Proxy Data Measurements

By understanding components of a system, scientists can determine properties of that system which can not be directly measured. Direct measurements may be impossible due to passage of time or inability to trace materials within the system. These indirect measurements are called "proxy measurements" and provide "proxy data" to the researcher. By correlating different proxy measures, confidence in the accuracy and applicability of the proxy data is increased.

Proxy Measurement Application Reference
Date of tree's life Dendrochronology
  • Examining the seasonal growth rings of trees.
  • Variations in width patterns correlate to variations in environmental factors.
  • This is not just counting rings.
Dendrochronology at Univ. of AZ. Laboratory of Tree-Ring Research. external arrow
Time of death 14C
  • Radioisotope 14C created in atmosphere and taken up by plants.
  • 14C uptake stops with organism's death.
  • Ratio of 14C to 12C allows date estimate.
Radiocarbon dating
Diet of animals 13C/12C
  • C3 plants (trees, shrubs, herbs) have low 13C/12C.
  • C4 plants (grasses) have high 13C/12C.
  • Grazing animals therefore have high 13C/12C.
  • So do their predators
A Tool for All Seasons, Science 10 November 2006: Vol. 314 no. 5801 pp. 930-931
Diet of animals
  • 18O/16O increases with temp, evaporation and low humidity.
  • 18O/16O enrichment is amplified in leaf water.
  • Leaf water supplies most of the water for browsing herbivores.
A Tool for All Seasons. Science 10 November 2006: Vol. 314 no. 5801 pp. 930-931
Sources of nitrogen for PNW forests. 15N
  • Marine algae has more 15N than terrestrial vegetation.
  • Salmon at the 4th trophic level are very enriched with 15N.
  • Riparian plants (W. hemlock, devil's club, huckleberry) of PNW forests get up to 40% of their nitrogen from salmon nutrients.
Reimchen, Tom. Fall 2001. Salmon nutrients, nitrogen isotopes and coastal forests. pp13-16. Ecoforestry external arrow
BMC Ecology 2002, 2:4 external arrow.
Molting latitudes δD (hydrogen isotope)
  • Higher latitudes in eastern N.America have lower amounts of δD.
  • The amount of δD in a bird's feathers indicates that latitude at which the feather was formed.
  • The amount of δD in American Redstart's tail feathers shows if it stayed in the northern breeding grounds to raise young or if it headed south early.
  • The birds with greater breeding success stayed up north longer, but under went molt on the trip south.
  • Birds molting in migration were more likely to die that winter by delaying their arrival in the tropics.
  • Birds molting in migration also presented lowered fitness signals (red feathers) for the next year's breeding season.
Norris, D.R., et al. Reproductive Effort, Molting Latitude, and Feather Color in a Migratory Songbird. (24 Dec 2004). Science. Vol 306, pp2249-2250. external arrow
Paleoelevation δD
  • Isotopic composition of rain varies with altitude. Higher altitudes have less δD.
  • Kaolin (clay) incorporates water in its structure at formation.
  • By sampling clay found in river paleosediments, a δD profile was created.
  • The data suggests a tall Sierra Nevada "consistent with the Sierra Nevada representing the edge of the pre-Eocene continental plateau."
Mulch, A, et al. Hydrogen Isotopes in Eocene River Gravels and Paleoelevation in the Sierra Nevada. (7 July 2006). Science. Vol 313, pp87-89. external arrow
Glacial melting 10Be
  • 10Be forms in a sample from cosmic rays striking quartz.
  • 10Be builds up on the surface of boulders after being exposed to the atmosphere when the glaciers melt.
Schaefer, J.M., et al. Near-Synchronus Interhemispheric Termination of the Last Glacial Maximum in Mid-Latitudes. (9 June 2006). Science. Vol 312, pp151-1513. external arrow
Formation of Moon 182W / 184W
  • 184W amounts fixed since birth of solar system.
  • 182W is decay product of hafnium.
  • Remixing of Earth's crust (impactor) allows metals to sink and reduces metals in crust.
  • This alters the 182W / 184W ratio.
When did the giant impact that formed the Moon take place? Trimmer, John. Arstechnica. 18 Oct 2011. external arrow
Oceanic oxygen 98Mo / 95Mo Devonian rise in atmospheric oxygen correlated to the radiations of terrestrial plants and large predatory fish. T.W. Dahl, et al. PNAS October 19, 2010 vol. 107 no. 42 17911-17915 external arrow.
Glacial erosion 4He / 3He thermochronometry Rapid Glacial Erosion at 1.8 Ma Revealed by 4He/3He Thermochronometry. David L. Shuster, Todd A. Ehlers, Margaret E. Rusmoren, and Kenneth A. Farley Science 9 December 2005: 310 (5754), 1668-1670. external arrow