Porewater and particulate geochemistry during Maria S. Merian cruise MSM17/4 ...

• Main Authors: Dale, Andy W, Sommer, Stefan, Ryabenko, Evgenia, Noffke, Anna, Bohlen, Lisa, Wallmann, Klaus, Stolpovsky, Konstantin, Greinert, Jens, Pfannkuche, Olaf
• Format: Article in Journal/Newspaper
• Language: English
• Published: PANGAEA 2014
• Subjects: Climate - Biogeochemistry Interactions in the Tropical Ocean SFB754; Klaus; North Atlantic
• Online Access: https://dx.doi.org/10.1594/pangaea.835700; https://doi.pangaea.de/10.1594/PANGAEA.835700

We present sedimentary geochemical data and in situ benthic flux measurements of dissolved inorganic nitrogen (DIN: NO3-, NO2-, NH4+) and oxygen (O2) from 7 sites with variable sand content along 18°N offshore Mauritania (NW Africa). Bottom water O2 concentrations at the shallowest station were hypoxic (42 µM) and increased to 125 µM at the deepest site (1113 m). Total oxygen uptake rates were highest on the shelf (-10.3 mmol O2 /m2 d) and decreased quasi-exponentially with water depth to -3.2 mmol O2 /m2 d. Average denitrification rates estimated from a flux balance decreased with water depth from 2.2 to 0.2 mmol N /m2 d. Overall, the sediments acted as net sink for DIN. Observed increases in delta 15NNO3 and delta 18ONO3 in the benthic chamber deployed on the shelf, characterized by muddy sand, were used to calculate apparent benthic nitrate fractionation factors of 8.0 pro mille (15epsilon app) and 14.1 pro mille (18epsilon app). Measurements of delta 15NNO2 further demonstrated that the sediments acted ... : Supplement to: Dale, Andy W; Sommer, Stefan; Ryabenko, Evgenia; Noffke, Anna; Bohlen, Lisa; Wallmann, Klaus; Stolpovsky, Konstantin; Greinert, Jens; Pfannkuche, Olaf (2014): Benthic nitrogen fluxes and fractionation of nitrate in the Mauritanian oxygen minimum zone (Eastern Tropical North Atlantic). Geochimica et Cosmochimica Acta, 134, 234-256 ...