North Pacific Chlorophyll Blooms

Recent conditions

Jul2026

Monthly composites of chlorophyll in the bloom region from the 2026 bloom season: ERDDAP™ download

2026-08-05

NOAA VIIRS Near Real-Time Weekly Chlorophyll: ERDDAP™ download

Bloom Location and Timing

The blooms develop in a very specific locality. The most intense and the most frequent blooms occur between 130°-150°W and 28°-32° N, but blooms also develop due north of Hawaii. The time integrated location of the blooms can be seen in the figure which shows the number of times when chl values > 0.1 mg/m3 occurred in the Pacific during July-Oct from 1997-2017.

Phytoplankton blooms in the ocean usually occur in spring or fall when there is temporal overlap between nutrient injection into the surface mixed layer from mixing, sufficient light levels for photosynthesis, and decreased grazing to allow net biomass accumulation. The chlorophyll blooms that occur in the open NE Pacific are unusual in that they develop in late summer, July-Oct during the seasonal stratification maximum. The NE Pacific in unique in having late summer blooms consistently occur almost every year in the same general area (Wilson and Qiu (2008)).

Number of months during July-Oct from 1997-2017 where chl > 0.1 mg/m3, using OC-CCI chlorophyll data. Modified from Wilson and Qiu (2008)

Bloom Forcing

The blooms along 30°N are often made up of diatom-diazotroph assemblages (DDAs) (Villareal et al. (2011); Villareal et al. (2012));. Hemiaulus and Rhizosolenia diatoms occur in this region containing the diazotrophic endosymbiont Richelia. Richelia release fixed nitrogen as ammonium or dissolved organic nitrogen, which is then available to the host diatom. Nitrogen-fixing diatom symbioses (diatom-diazotroph associations: DDAs) often increase 102–103 fold in these blooms and contribute to elevated export flux. Diazotophy mitigates nitrate-base nutrient limitation but phytoplankton growth will still be controlled by the amount of phosphate and or silicate. This part of the ocean does not appear to be iron limited.

Episodic injections of subsurface nutrients are likely the cause of these blooms but the exact mechanism is unknown. Suggested mechanisms include dynamics associated with the convergent zone (Wilson et al. (2008)), the subtropical front (STF) (Wilson (2003); Wilson et al. (2008)), the breaking of internal waves at the critical latitude (Wilson (2011)), eddy interactions (Calil and Richards (2010); Fong (2008); Guidi et al. (2012)) dust deposition (Calil et al. (2011)) and winter mixing of phosphate into the mixed layer (Dore et al. (2008)). Most of the proposed mechanisms of nutrient injection are impossible to investigate without in-situ data, which is difficult to obtain in this relatively isolated part of the ocean. We have been involved in a few missions to collect in situ data, see Mission section.

References

Calil, P. H. R., and K. J. Richards. 2010. “Transient Upwelling Hot Spots in the Oligotrophic North Pacific.” Journal of Geophysical Research: Oceans 115 (C2). https://doi.org/10.1029/2009JC005360.

Calil, Paulo H. R., Scott C. Doney, Keiya Yumimoto, Kenta Eguchi, and Toshihiko Takemura. 2011. “Episodic Upwelling and Dust Deposition as Bloom Triggers in Low-Nutrient, Low-Chlorophyll Regions.” Journal of Geophysical Research: Oceans 116 (C6). https://doi.org/10.1029/2010JC006704.

Dore, John E., Ricardo M. Letelier, Matthew J. Church, Roger Lukas, and David M. Karl. 2008. “Summer Phytoplankton Blooms in the Oligotrophic North Pacific Subtropical Gyre: Historical Perspective and Recent Observations.” Progress in Oceanography 76 (1): 2–38. https://doi.org/10.1016/j.pocean.2007.10.002.

Fong, Karl, A. A. 2008. “Nitrogen Fixation in an Anticyclonic Eddy in the Oligotrophic North Pacific Ocean.” The ISME Journal 2 (6): 663–76. https://doi.org/10.1038/ismej.2008.22.

Guidi, L., P. H. R. Calil, S. Duhamel, et al. 2012. “Does Eddy-Eddy Interaction Control Surface Phytoplankton Distribution and Carbon Export in the North Pacific Subtropical Gyre?” Journal of Geophysical Research: Biogeosciences 117 (G2). https://doi.org/10.1029/2012JG001984.

Villareal, T. A., C. G. Brown, M. A. Brzezinski, and C. Wilson. 2012. “Summer Diatom Blooms in the North Pacific Subtropical Gyre: 2008-2009.” PLoS ONE 7 (4). https://doi.org/10.1371/journal.pone.0033109.

Villareal, T., L. Adornato, C. Wilson, and C. Schoenbaechler. 2011. “Summer Blooms of Diatom-Diazotroph Assemblages and Surface Chlorophyll in the North Pacific Gyre: A Disconnect.” J. Geophys. Res 116 (March). https://doi.org/10.1029/2010JC006268.

Wilson, C. 2003. “Late Summer Chlorophyll Blooms in the Oligotrophic North Pacific Subtropical Gyre.” Geophysical Research Letters 30 (18). https://doi.org/10.1029/2003GL017770.

Wilson, C. 2011. “Chlorophyll Anomalies Along the Critical Latitude at 30°n in the NE Pacific.” Geophysical Research Letters 38 (15). https://doi.org/10.1029/2011GL048210.

Wilson, C., and X. Qiu. 2008. “Global Distribution of Summer Chlorophyll Blooms in the Oligotrophic Gyres.” Progress in Oceanography 78: 107–34. https://doi.org/10.1016/j.pocean.2008.05.002.

Wilson, C., T. A. Villareal, N. Maximenko, S. J. Bograd, J. P. Montoya, and C. A. Schoenbaechler. 2008. “Biological and Physical Forcings of Late Summer Chlorophyll Blooms at 30°n in the Oligotrophic Pacific.” Journal of Marine Systems 69 (3): 164–76. https://doi.org/10.1016/j.jmarsys.2005.09.018.