The Role of Snow in Ecosystem Carbon Balance

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The Role of Snow in Ecosystem Carbon Balance

• Musa KUKUL

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Carbon

• Carbon (C), the fourth most abundant element in
  the Universe, after hydrogen (H), helium (He),
  and oxygen (O), is the building block of life
• On Earth, carbon cycles through the land, ocean,
  atmosphere, and the Earths interior in a major
  biogeochemical cycle
• (the circulation of chemical components through
  the biosphere from or to the lithosphere,
  atmosphere, and hydrosphere).

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Carbon Cycles

• Geological Carbon Cycle
• Biological Carbon Cycle
• The modern carbon cycle

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Geological Carbon Cycle

• Carbon moves between rocks and minerals,
  seawater, and the atmosphere. Carbon dioxide in
  the atmosphere reacts with some minerals to form
  the mineral calcium carbonate (limestone). This
  mineral is then dissolved by rainwater and
  carried to the oceans. Once there, it can
  precipitate out of the ocean water, forming
  layers of sediment on the sea floor. As the
  Earths plates move, through the processes of
  plate tectonics, these sediments are subducted
  underneath the continents. Under the great heat
  and pressure far below the Earths surface, the
  limestone melts and reacts with other minerals,
  releasing carbon dioxide. The carbon dioxide is
  then re-emitted into the atmosphere through
  volcanic eruptions. (Illustration by Robert
  Simmon, NASA GSFC)

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Biological Carbon Cycle

• Through the process of photosynthesis, green
  plants absorb solar energy and remove carbon
  dioxide from the atmosphere to produce
  carbohydrates (sugars).
• Plants and animals effectively burn these
  carbohydrates through the process of respiration,
  the reverse of photosynthesis.
• The presence of land vegetation enhances the
  weathering of soil, leading to the long-term-but
  slow-uptake of carbon dioxide from the
  atmosphere. In the oceans, some of the carbon
  taken up by phytoplankton (microscopic marine
  plants that form the basis of the marine food
  chain) to make shells of calcium carbonate
  (CaCO3) settles to the bottom (after they die) to
  form sediments. During times when photosynthesis
  exceeded respiration, organic matter slowly built
  up over millions of years to form coal and oil
  deposits. All of these biologically mediated
  processes represent a removal of carbon dioxide
  from the atmosphere and storage of carbon in
  geologic sediments

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The modern carbon cycle

• On land, the major exchange of carbon with the
  atmosphere results from photosynthesis and
  respiration. During the daytime in the growing
  season, leaves absorb sunlight and take up carbon
  dioxide from the atmosphere. When conditions are
  too cold or too dry, photosynthesis and
  respiration cease along with the movement of
  carbon between the atmosphere and the land
  surface

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The modern carbon cycle

• The amounts of carbon that move from the
  atmosphere through photosynthesis, respiration,
  and back to the atmosphere are large and produce
  oscillations in atmospheric carbon dioxide
  concentrations
• these biological fluxes of carbon are over ten
  times greater than the amount of carbon
  introduced to the atmosphere by fossil fuel
  burning.

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The modern carbon cycle

• Global biosphere. Normalized Difference
  Vegetation Index measures the amount and health
  of plants on land, while chlorophyll a
  measurements indicate the amount of phytoplankton
  in the ocean. Land vegetation and phytoplankton
  both consume atmospheric carbon dioxide.
• In the oceans, carbon dioxide exchange is largely
  controlled by sea surface temperatures,
  circulating currents, and by the biological
  processes of photosynthesis and respiration.
  Carbon dioxide can dissolve easily into the ocean
  and the amount of carbon dioxide that the ocean
  can hold depends on ocean temperature and the
  amount of carbon dioxide already present. Cold
  ocean temperatures favor the uptake of carbon
  dioxide from the atmosphere whereas warm
  temperatures can cause the ocean surface to
  release carbon dioxide. Cold, downward moving
  currents such as those that occur over the North
  Atlantic absorb carbon dioxide and transfer it to
  the deep ocean. Upward moving currents such as
  those in the tropics bring carbon dioxide up from
  depth and release it to the atmosphere.

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Temperature and CO2 Changing since The Last Ice
Age

• temperatures and atmospheric carbon dioxide
  levels can be measured using ice cores
• Twenty thousand years ago, the earth was in the
  grip of an ice age. around fifteen thousand years
  ago, the temperature started to warm (probably as
  a result of variations in the earth's orbit)
• past ten thousand years, however, the earth's
  temperature and atmospheric CO2 has been
  relatively stable
• due to combinations of variation in solar
  activity and periodic changes in ocean currents
• The near-vertical red line at the far left marks
  the rise in atmospheric CO2 since the start of
  the industrial revolution.

