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Microbial biomarkers support organic carbon transport from methane-rich Amazon wetlands to the shelf and deep sea fan during recent and glacial climate conditions

Lookup NU author(s): Professor Thomas Wagner, Dr Helen Talbot

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Abstract

Normal 0 false false false DE JA X-NONE We have investigated the delivery of terrestrial organic carbon (OC) to the Amazon shelf and deep sea fan based on soil-marker bacteriohopanepolyols (BHPs; adenosylhopane and related compounds) and branched glycerol dialkyl glycerol tetraethers (GDGTs), as well as of ¹⁴C dating of bulk organic matter. The microbial biomarker records show persistent burial of terrestrial OC, evidenced by almost constant and high BIT values (0.6) and soil-marker BHP concentration [80-230 µg/g TOC (total organic carbon)] on the late Holocene shelf and even higher BIT values (0.8-0.9), but lower and more variable soil-marker BHP concentration (40-100 µg/g TOC) on the past glacial deep sea fan. Radiocarbon data show that OC on the shelf is 3-4 kyr older than corresponding bivalve shells, emphasizing the presence of old carbon in this setting. We observe comparable and unexpectedly invariant BHP compositions in both marine sediment records, with a remarkably high relative abundance of C-35 amino-BHPs including compounds specific for aerobic methane oxidation on the shelf (avg. 50% of all BHPs) and the fan (avg. 40%). Notably, these marine BHP signatures are strikingly similar to those measured from a methane-producing floodplain area in one of the Amazonian wetland (várzea) regions. This observation indicates that BHPs measured in the marine sediments may have initially been produced within wetland regions of the Amazon basin and therefore document persistent export from terrestrial wetland regions with subsequent re-working in the marine environment, both during recent and past glacial climate conditions.

Publication metadata

Author(s): Wagner T, Kallweit W, Talbot HM, Mollenhauer G, Boom A, Zabel M

Publication type: Article

Publication status: Published

Journal: Organic Geochemistry

Year: 2014

Volume: 67

Pages: 85-98

Print publication date: 15/12/2013

ISSN (print): 0146-6380

ISSN (electronic): 1873-5290

Publisher: Elsevier Ltd.

URL: http://dx.doi.org/10.1016/j.orggeochem.2013.12.003

DOI: 10.1016/j.orggeochem.2013.12.003

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