Aeolian transport and deposition of plant wax n-alkanes across the tropical North Atlantic Ocean

Laura T. Schreuder, Jan Berend W. Stuut, Laura F. Korte, Jaap S. Sinninghe Damsté, Stefan Schouten*

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Long chain n-alkanes are terrestrial higher plant biomarkers analysed in marine sedimentary archives to reconstruct continental palaeoclimatic and palaeohydrological conditions. Latitudinal variation in their concentration and distribution in marine sediments relatively close to the continent has been widely studied, but little is known on the extent to which this continental signal extends to the ocean. Furthermore, no studies have examined the seasonal variation in the deposition of these biomarkers in marine sediments. Here we studied longitudinal variation in the composition of long chain n-alkanes and two other terrestrial higher plant biomarkers (long chain n-alkanols and long chain fatty acids) in atmospheric particles, as well as longitudinal and seasonal variation in long chain n-alkanes in sinking particles in the ocean at different water depths and in surface sediments, all collected along a 12°N transect across the tropical North Atlantic Ocean. The highest abundance of all three biomarker classes was closest to the African coast, as expected, because they are transported with Saharan dust and the largest part of the dust is deposited close to the source. At this proximal location, the seasonal variability in long chain n-alkane flux and the chain length distribution of the n-alkanes in sinking particles was most pronounced, due to seasonal change in the dust source or to change in vegetation composition in the source area, related to the position of the Intertropical Convergence Zone (ITCZ). In contrast, in the open ocean the seasonal variability in both the long chain n-alkane flux and chain length distribution of the n-alkanes was low. The abundance of the alkanes was also lower, as expected because of the larger source-to-sink distance. At the western part of the transect, close to South America, we found an additional source of the alkanes in the sinking particles during spring and autumn in the year 2013. The δ13C values of the alkanes in the surface sediment closest to the South American continent indicated that the isotope signal was likely derived from C3 vegetation from the Amazon, implying an input from the Amazon River, as there is no significant aeolian input from South America there since the prevailing wind direction is from the east. Finally, the concentration of the alkanes was similar in the material collected from the atmosphere, the particles collected while settling through the marine water column, and in the surface sediments, providing evidence that degradation of long chain n-alkanes from the atmosphere to settling at the sediment–water interface at deep open ocean sites is minimal.

Original languageEnglish
Pages (from-to)113-123
Number of pages11
JournalOrganic Geochemistry
Volume115
DOIs
Publication statusPublished - 1 Jan 2018

Funding

We thank the captains and crews of R/V Meteor (cruise M89 in 2012) and R/V Pelagia (cruises 64PE378 in 2013 and 64PE395 in 2015) for deploying and collecting all the instruments that facilitated the sampling of the atmosphere, ocean and seafloor. M. de Bar, D. Dorhout, M. Baas and M. Verweij are thanked for analytical support and M. van der Does for sampling and processing of the sediment trap samples. We also thank K. Wetterauer for measuring concentrations in the dust samples. We thank D.B. Nelson and an anonymous reviewer for constructive comments which improved the manuscript. The research was funded by The Netherlands Organization for Scientific Research (NWO; project 824.14.001 and project 822.01.008, TRAFFIC) and by the European Research Council (ERC) project 311152, DUSTTRAFFIC. S.S. and J.S.S.D. are supported by the Netherlands Earth System Science Center (NESSC) funded by the Dutch Ministry of Science, Culture and Education . Appendix A

FundersFunder number
Dutch Ministry of Science, Culture and Education
Netherlands Organization for Scientific Research
Seventh Framework Programme311152
European Research Council
Nederlandse Organisatie voor Wetenschappelijk Onderzoek824.14.001, 822.01.008
Netherlands Earth System Science Centre

    Keywords

    • Higher plant biomarkers
    • Long chain n-alkanes
    • Saharan dust
    • Tropical North Atlantic Ocean

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