[1] Virginia Polytech Inst & State Univ, Dept Geosci, Blacksburg, VA 24061 USA
[2] CSIC, Estac Expt Zaidin, Lab Biogeoquim Isotopes Estables, E-18008 Granada, Spain
[3] Univ La Laguna, Fac Biol, Dept Biol Anim, E-38206 Tenerife, Canary Islands, Spain
[4] Univ La Laguna, Fac Biol, Dept Edafol & Geol, E-38206 Tenerife, Canary Islands, Spain