Carbon isotopes in ombrogenic peat bog plants as climatic indicators: calibration from an altitudinal transect in Switzerland

The accumulation of organic matter in peat bogs potentially constitutes a continuous and high-resolution record of continental climate for the Holocene period. In order to interpret the carbon isotopic values of bog plant macrofossils as a record of environmental parameters, we attempted to calibrate plant-climate relationships by sampling a set of modern plant species (both vascular plants and mosses) along an altitudinal transect in Switzerland. Carbon isotope ratios were measured by an on-line combustion/continuous flow method on both bulk plant material and the α-cellulose fraction. For most of the species studied, the δ13C-values increase with altitude, although the slopes of the trends vary considerably. The primary cause of the δ13C increase with altitude is thought to be decreased atmospheric CO2 partial pressure. In addition, for vascular plants the increase of δ13C-values might also partially be due to decreasing temperature. For mosses, the cell water content (and thus precipitation regime) is also an important factor influencing δ13C-values.