Amino acid biogeochemistry and organic matter degradation state across the Pakistan margin oxygen minimum zone

Sandra Vandewiele, Gregory Cowie, Karline Soetaert, Jack J. Middelburg

Research output: Contribution to journalArticlepeer-review

Abstract

To assess whether the oxygen minimum zone (OMZ) across the Pakistan Margin causes differences in the lability of sedimentary organic matter, sediments were collected in the core of the OMZ, in the upper and lower transition zones and below the OMZ. Sediment samples were analysed for total nitrogen (TN) and organic carbon (OC) contents, mineral surface area (SA), and total hydrolysable amino acids (THAA) and enzymatically hydrolysable amino acids (EHAA). OC contents and organic carbon per unit of mineral surface area (OC/SA) values were clearly elevated in the core and lower OMZ transition zone. These sediments also contained more labile sedimentary organic matter, as discerned by higher concentrations of THAA and the contribution of N in THAA to TN. A protein amino acid-based degradation index revealed that all sedimentary organic matter has undergone significant degradation, but sediments in the upper OMZ transition zone and below the OMZ are more degraded than inside the OMZ. Changes in amino acid composition during diagenesis are attributed to a combination of factors: (I) selective preservation in which amino acids in cell walls are better preserved than amino acids in cell plasma, (2) formation and accumulation of bacterially derived organic matter; there were relatively more living bacteria in the core of the OMZ and an accumulation of peptidoglycan-derived amino acids in degraded sediments in the upper OMZ transition zone and below the OMZ, and (3) bacterial transformation, as the molar percentages of bacterial transformation products beta-alanine (Bala), gamma-amino butyric acid (Gaba), and ornithine (Orn), increased with increasing degradation. (C) 2008 Elsevier Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)376-392
Number of pages17
JournalDeep Sea Research Part II: Topical Studies in Oceanography
Volume56
Issue number6-7
Early online date8 Nov 2008
DOIs
Publication statusPublished - 1 Mar 2009

Keywords

  • Oxygen minimum zone
  • Hypoxia
  • Benthic foraminifera
  • Organic matter cycling
  • Deep-sea benthos
  • Phytodetrital fluxes
  • DEEP ARABIAN SEA
  • COASTAL MARINE-SEDIMENTS
  • CONTINENTAL-MARGIN
  • ENHANCED PRESERVATION
  • DIAGENETIC ALTERATION
  • CARBON PRESERVATION
  • INTERTIDAL SEDIMENT
  • MINERAL SURFACES
  • SLOPE SEDIMENTS
  • VERTICAL FLUX

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