The isotopic composition of nitrogen in pore water ammonium and in sedimentary organic matter (Norg) was measured at Sites 1234 and 1235 in order to evaluate the impact of long-term (>100 k.y.) diagenesis on d15N of preserved organic matter. At both sites, the average d15N of pore water ammonium and Norg are within 0.2 per mil to 0.4 per mil. The small difference is less than the analytical uncertainty, indicating that no significant isotopic fractionation is associated with decomposition of organic matter in these sediments. A mass balance for nitrogen was also computed, indicating that ~20% of the organic matter flux buried below 1.45 meters composite depth (mcd) is degraded between this depth and 40 mcd (Site 1235) to 60 mcd (Site 1234) depth. Two factors determine the absence of isotopic fractionation in these sediments: 1. A high degree of organic matter preservation due to rapid sediment accumulation rates at both sites. 2. The dominance of a marine component in the sedimentary organic matter (with only a small fraction contributed by a terrestrial component).

Supplement to: Prokopenko, Maria G; Hammond, Douglas E; Stott, Lowell D (2006): Lack of isotopic fractionation of d15N of organic matter during long-term diagenesis in marine sediments, ODP Leg 202, Sites 1234 and 1235. In: Tiedemann, R; Mix, AC; Richter, C; Ruddiman, WF (eds.) Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 202, 1-22