Open AccessGlobal‐scale quantification of mineralization pathways in marine sediments: A reaction‐transport modeling approach
Author(s) -
Thullner Martin,
Dale Andrew W.,
Regnier Pierre
Publication year - 2009
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2009gc002484
Subject(s) - sediment , carbon cycle , mineralization (soil science) , sulfate , remineralisation , organic matter , biogeochemical cycle , total organic carbon , geology , denitrification , environmental chemistry , oceanography , environmental science , soil science , chemistry , nitrogen , geomorphology , ecosystem , ecology , inorganic chemistry , fluoride , organic chemistry , biology , soil water
The global‐scale quantification of organic carbon (C org ) degradation pathways in marine sediments is difficult to achieve experimentally due to the limited availability of field data. In the present study, a numerical modeling approach is used as an alternative to quantify the major metabolic pathways of C org oxidation (C ox ) and associated fluxes of redox‐sensitive species fluxes along a global ocean hypsometry, using the seafloor depth (SFD) as the master variable. The SFD dependency of the model parameters and forcing functions is extracted from existing empirical relationships or from the NOAA World Ocean Atlas. Results are in general agreement with estimates from the literature showing that the relative contribution of aerobic respiration to C ox increases from <10% at shallow SFD to >80% in deep‐sea sediments. Sulfate reduction essentially follows an inversed SFD dependency, the other metabolic pathways (denitrification, Mn and Fe reduction) only adding minor contributions to the global‐scale mineralization of C org . The hypsometric analysis allows the establishment of relationships between the individual terminal electron acceptor (TEA) fluxes across the sediment‐water interface and their respective contributions to the C org decomposition process. On a global average, simulation results indicate that sulfate reduction is the dominant metabolic pathway and accounts for approximately 76% of the total C ox , which is higher than reported so far by other authors. The results also demonstrate the importance of bioirrigation for the assessment of global species fluxes. Especially at shallow SFD most of the TEAs enter the sediments via bioirrigation, which complicates the use of concentration profiles for the determination of total TEA fluxes by molecular diffusion. Furthermore, bioirrigation accounts for major losses of reduced species from the sediment to the water column prohibiting their reoxidation inside the sediment. As a result, the total carbon mineralization rate exceeds the total flux of oxygen into the sediment by a factor of 2 globally.