Anomalously low radiocarbon content of modern n-alkanes

Lane, Chad S.; Yanuskiewicz, Elizabeth A.; Mead, Ralph N.; Horn, Sally P.

doi:10.1016/j.orggeochem.2020.104170

Cited by 4 publications

(17 citation statements)

References 23 publications

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“…Despite this established practice, Lane et al (2021) recently extracted long-chain n-alkanes from the leaves of living plants and found biomarker 14 C ages that are up to %1500yr older than bulk leaf tissue. In their original article and in a subsequent corrigendum (Lane et al, 2021b), they argued that this signal cannot be entirely explained as contamination by 14 C-free (''dead") carbon-for example from solvent extraction or chemical processing steps-and instead interpret this ''pre-aging" as a result of large, anomalous fractionation against 14 C during lipid biosynthesis. Because of this, they conclude that biomarkers violate a fundamental assumption of the radiocarbon geochronometer and urge caution when interpreting their 14 C ages.…”

Section: ⁎ Corresponding Authormentioning

confidence: 99%

“…Here, I evaluate the Lane et al (2021) hypothesis by focusing specifically on the plausibility of calculated b values that would be required to explain these data. Because multiple-isotope analysis is an established practice for many light element systems (e.g., O, Si, S), there exist robust theoretical derivations for determining mass laws.…”

Section: ⁎ Corresponding Authormentioning

confidence: 99%

“…Given these results, I estimate that fractionation during lipid biosynthesis can only explain 14 C age offsets up to %40yr and conclude that biomarker radiocarbon results can be confidently interpreted to reflect aging in the environment. I briefly offer alternative explanations to interpret the data of Lane et al (2021).…”

Section: ⁎ Corresponding Authormentioning

confidence: 99%

“…I use Eq. ( 7) and data reported in Lane et al (2021) to estimate b p=r values that would be required if their 14 C offsets between bulk leaf tissue and n-alkanes were due to fractionation (Table 1). When bulk leaf tissue F 14 C is not reported (i.e., for the species L. styraciflua L. and Q. nigra L.), I assume F 14 C ¼ 1:003 AE 0:003, the average of all reported values (l AE 1r; n ¼ 4).…”

Section: Radiocarbon Nomenclature and Mass Law Calculationsmentioning

confidence: 99%

“…Given the range of kinetic, equilibrium, and net reaction mass laws observed here, it is possible to assess the claim made by Lane et al (2021) that biosynthetic fractionation imparts 14 C age biases up to %1500 yr. In contrast to the large mass laws required for this hypothesis, I find that b values for all investigated kinetic and equilibrium fractionation process are within the canonical range of 1:8 to 2:0 (Fig.…”

Section: Are Large Biosynthetic 14 C Age Biases Possible?mentioning

confidence: 99%

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Biosynthetic isotope fractionation negligibly impacts biomarker 14C ages

Hemingway

2021

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Radiocarbon ( 14 C) ages of acetogenic lipid biomarkers such as n-alkanes represent a powerful tool to track carbon-cycle turnover times in a range of environments including soils, fluvially exported sediments, and marine sediments. However, the fidelity of this approach requires that biomarker 14 C ages accurately reflect the time that has passed since biosynthesis and are not complicated by issues such as isotope fractionation. Reported 14 C ages are thus always corrected for mass-dependent fractionation using a 14 C/ 13 C mass law, b, of 2:0. However, anomalous deviations from mass dependence could theoretically lead to biases in measured 14 C ages, particularly for compounds such as acetogenic lipids that undergo large 13 C fractionations. Here, I test this possibility by estimating kinetic and equilibrium mass laws for various processes involved in acetogenic lipid biosynthesis using simple approximations and more robust computational chemistry methods. I find that kinetic b values range from 1:890 to 1:995 and that equilibrium b values for several chain elongation steps range from 1:856 to 1:880, consistent with previous results for other chemical and biological processes. In contrast, complex reaction networks may lead to large expressed b values, but only when net lnð 13 aÞ ! 0. Combined, these results imply maximum 14 C age offsets due to biosynthetic fractionation of ~20 to 40 yr. Biomarker 14 C ages are therefore robust to biosynthetic isotope fractionation and can be confidently interpreted to reflect carbon-cycle turnover times.

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Section: ⁎ Corresponding Authormentioning

confidence: 99%

Section: ⁎ Corresponding Authormentioning

confidence: 99%

Section: ⁎ Corresponding Authormentioning

confidence: 99%

Section: Radiocarbon Nomenclature and Mass Law Calculationsmentioning

confidence: 99%

Section: Are Large Biosynthetic 14 C Age Biases Possible?mentioning

confidence: 99%

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Biosynthetic isotope fractionation negligibly impacts biomarker 14C ages

Hemingway

2021

Preprint

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Holocene hydroclimate in highland Costa Rica: new evidence from hydrogen and carbon isotopes in n‐alkanes of terrestrial leaf waxes in a 10 000‐year sediment profile

Kerr,

Horn,

Lane

2024

J Quaternary Science

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We conducted compound‐specific stable hydrogen (δD) and carbon (δ13C) isotope analysis on n‐alkanes from terrestrial leaf waxes preserved in a 10 000‐year sediment profile from Lago de las Morrenas 1 (9.4925° N, 83.4848° W, 3480 m), a glacial lake on the Chirripó massif of the Cordillera de Talamanca in Costa Rica. Our results demonstrate millennial‐scale variations in hydroclimate across the Holocene, with drier than average conditions in the highlands during the early Holocene, but with gradually increasing precipitation; mesic conditions during the middle Holocene with a gradual drying trend; and highly variable conditions during the late Holocene. This general pattern is punctuated by several centennial‐scale manifestations of global climate events, including dry conditions during the 8200, 5200 and 4200 cal a bp events and the Terminal Classic Drought (1200–850 cal a bp). Our δ13C analyses demonstrate that carbon isotope signals are responding to changes in hydroclimate at the site and reinforce prior interpretations of a stable páramo plant community that established following deglaciation and persisted throughout the Holocene. The shifts in hydroclimate inferred from analyses of n‐alkanes in Lago de las Morrenas 1 sediments show correspondence with charcoal records in multiple lakes, with fires most common during drier intervals.

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