We evaluate potential process blanks associated with 14C measurement of microgram to milligram quantities of alkenones at NOSAMS.
Two strategies to constrain the contribution of blanks to alkenone 14C dates were followed: 1) Dating of samples of known age, and 2) multiple measurements of identical samples.
Our results indicate that alkenones record Δ14C of ambient DIC with an accuracy of approximately 10‰.
A conservative estimate of measurement precision is 17‰ for modern samples.
Here, we describe a method for isolation of alkenones from sediments as a compound class based on a sequence of wet chemical techniques.
The steps involved, which include silica gel column chromatography, urea adduction, and silver nitrate-silica gel column chromatography, exploit various structural attributes of the alkenones.
We show that there is no systematic contamination associated with the procedure that would bias the results of alkenone dating to either younger or older ages.
We evaluate potential process blanks associated with radiocarbon measurement of microgram to milligram quantities of alkenones at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility.Alkenone 14C ages are expected to be reliable within 500 yr for samples younger than 10,500 14C yr. © Arizona Board of Regents on behalf of the University of Arizona, 2005. of Geosciences, University of Arizona for personal use, not for redistribution.The definitive version was published in Radiocarbon 47 (2005): 413-424.Amounts of purified alkenones estimated by GC/FID measurements were highly correlated with CO2 yields after sample combustion, indicating purities of greater than 90% for samples containing ≥100 μg C.The degree of alkenone unsaturation ( ) also varied minimally through the procedure.Lateral advection of (recycled) alkenone-bearing material may influ- ence the signal preserved in the sediments as has been postulated in previous studies for certain sites (e.g. Large age offsets between alkenones and foraminifera attributable to advection of old material have been observed on the Bermuda rise (Ohkouchi et al., in prep.).