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The evolution and termination of an iron-induced mesoscale bloom in the northeast subarctic Pacific


Boyd, PW and Strzepek, R and Takeda, S and Jackson, G and Wong, CS and McKay, RM and Law, C and Kiyosawa, H and Saito, H and Sherry, N and Johnson, K and Gower, J and Ramaiah, N, The evolution and termination of an iron-induced mesoscale bloom in the northeast subarctic Pacific, Limnology and Oceanography, 50, (6) pp. 1872-1886. ISSN 0024-3590 (2005) [Refereed Article]

Copyright Statement

Copyright 2005, by the American Society of Limnology and Oceanography, Inc.

DOI: doi:10.4319/lo.2005.50.6.1872


We initiated and mapped a diatom bloom in the northeast subarctic Pacific by concurrently adding dissolved iron and the tracer sulfur hexafluoride to a mesoscale patch of high-nitrate, low-chlorophyll waters. The bloom was dominated by pennate diatoms and was monitored for 25 d, which was sufficiently long to observe the evolution and termination of the bloom and most of the decline phase. Fast repetition–rate fluorometry indicated that the diatoms were iron-replete until day 12, followed by a 4–5-d transition to iron limitation. This transition period was characterized by relatively high rates of algal growth and nutrient uptake, which pointed to diatoms using intracellularly stored iron. By days 16–17, the bloom was probably limited simultaneously by both iron and silicic acid supply, because low silicic acid concentrations were evident. Modeling simulations, using data from our study, provided an estimate of the critical threshold for algal aggregation. Observed diatom abundances during the bloom exceeded this threshold between days 13 and 17. Mass sedimentation of diatoms and diatom aggregates was recorded in surface-tethered free-drifting sediment traps at 50 m in depth on day 21. Although the termination of the bloom was probably controlled by the availability of both iron and silicic acid, we cannot rule out the role of algal aggregation. The bloom decline was likely triggered by the onset of mass sedimentation. During our study, evidence of both diatom species succession and species-specific aggregation point to important links between algal nutrient stress and the initiation of algal aggregation.

Item Details

Item Type:Refereed Article
Keywords:phytoplankton, bloom, subarctic, iron, fertilization
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Biological oceanography
Objective Division:Environmental Management
Objective Group:Marine systems and management
Objective Field:Oceanic processes (excl. in the Antarctic and Southern Ocean)
UTAS Author:Boyd, PW (Professor Philip Boyd)
UTAS Author:Strzepek, R (Dr Robert Strzepek)
ID Code:147709
Year Published:2005
Web of Science® Times Cited:83
Deposited By:Australian Antarctic Program Partnership
Deposited On:2021-11-11
Last Modified:2021-12-03

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