Dual isotope evidence for sedimentary integration of plant wax biomarkers across an Andes-Amazon elevation transect

Abstract

 Leaf wax biomarkers were studied in soils and rivers from the Andes to the Amazon.  Elevation trend found in C and H isotopic compositions of plant wax in soils.  Plant wax in river-suspended sediments approximated uniform spatial integration.  Carbon isotopic composition of n-alkanes differentiated with depth in soil and river.  Petrogenic inputs of n-alkanes discerned by CPI and dual isotopic analyses.

From leaf to soil: <i>n</i>-alkane signal preservation, despite degradation along an environmental gradient in the tropical Andes

“…The inverse correlation between temperature and soil CPI has been observed before in soils and has been hypothesized to be due to increased microbial degradation of nalkanes under favourable (warm and wet) conditions, independent of local standing vegetation (Luo et al, 2012;Rao et al, 310 2009). Along an altitudinal transect in Peru similar to our study, lower CPI values at lower elevations (warmer) have also been observed in soils and suspended river sediments (Feakins et al, 2018;Wu et al, 2019). Contrastingly, Bush and McInerney (2015) do not find a clear correlation between soil CPI and environment.…”

From Andes to Amazon: Assessing Branched Tetraether Lipids as Tracers for Soil Organic Carbon in the Madre de Dios River System

“…The lower intercept of the SPM‐based lapse rate compared to that of the soil‐based lapse rates, together with the accumulation of brGDGTs in SPM, indicates that brGDGTs in the river integrate the signature of upstream soils and suggests relative persistence of soil‐derived brGDGTs during river transport. In contrast, plant waxes carried by the Madre de Dios (Feakins et al, ; Ponton et al, ) were found undergo mineralization and replacement in transit and thus export no predominantly Andean signal.…”

“…Feng et al () found that the Madre de Dios River has the expected grain size sorting within deep river channels and a “woody undercurrent” that transports high concentrations of relatively undegraded lignin above the sand layer. In contrast, plant wax n ‐alkanoic acids have been found to be well mixed based on their hydrogen isotopic composition (Ponton et al, ), although some sorting of the n ‐alkanes was noted based on their carbon isotopic composition (Feakins et al, ). The concentration of brGDGTs generally decreases with depth (Figure d) but is constant when normalized to SSA (Figure e).…”

Leaf Wax δD and δ13C in Soils Record Hydrological and Environmental Information Across a Climatic Gradient in Israel

“…Likewise, the effect of degradation on plant δD wax and δ 13 C wax is unclear. Some studies find little or no indication of isotopic modification during incorporation into soils (Huang et al, 1997;Mazeas et al, 2002;Pond et al, 2002;Zech et al, 2011), while others found that soil δ 13 C wax is enriched (Chikaraishi & Naraoka, 2006;Feakins et al, 2018;Nguyen Tu et al, 2004) or depleted (Wiesenberg et al, 2004) with respect to plant isotopic values.…”

“…By the time leaf wax nalkanes are deposited in lakes, the δD wax and δ 13 C wax variability is reduced at least threefold in respect to that of plant tissues, to an extent that δD wax shows a significant correlation with rainfall δD and can be applied to study past climate (Garcin et al, 2012;Guenther et al, 2013;Hou et al, 2008;Polissar & Freeman, 2010;Sachse et al, 2004). However, it is less clear where in the sedimentary cycle the homogenization process and variability reduction occurs, what processes are involved (Feakins et al, 2018;Huang et al, 1997;Mazeas et al, 2002;Mendez-Millan et al, 2014;Nguyen Tu et al, 2011;Zech et al, 2011) and how well soil δ 13 C wax and δD wax reflect the parent plant material (Chikaraishi & Naraoka, 2006;Garcin et al, 2014). Specifically, we are interested in understanding where the homogenization process occurs and to what extent the variability at the leaf and plant level is reduced in soils.…”