Isotope fractionation during nitrogen remineralization (ammonification): Implications for nitrogen isotope biogeochemistry

The N-15/N-14 isotopic ratio of marine particulate organic matter usually increases as a consequence of preferential N-14-remineralization (ammonification) during decay in the oxic water-column and at the oxic seafloor. However, a fractionation factor (15)epsilon of sediment ammonification in natural environments has not been determined yet. Here, the (15)epsilon of sedimentary ammonification is calculated in a set of seven sapropel containing sediment cores, two subrecent sediment cores and four sediment trap deployments from the Eastern Mediterranean Sea. Data clearly reveal Rayleigh type isotope fractionation and a fractionation factor (15)epsilon between -1.43 parts per thousand and -2.3 parts per thousand. Hence, sediments - and probably sinking particulate organic matter as well - can be important sources of isotopically depleted reactive nitrogen. The knowledge of (15)epsilon further enables to reconstruct paleo export fluxes from sediment cores if original and actual delta N-15 as well as N accumulation rates are known. (C) 2012 Elsevier Ltd. All rights reserved.