What can we learn from amino acids about oceanic organic matter cycling 1 and degradation ?

14 Amino acids (AA) mainly bound in proteins are major constituents of living biomass and non15 living organic material in the oceanic particulate and dissolved organic matter pool. Uptake and 16 cycling by heterotrophic organisms lead to characteristic changes in AA composition so that 17 AA based biogeochemical indicators are often used to elucidate processes of organic matter 18 cycling and degradation. We analyzed particulate AA in a large sample set collected in various 19 oceanic regions covering sinking and suspended particles in the water column, sediment 20 samples as well as dissolved AA from water column and pore water samples. The aim of this 21 study was to test and improve the use of AA derived biogeochemical indicators as proxies for 22 organic matter sources and degradation, and to better understand particle dynamics and 23 interaction between the dissolved and particulate organic matter pools. A principal component 24 analysis (PCA) of all data delineates diverging AA compositions of sinking and suspended 25 particles with increasing water depth. A new sinking particle and sediment degradation 26 indicator (SDI) allows a fine-tuned classification of sinking particles and sediments with respect 27 to the intensity of degradation, which is associated with changes of bulk N ratios. This new 28 indicator furthermore is sensitive to sedimentary redox conditions and can be used to detect 29 past anoxic early diagenesis. A second indicator emerges from the AA spectra of suspended 30