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Techniques and Proxies

The “debate” in the global climate debate arises partly because of uncertainty about natural variability in global climate. The instrumental record (daily measurements of temperature, barometric pressure, rainfall, wind speed and the like, supplemented more recently by satellite imagery, upper atmospheric monitors and marine buoys) only extends back to the middle of the nineteenth century, about 150 years or so, and the perennial question is “how certain can we be that this record contains all possible or relevant variation?”

To look further back in time before the instrumental data were collected, researchers in the discipline of paleoclimatology study records (called proxies) of climate change preserved in rock, sediment or biological materials. A proxy is any parameter in the natural environment that responds to a climate variable, and a well-known example would be changes in the thickness or density of tree rings in response to changes in precipitation. In most cases individual proxies have ambiguous interpretations with respect to climate, and it is necessary to investigate several from the one location (called a multiproxy study) in order to unravel the complete story.

In order for the proxy to be useful in a palaeoclimate study, it must be able to be “interpreted” as an indicator of a climate parameter such as air or water (sea surface) temperature, humidity and salinity to name a few. Ideally, these parameters should be quantifiable in the units of the climate parameter, but as this is not always possible, indications of relative “wetness or dryness”, or “flood/drought” can be helpful. Note, in some definitions the terms “proxy” and “palaeoclimate archive” or “record” are used interchangeably.

To construct a global picture of prehistoric climate change, scientists must study proxies from a range of surface habitats, including marine through to terrestrial, and tropical through to polar, just as it is necessary to have a number of weather stations to build up a picture of regional or national rainfall distribution.


Geochemical Techniques

  • Determination of TOC/TC
  • Elemental Carbon/Nitrogen
  • Sr/Ca Ratio LINK
  • Biogenic silica content

Stable Isotope Studies

  • O-18 LINK
  • C-13
  • N-15
  • Si-34

Radiogenic Techniques

  • C-14 LINK
  • Be-10
  • Cs-137
  • Pb-210
  • Uranium Series LINK
  • Gamma ray attenuation
  • Si-32 LINK

Mineralogy

  • X-ray Diffraction (XRD)
  • X-ray Fluorescence (XRF)
  • Mineral idenitifcation
  • Magnetic mineral content

Biological Information

  • Microfossil content (benthic and pelagic) (Forams, Diatoms, ... )
  • Pollen and spore analysis
  • Magnetotactic bacteria

Image Analysis

  • Image scanning

Other Geophysical Data

  • Resistivity
  • P-wave velocity
  • Magnetic susceptibility