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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Origin, transport and deposition of leaf-wax biomarkers in the Amazon Basin and the adjacent Atlantic

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Haeggi, Christoph ; Sawakuchi, Andre O. ; Chiessi, Cristiano M. ; Mulitza, Stefan ; Mollenhauer, Gesine ; Sawakuchi, Henrique O. ; Baker, Paul A. ; Zabel, Matthias ; Schefuss, Enno
Total Authors: 9
Document type: Journal article
Source: GEOCHIMICA ET COSMOCHIMICA ACTA; v. 192, p. 149-165, NOV 2016.
Web of Science Citations: 15

Paleoenvironmental studies based on terrigenous biomarker proxies from sediment cores collected close to the mouth of large river systems rely on a proper understanding of the processes controlling origin, transport and deposition of biomarkers. Here, we contribute to the understanding of these processes by analyzing long-chain n-alkanes from the Amazon River system. We use the delta D composition of long-chain n-alkanes from river bed sediments from the Amazon River and its major tributaries, as well as marine core-top samples collected off northeastern South America as tracers for different source areas. The delta C-13 composition of the same compounds is used to differentiate between long-chain n-alkanes from modern forest vegetation and petrogenic organic matter. Our delta C-13 results show depleted delta C-13 values (-33 to -36%) in most samples, indicating a modern forest source for most of the samples. Enriched values (-31 to -33%) are only found in a few samples poor in organic carbon indicating minor contributions from a fossil petrogenic source. Long-chain n-alkane delta D analyses show more depleted values for the western tributaries, the Madeira and Solimoes Rivers (-152 to -168%), while n-alkanes from the lowland tributaries, the Negro, Xingu and Tocantins Rivers (-142 to -154%), yield more enriched values. The n-alkane delta D values thus reflect the mean annual isotopic composition of precipitation, which is most deuterium-depleted in the western Amazon Basin and more enriched in the eastern sector of the basin. Samples from the Amazon estuary show a mixed long-chain n-alkane delta D signal from both eastern lowland and western tributaries. Marine core-top samples underlying the Amazon freshwater plume yield delta D values similar to those from the Amazon estuary, while core-top samples from outside the plume showed more enriched values. Although the variability in the river bed data precludes quantitative assessment of relative contributions, our results indicate that long-chain n-alkanes from the Amazon estuary and plume represent an integrated signal of different regions of the onshore basin. Our results also imply that n-alkanes are not extensively remineralized during transport and that the signal at the Amazon estuary and plume includes refractory compounds derived from the western sector of the Basin. These findings will aid in the interpretation of plant wax-based records of marine sediment cores collected from the adjacent ocean. (C) 2016 Elsevier Ltd. All rights reserved. (AU)

FAPESP's process: 11/06609-1 - Provenance, transport and storage of sediments in Amazon rivers
Grantee:André Oliveira Sawakuchi
Support type: Regular Research Grants
FAPESP's process: 11/14502-2 - Regulating factors of methane (CH4) emission in depositional environments of the Rivers Negro, Tapajos, Xingu and Amazonas
Grantee:Henrique Oliveira Sawakuchi
Support type: Scholarships in Brazil - Doctorate
FAPESP's process: 12/17517-3 - Response of the Western Atlantic Ocean to changes in the Atlantic meridional overturning circulation: from millennial to seasonal variability
Grantee:Cristiano Mazur Chiessi
Support type: Research Program on Global Climate Change - Young Investigators