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Dissolved Organic and Inorganic 14C Concentrations and Ages for Coastal Plain Aquifers in Southern Maryland

Published online by Cambridge University Press:  18 July 2016

C. B. Purdy ,
G. S. Burr ,
Meyer Rubin ,
G. R. Helz  and
A. C. Mignerey
C. B. Purdy*
Affiliation:
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742 USA
G. S. Burr
Affiliation:
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742 USA Department of Physics, The University of Arizona, Tucson, Arizona 85721 USA
Meyer Rubin
Affiliation:
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742 USA U.S. Geological Survey, National Center 971, Reston, Virginia 22092 USA
G. R. Helz
Affiliation:
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742 USA
A. C. Mignerey
Affiliation:
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742 USA
*
1Present address: The Department of Energy, EM-542, Trevion II, Washington, D. C. 20585-0002
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Abstract

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The Aquia (Paleocene) and Magothy (Late Cretaceous) Formations of the Atlantic Coastal Plain represent two well-characterized (hydrodynamically and geochemically) aquifers in southern Maryland. 14C measurements of the dissolved organic (DOC) and inorganic carbon (DIC) of Aquia and Magothy groundwaters have been made using accelerator mass spectrometry (AMS). Both DI14C and DO14C concentrations in the initial flow path are unexpectedly low. As the water progresses farther from the recharge area, the DI14C percent modern carbon (pMC) is consistently lower than the DO14C pMC; this difference stays constant for all samples. The 14C-derived ages for an Aquia water sample downgradient at Site 4 are 17 ka and 12 ka for DI14C and DO14C, respectively. Radiocarbon ages have been compared to ages determined by two other independent dating methods: computer-simulated hydrodynamic modeling and age estimates based on changes in Cl−, 18O and 2H distributions, which are interpreted to be influenced by sea level and climate.

Type
II. Applied Isotope Geochemistry
Information
Radiocarbon , Volume 34 , Issue 3: Proceedings of the 14th International Radiocarbon Conference , 1992 , pp. 654 - 663
Copyright
Copyright © The American Journal of Science 

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