title: Diagenetic transformation of dissolved organic nitrogen compounds under contrasting sedimentary redox conditions in the Black Sea.
abstract: Remineralization of organic matter in reactive marine sediments releases nutrients and dissolved organic matter (DOM) into the ocean. Here we focused on the molecular-level characterization of DOM by high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) in sediment pore waters and bottom waters from contrasting redox regimes in the northern Black Sea with particular emphasis on nitrogen-bearing compounds to derive an improved understanding of the molecular transformations involved in nitrogen release. The number of nitrogen-bearing molecules is generally higher in pore waters than in bottom waters. This suggests intensified degradation of nitrogen-bearing precursor molecules such as proteins in anoxic sediments: No significant difference was observed between sediments deposited under oxic vs anoxic conditions (average O/C ratios of 0.55) suggesting that the different organic matter quality induced by contrasting redox conditions does not impact protein diagenesis in the subseafloor. Compounds in the pore waters were on average larger, less oxygenated, and had a higher number of unsaturations. Applying a mathematical model, we could show that the assemblages of nitrogen-bearing molecular formulas are potential products of proteinaceous material that was transformed by the following reactions: (a) hydrolysis and deamination, both reducing the molecular size and nitrogen content of the products and intermediates; (b) oxidation and hydration of the intermediates; and (c) methylation and dehydration.
authors.affiliation: MARUM - Center for Marine Environmental Sciences, Bremen, Germany. frauke.schmidt@uni-bremen.de
authors.forename: Frauke
authors.initials: F
authors.lastname: Schmidt
authors.forename: Boris P
authors.initials: BP
authors.lastname: Koch
authors.forename: Marcus
authors.initials: M
authors.lastname: Elvert
authors.forename: Gunnar
authors.initials: G
authors.lastname: Schmidt
authors.forename: Matthias
authors.initials: M
authors.lastname: Witt
authors.forename: Kai-Uwe
authors.initials: KU
authors.lastname: Hinrichs
mesh_terms: D000596:Amino Acids / Q000032:analysis; D059038:Black Sea; D002244:Carbon / Q000032:analysis; D017357:Cyclotrons; D005583:Fourier Analysis; D019015:Geologic Sediments / Q000737:chemistry*; D006868:Hydrolysis; D013058:Mass Spectrometry; D008970:Molecular Weight; D009584:Nitrogen / Q000032:analysis; D017672:Nitrogen Compounds / Q000032:analysis*; D009930:Organic Chemicals / Q000032:analysis*; D010084:Oxidation-Reduction; D010316:Particle Size; D010455:Peptides / Q000737:chemistry; D016062:Porosity; D052616:Solid Phase Extraction; D012995:Solubility; D014867:Water / Q000737:chemistry
chemical_list: D000596:Amino Acids; D017672:Nitrogen Compounds; D009930:Organic Chemicals; D010455:Peptides; D014867:Water; D002244:Carbon; D009584:Nitrogen