Do n-alkane biomarkers in soils/sediments reflect the δ²H isotopic composition of precipitation? A case study from Mt. Kilimanjaro and implications for paleoaltimetry and paleoclimate research.

摘要: During the last decade compound-specific deuterium ((2)H) analysis of plant leaf wax-derived n-alkanes has become a promising and popular tool in paleoclimate research. This is based on widely accepted assumption that soils sediments generally reflect δ(2)H precipitation (δ(2)H(prec)). Recently, several authors suggested (δ(2)H(n-alkanes)) can also be used as proxy paleoaltimetry studies. Here, we present results from transect study (∼1500 to 4000 m above sea level [a.s.l.]) carried out soil samples taken humid southern slopes Mt. Kilimanjaro. Contrary earlier suggestions, distinct altitude effect δ(2)H(prec) ∼2000 a.s.l., is, values more negative with increasing altitude. The nC27 nC29 do not confirm this altitudinal trend, but rather positive both O-layers (organic layers) Ah-horizons (mineral topsoils). Although our δ(2)H(n-alkane) are agreement previously published Kilimanjaro [Peterse F, van der Meer M, Schouten S, Jia G, Ossebaar J, Blokker Sinninghe Damste J. Assessment n-alkane δD branched tetraether membrane lipid distributions tools for paleoelevation reconstruction. Biogeosciences. 2009;6:2799-2807], re-interpretation required given results. theoretical framework evaporative isotopic enrichment water associated transpiration process. Modelling show relative humidity, decreasing considerably along (from 78% a.s.l. 51% a.s.l.), strongly controls δ(2)H(leaf water). modelled (2)H matches well measured assessed by using biosynthetic fractionation during biosynthesis leaves. Given clearly demonstrate simply water), conclude care over-interpret records when reconstructing paleoprecipitation. Both studies changes humidity consequently completely mask altitudinally or climatically controlled δ(2)H(prec).