Oxygen isotope ratios (18O/16O) of hemicellulose-derived sugar biomarkers in plants, soils and sediments as paleoclimate proxy II: Insight from a climate transect study

Tuthorn, Mario; Zech, Michael; Ruppenthal, Marc; Oelmann, Yvonne; Kahmen, Ansgar; Valle, Héctor F. del; Wilcke, Wolfgang; Glaser, Bruno

doi:10.1016/j.gca.2013.11.002

Cited by 32 publications

(36 citation statements)

References 51 publications

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“…So the central question of this study has to be answered as follows: Downloaded by [New York University] at 16:45 14 July 2015 n-alkanes in soils do not necessarily reflect δ 2 H prec but rather δ 2 H leaf water . This finding is well in agreement with the interpretation of compound-specific δ 18 O results of hemicellulose-derived sugar biomarkers extracted from topsoils along an Argentinian climate transect [66].…”

Section: Discussionsupporting

confidence: 90%

“…Like the 18 O isotopic composition of (hemi-)cellulose [66,67], the deuterium isotopic composition of plant biomarkers can be expected to depend on three main factors: (i) the 2 H content in source water, (ii) the 2 H evaporative enrichment of leaf water due to isotope effects associated with phase change and transport of water during transpiration, and (iii) a 2 H isotope fractionation associated with biosynthesis of plant biomarkers. It is generally accepted that the uptake of soil water by plants is not associated with discernible isotopic fractionation [68,69].…”

Section: Model-data Comparison: N-alkanes In Soils Reflect δ 2 H Leafmentioning

confidence: 99%

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Don-alkane biomarkers in soils/sediments reflect theδ²H isotopic composition of precipitation? A case study from Mt. Kilimanjaro and implications for paleoaltimetry and paleoclimate research

Zech

Różański

et al. 2015

Isotopes in Environmental and Health Studies

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

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Section: Discussionsupporting

confidence: 90%

Section: Model-data Comparison: N-alkanes In Soils Reflect δ 2 H Leafmentioning

confidence: 99%

Don-alkane biomarkers in soils/sediments reflect theδ²H isotopic composition of precipitation? A case study from Mt. Kilimanjaro and implications for paleoaltimetry and paleoclimate research

Zech

Różański

et al. 2015

Isotopes in Environmental and Health Studies

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“…Zech et al (2013) proposed coupling δ 2 H n-alkane results with oxygen stable isotopes of hemicellulose-derived sugars (δ 18 O sugar ). Assuming constant biosynthetic fractionation (ε bio ) for the different compound classes (n-alkanes and hemicellulose sugars), this coupling enables the reconstruction of the isotopic composition of leaf water, RH, δ 2 H and δ 18 O of plant source water (≈ δ 2 H and δ 18 O of precipitation; Tuthorn et al, 2015). So far, a detailed evaluation of this approach on the European scale, as well as related effects concerning vegetation changes, is missing.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of bacterial glycerol dialkyl glycerol tetraether and <sup>2</sup>H–<sup>18</sup>O biomarker proxies along a central European topsoil transect

et al. 2020

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Molecular fossils, like bacterial branched glycerol dialkyl glycerol tetraethers (brGDGTs), and the stable isotopic composition of biomarkers, such as δ 2 H of leaf waxderived n-alkanes (δ 2 H n-alkane ) or δ 18 O of hemicellulosederived sugars (δ 18 O sugar ), are increasingly used for the reconstruction of past climate and environmental conditions. Plant-derived δ 2 H n-alkane and δ 18 O sugar values record the isotopic composition of plant source water (δ 2 H source-water and δ 18 O source-water ), which usually reflects mean annual precipitation (δ 2 H precipiation and δ 18 O precipiation ), modulated by evapotranspirative leaf water enrichment and biosynthetic fractionation (ε bio ). Accuracy and precision of respective proxies should be ideally evaluated at a regional scale. For this study, we analysed topsoils below coniferous and deciduous forests as well as grassland soils along a central European transect in order to investigate the variability and robustness of various proxies and to identify effects related to vegetation. Soil pH values derived from brGDGTs correlate reasonably well with measured soil pH values but are systematically overestimated ( pH = 0.6 ± 0.6). The branched vs. isoprenoid tetraether index (BIT) can give some indication whether the pH reconstruction is reliable. Temperatures derived from brGDGTs overestimate mean annual air temperatures slightly ( T MA = 0.5 • C ± 2.4). Apparent isotopic fractionation (ε n-alkane/precipitation and ε sugar/precipitation ) is lower for grassland sites than for forest sites due to signal damping; i.e. grass biomarkers do not record the full evapotranspirative leaf water enrichment. Coupling δ 2 H n-alkane with δ 18 O sugar allows us to reconstruct the stable isotopic composition of the source water more accurately than without the coupled approach ( δ 2 H = ∼ −21 ‰ ± 22 ‰ and δ 18 O = ∼ −2.9 ‰ ± 2.8 ‰). Similarly, relative humidity during daytime and the vegetation period (RH MDV ) can be reconstructed using the coupled isotope approach ( RH MDV =∼ −17 ± 12). Especially for coniferous sites, reconstructed RH MDV values as well as source water isotope composition underestimate the measured values. This can likely be explained by understorey grass vegetation at the coniferous sites contributing significantly to the n-alkane pool but only marginally to the sugar pool in the topsoils. Vegetation-dependent variable signal damping and ε bio (regarding 2 H between n-alkanes and leaf water) along our European transect are difficult to quantify but likely contribute to the observed underestimation in the source water isotope composition and RH reconstructions. Microclimate variability could cause the rather large uncertainties. Vegetation-related effects do, by contrast, not affect the brGDGT-derived reconstructions. Overall, GDGTs and the coupled δ 2 H n-alkane -δ 18 O sugar approach have great potential for more quantitative paleoclimate reconstructions.

