GSC 111 Chapter Notes - Chapter 10: Atmospheric Chemistry, Water Cycle, Global Warming
13 Jan 2017
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Chapter 10: Major Chemical Cycles
1. Chemical reservoirs
a. Reservoirs: bodies of chemical entities that occupy particular spaces
i. Ex: total volume of carbon dioxide in the atmosphere, total volume of
glacial ice on land
ii. Also included in the biomass of living organisms
b. Expand and contract through changes in the rates at which elements or
compounds flow to or from them
c. Fluxes are rates of movement between reservoirs
i. When one reservoir increases in size, one or more must shrink
ii. Flux: the rate at which reservoirs expand or contract because of the rate at
which they gain or lose their content
d. Feedback affect fluxes
i. Imagine a balloon with two openings in it, so water can flow in at one end
and out at the other
ii. Water in balloon increases in volume until its pressure forces water out as
rapidly as it is flowing in
1. Pressure exerted by balloon operate as negative feedback,
opposing the expansion of the reservoir within the balloon more
and more strongly, until the fluxes to and from the reservoir are
balanced
a. Ex: biomass of plants is a reservoir for carbon dioxide, so
plants taking in carbon dioxide is negative feedback against
the buildup of gas in the atmosphere
iii. A positive feedback operate in the opposite way, accelerating a change
instead of braking it
1. Ex: climate warming causes coniferous forests to expand
northward and replace tundra. Expansion of forest increases global
warming
2. Carbon dioxide, oxygen, and biological processes
a. Plants employ a photosynthesis-respiration cycle
i. Photosynthesis employs energy from the sun, while respiration releases
energy
ii. In photosynthesis, plants combine carbon dioxide and water to form what
we can call sugars
1. Compounds of carbon, hydrogen, oxygen
iii. Oxygen is a by-product of photosynthesis
iv. Respiration
1. Combining sugar and oxygen to release sugar’s energy
2. Carbon dioxide and water and products of respiration
v. Reduced carbon: carbon atoms within organic compounds that contain
relatively small amounts of oxygen
b. Photosynthesis produces tissue growth
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i. Sugars help build tissues while growing
c. Respiration releases energy
i. Animals employ respiration to gain energy from the sugars of the plants
they eat
d. Decomposers employ respiration
i. Use it to break down tissues
e. Burial of plant debris alters atmospheric chemistry
i. Some dead plant debris escapes from the photosynthesis-respiration cycle
through burial
ii. Buried organic matter constitutes a reservoir for reduced carbon
compounds
iii. Erosion exposes it to the atmosphere, where it is soon oxidized by
decomposers or inorganic processes
iv. Cycle of burial and erosion has been in balance, so the atmosphere has
remained relatively stable
v. Excess burial of reduced carbon compounds removes carbon dioxide from
the photosynthesis-resperation cycle and stores it in a subterranean
reservoir
1. As a result, concentration of carbon dioxide in the atmosphere
declines
2. Oxygen becomes more abundant in the atmosphere; had the large
volume of reduced carbon compounds not been buried,
decomposers would have oxidized it through respiration
vi. Anoxic: the virtual abscene of O2.
1. Allow debris from dead plants to survive on the floor of a body po
water and eventually become deeply buried
a. Decomposers need oxygen to survive
f. Marine cycles resemble terrestrial cycles
i. Dissolved CO2 is available for photosynthesis
1. Main producers of sugar are single-celled algae
ii. In marine environments, animals consume a larger percentage of biomass
of marine plankton than that of the biomass of land plants consumed by
animals
1. A smaller proportion of the sugars is available for decomposition
or burial
3. Use of Carbon Isotopes to Study Global Chemical Cycles
a. Carbon isotopes record the cycling of organic carbon
i. When Carbon 12 is buried rapidly and weathering rates remain
unchanged, a large proportion of carbon 12 is locked up in underground
reservoirs. This means that there is an elevated ration of carbon 13 to
carbon 12 in the atmosphere.
b. Isotope ratios of limestones and deep-sea sediments record changes in rates of
carbon burial
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