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Stable isotope analyses of soils significantly contribute to a better understanding of biogeochemical and paleoenvironmental processes. This paper presents and discusses stable carbon, nitrogen and oxygen isotope (delta C-13, delta N-15 and delta O-18) data of representative soils of Buryatia, southern Siberia.

In undisturbed soils (kastanozem, phaeozem, gleysol, podzol, leptosol) delta C-13 and delta N-15 values of soil organic matter (SOM) increase from the organic layers (O-layers) to the mineral topsoils (A(h)-horizons) and subsoils. This primarily indicates advanced C and N-mineralization in lower soil horizons and reflects the input of fresh litter in the O-layers. Combined with numerical ages, these data indicate that during the last ca. 40 ka no C4 grasses prevailed in semiarid regions of Buryatia. Disturbed soils (ploughed chernozem and an anthrosol) do not show with depth increasing delta C-13 and delta N-15 values but are characterized by fluctuating depth profiles. High delta N-15 values in the anthrosol (up to 10.5 parts per thousand) point to an open N cycle. In a middle and late Holocene aeolian paleosol record (Burdukovo), delta O-18 of the hemicellulose-biomarkers arabinose and xylose show minima in the dark humic buried A horizons and maxima in the greyish silty fine sand layers. This reflects the alternation of more arid and more humid conditions. This interpretation is also in agreement with higher grain size ratios (20-63 mu m)/(2-6 mu m) in the greyish fine sand layers, documenting increased wind strength and dust supply.

SOM delta C-13 and delta N-15 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, delta N-15 values decrease with increasing altitude giving evidence of more closed N cycles at higher altitudes, which are characterized by lower temperatures. As an exception, delta N-15 of the A(h)-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. delta C-13 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 delta O-18 of the hemicellulose-biomarkers arabinose and xylose do not reflect the ’altitude-effect’ as it could be expected from delta O-18 of precipitation. (c) 2012 Elsevier Ltd and INQUA. All rights reserved.