Summary Earth's Life Support Systems - To what extent are the water and carbon cycles linked?

Earth’s Life Support Systems SG6
To What Extent are the Water and Carbon Cycles Linked?
The Two Cycles are Linked and Interdependent
How are the Water and Carbon Cycle Interlinked and Independent via Earth’s Atmosphere?

The atmosphere is a space where the water cycle and the carbon cycle are linked – both water and carbon are
stored and transferred to and from

 Transpiration
Into the Atmosphere  Evapotranspiration
Flows of Water  Evaporation
 Precipitation
Out of the Atmosphere
 Interception
 Combustion
Into the Atmosphere
 Respiration from plants and decomposers
Flows of Carbon  Photosynthesis by plants
Out of the Atmosphere  Photosynthesis by phytoplankton
 Diffusion of CO2 (especially by cold oceans)

How are the Water and Carbon Cycle Interlinked and Independent via Oceans?

1) Atmospheric CO2 levels rise
2) More infrared radiation is trapped within the atmosphere which causes the enhanced greenhouse
effect
3) This leads to global warming

Impacts of Global Warming on Oceans:

 Sea surface temperatures rise causing more evaporation
 As oceans warm thermal expansion occurs which contributes to rising sea levels
 The ability of the oceans to absorb CO 2 decreases as they warm. This will mean higher atmospheric
CO2 levels as less is taken in by the oceans – a positive feedback mechanism
 Increased melting ice sheets and glaciers causing sea levels to rise

How are the Water and Carbon Cycle Interlinked and Independent via Vegetation and Soil?

The water and carbon cycles are linked via the vegetation and soil because a water shortage has serious
impacts for the carbon cycle:

1) A water shortage occurs
2) Rates of photosynthesis will decrease
3) Therefore, Net Primary Productivity will decrease
4) This means that rates of transpiration will decrease
5) In addition, the amount of organic litter added to the soil will decrease
6) This is partially because the lack of water means that decomposition rates will be decreased
7) Therefore, the exchange of CO2 with the atmosphere is affected. The amount of carbon entering the
atmosphere from respiration and decomposition will decrease
8) Not only does the soil store of carbon reduce, as organic content of the soil falls so does its ability to
retain water

Changes in the water cycle soils and vegetations leads to implications on carbon cycle stores and transfers

, How are the Water and Carbon Cycle Interlinked and Independent via the Cryosphere?

A change in the cryospheric store of water (due to the enhanced greenhouse effect) not only causes a change
in the flows and stores of water, but creates a positive feedback loop which changes the stores and flows of
carbon:

1) Increased atmospheric CO2 leads to a rise in global temperatures
2) This causes increased melting of ice
3) Loss of ice (land and sea) decreases the albedo and increases absorption of solar radiation
4) This increases temperatures further
5) Flows of water from land to oceans increase
6) Thawing of permafrost increases rates of oxidation and decomposition of organic matter
7) This increases the release of CO2 and CH4 to the atmosphere where they trap more solar radiation


The Impact of Long Term Climate Change on the Water and Carbon Cycle
Water Cycle

The Impact of Climate Change on the Stores of Water

The Atmosphere:

 Increased evaporation has increased the amount of water vapour in the atmosphere
 More water vapour has a feedback effect, helping to raise global temperatures
 This increases evaporation and precipitation

The Biosphere:

 Warmer global temperatures means more photosynthesis takes place, so there is a bigger store of
water in the biosphere
 Increases in precipitation result in higher interception and evapotranspiration

The Cryosphere:

 Global warming is accelerating the melting of glaciers, ice sheets and permafrost
 This means water storage in the cryosphere shrinks, as water is transferred to the oceans and
atmosphere

The Hydrosphere:

 Increased precipitation leads to increased run-off and surface stores of water (e.g. lakes, rivers)
 Melting of cryosphere means water is transferred to oceans

Carbon Cycle

The Impact of Climate Change on the Stores of Carbon

The Atmosphere:

 Increased decomposition accelerates transfers of carbon from the biosphere and soil to the
atmosphere
 Carbon released from thawing permafrost
 Plants previously frozen in permafrost able to decompose, releasing carbon to atmosphere

The Biosphere:

 Forests in tropical biomes are replaced by grassland due to climate becoming arid, leading to
decreased biosphere store