Summer diatom blooms in the North Pacific subtropical gyre: 2008-2009

The summertime North Pacific subtropical gyre has widespread phytoplankton blooms between Hawaii and the subtropical front (∼30°N) that appear as chlorophyll (chl) increases in satellite ocean color data. Nitrogen-fixing diatom symbioses (diatom-diazotroph associations: DDAs) often increase 10(2)-10...

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Bibliographic Details
Published in:PloS one 2012-04, Vol.7 (4), p.e33109-e33109
Main Authors: Villareal, Tracy A, Brown, Colbi G, Brzezinski, Mark A, Krause, Jeffrey W, Wilson, Cara
Format: Article
Language:English
Subjects:
Abundance
Bacillariophyceae
Biology
Biomass
Carbon
Chlorophyll
Color
Color imagery
Cyanobacteria
Cyanobacteria - physiology
Cyanophyceae
Diatoms
Diatoms - physiology
Earth Sciences
Exports
Hawaii
Hemiaulus
Hydrography
Image processing
Limnology
Marine ecology
Microscopy
Mixed layer depth
Nitrogen
Nitrogen fixation
Nitrogen Fixation - physiology
Ocean circulation
Ocean color
Oceanography
Oceans
Pacific Ocean
Phytoplankton
Phytoplankton - physiology
Plankton
Rhizosolenia
Salinity
Satellite ocean color data
Satellites
Science
Seasons
Signatures
Silica
Silicon dioxide
Spacecraft
Spatial variability
Symbiosis
Temperature
Temperature range
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Summary:The summertime North Pacific subtropical gyre has widespread phytoplankton blooms between Hawaii and the subtropical front (∼30°N) that appear as chlorophyll (chl) increases in satellite ocean color data. Nitrogen-fixing diatom symbioses (diatom-diazotroph associations: DDAs) often increase 10(2)-10(3) fold in these blooms and contribute to elevated export flux. In 2008 and 2009, two cruises targeted satellite chlorophyll blooms to examine DDA species abundance, chlorophyll concentration, biogenic silica concentration, and hydrography. Generalized observations that DDA blooms occur when the mixed layer depth is < 70 m are supported, but there is no consistent relationship between mixed layer depth, bloom intensity, or composition; regional blooms between 22-34°N occur within a broader temperature range (21-26°C) than previously reported. In both years, the Hemiaulus-Richelia and Rhizosolenia-Richelia DDAs increased 10(2)-10(3) over background concentrations within satellite-defined bloom features. The two years share a common trend of Hemiaulus dominance of the DDAs and substantial increases in the >10 µm chl a fraction (∼40-90+% of total chl a). Integrated diatom abundance varied 10-fold over 10 µm size fraction, and increased up to 5-fold in the blooms. The two years differed in the magnitude of the surface chl a increase (2009>2008), the abundance of pennate diatoms within the bloom (2009>2008), and the substantially greater mixed layer depth in 2009. Only the 2009 bloom had sufficient chl a in the >10 µm fraction to produce the observed ocean color chl increase. Blooms had high spatial variability; ocean color images likely average over numerous small events over time and space scales that exceed the individual event scale. Summertime DDA export flux noted at the Hawaii time-series Sta. ALOHA is probably a generalized feature of the eastern N. Pacific north to the subtropical front.
ISSN:1932-6203
1932-6203
DOI:10.1371/journal.pone.0033109