Biosphere Lecture 5:

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Biogeochemistry:
Studying how the biosphere functions and understanding the life support systems of the planet
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and Biogeochemistry:
study of the biological, geological and chemical processes cycling elements through the Earth System
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The long-term carbon cycle operates over
millions of years and involves the exchange of carbon between rocks and the Earth's surface
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New calculations of carbon fluxes during the Phanerozoic eon (the past 550 million years) illustrate how the long-term carbon cycle has affected the
burial of organic matter and fossil-fuel formation, as well as the evolution of atmospheric composition
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The deposition of carbonates derived from the weathering of carbonates is not shown because these processes essentially
balance one another over the long term as far as carbon dioxide is concerned. However, carbonate deposition derived from carbonate weathering leads to additional degassing of carbon dioxide upon deep burial and thermal decomposition
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Diagenesis, chemical changes at
low temperatures during burial
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The cycle can be subdivided into two subcycles involving
Organic Matter (silicate weathering) and carbonate deposition
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Link between co2 and organic matter
photosynthesis (burrial)
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Photosynthesis equation
6CO2 + 6H2O ------> C6H12O6 + 6O2.
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Cellular respiration extracts the energy stored in (this is all linked to heterotrophs)
sugars & other molecules
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This energy is then used for “work”
Biosynthesis of large complex compounds such as proteins Maintenance of cellular structures and body temperature Mechanical work – transport… Other processes
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Contemporary organic C cycle summary
Photosynthesis is the critical process for life on Earth, it fixes CO2 and releases O2 Aerobic respiration returns CO2 to atmosphere & consumes O2 The balance between the two processes is critical in determining how much O2 and CO2 there is in the at
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example of Coal: Terrestrial C accumulation & burial
Peatlands
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Coal is an example of
Terrestrial carbon burial
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Oil and gas burial: is a
biological pump
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The biological pump:
phytoplankton and cocolyths made of carbonates
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Marine sediments:
zoo and phytoplankton got buried under anoxic conditions. More sediment increased the pressure and temperature and the organic matter got converted into oil & gas.
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Petroleum is a fossil fuel derived from ancient fossilized organic materials, such as
zooplankton and algae.[
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Vast quantities of these remains settled to sea or lake bottoms, mixing with sediments and being buried under
anoxic conditions
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As further layers settled to the sea or lake bed, intense heat and pressure build up in the lower regions. This process caused the organic matter to change, first into a waxy material known as
as kerogen, which is found in various oil shales around the world, and then with more heat into liquid and gaseous hydrocarbons via a process known as catagenesis
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Formation of petroleum occurs from hydrocarbon pyrolysis in a variety of mainly
endothermic reactions at high temperature and/or pressure.[47]
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Burial of organic matter
Huge amounts of carbon in these sediments (100,000s of giga tonnes) Link between photosynthesis and burial of organic matter was key to allowing oxygen to build up in atmosphere Without burial, decomposition would have released almost all the carbon
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Link between biological and geological processes was key =
Biogeochemistry
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Burning fossil fuels has increassed the long term carbon releasse by
100 times
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Photosynthesis makes life possible ( part of long term organic c cycle)
Carbohydrate production Oxygen release
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Respiration returns
carbon to atmosphere, and consumes oxygen
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Interactions between biological and geological processes were critical in allowing an
oxygen-rich atmosphere to form
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Burial of organic matter containing sediments also allowed
fossil fuels to form
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Human activity has dramatically sped up the of release of carbon from
organic-matter containing sediments back to atmosphere
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Nitrogen
Proteins, Nucleic acids (DNA)
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Phosphorus
Nucleic acids, ATP, membranes
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Potassium
Osmosis, transport
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Sulphur
Proteins
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Calcium
Membrane & enzyme function
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Magnesium
Chlorophyll
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Iron
Chlorophyll synthesis, oxygen transport
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Others:
Sodium, Manganese Boron, Copper, Zinc, Molybdenum
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Key biological processes in the N cycle:
Nitrogen (N2) fixation (input) N mineralisation/ammonification Nitrification – leading to negative charge and runoff Denitrification (output)
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Human activity is having a major impact on the
nitrogen cycle: fertilizers
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The impacts of human domination of the nitrogen cycle that we have identified with certainty include:
Increased global concentrations of nitrous oxide (N2O and other nitrogen oxides), Losses of soil nutrients such as calcium and potassium, Substantial acidification of soils and of the waters , Greatly increased transport of nitrogen by rivers etc
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We are also confident that human alterations of the nitrogen cycle have:
Accelerated losses of biological diversity, and Caused changes in the plant and animal life and ecological processes of estuarine and nearshore ecosystems, and contributed to long-term declines in coastal marine fisheries.
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Phosphorus - PO3-3
Essential in living organisms: - phospholipids in cell membranes - DNA and RNA - ATP, NADPH
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Phosphorus cycle:
the slow cycle and the broken cycle
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Saharan dust
Dust blown off the Sahara crosses the Atlantic and fertilises the Amazon The most productive ecosystem on the planet is dependent on one of the least productive for key nutrients
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We note that the terrestrial biosphere takes up CO2at a decreasing rate from about 2010 onwards, becoming a net source at around 2050. By 2100 this source from the land
almost balances the oceanic sink, so that atmospheric carbon content is increasing at about the same rate as the integrated emission
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Nitrogen versus Phosphorus SIMILARITIES:
Effective recycling within terrestrial ecosystems Transport to oceans through rivers Long-term burial in sediments Human addition through fertilizers
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Nitrogen versus Phosphorus DIFFERENCES:
No gaseous phase in phosphorus cycle Main inputs differ Biological nitrogen fixation Geological rock weathering
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N deposition and plant growth
Positive relationship between plant growth and nitrogen deposition (N fertilisation)
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The total amount of carbon in the ocean is about
50 times greater than the amount in the atmosphere, and is exchanged with the atmosphere on a time-scale of several hundred years.
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At least 1/2 of the oxygen we breathe comes from the photosynthesis of
marine plants
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Currently, 48% of the carbon emitted to the atmosphere by fossil fuel burning is sequestered into the
ocean
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But the future fate of this important carbon sink is quite uncertain because of
potential climate change impacts on ocean circulation, biogeochemical cycling, and ecosystem dynamics.
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How much carbon will be lost from permafrost soils alone?
Estimated that by 2100 extensively-thawed areas could lose 4-6 Kg C m-2 This represents 10% of the carbon in the top 1 metre Rates of carbon loss could equal 1 GT of C per year ~5-10 times greater than current emissions from air travel!!!
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and Biogeochemistry:

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study of the biological, geological and chemical processes cycling elements through the Earth System

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The long-term carbon cycle operates over

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Card 4

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New calculations of carbon fluxes during the Phanerozoic eon (the past 550 million years) illustrate how the long-term carbon cycle has affected the

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Card 5

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The deposition of carbonates derived from the weathering of carbonates is not shown because these processes essentially

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