Depth trends of δ13C and δ15N values in peatlands in aeolian environments of Iceland

Abstract

Depth patterns of δ¹³C and δ¹⁵N values in peatlands are used to reconstruct their environmental history, e.g. their hydrology, temperature changes and degradation. However, the suitability of δ¹³C and δ¹⁵N as proxies for environmental reconstructions needs to be verified by studies in a diverse range of environments. We present a study on the influence of aeolian deposits on δ¹³C and δ¹⁵N values in peatlands in Iceland. Large areas in Iceland comprise highly active aeolian environments due to tephra from volcanic eruptions, and material from eroding drylands. The study is a first step toward assessing if depth profiles of δ¹³C and δ¹⁵N values can provide insight into the environmental history of peatlands in aeolian environments. We compare δ¹³C and δ¹⁵N values with several conventional proxies of decomposition (dry bulk density, C/N ratio and two ratios derived from ¹³C NMR spectra). We also interpret variations in δ¹³C and δ¹⁵N values in relation to the pedogenic minerals allophane and ferrihydrite and total mineral content. The complexity of depth trends of δ¹³C and δ¹⁵N values increases with proximity to source areas of windborne material. Particularly, there are turning points adjacent to major tephra layers. These patterns appear to be related to the influence of the volcanic deposits on factors like hydrology and fertility of the peatlands, microbial activity and vegetation composition. Depth trends of δ¹³C and δ¹⁵N values in peatlands of aeolian environments need to be interpreted in relation to other proxies reflecting the organic matter chemistry, and mineral soil constituents.