Class Business

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Class Business

• February 6th, Guest lecture Dr. Cathy Paris (I
  will post this lecture after class)
• Feburary 8th, Chapter 3 and Chapter 4 of Kolbert
• February 15th, First in-class exam

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Greenland ice sheet
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Review of Ocean Conveyor system

• What factors control the ocean conveyor system?

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• Differences in salinity between the North
  Atlantic and the Pacific
• Differences in temperature between the North
  Atlantic and Pacific
• Why?

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Gulf stream
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Questions from the reading

• Chapter 3 Under the glacier
• Greenland, Iceland
• Chapter 4 The butterfly and the toad

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On 1 July 1993, after five years of drilling, the
Greenland Ice Sheet Project Two (GISP2,)
penetrated through the ice sheet and 1.55 meters
into bedrock recovering an ice core 3053.44
meters in depth, the deepest ice core thus far
recovered in the world.
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Ice Cores

• Records go back 100,000 for Greenland
• And 400,000 years for Antarctica

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Greenland Ice core
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• Throughout each year, layers of snow fall over
  the ice sheets.
• Each layer of snow is different in chemistry and
  texture, summer snow differing from winter snow.
• Summer brings 24 hours of sunlight to the polar
  regions, and the top layer of the snow changes in
  texturenot melting exactly, but changing enough
  to be different from the snow it covers. The
  season turns cold and dark again, and more snow
  falls, forming the next layers of snow.

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Information from ice cores

• The ice cores can provide an annual record of
  temperature, precipitation, atmospheric
  composition, volcanic activity, and wind
  patterns.
• The make-up of the snow can tell scientists about
  past temperatures.

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How is it done?

• Scientists employ heated drills,
• The ice cores are then sampled, and the
  composition of the water is measured.
• the ratio of isotopes is determined
• the percent deviation of the isotope ratio from
  the a standard of known composition,

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What is an isotope?

• Atoms with the same number of protons, but
  differing numbers of neutrons. Isotopes are
  different forms of a single element.
• Examples Carbon 12 and Carbon 14 are both
  isotopes of carbon, one with 6 neutrons and one
  with 8 neutrons (both with 6 protons).

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The ratio of O-18 to O-16 is a proxy for
temperature change

• Oxygen occurs in two common stable isotopes, O-16
  and O-18
• O-16 is the most abundant
• Ratio of O-18/O-16 is called delta (d)

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Oxygen-Isotope composition of water

• The isotopic concentration of sea water is the
  standard against all other waters are measured
• THEREFORE delta0 for the sea water.
• Measure deviations from this standard.

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How can we use this to examine temperature?

• When sea water evaporates, the heavier isotope is
  left behind in the remaining sea water, while the
  water vapor has more of the lighter isotope.
• So evaporated water is higher in the lighter
  element but the sea water is higher in the
  heavier element
• In snow, colder temperatures (less evaporation
  from the ocean) result in higher concentrations
  of light oxygen.

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Direct temperature measurements from ice

• Scientists can confirm these chemistry-based
  temperature measurements by observing the
  temperature of the ice sheet directly.
• The ice sheets thickness makes its temperature
  much more resistant to change than the six inches
  of snow that might fall on your driveway during a
  winter snowstorm.
• the ice sheet can be compared to a frozen roast
  that is put directly into the oven. The outside
  heats up quickly, but the center remains cold,
  close to the temperature of the freezer, for a
  long time.
• Similarly, the ice sheet has warmed somewhat
  since the Ice Age, but not completely. The top
  has warmed as global temperatures have warmed,
  while the bottom has been warmed by heat flow
  from deep inside the Earth. But in the middle of
  an ice sheet, the ice remains close to the Ice
  Age temperatures at which it formed.

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Isotopic rations

• Oxygen isotope ratios
• 1 glacial ice fossils
• 2 ocean floor
• 3 coral reefs

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Coral reefs

• The oxygen isotopes in coral skeletons are a
  record of water temperature

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(red is warmer than average, blue cooler than
average) Yellow bars indicate El Nino years.
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Other isotope ratios
Deuterium is heavier than Hydrogen
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• The coldest snow is the lightest because as air
  cools down, it loses moisture, in essence, the
  heavier isotopes drop out earlier so what is left
  when snow is finally formed is the lighter
  elements.

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Biological signal

• Examples from the book

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Interview with Chris Thomas

•   Why do you think your paper is highly cited?
• We showed that it is possible to tackle the
  question "what proportion of species might 
  become extinct as a result of climate change...
• This paper attempts to quantify a major
  environmental crisisthat climate change may
  drive a substantial percentage of species to
  extinction. While this has been mentioned by
  previous papers, this is the first paper to
  tackle the issue head on. Our preliminary
  conclusions have surprised a lot of people.
•   Does it describe a new discovery or a new
  methodology that's useful to others?
• The approach we developed is probably the key
  advance. We showed that it is possible to tackle
  the question "what proportion of species might
  become extinct as a result of climate change"
  through a series of logical steps involving a set
  of analyses and simulations, each of which can be
  improved in the future or even replaced by a
  better method. We hope that our paper will spur
  others on to achieve these improvements.
•   Could you summarize the significance of your
  paper in layman's terms?
• Climate change may drive approximately 10 to 40
  of species to extinction because they either will
  not have anywhere climatically suitable to live
  in future, or because they will not be able to
  cross human-dominated landscapes to reach areas
  that will be suitable.
•   How did you become involved in this research?
• It came about initially, by my realizing that a
  substantial proportion of the British butterfly
  species on which I had been workingthe Orange
  Tip butterfly (Anthocharis cardamines)were
  shifting their distributions northwards.
• Chris D. Thomas