Fig. 3: Pore water chemistry and turnover of reactants involved in organic matter mineralization.

Open circles show concentrations in sediment pore water. The black lines show the modeled concentration profiles, R² showing the correlation coefficient of the fit. The pink solid line shows the calculated mean reaction rate profile together with its standard deviation (gray line). Top x-axis shows the concentration, bottom x-axis indicates the reaction rate, positive values indicate net production, negative values net consumption of the respective compound. Error bars were omitted for clarity; reproducibility of the measured concentrations is always better by 5%. For the potential sulfate reduction rates (pSRR), measured via radiotracer incubations (pink circles in panel a), the individual measurements are plotted. Rates of potential sulfate reduction (a) and iron reduction (b) are much smaller than rates of methanogenesis (c). Net production of ammonium (d) and various volatile fatty acids (e–h) indicates that there is sufficient sedimentary organic matter to fuel heterotrophic microbial activity. See Supplementary Information for details.