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Temperature and CO2

• A record of temperature and atmospheric CO2 over
  the past 400,000 years
• It is thought that these large temperature
  fluctuations are triggered variations in the
  earth's orbit that change the amount of energy
  from the sun that reaches us
• Small change in temperature caused by the
  changing orbit are amplified by natural processes
  on earth. These cause CO2 to be released from the
  oceans and the biosphere, causing an increased
  greenhouse effect.

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SNOW

• Snow is a critical regulator of soil
  processes
• temperate forests during winter,
• acting as an insulator, preventing soil from
  freezing in many cases
• providing moisture to support biological
  processes
• microbial processes are active in cold (0 to 5
  ?C) and even frozen soils
• 2050of annual ecosystem C cycling and
  soil-atmosphere trace gas fluxes can occur during
  winter.

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Meteorological Conditions (Temperature as
acontrol over ecosystem CO2 fluxes in a
high-elevation,subalpine forest)

• Mean monthly temperatures during the growing
  season range from 0 in April to a peak of 10.5C
  during July(Monson, Turnipseed
• et. all.)
• Mean maximum air temperature is greater than 5C
  from April through October however, freezing
• temperatures are possible at any time of the
  year and the mean minimum temperature is
  consistently less than 5C

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DAILY NET ECOSYSTEM CO2 EXCHANGE

• high-elevation, subalpine forest
• During 1999 and 2000,
• maximum carbon uptake was observed during the
  early season in late-May and early-June, when air
  temperatures were relatively cool (mean
• 710C)
• The ground was still covered with several
  centimeters of snow

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NET ECOSYSTEM CO2 EXCHANGE

• There is a significant variation in the
  temperature response of NEEsat, as determined
  from the parameters generated from the
  least-squares regression model for the 1999 and
  2000 growing seasons
• Respiration at the ecosystem level (determined as
  the respiration parameter from the regression
  model Re) decrease significantly with increasing
  air temperature in
• both 1999 and 2000

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NET ECOSYSTEM CO2 EXCHANGE (Net ecosystem CO2
exchange measuredbyautochambers during the
snow-covered season at a temperatepeatland)

• NEE for all chambers
• The magnitude of NEE ranged from 1 to -3 µmol m2/
  s1 from the end of November 2000 until the end of
  March 2001
• Although most of the fluxes were negative, small
  positive fluxes persisted during the daytime,
  suggesting that photosynthesis was occurring at a
  very low level at times.
• Day of year (DOY) begins with 1 January 2000 and
  1 January 2001 is DOY 366

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• The patterns of soil temperature and snow depth
  show that the soil temperature varied widely from
  6 to 11 C before the snow pack developed

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• Atmospheric pressure and NEE during February 2001
  (days 400425), showing increases in CO2 emission
  as barometric pressure declines.

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• Relationship between NEE and ground temperature
  at 5 cm depth. Largest respiration rates occur at
  T 0 C. This pattern is seen in all chambers
• Most of the positive values (CO2 uptake) occurred
  at T gt 0 C, but negative values (CO2 emission)
  were more complex
• The largest CO2 emissions occurred at T 0 C and
  were smaller at both lower and higher
  temperatures, suggesting a release of stored CO2
  during thaw events or an enhancement of microbial
  activity from freezethaw dynamics.

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• NEE for all chambers from 22 November 2000
  through 22 March 2001 by hour of day
• Note that all positive fluxes (uptake by
  ecosystem) occur during daylight, which suggests
  that photosynthesis is occurring. Highest
  negative fluxes (efflux to atmosphere) also occur
  during daylight hours. This corresponds with
  higher temperatures during daytime.

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• Relationship between mean winter dark CO2 flux by
  chamber and (a) mean winter ground temperature,
  (b) late summer water table position, and (c)
  above-ground plant biomass.
• Ground temperature is the only variable that has
  a significant correlation with CO2 flux.

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CONCLUSIONS

• CO2 fluxes were continuous throughout the
  snow-covered season from December through March
• The largest emissions of CO2 occurred when the
  ground temperature reached 0 C and during
  periods of declining atmospheric pressure.

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CONCLUSIONS

• If warmer winter temperatures yield less snow in
  the temperate region, then soils could freeze
  more deeply and result in lower CO2 emission.
• If less snow results in a higher frequency of
  freezethaw events, then winter CO2 emissions
  could be larger with a warmer climate

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Sources

• Monson R. K., A. A. Turnipseed et al.,
  Temperature as a
• control over ecosystem CO2 fluxes in a
  high-elevation,
• subalpine forest. Ecosystems Ecology
• Bubier J., P. Crill et all., Net ecosystem CO2
  exchange measured
• byautochambers during the snow-covered season at
  a temperate
• peatland. Hydrological Processes
• http//earthobservatory.nasa.gov/Library/CarbonCyc
  le/
• http//www.acad.carleton.edu/curricular/GEOL/DaveS
  TELLA/Carbon/carbon_intro.htm