Water and Carbon 3 The Carbon Cycle

The Carbon Cycle:

• CO2: as a gas found in the atmosphere, soils and oceans
• CH4: as a gas found in the atmosphere, soils and oceans and sedimentary rocks
• CaCO3: a solid compound found in calcareous rocks, oceans and in the skeletons and shells ocean creatures
• hydrocarbons: solids, liquids or gases usually found in sedimentary rocks
• bio-molecules: complex carbon produced in living things. proteins, carbohydrates, fats, oils and DNA

Origins of Carbon on Earth:

• CO2 escapes the mantle at constructive and destructive plate boundaries as well as hot-spots
• It is derived from metamorphism of carbonate rocks sub-ducting with the oceanic crust

The Major Stores of Carbon:

Lithosphere:

• includes: the crust and the upper most mantle
• Stored organically and inorganically
  • organic: litter, humus
  • inorganic: coal, oil, natural gas, oil shale, carbonate-based sedimentary deposits like limestone
• Carbon is stored in:
  • Marine sediments
  • Soil organic matter
  • Fossil fuel deposits
  • Peat

Hydrosphere:

• Oceanic stores of carbon:
  • The surface layer (euphotic zone) where sunlight penetrates so that photosynthesis can take place
  • The intermediate (twilight zone) and the deep layer of water
  • Living organic matter (fish, plankton, bacteria, etc.) and dissolved organic matter
• When an organism dies their dead cells, shells and other parts sink to deep water. Some material sinks right to the bottom and forms a carbon-rich sediment. Over millions of years, chemical and physical processes turn these sediments to rocks

Biosphere:

• biosphere: the total sum of all living matter 
• Living vegetation:
  • 19% of the carbon in the Earth’s biosphere is stored in plants
  • The Russian reservoir holds 25% of the worlds forest carbon
  • The Amazon Basin holds 20% of the worlds forest carbon
• Plant litter:
  • Plant litter: fresh, undecomposed and easily recognisable plant debris
• Soil humus:
  • humus: thick brown or black substance that remains after most of the organic litter has decomposed
  • 69% of the carbon in forests is stored in the soil
  • 50% of the carbon in tropical forests is stored in the soil
  • Inorganic soil consist of carbon, calcite, dolomite and gypsum
  • The soil carbon pool is 3.1 times larger than the atmospheric pool
  • Only the oceans have a larger carbon store
• peat:
  • Peat forms in wetland conditions where almost permanent water saturation obstructs flows of oxygen from the atmosphere into the ground. This creates low anaerobic conditions that slow down the rates of plant litter decomposition

Atmosphere:

• 500 million years ago: Cambrian period, the CO2 levels were at 7,000ppm
• 2 million years ago: Quaternary Glaciation period, the CO2 levels sank to about 180ppm
• Today: 400ppm of CO2 in the atmosphere, 0.04% of the atmosphere
  • In the last 800,000 years the CO2 has been higher than it has been before
  • Increasing industrial processes have increased CO2 emissions on Earth
• The Mauna Loa Observatory:
  • Recording atmospheric carbon since 1958
  • The undisturbed air, remote location,  minimal influences of vegetation and human activity mean that it is ideal for measuring atmospheric constituents
  • Shows that the CO2 concentration has dramatically increased since the industrial revolution from 280ppm-318ppm in 1958 to 400.3ppm in 2015
  • Due to anthropogenic…