The oxygen isotopic composition of precipitation (delta O-18(prec)) is well known to be a valuable (paleo-)climate proxy. Paleosols and sediments and hemicelluloses therein have the potential to serve as archives recording the isotopic composition of paleo-precipitation. In a companion paper (Zech et al., 2014) we investigated delta O-18(hemicellulose) values of plants grown under different climatic conditions in a climate chamber experiment. Here we present results of compound-specific delta O-18 analyses of arabinose, fucose and xylose extracted from modern topsoils (n = 56) along a large humid-arid climate transect in Argentina in order to answer the question whether hemicellulose biomarkers in soils reflect delta O-18(prec). The results from the field replications indicate that the homogeneity of topsoils with regard to delta O-18(hemicellulose) is very high for most of the 20 sampling sites. Standard deviations for the field replications are 1.5 parts per thousand, 2.2 parts per thousand and 1.7 parts per thousand, for arabinose, fucose and xylose, respectively. Furthermore, all three hemicellulose biomarkers reveal systematic and similar trends along the climate gradient. However, the delta O-18(hemicellulose) values (mean of the three sugars) do not correlate positively with delta O-18(prec) (r = -0.54, p < 0.014, n = 20). By using a Peclet-modified Craig-Gordon (PMCG) model it can be shown that the delta O-18(hemicellulose) values correlate highly significantly with modeled delta O-18(leaf) water values (r = 0.81, p < 0.001, n = 20). This finding suggests that hemicellulose biomarkers in (paleo-) soils do not simply reflect delta O-18(prec) but rather delta O-18(prec) altered by evaporative O-18 enrichment of leaf water due to evapotranspiration. According to the modeling results, evaporative O-18 enrichment of leaf water is relatively low (-10 parts per thousand) in the humid northern part of the Argentinian transect and much higher (up to 19 parts per thousand) in the arid middle and southern part of the transect. Model sensitivity tests corroborate that changes in relative air humidity exert a dominant control on evaporative O-18 enrichment of leaf water and thus delta O-18(hemicellulose), whereas the effect of temperature changes is of minor importance. While oxygen exchange and degradation effects seem to be negligible, further factors needing consideration when interpreting delta O-18(hemicellulose) values obtained from (paleo-) soils are evaporative O-18 enrichment of soil water, seasonality effects, wind effects and in case of abundant stem/root-derived organic matter input a partial loss of the evaporative O-18 enrichment of leaf water. Overall, our results prove that compound-specific delta O-18 analyses of hemicellulose biomarkers in soils and sediments are a promising tool for paleoclimate research. However, disentangling the two major factors influencing delta O-18(hemicellulose), namely delta O-18(prec) and relative air humidity controlled evaporative O-18 enrichment of leaf water, is challenging based on delta O-18 analyses alone. (C) 2013 Elsevier Ltd. All rights reserved.