Toggle Main Menu Toggle Search

Open Access padlockePrints

Early diagenetic changes of sedimentary stable nitrogen and carbon isotope ratios

Lookup NU author(s): Professor Thomas Wagner


Full text for this publication is not currently held within this repository. Alternative links are provided below where available.


Stable isotopes of sedimentary nitrogen and organic carbon are widely used as proxy variables for biogeochemical parameters and processes in the water column. In order to investigate alterations of the primary isotopic signal by sedimentary diagenetic processes, we determined concentrations and isotopic compositions of inorganic nitrogen (IN), organic nitrogen (ON), total nitrogen (TN), and total organic carbon (TOC) on one short core recovered from sediments of the eastern subtropical Atlantic, between the Canary Islands and the Moroccan coast. Changes with depth in concentration and isotopic composition of the different fractions were related to early diagenetic conditions indicated by pore water concentrations of oxygen, nitrate, and ammonium. Additionally, the nature of the organic matter was investigated by Rock-Eval pyrolysis and microscopic analysis. A decrease in ON during aerobic organic matter degradation is accompanied by an increase of the 15N/14N ratio. Changes in the isotopic composition of ON can be described by Rayleigh fractionation kinetics which are probably related to microbial metabolism. The influence of IN depleted in 15N on the bulk sedimentary (TN) isotope signal increases due to organic matter degradation, compensating partly the isotopic changes in ON. In anoxic sediments, fixation of ammonium between clay lattices results in a decrease of stable nitrogen isotope ratio of IN and TN. Changes in the carbon isotopic composition of TOC have to be explained by Rayleigh fractionation in combination with different remineralization kinetics of organic compounds with different isotopic composition. We have found no evidence for preferential preservation of terrestrial organic carbon. Instead, both TOC and refractory organic carbon are dominated by marine organic matter. Refractory organic carbon is depleted in 13C compared to TOC.

Publication metadata

Author(s): Freudenthal T, Wagner T, Wenzhöfer F, Zabel M, Wefer G

Publication type: Article

Publication status: Published

Journal: Geochimica et Cosmochimica Acta

Year: 2001

Volume: 65

Issue: 11

Pages: 1795-1808

ISSN (print): 0016-7037

ISSN (electronic): 1872-9533

Publisher: Pergamon


DOI: 10.1016/S0016-7037(01)00554-3


Altmetrics provided by Altmetric