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Global Cycles

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Global Cycles Global Warming Greenhouse gases Carbon dioxide is the largest single contributer to climate forcing Carbon dioxide contributes about half of total ... – PowerPoint PPT presentation

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Title: Global Cycles


1
Global Cycles
2
Global Warming
3
Greenhouse gases
Carbon dioxide is the largest single contributer
to climate forcing
Carbon dioxide contributes about half of total
climate forcing from greenhouse gases
4
Carbon Cycle
Vegetation 500 Pg Soil 1500 Pg Atmosphere
730 Pg
Photosynthesis assimilates approximately 223 Pg
of C each year (land oceans).
Pools of carbon in living organisms, soil
organic matter and sediments 2,650
Pg Residence time 31 years
5
Carbon Cycle Oceans
1. Dissolved carbon dioxide is the main reservoir
30,000 Pg
2. Dissolution rate depends on wind speed, ocean
mixing
3. Pool of vegetation (algae) is small (5 Pg)
not thought to change that much with human
disturbance
6
Carbon Cycle Lithosphere
Calcium carbonate precipitates from carbon
dioxide dissolved in water, with calcium
CO2 H2O gt H2CO3 H2CO3 gt HCO3- H gt 2CO3-
2H Ca2 CO32- gt CaCO3
Precipitation is slow, lt1 Pg per year
7
Carbon Cycle Atmosphere
8
Carbon Cycle Atmosphere
Until the last 100 years, carbon dioxide
concentrations had been stable for the last 1000
years
Carbon dioxide concentration in the atmosphere is
higher now than it has been in the last 20
million years
At times in the Earths history, CO2
concentration was much higher than today, but the
climate was vastly different
9
Flask Network
10
Free Air CO2 Enrichment (FACE)
11
Nitrogen
12
Nitrogen Deposition
13
Nitrogen Cycle
14
Nitrogen Cycle
Ultimate source of nitrogen to organisms is N2
from the atmosphere. Many temperate zone
ecosystems limited by availability of Nitrogen
Nitrogen fixation is the chemical transformation
of N2 to NH3
Nitrogen fixation is energetically costly
Nitrogen fixation is done by microbes, often in a
symbiosis with plants
15
Nitrogen Fixation
Nodules on plant roots
16
Nutrient Cycling
Ecosystem element cycling can be driven by an
organisms need for growth, or by an organisms
need for energy
Ecosystem element cycling is also driven by
physical factors
17
Nitrogen Cycle
A source of energy for some microbes, and a
source of N for plants and microbes
1. Ammonification is the conversion of amino
acids to NH3
2. Nitrification is the oxidation of
ammonium ammonium (NH4) to nitrite
(NO2-) nitrite (NO2-) to nitrate (NO3-)
18
Nitrogen Cycle
3. Denitrification is the reduction of NO3- to
nitric oxide (NO), to nitrous oxide (N2O), and
finally to molecular nitrogen (N2) NO3- gt NO gt
N2O gt N2
Denitrification occurs when oxygen is not present
and nitrate acts as an electron acceptor
19
Nitrogen Cycle
NO3- and NH4 are used by plants and microbes
for protein synthesis
NO, N2O, N2 are gases that are lost from
ecosystems to the atmosphere
20
Phosphorus Loading
21
Phosphorus Cycle
22
Phosphorus Cycle
phosphate (PO43-) does not undergo
oxidation-reduction reactions under most
conditions
no gas forms of P
P can be bound tightly to soil minerals in soils
aquatic systems (lakes) are often limited by
P Old tropical soils can be limited by P
23
Mycorrhizae
symbiosis between fungi and plant roots ecto --
outside endo -- inside increase root surface
area fungi can dissolve soil mineral bound P
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