Table of Contents
International Journal of Oceanography
Volume 2010, Article ID 127493, 10 pages
Research Article

Nitrogen Uptake Rates during Spring in the NE Arabian Sea

1Geosciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, India
2Department of Crop Physiology, University of Agricultural Sciences, GKVK Campus, Bangalore 560 065, India
3Meteorology and Oceanography Division, Space Application Centre, Jodhpur Tekra, Ahmedabad 380 015, India

Received 14 June 2010; Accepted 21 September 2010

Academic Editor: Roberto Danovaro

Copyright © 2010 Naveen Gandhi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


We present new data on N uptake rates and f-ratios in the north-eastern (NE) Arabian Sea, where significant amounts of Trichodesmium were present in spring, 2006. The measured total nitrogen uptake rates ranged from 0.34 to 1.58 mmol N  m 2 d 1 . N 2 fixation associated with Trichodesmium varied from 0.002 to 0.54 mmol N m 2 d 1 estimated from the abundance of Trichodesmium and specific N 2 fixation rates of 1.5 pmol N trichome 1 h 1 . Inclusion of N 2 fixation rates significantly changes f-ratios particularly in the coastal stations. Nitrogen isotopic data of surface suspended particles suggest that recently fixed nitrogen contributes as high as ~79% of the nitrogen in surface suspended particles. In addition, water column gained ~30 mmol N m 2 in the form of nitrate, likely due to nitrification of ammonium released by Trichodesmium. For better estimations, direct measurement of N 2 fixation is recommended.