Comment on "Changes in atmospheric CO2 levels recorded by the isotopic signature of n-alkanes from plants" from K.S. Machado and S. Froehner


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Peter.Koehler [ at ] awi.de

Abstract

The recently published invited research article by Machado and Froehner (2017) is presenting δ13C values from sedimentary organic matter (n-alkane), measured on samples collected in the Barigui wa- tershed (Brazil) covering the last 400 years. The derived δ13C time series based on C27 n-alkane, beginning approximately in the calendar year 1600 (or 1600 CE; with CE for Common Era) until recent times is subsequently — in their Fig. 3 — compared with a record, which is believed to be a representative reconstruction of atmospheric CO2 concentrations covering approximately the last 650 years (with respect to the year 2005 CE). The final conclusion of this article, as reflected in its title, is that changes in atmospheric CO2 levels are recorded in isotopic signatures on n-alkane from plants. We argue, that this conclusion can not be drawn from the study of Machado and Froehner (2017), since what is shown in their Fig. 3 is not a time series of atmospheric CO2 concentration of the last 650 years. The authors show reconstruc- tions of atmospheric CO2 concentrations based on Antarctic ice cores over the past 650,000 years and use them for the past 650 years by ignoring the fact that the time scale in IPCC (2007), from which, ac- cording to the caption of their Fig. 3, they took this CO2 time series, is in kyr (1 kyr = 1 kilo year = 1000 years). This is wrong and any conclusion based on this comparison is incorrect. Instead they should have used for a correct CO2 time series for the comparison with their measurements.



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ISI/Scopus peer-reviewed
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Eprint ID
45369
DOI 10.1016/j.gloplacha.2017.08.003

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Köhler, P. , Nehrbass-Ahles, C. , Schmitt, J. , Stocker, T. F. and Fischer, H. (2017): Comment on "Changes in atmospheric CO2 levels recorded by the isotopic signature of n-alkanes from plants" from K.S. Machado and S. Froehner , Global and Planetary Change, 156 , pp. 24-25 . doi: 10.1016/j.gloplacha.2017.08.003


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