Assessing Sediment Age

Science  28 May 2004:
Vol. 304, Issue 5675, pp. 1215
DOI: 10.1126/science.304.5675.1215b

Marine sediments, one of the most important sources of paleoclimatic and paleoceanographic data for the past 50,000 years, are often difficult to date by radiocarbon analysis. This is because they contain a wide variety of organic compounds of different carbon ages, so a unique date of deposition is typically impossible to determine. One way to overcome this problem is by determining the radiocarbon age of a single type of molecule of known origin, called a biomarker. Such a method has become technically possible only since the development of accelerated mass spectrometry in the 1980s. The question remains: Which types of biomarkers are best suited to provide accurate sediment ages? Smittenberg et al. address this question by conducting a survey of radiocarbon ages of a variety of compounds found in independently dated sediments from Saanich Inlet, Canada. Good ages were provided by one particular kind of molecule, crenarchaeol. Other biomarkers had more variable ages, and so were less useful for dating purposes. This confirms the idea that the microscopic, single-celled marine organisms, the Crenarchaeota, which produce this biomarker, used dissolved inorganic carbon as their carbon source. — HJS

Paleoceanography 19, PA2012, 10.1029/2003PA000927 (2004).

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