title: Chlorine-36 in fossil rat urine: an archive of cosmogenic nuclide deposition during the past 40,000 years.
abstract: Knowledge of the production history of cosmogenic nuclides, which is needed for geological and archaeological dating, has been uncertain. Measurements of chlorine-36/chlorine (36Cl/Cl) ratios in fossil packrat middens from Nevada that are radiocarbon-dated between about 38 thousand years ago (ka) and the present showed that 36Cl/Cl ratios were higher by a factor of about 2 before approximately 11 ka. This raises the possibility that cosmogenic production rates just before the close of the Pleistocene were up to 50% higher than is suggested by carbon-14 calibration data. The discrepancy could be explained by addition of low-carbon-14 carbon dioxide to the atmosphere during that period, which would have depressed atmospheric radiocarbon activity. Alternatively, climatic effects on 36Cl deposition may have enhanced the 36Cl/Cl ratios.
authors.affiliation: Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Plummer
authors.forename: F M
authors.initials: FM
authors.lastname: Phillips
authors.forename: J
authors.initials: J
authors.lastname: Fabryka-Martin
authors.forename: H J
authors.initials: HJ
authors.lastname: Turin
authors.forename: P E
authors.initials: PE
authors.lastname: Wigand
authors.forename: P
authors.initials: P
authors.lastname: Sharma
mesh_terms: D000818:Animals; D001272:Atmosphere; D002250:Carbon Radioisotopes / Q000032:analysis; D002713:Chlorine / Q000652:urine*; D003359:Cosmic Radiation; D005580:Fossils; D009505:Nevada; D011868:Radioisotopes / Q000652:urine*; D016205:Sigmodontinae / Q000652:urine*; D013997:Time Factors
chemical_list: D002250:Carbon Radioisotopes; D011868:Radioisotopes; D002713:Chlorine