A comparison between conventional and AMS [sup 14]C dates on basal salt marsh peats from coastal Maine. [Accelerator Mass Spectroscopy]
- Univ. of Maine, Orono, ME (United States). Dept. of Geological Sciences
This study reports AMS dates from four Maine salt marshes: Webbannet Marsh (Wells), Morse and Sprague River marshes (Phippsburg), and Sanborn Cove marsh (Machiasport). The AMS dates are compared with conventional dates on bulk samples obtained from either the same cores or from other cores at comparable depths. Four AMS dates from the Webhannet and Sanborn Cove marshes were considerably older than their conventional counterparts, by as much as 1,000 years. Three causes for this age discrepancy are suggested. First, under slow rates of marsh accretion, peats remain within the root zone of modern plants for a relatively long period, causing a continued input of younger carbon. Intruded roots are undetectable in the highly macerated, 4,000--5,000 C-14 year old peats. Another source of contamination is the percolation of mobile humic acids along the impermeable Pleistocene substrate. Finally, a date on a bulk peat of 10 cm vertical extent represents an average age for a portion of peat that spans a time interval possibly of several centuries. The age difference between the bulk date and the AMS date from the base of the peat increases with decreasing rates of marsh accretion. The forested steep slopes of the upland surrounding the marsh seem a likely source of old carbon that can easily be washed onto the marsh surface. The slow rate of late-Holocene sea-level rise in Maine, as well as the geologic and hydrologic setting of the salt marshes, make conventional C-14 dating of salt marsh peats in Maine a problematic affair. This study implies that AMS dates may be needed to verify Holocene sea-level curves from other coastal areas that have hitherto been based solely on conventional C-14 peat dates.
- OSTI ID:
- 5907412
- Report Number(s):
- CONF-921058--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 24:7; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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Middle to Late Holocene Fluctuations of C3 and C4 Vegetation in a Northern New England Salt Marsh, Sprague Marsh, Phippsburg Maine
Relative sea-level trends along the coast of Maine during the past 5,000 [sup 14]C years
Related Subjects
011000* -- Coal
Lignite
& Peat-- Reserves
Geology
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AGE ESTIMATION
AQUATIC ECOSYSTEMS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBON 14
CARBON ISOTOPES
COAL DEPOSITS
COMPARATIVE EVALUATIONS
DEVELOPED COUNTRIES
ECOSYSTEMS
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MAINE
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MASS SPECTROSCOPY
MATTER
MINERAL RESOURCES
NORTH AMERICA
NUCLEI
ORGANIC MATTER
PEAT
RADIOISOTOPES
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SEA LEVEL
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USA
VARIATIONS
WETLANDS
YEARS LIVING RADIOISOTOPES