Class Lecture Notes

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Class Lecture Notes
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Air Molecules in Water and Ice Background Notes

• Information in ice cores comes from three
  sources
• from the water making up the ice itself
• from impurities such as dust, volcanic ash, and
  salts found within the ice
• from gases such as oxygen, carbon dioxide, and
  methane trapped in air bubbles in the ice.

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Air Molecules in Water and Ice Background Notes

• By analyzing the ice and the air trapped within
  the ice, scientists build a yearly record of
  temperature changes that go back thousands of
  years in time.
• Impurities in the ice core indicate drier,
  dustier, and windier times.
• These can be linked to periods of great cold.

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Air Molecules in Water and Ice Background Notes

• For instance, there is twenty times more dust in
  ice formed 18,000 years ago, during the coldest
  part of the last glacial period, than in ice
  formed within the last 10,000 years.
• This suggests that during colder periods the land
  surface was drier on average and relatively
  easily swirled out of place by winds.

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Air Molecules in Water and Ice Background Notes

• Large volcanic eruptions cause short-term cooling
  of the climate.
• Volcanic ash and aerosols, in particular sulfur
  dioxide, are injected high into the atmosphere
  and circulate around the earth by upper level
  winds.
• The aerosols and dust can block incoming solar
  radiation and reduce global surface temperatures
  up to two to four years following the eruption.

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Air Molecules in Water and Ice Background Notes

• These materials eventually rain down from the
  atmosphere, or are swept out during snow events,
  and settle upon glaciers and ice sheets where,
  over time, they become embedded in the ice.

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Air Molecules in Water and Ice Background Notes

• Air bubbles in the ice that contain samples of
  atmospheric gases during past eons are of
  particular interest because they allow scientists
  to determine the surface temperature, and the
  amount of CO2 and CH4 in past time periods.
• Scientists can also compare the atmospheric
  carbon content from many thousands of years ago
  to the present value.

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Air Molecules in Water and IceResults

• Warm Carbonated Water
• of times opened 38
• Trial 1 more whoosh and bubbles than cold
• Trial 4 more whoosh and bubbles than cold
• What does it all mean?
• Warm does not hold CO2 well

• Cold Carbonated Water
• of times opened 20
• Trial 1 less whoosh and bubbles than warm
• Trial 4 less whoosh and bubbles than warm
• Cold holds onto CO2 well

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Air Molecules in Water and IceAnswers!

• This teaches about the solubility of gases.
• Most substances have a solubility that gets
  better with increased temperature, but gases are
  the opposite.
• As the temperature increases, the solubility of a
  gas in a liquid decreases.

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Air Molecules in Water and IceAnswers!

• Warm pop does not taste good because it is warm
  and not very refreshing, but also because it has
  lost its "fizz" or its dissolved carbon dioxide.
• Cold pop is refreshing and still maintains its
  "fizz". It dissolves more carbon dioxide than
  does warm pop.
• The carbon dioxide stays dissolved in the cold
  but is released as the whoosh and bubbles in the
  warm.

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Dissolved Salts in Ice Cores Background Notes

• Each time snow falls it cleans the atmosphere of
  dust and chemicals. As mentioned earlier, these
  chemicals remain in the snow pack and become
  incorporated into the glacier ice.
• Presence of particular gases and chemicals within
  an ice core can indicate to researchers the types
  of substances in the atmosphere for a given
  period of time.

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Dissolved Salts in Ice Cores Background Notes

• Sulfate from volcanoes, salt from the oceans,
  trace metals from asteroids, and nitrates and
  sulfates from fossil fuels can all be detected
  using a volt meter.
• A voltmeter detects electrical current conducted
  by the movement of protons associated with the H
  of strong acids.

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Dissolved Salts in Ice Cores Background Notes

• Pure water is a poor conductor of electricity.
• However, water that has dust or chemical
  materials in it conducts electricity quite
  easily.
• This is true for ice as well.

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Dissolved Salts in Ice Cores Background Notes

• In ice, the movement of the ions is restricted by
  the solid structure of the ice, which reduces the
  ability of the ions to conduct a direct current.
• The strength of the electrical reading helps
  determine the type of acid within the layers of
  ice.

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Dissolved Salts in Ice Cores Background Notes

• For instance, the presence of nitrates registers
  a high value on a voltmeter.

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Dissolved Salts in Ice Cores Background Notes

• A high amount of dust in the record would have
  the opposite reaction.
• Dust contains little to none of the necessary H
  ions.

