31 Aug 2021

31 Aug 2021

Review status: this preprint is currently under review for the journal BG.

What can we learn from amino acids about oceanic organic matter cycling and degradation?

Birgit Gaye1, Niko Lahajnar1, Natalie Harms1, Sophie Anna Luise Paul2,3, Tim Rixen1,4, and Kay-Christian Emeis1 Birgit Gaye et al.
  • 1Institute for Geology, Universität Hamburg, 20146 Hamburg, Germany
  • 2Department of Physics and Earth Sciences, Jacobs University Bremen, 28759 Bremen, Germany
  • 3GEOMAR, Helmholtz-Zentrum für Ozeanforschung, 24148 Kiel, Germany
  • 4Leibniz Centre for Tropical Marine Research (ZMT), 28359 Bremen, Germany

Abstract. Amino acids (AA) mainly bound in proteins are major constituents of living biomass and non-living organic material in the oceanic particulate and dissolved organic matter pool. Uptake and cycling by heterotrophic organisms lead to characteristic changes in AA composition so that AA based biogeochemical indicators are often used to elucidate processes of organic matter cycling and degradation. We analyzed particulate AA in a large sample set collected in various oceanic regions covering sinking and suspended particles in the water column, sediment samples as well as dissolved AA from water column and pore water samples. The aim of this study was to test and improve the use of AA derived biogeochemical indicators as proxies for organic matter sources and degradation, and to better understand particle dynamics and interaction between the dissolved and particulate organic matter pools. A principal component analysis (PCA) of all data delineates diverging AA compositions of sinking and suspended particles with increasing water depth. A new sinking particle and sediment degradation indicator (SDI) allows a fine-tuned classification of sinking particles and sediments with respect to the intensity of degradation, which is associated with changes of bulk δ15N ratios. This new indicator furthermore is sensitive to sedimentary redox conditions and can be used to detect past anoxic early diagenesis. A second indicator emerges from the AA spectra of suspended particulate matter (SPM) in the epipelagic and that of the meso- and bathypelagic ocean and is a residence time indicator (RTI). The characteristic changes in AA patterns from shallow to deep SPM are recapitulated in the AA spectra of the dissolved organic matter (DOM) pool, so that deep SPM is more similar to DOM than to any of the other organic matter pools. This implies that there is equilibration between finely dispersed SPM and DOM in the deep sea, which may be driven by microbial activity combined with annealing and fragmentation of gels. As these processes strongly depend on physico-chemical conditions in the deep ocean, changes in quality and degradability of DOM may strongly affect the relatively large pool of suspended and dissolved AA in the ocean that amounts to 15 Pg amino acid carbon (AAC) and 89 ± 29 Pg AAC, respectively.  

Birgit Gaye et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-229', Anonymous Referee #1, 14 Sep 2021
  • RC2: 'Comment on bg-2021-229', Anonymous Referee #2, 01 Oct 2021

Birgit Gaye et al.

Data sets

N-isotopes and amino acids from sediment push cores of SONNE cruise SO242/2 at the DISCOL area, Peru Basin Paul, Sophie Anna Luise; Koschinsky, Andrea; Gaye, Birgit; Dähnke, Kirstin

N-isotopes and amino acids from CTD station SO242/1_58-1_CTD 4 at the DISCOL area, Peru Basin Paul, Sophie Anna Luise; Koschinsky, Andrea; Gaye, Birgit; Dähnke, Kirstin

N-isotopes and amino acids from sediment multi cores of SONNE cruise SO242/1 at the DISCOL area, Peru Basin Paul, Sophie Anna Luise; Koschinsky, Andrea; Gaye, Birgit; Dähnke, Kirstin

Birgit Gaye et al.


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Short summary
Amino acids were analyzed in a large number of samples of particulate and dissolved organic matter from coastal regions and the open ocean. A statistical analysis produced two new biogeochemical indicators. An indicator of sinking particle and sediment degradation (SDI) traces the degradation of organic matter from the surface waters into the sediments. A second indicator of shows the residence time of suspended matter in the ocean (RTI).