Table of Contents
International Journal of Oceanography
Volume 2010, Article ID 819029, 11 pages
Research Article

Nitrogen Uptake in the Northeastern Arabian Sea during Winter Cooling

1Physical Research Laboratory, Geosciences Division, Navrangpura, Ahmedabad 380 009, India
2Marine and Water Resources Division, Space Applications Centre, Ahmedabad 380 015, India
3Department of Crop Physiology, University of Agricultural Sciences, Bangalore 560 065, India
4Chemical Oceanography Division, National Institute of Oceanography, Goa 403 004, India
5Faculty of Natural Resources Management, Lakehead University, Thunder Bay, ON, Canada P7B 5E1
6Department of Chemistry, Goa University, Goa 403 206, India

Received 1 October 2009; Accepted 5 April 2010

Academic Editor: Walker Smith

Copyright © 2010 S. Kumar 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.


The uptake of dissolved inorganic nitrogen by phytoplankton is an important aspect of the nitrogen cycle of oceans. Here, we present nitrate ( ) and ammonium ( ) uptake rates in the northeastern Arabian Sea using tracer technique. In this relatively underexplored region, productivity is high during winter due to supply of nutrients by convective mixing caused by the cooling of the surface by the northeast monsoon winds. Studies done during different months (January and late February-early March) of the northeast monsoon 2003 revealed a fivefold increase in the average euphotic zone integrated uptake from January (2.3 mmolN ) to late February-early March (12.7 mmolN ). The -ratio during January appeared to be affected by the winter cooling effect and increased by more than 50% from the southernmost station to the northern open ocean stations, indicating hydrographic and meteorological control. Estimates of residence time suggested that entrained in the water column during January contributed to the development of blooms during late February-early March.