• Saharan Dust Blowing off Northwest AfricaThis is
  an image of dust storms taken by NASAs SeaWiFS
  satellite, taken on Feb. 28, 2000. Credit NASA

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Dissolved Salts in Ice Cores Background Notes

• If the reading on a voltmeter is close to zero,
  scientists are still able to obtain a significant
  amount of information from the ice core.

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Dissolved Salts in Ice Cores Background Notes

• Very cold periods are correlated with dusty,
  highly alkaline ice cores
• Warmer periods have greater amounts of acidic
  chemical compounds.

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Dissolved Salts in Ice Cores Data Collection

• Researchers studying the electrical conductivity
  of the GISP2 ice core first cut the ice core down
  the middle to remove areas that might have been
  contaminated in the process of extracting the
  core from the ice.

• A researcher looks at an ice core retrieved from
  the Greenland summit. 

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Dissolved Salts in Ice Cores Data Collection

• Then, by keeping the temperature of the ice at
  -20 degrees Celsius and running the electrodes
  from the voltmeter along the ice, it was possible
  to detect the presence of dust and chemicals such
  as sulfates and nitrates within the ice cores.

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Dissolved Salts in Ice Cores Data Collection

• Core Depth (m) ECM (micro amps) 3.020
  5.0000
• 3.025 4.4000
• 3.030 4.6000
• 3.035 5.1000
• 3.040 6.1000

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Relating Oxygen Isotopes in Ice Cores to
Temperatures Background Notes

• By far the most common isotope of oxygen is
  oxygen 16 with an atomic mass of 16.
• The next most common oxygen isotope is oxygen 18,
  whose two additional neutrons in the nucleus give
  it an atomic mass of 18.

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Relating Oxygen Isotopes in Ice Cores to
Temperatures Background Notes

• Water that contains oxygen 18 condenses more
  readily than oxygen 16 containing water, enabling
  scientists to use the ratio of oxygen 18 to
  oxygen 16 in a given sample of water to determine
  the temperature at which the water condensed from
  vapor.

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Relating Oxygen Isotopes in Ice Cores to
Temperatures Background Notes

• In other words
• A high O18/O16 ratio indicates warmer conditions
  because O18, being heavier than O16, requires
  warmer conditions for evaporation from the ocean.

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Relating Oxygen Isotopes in Ice Cores to
Temperatures Background Notes

• Thus, measuring the O18/O16 ratio in the ice core
  makes it possible to calculate the temperature at
  the time the snow fell.
• This 'isotopic thermometer' records seasonal
  variations in temperature as well as longer-term
  climatic changes and is one of the measurements
  used in counting annual layers in the ice.

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Relating Oxygen Isotopes in Ice Cores to
Temperatures Activity

• Materials O18/O16 ratio data from GISP2
• Activity and Questions1. Graph the O18/O16 data
  from GISP2 data. The vertical axis will be the
  ratio of O18/O16 and the horizontal axis will be
  core depth (corresponding to age of the ice
  core). 2. The data will show seasonal and yearly
  variations, so draw a smoother line through the
  data to show the trends. 3. Indicate the periods
  of warmer and of colder climates.

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HISTORICAL CLIMATE RECORDS

• Weather on a daily, monthly, or even yearly basis
  is highly variable, yet climate over a longer
  period is thought to be relatively stable.
• How can we assess if the warmer summers we
  experienced in the United States during the 1980s
  and 1990s are due to short-term variability in
  weather or are a result of longer-term changes in
  global climate?

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HISTORICAL CLIMATE RECORDS

• To separate daily weather from climate, the
  National Weather Service uses values from the
  past 30 years to compile 'average' weather.
• This 30-year average is generally considered to
  represent the climate of the region being
  measured.

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HISTORICAL CLIMATE RECORDS

• In these activities, we are going to be looking
  at temperature data in several different ways to
  assess trends or changes in climate have been
  occurring in various regions over the past 100
  years.

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HISTORICAL CLIMATE RECORDS

• Any change in climate is related to a change in
  some component of the energy budget.
• Changing the local character of the earth's
  surface or the composition of the atmosphere can
  alter the heating patterns of the climatic
  system.

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HISTORICAL CLIMATE RECORDS

• Earth's climate has changed continuously during
  the course of its history.
• From changes in the atmosphere of our planet to
  the evolution of life, the climate has bounced
  from periods of great heat to great cold.

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HISTORICAL CLIMATE RECORDS

• In historical time, climate variations have been
  associated with cycles of sunspot activity,
  variations in dust from volcanoes, and
  atmospheric CO2.
• This activity will allow you to look at
  temperature variations decade by decade at
  various latitudes to note trends during the past
  century.