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

[摘要] Amino acids (AAs) mainly bound in proteins are major constituents of livingbiomass and non-living organic material in the oceanic particulate anddissolved organic matter pool. Uptake and cycling by heterotrophic organismslead to characteristic changes in AA composition so that AA-basedbiogeochemical indicators are often used to elucidate processes of organicmatter cycling and degradation. We analyzed particulate AA in a large sampleset collected in various oceanic regions covering sinking and suspendedparticles in the water column, sediment samples, and dissolved AA fromwater column and pore water samples. The aim of this study was to test andimprove the use of AA-derived biogeochemical indicators as proxies fororganic matter sources and degradation and to better understand particledynamics and interaction between the dissolved and particulate organicmatter pools. A principal component analysis (PCA) of all data delineatesdiverging AA compositions of sinking and suspended particles with increasingwater depth. A new sinking particle and sediment degradation indicator (SDI)allows a fine-tuned classification of sinking particles and sediments withrespect to the intensity of degradation, which is associated with changes ofstable isotopic ratios of nitrogen ( δ 15 N). This new indicatoris furthermore sensitive to sedimentary redox conditions and can be used todetect past anoxic early diagenesis. A second indicator emerges from the AAspectra of suspended particulate matter (SPM) in the epipelagic and that ofthe meso- and bathypelagic ocean and is a residence time indicator (RTI).The characteristic changes in AA patterns from shallow to deep SPM arerecapitulated 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 organicmatter pools. This implies that there is equilibration between finelydispersed SPM and DOM in the deep sea, which may be driven by microbialactivity combined with annealing and fragmentation of gels. As theseprocesses strongly depend on physico-chemical conditions in the deep ocean,changes in quality and degradability of DOM may strongly affect therelatively large pool of suspended and dissolved AA in the ocean thatamounts to 15 Pg amino acid carbon (AAC) and 89  ±  29 Pg AAC,respectively.

[学科分类] 大气科学