensation not taking place) cools
- cooling (caused by adiabatic expansion) is 10C/km
SATURATED ADIABATIC LAPSE RATE (SALR)
Rate at which saturated parcel of air (one in which condensation occurring) cools as it rises through atmosphere
- as condensation releases latent heat, SALR, at around 7C/km is lower than DALR
Water cycle budget
Annual volume of movement of water by precipitation, evapotranspiration, run-off etc between stores (oceans, permeable rocks, ice sheets, vegetation, soil etc)
