Leaf wax <i>n</i>-alkane pattern and compound-specific δ<sup>13</sup>C of plants and topsoils from semi-arid Mongolia

Abstract

<p><strong>Abstract.</strong> <i>n</i>-Alkane pattern and their compound-specific δ<sup>13</sup>C signatures are valuable proxies for paleoenvironmental reconstructions. So far, their potential has not been investigated in semi-arid to arid regions. We have therefore analysed the leaf wax <i>n</i>-alkanes and their compound-specific δ<sup>13</sup>C of five plant species (<i>Poaceae</i>, <i>Cyperaceae</i>, <i>Artemisia spp.</i>, <i>Caragana spp.</i> and <i>Larix sp.</i>), and topsoils (0–5 cm) along two transects in central and southern Mongolia. Grasses depict a distinct dominance of the <i>n</i>-C<sub>31</sub> homologue, whereas <i>Caragana spp.</i> and <i>Artemisia spp.</i> are dominated by <i>n</i>-C<sub>29</sub>. <i>Larix sp.</i> is characterized by the mid-chain <i>n</i>-alkanes <i>n</i>-C<sub>23</sub> and <i>n</i>-C<sub>25</sub>. From plant to soil, <i>n</i>-alkane homologue pattern show the potential to differentiate between grass covered sites from those covered by <i>Caragana spp</i>. <i>n</i>-Alkane concentrations and OEP values of the topsoils are distinctly influenced by mean annual temperature, mean annual precipitation and aridity, likely reflecting the degree of <i>n</i>-alkane degradation and biomass production. In contrast, the <i>n</i>-alkane average chain-length and the <i>n</i>-alkane ratio (<i>n</i>-C<sub>31</sub> / <i>n</i>-C<sub>29</sub> + <i>n</i>-C<sub>31</sub>) are not affected by climatic parameters. The compound-specific δ<sup>13</sup>C signatures are strongly corelated to climate, showing a significant enrichment with increasing aridity, indicating the effect of water use efficiency. Our calibration results suggest that long-chain <i>n</i>-alkanes and their compound-specific δ<sup>13</sup>C signatures have great potential to reconstruct paleoenvironmental and -climatic conditions when used in sediment archives from Mongolia.</p>

Fossil leaf wax hydrogen isotopes reveal variability of Atlantic and Mediterranean climate forcing on the southeast Iberian Peninsula between 6000 to 3000 cal. BP

“…Aridity is closely related to evapotranspiration, which is potentially an important parameter to be considered, when interpreting δD Cx data in semi-arid climates such as southeast Iberia. Evapotranspiration can be studied using δ 13 C values, which are claimed to record plant water stress [71,85]. As noted before, all individual δ 13 C records suggest a constant dominance of C3 plant species, enabling the interpretation of the δ 13 C WMA record as indicator of plant water stress [71].…”

n-Alkane Characteristics of Thawed Permafrost Deposits Below a Thermokarst Lake on Bykovsky Peninsula, Northeastern Siberia

“…The starting values depend on the composition of the source material. These indices were calculated following Equation 2 (Marzi et al, 1993) and 3 (Zech et al, 2009;Struck et al, 2019), respectively. As both indices are used in other studies, both parameters are presented here.…”

“…First, one cannot assume a similar plant composition in Arctic regions compared to temperate regions. Second, some plant genera such as Artemisia or Sphagnum, have been found to have a dominance of the n-C 29 alkane, thereby 'mimicking' deciduous trees and shrubs (Ficken et al, 1998;Struck et al, 2019). Third, lake aquatic organisms can contribute to mid-chain alkanes (n-C 21 to n-C 27 ), which also leads to the overestimation of the presence of trees and shrubs (Ficken et al, 2000).…”

“…Long chained n-alkanes (>22 carbon atoms) mainly originate from vascular plants, for example in leaf waxes, whereas short chains (12-20 carbon atoms) are produced by bacteria and algae (Killops and Killops, 2013). The ratio of odd to even chains -expressed as carbon preference index (CPI) (Bray and Evans, 1961;Marzi et al, 1993) or odd-over-even predominance (OEP) (Zech et al, 2009;Struck et al, 2019) -is an indicator for OM degradability and decreases with ongoing alteration of the OM. Furthermore, several studies in temperate latitudes showed that relative n-alkane proportions can be used to distinguish between vegetation types.…”

Holocene sea level and environmental change at the southern Cape – an 8.5 kyr multi-proxy paleoclimate record from lake Voёlvlei, South Africa

“…δ 13 Cn-alkane is a suitable proxy to infer past changes in the vegetation composition (e.g., Diefendorf and Freimuth, 2017) as well as variations in plant water use efficiency and thus drought stress (Diefendorf and Freimuth, 2017;Struck et al, 2020).…”