Stable isotope (δ13C, δ15N, δ18O) record of soils in Buryatia, southern Siberia: Implications for biogeochemical and paleoclimatic interpretations

SOM δ13C and δ15N values of O-layers and Ah-horizons were furthermore investigated along an altitudinal transect in the Khamar Daban Mts (from 470 m to 1800 m a.s.l.). Generally, δ15N values decrease with increasing altitude giving evidence of more closed N cycles at higher altitudes, which are characterized by lower temperatures. As an exception, δ15N of the Ah-horizons above 1500 m reveals conspicuously positive values, presumably because of frequent burning of the dwarf pine belt with high N losses due to volatilization. δ13C shows no significant altitudinal trend above 750 m a.s.l., but more negative values below 750 m a.s.l. This may be attributed to frequent temperature inversions close to Lake Baikal. Similarly, this inversion inducing fog and higher humidity close to Lake Baikal could also explain why δ18O of the hemicellulose-biomarkers arabinose and xylose do not reflect the 'altitude-effect' as it could be expected from δ18O of precipitation.