Nitrogen Uptake Rates during Spring in the NE Arabian Sea

[摘要] We present new data on N uptake rates andf-ratios in the north-eastern (NE) Arabian Sea, where significant amounts ofTrichodesmiumwere present in spring, 2006. The measured total nitrogen uptake rates ranged from 0.34 to 1.58 mmol N m−2 d−1.N2fixation associated withTrichodesmiumvaried from 0.002 to 0.54 mmol Nm−2d−1estimated from the abundance ofTrichodesmiumand specificN2fixation rates of 1.5 pmol N trichome−1 h−1. Inclusion ofN2fixation rates significantly changesf-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 Nm−2in the form of nitrate, likely due to nitrification of ammonium released byTrichodesmium. For better estimations, direct measurement ofN2fixation is recommended.

[学科分类] 地质学