The decline and fate of an iron-induced subarctic phytoplankton bloom
- Philip W Boyd 1, Cliff S Law , C S Wong , Yukihiro Nojiri , Atsushi Tsuda , Maurice Levasseur , Shigenobu Takeda , Richard Rivkin , Paul J Harrison , Robert Strzepek , Jim Gower , Mike McKay , Edward Abraham , Mike Arychuk , Janet Barwell-Clarke , William Crawford , David Crawford , Michelle Hale , Koh Harada , Keith Johnson , Hiroshi Kiyosawa , Isao Kudo , Adrian Marchetti , William Miller , Joe Needoba , Jun Nishioka , Hiroshi Ogawa , John Page , Marie Robert , Hiroaki Saito , Akash Sastri , Nelson Sherry , Tim Soutar , Nes Sutherland , Yosuke Taira , Frank Whitney , Shau-King Emmy Wong , Takeshi Yoshimura
- 1NIWA Centre for Chemical and Physical Oceanography, Department of Chemistry, University of Otago, PO Box 56, Dunedin, 9003, New Zealand. p.boyd@niwa.co.nz
- 0NIWA Centre for Chemical and Physical Oceanography, Department of Chemistry, University of Otago, PO Box 56, Dunedin, 9003, New Zealand. p.boyd@niwa.co.nz
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View abstract on PubMed
Summary
This summary is machine-generated.Iron fertilization spurs phytoplankton blooms, but much fixed carbon is lost to bacteria and grazers, not deep ocean export. Silicic acid depletion and inefficient carbon transfer limit sequestration potential.
Area Of Science
- Oceanography
- Biogeochemistry
- Marine Ecology
Background
- High-nitrate, low-chlorophyll (HNLC) oceanic regions are often limited by iron availability.
- Phytoplankton blooms, stimulated by iron, play a critical role in oceanic carbon cycling.
- The efficiency of carbon export from surface waters to the ocean interior following these blooms is poorly understood.
Purpose Of The Study
- To investigate the decline and fate of particulate organic carbon (POC) from an iron-stimulated diatom bloom.
- To quantify carbon export efficiency and identify loss pathways.
- To assess implications for past iron fertilization events and future carbon sequestration strategies.
Main Methods
- Monitoring of a diatom bloom in the Gulf of Alaska following iron addition.
- Measurement of mixed-layer particulate organic carbon (POC) and particulate silica.
- Deployment of sediment traps to quantify export flux at 50-125 m depths.
- Assessment of bacterial remineralization and mesozooplankton grazing impacts.
Main Results
- The bloom terminated due to iron and silicic acid depletion.
- Mixed-layer POC declined rapidly after bloom termination.
- Increased particulate silica export preceded significant POC export.
- Bacterial remineralization and grazing accounted for over half the POC deficit.
- Only a small fraction of POC was exported below the permanent thermocline.
Conclusions
- Silicic acid depletion limits diatom bloom duration and subsequent carbon export.
- Iron-stimulated carbon export to the deep ocean is inefficient.
- Findings challenge assumptions about geological iron fertilization and proposed ocean carbon sequestration methods.
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