title: Isotopic composition of sheep wool records seasonality of climate and diet.
abstract: BACKGROUND
  Hair keratin is a very important material in ecological and archaeological studies because it grows continuously, can be obtained non-invasively, does not require extensive processing prior to analysis and can be found in archaeological sites. Only a few studies have examined seasonal variations in hair isotope values, and there is no published dataset examining the isotope variability recorded in the keratinous tissues of stationary (i.e., non-migrating) domestic mammals.
  
  
  METHODS
  Thirty-six Irish sheep were sampled in eight farms every three months between September 2006 and June 2007. A shearing strategy was adopted to sample only the most recently grown wool in order to represent an average of the summer, autumn, winter and spring conditions. The stable isotope ratios of the ground samples were measured using two different stable isotope mass spectrometers operated in dual-inlet (C, N) and continuous-flow (O, H) mode.
  
  
  RESULTS
  Wool O isotope ratios are a good proxy for seasonal variability in climate and can be used to anchor a chronology independently of other isotope records (C, N) that are influenced by diet or physiology. By contrast, interpretation of seasonal variations in hair H isotope composition in terms of climate is more complex probably due to the influence of dietary H. The C and N isotope values of grass-fed animals varied seasonally, probably reflecting the annual cycle of seasonal variation in grass isotope values. The highest δ(13) C values were measured in summer-grown wool, while the highest δ(15) N values were measured in winter-grown wool. Supplementation of the sheep diet with concentrates was detected easily and was marked by an increase in δ(13) C values and a decrease in δ(15) N values in winter-grown wool.
  
  
  CONCLUSIONS
  The present study demonstrates that time-resolved sampling and stable isotope ratio analysis of sheep wool can be used to identify short-term changes in diet and climate and therefore offer a tool to examine a wide variety of present and past husbandry practices.
authors.affiliation: CNRS UMR 7209, Muséum National d'Histoire Naturelle, "Archéozoologie, Archéobotanique: Sociétés, Pratiques et Environnements", Département "Ecologie et Gestion de la Biodiversité", CP 56, 55 rue Buffon, F-75005, Paris, France.
authors.forename: A
authors.initials: A
authors.lastname: Zazzo
authors.affiliation: Department of Geology and Geophysics, Department of Biology, University of Utah, Salt Lake City, UT, 84112, USA.
authors.forename: T E
authors.initials: TE
authors.lastname: Cerling
authors.affiliation: Global Change and Sustainability Center and Department of Biology, University of Utah, Salt Lake City, UT, 84112, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Ehleringer
authors.affiliation: Teagasc, Animal and Grassland Research and Innovation Centre, Dunsany, Co. Meath, Ireland.
authors.forename: A P
authors.initials: AP
authors.lastname: Moloney
authors.affiliation: UCD School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: F J
authors.initials: FJ
authors.lastname: Monahan
authors.affiliation: UCD School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Ireland.|UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: O
authors.initials: O
authors.lastname: Schmidt