Stable Carbon and Nitrogen Isotopes in a Peat Profile Are Influenced by Early Stage Diagenesis and Changes in Atmospheric CO₂ and N Deposition
2012
Esmeijer-Liu, Alice J. | Kürschner, Wolfram M. | Lotter, André F. | Verhoeven, J. T. A. | Goslar, Tomasz
In this study, we test whether the δ¹³C and δ¹⁵N in a peat profile are, respectively, linked to the recent dilution of atmospheric δ¹³CO₂ caused by increased fossil fuel combustion and changes in atmospheric δ¹⁵N deposition. We analysed bulk peat and Sphagnum fuscum branch C and N concentrations and bulk peat, S. fuscum branch and Andromeda polifolia leaf δ¹³C and δ¹⁵N from a 30-cm hummock-like peat profile from an Aapa mire in northern Finland. Statistically significant correlations were found between the dilution of atmospheric δ¹³CO₂ and bulk peat δ¹³C, as well as between historically increasing wet N deposition and bulk peat δ¹⁵N. However, these correlations may be affected by early stage kinetic fractionation during decomposition and possibly other processes. We conclude that bulk peat stable carbon and nitrogen isotope ratios may reflect the dilution of atmospheric δ¹³CO₂ and the changes in δ¹⁵N deposition, but probably also reflect the effects of early stage kinetic fractionation during diagenesis. This needs to be taken into account when interpreting palaeodata. There is a need for further studies of δ¹⁵N profiles in sufficiently old dated cores from sites with different rates of decomposition: These would facilitate more reliable separation of depositional δ¹⁵N from patterns caused by other processes.
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