Mesoscale Fe enrichment produces a large diatom bloom, draws down CO sub(2), but with limited production of DMS and carbon export in the NE Subarctic Pacific

• Main Authors: Harrison, P., Levasseur, M., Boyd, P., Wong, CS, Rivkin, R., Pedersen, T.
• Format: Conference Object
• Language: English
• Published: 2006
• Subjects: Algal blooms; Books; Carbon; Carbon dioxide; Chlorophyll; Chlorophylls; Data processing; Diatoms; Dimethyl sulfide; Disseminated intravascular coagulation; Fertilization; Food webs; Global warming; Greenhouse effect; Iron; Metabolism; Nitrate; Periphyton; Phosphate; Phytoplankton; Primary production; Secondary production; Sediments; Silicic acid; Transport processes; Zooplankton; Bacillariophyceae; Copepoda; INE; Subarctic Pacific; PICES; Pacific; Subarctic; Copepods
• Online Access: http://repository.ust.hk/ir/Record/1783.1-28962

The Subarctic Ecosystem Response to Iron Enrichment Study (SERIES) was conducted in the NE subarctic Pacific, one of the three major high nitrate low chlorophyll (HNLC) regions of the world where Fe limits primary productivity. SERIES is part of the Canadian SOLAS network project. During the first phase of the bloom, small phytoplankton (mainly prymnesiophytes) increased and there was a record increase in dimethylsulphide (DMS). During the second phase, the bloom was dominated by large pennate and centric diatoms and chlorophyll-a was 8-fold higher than initial values. The fugacity of CO sub(2) (fCO sub(2)) decreased from 340 to 260 mu atm and DIC from 2010 to 1970 mu mol kg super(-1). In contrast, DMS decreased and often became undetectable due to the metabolism of DMSP by bacteria. There was no significant difference in the zooplankton community dominated by small copepods inside the patch and outside. The bloom was terminated on Day 20 by silicate and low Fe concentrations, while sufficient nitrate and phosphate remained. Using sediment trap information and other data, it was estimated that <5% of the carbon associated with the Feinduced bloom, was exported below the mixed layer depth during this 30 day experiment. About 25% of the Fe-enhanced primary production in the mixed layer was channeled through the microbial food web, thus reducing the amount of organic carbon for export. Hence large scale Fe 'fertilization' may not be a viable solution to drawing down CO sub(2) and offsetting global warming.