Riverine influence on nitrogen fixation in the upwelling region off Vietnam, South China Sea

• Published in: Geophysical research letters Vol. 33; no. 7; pp. L07604 - n/a
• Main Authors: Voss, Maren, Bombar, Deniz, Loick, Natalie, Dippner, Joachim W.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Geophysical Union 01.04.2006; Blackwell Publishing Ltd
• Subjects: Biogeochemical cycles, processes, and modeling; Biogeosciences; Biological and Chemical; Cyanobacteria; Earth sciences; Earth, ocean, space; Estuarine and nearshore processes; Exact sciences and technology; Marine; Oceanography; Phytoplankton; South China Sea; Vietnam; West Pacific; Far East; South America, Amazonia, Amazon R; Asia, Mekong R; ISEW, Vietnam; South America, Amazon R; ISEW, South China Sea; rivers; trace metals; plumes; nitrogen; Plantae; algae; offshore; diatoms; upwelling; Asia; fixation; Pacific Ocean; growth; monsoons; stability; Thallophyta
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2005GL025569

Nitrogen fixation is assumed to be most important in oligotrophic subtropical regions of the oceans. Here we show that nitrogen fixation can also be pronounced in the upwelling region off Vietnam. We compare nitrogen fixation rates and other hydro‐chemical variables from the monsoon season with the intermonsoon season and find that nitrogen fixation rates are app. 10 times higher during the monsoon season. However, this was not the case in the actual upwelling region – a 40–50 km wide strip along the coast – but further offshore, where the Mekong plume was noticeable. Therefore, we hypothesize that the stability of the water column, micronutrients and/or trace metals in the Mekong river plume may be responsible for enhanced cyanobacterial growth. These cyanobacteria may be either Trichodesmium, unicellular, or diatom‐associated symbionts, the latter are known from other river plumes like the Amazon.