15N enrichment in the surface Particulate Organic Nitrogen of the north-eastern Arabian Sea from the middle to the waning phase of the winter monsoon: possible causes
S. Kumar1,2 and R. Ramesh11Planetary and Geosciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad- 380 009, India 2Environmental Sciences Research Centre, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada
Received: 06 Feb 2007 – Discussion started: 27 Feb 2007
Abstract. A temporal increase of ~5‰ in the average nitrogen isotopic composition (δ15NPON) of surface particulate organic nitrogen was observed in the open north-eastern Arabian Sea during January to late February-early March 2003, despite the presence of T. erithraeum (up to ~11%), a diazotroph that fixes atmospheric N2, in the latter period. Hydrographic conditions and residence time of nitrate in the water column suggested that this increase could be a combined effect of denitrification in the subsurface layer and inefficient utilization of nitrate entrained in the water column during January.
Kumar, S. and Ramesh, R.: 15N enrichment in the surface Particulate Organic Nitrogen of the north-eastern Arabian Sea from the middle to the waning phase of the winter monsoon: possible causes, Ocean Sci. Discuss., 4, 245-264, doi:10.5194/osd-4-245-2007, 2007.