Late Glacial fire and nitrogen dynamics at lacustrine sites in Alabama and Michigan: evidence of an acid rain event?
is part of the Paper Session:
Paleorecords II. Climate and Environmental History in the Eastern U.S.
scheduled on Tuesday, 4/8/2014 at 10:00 AM.
Click below for author bios:
Joanne P Ballard* – University of Tennessee
Sally P Horn – University of Tennessee
Chad S Lane – Chad Lane, University of North Carolina, Wilmington
Zheng-Hua Li – NASA Marshall Space Flight Center
Steven G Driese – Baylor University
Thomas V Lowell – University of Cincinnati
We analyzed stable nitrogen isotopes, total nitrogen, and macroscopic charcoal in sediments from three lakes in Alabama and Michigan to characterize temporal patterns in nitrogen cycling and explore links between nitrogen, climate, and fire across the late glacial in eastern North America. We used cores from Cahaba Pond, Alabama, recovered by Delcourt et al. (1983, Ecology), and matched our isotope and charcoal analyses to their pollen stratigraphy. Cores from Swift and Slack Lakes in Michigan were obtained in 2008. Thin-section analysis across a 20-cm section from Cahaba Pond that encompasses the Younger Dryas shows a transition from mineral-rich to organic-rich sediments, with loessal silt aggregates. All three lakes recorded roughly coeval nitrogen perturbations at the onset of the Younger Dryas, when a dramatic shift occurred in terrestrial and aquatic vegetation at Cahaba Pond. All three sites also registered fire events across the late glacial. We explore the possibility that observed perturbations to the nitrogen cycle are evidence of nitric acid rain. Such an event could result from nitrate production in the atmosphere due to shock waves from an extraterrestrial event as discussed by Prinn and Fegley (1987, Earth and Planetary Science Letters). If our nitric acid rain idea is correct, it would lend support to the Firestone extraterrestrial impact hypothesis. Concentrations of nitrate and ammonium in ice cores, and sudden eutrophication and shifts from alkaliphilous to acidiphilous diatoms in lake sediments, might also support a nitric acid rain event at the onset of the Younger Dryas.
Younger Dryas, Late Glacial, nitrogen, isotopes, extraterrestrial, acid, rain, Cahaba Pond, climate, paleofire, charcoal, lake sediments, Slack Lake, Swift Lake
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