- Plant wax lipids and lignin phenols are the two most common classes of molecular markers that are used to trace vascular
plant-derived OM in the marine environment. However, their ¹³C and ¹⁴C compositions have not been directly compared,
which can be used to constrain the flux and attenuation of terrestrial carbon in marine environment. In this study, we describe
a revised method of isolating individual lignin phenols from complex sedimentary matrices for ¹⁴C analysis using high pressure
liquid chromatography (HPLC) and compare this approach to a method utilizing preparative capillary gas chromatography
(PCGC). We then examine in detail the ¹³C and ¹⁴C compositions of plant wax lipids and lignin phenols in sediments
from the inner and mid shelf of the Washington margin that are influenced by discharge of the Columbia River. Plant wax
lipids (including n-alkanes, n-alkanoic (fatty) acids, n-alkanols, and n-aldehydes) displayed significant variability in both σ¹³C
(-28.3%₀ to -37.5%₀) and Δ¹⁴C values (-204%₀ to +2%₀), suggesting varied inputs and/or continental storage and transport
histories. In contrast, lignin phenols exhibited similar σ¹³C values (between -30%₀ and -34%₀) and a relatively narrow range
of Δ¹⁴C values (-45%₀ to -150%₀; HPLC-based measurement) that were similar to, or younger than, bulk OM (-195%₀ to
-137%₀). Moreover, lignin phenol ¹⁴C age correlated with the degradation characteristics of this terrestrial biopolymer in that
vanillyl phenols were on average ~500 years older than syringyl and cinnamyl phenols that degrade faster in soils and sediments.
The isotopic characteristics, abundance, and distribution of lignin phenols in sediments suggest that they serve as
promising tracers of recently biosynthesized terrestrial OM during supply to, and dispersal within the marine environment.
Lignin phenol ¹⁴C measurements may also provide useful constraints on the vascular plant end member in isotopic mixing
models for carbon source apportionment, and for interpretation of sedimentary records of past vegetation dynamics.
- Feng, X., Benitez-Nelson, B. C., Montluçon, D. B., Prahl, F. G., McNichol, A. P., Xu, L., . . . Eglinton, T. I. (2013). 14C and 13C characteristics of higher plant biomarkers in washington margin surface sediments. Geochimica Et Cosmochimica Acta, 105, 14-30. doi: 10.1016/j.gca.2012.11.034
|Funding Statement (additional comments about funding)
- GrantsOCE-9907129, OCE-0137005, and OCE-0526268 (to T.I.E.) fromthe National Science Foundation (NSF) supported this research.
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