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Abstract Northern Arizona University, Flagstaff, Arizona, USA, recently installed a MIni CArbon DAting System (MICADAS) with a gas interface system (GIS) for determining the14C content of CO2gas released by the acid dissolution of biogenic carbonates. We compare 48 paired graphite, GIS, and direct carbonate14C determinations of individual mollusk shells and echinoid tests. GIS sample sizes ranged between 0.5 and 1.5 mg and span 0.1 to 45.1 ka BP (n = 42). A reduced major axis regression shows a strong relationship between GIS and graphite percent Modern Carbon (pMC) values (m = 1.011; 95% CI [0.997–1.023], R2= 0.999) that is superior to the relationship between the direct carbonate and graphite values (m = 0.978; 95% CI [0.959-0.999], R2= 0.997). Sixty percent of GIS pMC values are within ±0.5 pMC of their graphite counterparts, compared to 26% of direct carbonate pMC values. The precision of GIS analyses is approximately ±7014C yrs to 6.5 ka BP and decreases to approximately ±13014C yrs at 12.5 ka BP. This precision is on par with direct carbonate and is approximately five times larger than for graphite. Six Plio-Pleistocene mollusk and echinoid samples yield finite ages when analyzed as direct carbonate but yield non-finite ages when analyzed as graphite or as GIS. Our results show that GIS14C dating of biogenic carbonates is preferable to direct carbonate14C dating and is an efficient alternative to standard graphite14C dating when the precision of graphite14C dating is not required.
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Atmospheric 14 C/ 12 C changes during the last glacial period from Hulu Cave
Paired measurements of14C/12C and230Th ages from two Hulu Cave stalagmites complete a precise record of atmospheric14C covering the full range of the14C dating method (~54,000 years). Over the last glacial period, atmospheric14C/12C ranges from values similar to modern values to values 1.70 times higher (42,000 to 39,000 years ago). The latter correspond to14C ages 5200 years less than calibrated ages and correlate with the Laschamp geomagnetic excursion followed by Heinrich Stadial 4. Millennial-scale variations are largely attributable to Earth’s magnetic field changes and in part to climate-related changes in the oceanic carbon cycle. A progressive shift to lower14C/12C values between 25,000 and 11,000 years ago is likely related, in part, to progressively increasing ocean ventilation rates.
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- PAR ID:
- 10081450
- Publisher / Repository:
- American Association for the Advancement of Science (AAAS)
- Date Published:
- Journal Name:
- Science
- Volume:
- 362
- Issue:
- 6420
- ISSN:
- 0036-8075
- Page Range / eLocation ID:
- p. 1293-1297
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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