Universität zu Köln

Jaeschke, Andrea, Rethemeyer, Janet, Lappe, Michael, Schouten, Stefan, Boeckx, Pascal and Schefuss, Enno (2018). Influence of land use on distribution of soil n-alkane delta D and brGDGTs along an altitudinal transect in Ethiopia: Implications for (paleo) environmental studies. Org. Geochem., 124. S. 77 - 88. OXFORD: PERGAMON-ELSEVIER SCIENCE LTD. ISSN 0146-6380

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Abstract

The combined use of plant wax n-alkane delta D values and branched glycerol dialkyl glycerol tetraether lipid (brGDGT) distributions provides a novel approach for paleoaltitude reconstruction. Studies from East Africa revealed, however, inconsistent results between the proxy estimates and altitudinal parameters. Here, we explore these proxies in soils of different land use (forest, cropland and pasture) along an altitudinal transect in the Jimma zone of the southwest Ethiopian highlands to better understand environmental and plant-specific factors controlling the isotopic composition and distribution of n-alkanes and brGDGTs. The hydrogen isotope composition of individual n-alkanes does not unambiguously reflect the altitude effect on precipitation delta D, but seems largely influenced by the specific land use. Only forest soil-derived n-C-27 and n-C-29 alkane delta D values exhibit a significant linear relationship with altitude (r -0.87, p < 0.05), likely reflecting the most stable ecosystem. The resulting lapse rate of -17 parts per thousand/1000 m is comparable with that of local precipitation in the southwest Ethiopian highlands. In addition, the linear correlation of the average chain length (ACL) and delta C-13 values of forest soil n-alkanes suggests a physiological adaptation of the specific plant type waxes to altitude-induced environmental changes in the study area. The distribution of brGDGTs also reveals a significant linear correlation with altitude (r -0.97, p < 0.01), reflecting the decrease in temperature with higher elevation, independent of land use. In addition, brGDGT-based mean annual air temperature (MAT) estimates of 19.5-14.0 degrees C and temperature lapse rate of -6 degrees C/1000 m are in good agreement with direct measurements in the Jimma zone. In contrast to previous studies from East Africa, our results show that both soil n-alkane dD values and brGDGT-based MAT distributions track present day altitude effects on local environmental gradients in the southwest Ethiopian highlands. (C) 2018 Elsevier Ltd. All rights reserved.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Jaeschke, Andrea UNSPECIFIED UNSPECIFIED UNSPECIFIED Rethemeyer, Janet UNSPECIFIED UNSPECIFIED UNSPECIFIED Lappe, Michael UNSPECIFIED UNSPECIFIED UNSPECIFIED Schouten, Stefan UNSPECIFIED UNSPECIFIED UNSPECIFIED Boeckx, Pascal UNSPECIFIED UNSPECIFIED UNSPECIFIED Schefuss, Enno UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-170458
DOI:	10.1016/j.orggeochem.2018.06.006
Journal or Publication Title:	Org. Geochem.
Volume:	124
Page Range:	S. 77 - 88
Date:	2018
Publisher:	PERGAMON-ELSEVIER SCIENCE LTD
Place of Publication:	OXFORD
ISSN:	0146-6380
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language DIALKYL GLYCEROL TETRAETHER; CARBON-ISOTOPE DISCRIMINATION; LIPID DISTRIBUTIONS; WATER AVAILABILITY; AFRICAN HYDROLOGY; SEDIMENT TRANSECT; MT. KILIMANJARO; BRANCHED GDGTS; D VALUES; PRECIPITATION Multiple languages Geochemistry & Geophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/17045