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“…Precipitation shows a systematic southward trend towards more negative δ 18 O and δ 2 H values (δ 18 O prec and δ 2 H prec , respectively) (Bowen, 2012; GeoINTA, 2012). The transect is described in detail by Tuthorn et al (2014). Briefly, it is characterized by warm humid subtropical conditions in the north (Zárate, Buenos Aires Province), Figures pronounced arid conditions in the middle part of the transect and cool temperate conditions in the south (Las Heras, Santa Cruz Province).…”

Section: Transect Description and Samplesmentioning

confidence: 99%

Coupled isotopes of plant wax and hemicellulose markers record information on relative humidity and isotopic composition of precipitation

Tuthorn¹,

Zech²,

Ruppenthal³

et al. 2015

Preprint

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Abstract. The δ2H isotopic composition of leaf waxes is used increasingly for paleohydrological and -climate reconstructions. However, it is challenging to disentangle past changes in the isotopic composition of precipitation and changes in evapotranspirative enrichment of leaf water. We analyzed δ2H on n-alkanes and fatty acids in topsoils along a climate transect in Argentina, for which we had previously measured δ18O on plant-derived sugars. Our results indicate that leaf wax biomarker δ2H values (δ2Hlipids) primarily reflect δ2Hsource water (precipitation), but are modulated by evapotranspirative enrichment. A mechanistic model is able to produce the main trends in δ2Hlipids along the transect, but seems to slightly underestimate evapotranspirative enrichment in arid regions and overestimate it in grass-dominated ecosystems. Furthermore, the (i) coupling of the δ2Hlipid and δ18Osugar biomarker results and (ii) application of biosynthetic fractionation factors allows calculating the δ2H-δ18O isotopic composition of leaf water along the transect. This also yields the deuterium excess (d excess) of leaf water, which mainly reflects evapotranspirative enrichment, and can be used to model relative air humidity (RH). The high correlation of modeled (reconstructed based on biomarker results) and measured RH, as well as the good agreement between modeled and actual δ2H and δ18O of precipitation along the transect lends support to the coupled δ2Hlipid and δ18Osugar biomarker approach for future paleoclimate research.

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Oxygen isotope ratios (18O/16O) of hemicellulose-derived sugar biomarkers in plants, soils and sediments as paleoclimate proxy II: Insight from a climate transect study

Cited by 32 publications

References 51 publications

Don-alkane biomarkers in soils/sediments reflect theδ²H isotopic composition of precipitation? A case study from Mt. Kilimanjaro and implications for paleoaltimetry and paleoclimate research

Don-alkane biomarkers in soils/sediments reflect theδ²H isotopic composition of precipitation? A case study from Mt. Kilimanjaro and implications for paleoaltimetry and paleoclimate research

Evaluation of bacterial glycerol dialkyl glycerol tetraether and <sup>2</sup>H–<sup>18</sup>O biomarker proxies along a central European topsoil transect

Coupled isotopes of plant wax and hemicellulose markers record information on relative humidity and isotopic composition of precipitation

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Oxygen isotope ratios (18O/16O) of hemicellulose-derived sugar biomarkers in plants, soils and sediments as paleoclimate proxy II: Insight from a climate transect study

Cited by 32 publications

References 51 publications

Don-alkane biomarkers in soils/sediments reflect theδ2H isotopic composition of precipitation? A case study from Mt. Kilimanjaro and implications for paleoaltimetry and paleoclimate research

Don-alkane biomarkers in soils/sediments reflect theδ2H isotopic composition of precipitation? A case study from Mt. Kilimanjaro and implications for paleoaltimetry and paleoclimate research

Evaluation of bacterial glycerol dialkyl glycerol tetraether and &lt;sup&gt;2&lt;/sup&gt;H–&lt;sup&gt;18&lt;/sup&gt;O biomarker proxies along a central European topsoil transect

Coupled isotopes of plant wax and hemicellulose markers record information on relative humidity and isotopic composition of precipitation

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Don-alkane biomarkers in soils/sediments reflect theδ²H isotopic composition of precipitation? A case study from Mt. Kilimanjaro and implications for paleoaltimetry and paleoclimate research

Don-alkane biomarkers in soils/sediments reflect theδ²H isotopic composition of precipitation? A case study from Mt. Kilimanjaro and implications for paleoaltimetry and paleoclimate research

Evaluation of bacterial glycerol dialkyl glycerol tetraether and <sup>2</sup>H–<sup>18</sup>O biomarker proxies along a central European topsoil transect