Non-marine paleoclimatic evidence

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Non-marine paleoclimatic evidence

• Speleothems

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Speleothems

• Commonly known as stalagmites and stalactites.
• Like trees, speleothems form growth rings that
  develop over hundreds or thousands of years.
• Growth rate depends on amount and rate of
  precipitation and on cave temperature and
  humidity.

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Speleothem

• Dating of speleothems is based on U-Th series.
• Theoretical precision lt1 (10 yr in 10 kyr).
  Realistically, precision is better than 1 (100
  yr in 10 kyr).

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Lachniet et al., 2004. Costa Rican speleothem.
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Speleothem-Paleoclimatic proxies

• Carbon and oxygen isotopes of calcite reflect
  vegetation and climate, respectively.
• Growth rate appears to reflect precipitation.
• Recent techniques Mg/Ca, radiocarbon.

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Speleothem-oxygen isotopes

• Oxygen isotopes in speleothem calcite ultimately
  come from rainwater.
• Some researchers argue that oxygen isotope ratios
  in rainwater depend on temperature.
• Others argue that the isotope ratios depend on
  rainfall amount, particularly in tropical
  regions.
• Also, some argue that the isotope ratios depend
  on evaporation taking place in soils or in the
  cave.

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Speleothem-oxygen isotopes

• Colder climate lower d18O values.
• Speleothem d18O-MAT relationship is 0.35 per
  mil/C.

4oC
Dorale et al., 1998.
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Speleothem-oxygen isotopes

• Site-specific calibrations are the best approach.
• Rainfall amount, rain d18O values, and surface
  and cave temperatures are measured over some
  time. Simultaneously, d18O values of cave drips
  and newly formed calcite are measured.
• A transfer function can then be developed for the
  cave.

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Isotopic composition of rain water in Israel
(Bar-Matthews et al., 2003)
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Relationship between oxygen isotope ratios of
rain water and rainfall in Israel (Bar-Matthews
et al., 2003).
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Bar-Matthews et al., 2003).
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Speleothem-carbon isotopes

• It appears that speleothem carbon isotopes
  primarily come from plants above the cave.
• Based on photosynthetic pathways, there are two
  major groups of land plants C3 and C4 plants.
• C4 plants warm season grasses adapted to high
  temperatures and relatively drier climates.
• C3 plants Trees, shrubs, and cool season grasses.

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Speleothem-carbon isotopes

• C4 grasses show high d13C values.
• C3 plants show low d13C values.
• Speleothem high d13C values are then interpreted
  to indicate more C4 grasses.

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Crevice Cave, MO (Dorale et al., 1998)
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Crevice Cave, MO (Dorale et al., 1998)
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