Insoluble prokaryotic membrane lipids in continental shelf sediments offshore Cape Town: implications for organic matter preservation

Lidia Chaves Torres*, Leanne Melbourne, Maria T. Hernandez-Sancheza, Gordon Inglis, Rich Pancost

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

1 Citation (Scopus)
162 Downloads (Pure)

Abstract

The largest organic carbon (OC) reservoir on Earth is in the geosphere, mainly comprising insoluble organic matter (IOM). IOM formation, therefore, plays an important role in the short and long-term carbon cycle, carbon bioavailability and formation of source rocks. To explore the mechanism of insolubilization of organic matter (OM), we have analysed soluble and IOM fractions of continental shelf marine sediments. We have applied sequential solvent-extractions followed by a selective chemical degradation of the post-extraction residue, specifically targeting prokaryotic membrane lipids (branched fatty acids – FAs, hopanoids, archaeol and glycerol dialkyl glycerol tetraethers – GDGTs). Up to 80% of
prokaryotic membrane lipids are not solvent-extractable, and we observe compound-specific differences in partitioning between soluble and IOM fractions. Based on these observations, we propose a variety of mechanisms for the incorporation of prokaryotic lipids into IOM in marine sediments: First, OM association with authigenic carbonates; second, cross-linking via esterification reactions with time, which could be particularly relevant for FAs; third, competition between reactivity and loss of polar head groups, the latter rendering the OM less susceptible to incorporation; and finally, inherent solvent-insolubility of some lipids associated with prokaryotic cells.
Original languageEnglish
Pages (from-to)38-51
Number of pages14
JournalMarine Chemistry
Volume197
Early online date19 Oct 2017
DOIs
Publication statusPublished - 20 Dec 2017

Keywords

  • Carbonates
  • GDGTs
  • Insoluble organic matter
  • Marine sediments
  • Selective chemical degradation
  • TEX

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