Assessment of soil n-alkane delta D and branched tetraether membrane lipid distributions as tools for paleoelevation reconstruction

delta O-18 values of pedogenic minerals forming from soil water are commonly used to reconstruct paleoelevation. To circumvent some of the disadvantages of this method, soil n-alkane delta D values were recently proposed as a new tool to reconstruct elevation changes, after showing that soil n-alkane delta D values track the altitude effect on precipitation delta D variations (r(2)=0.73 along Mt. Gongga, China). To verify the suitability of soil n-alkane delta D values as a paleoelevation proxy we measured the delta D of soil n-alkanes along Mt. Kilimanjaro (Tanzania). At midslope, soil n-alkane delta D values are possibly influenced by the present precipitation belt, causing D-depletion in precipitation, and hence in the soil n-alkanes. Consequently, soil n-alkane delta D values do not linearly relate with altitude (r(2)=0.03), suggesting that, in this case, they can not serve as an unambiguous proxy to infer past elevation changes. In contrast, it was recently shown that the MBT/CBT temperature proxy, which is based on the distribution of branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids, is linearly related with MAT, and thus altitude (r(2)=0.77), at Mt. Kilimanjaro. This suggests that this proxy may be more suitable for paleoelevation reconstruction for this region. However, application of the MBT/CBT proxy on the altitude gradient along Mt. Gongga showed that, although the MBT/CBT-derived temperature lapse rate (-5.9 degrees C/1000 m) resembles the measured temperature lapse rate (-6.0 degrees C/1000 m), there is a relatively large degree of scatter (r(2)=0.55). Our results thus show that both proxies can be subject to relatively large uncertainties in their assessment of past elevation changes, but that a combination of the soil n-alkane delta D and MBT/CBT proxies can likely result in a more reliable assessment of paleoelevation.