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Marine Ecology Progress Series

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MEPS 427:29-49 (2011)  -  DOI: https://doi.org/10.3354/meps09043

Effects of surface forcing on interannual variability of the fall phytoplankton bloom in the Gulf of Maine revealed using a process-oriented model

Song Hu1,*, Changsheng Chen1,2, Rubao Ji1,3, David W. Townsend4, Rucheng Tian2, Robert C. Beardsley5, Cabell S. Davis3

1Marine Ecosystem and Environmental Laboratory, College of Marine Sciences, Shanghai Ocean University,
999 Hucheng Huanlu, Lingang New City, Shanghai 201306, PR China
2School for Marine Science and Technology, University of Massachusetts Dartmouth, 706 South Rodney French Blvd., New Bedford, Massachusetts 02744, USA
3Department of Biology, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
4School of Marine Sciences, University of Maine, 5706 Aubert Hall, Orono, Maine 04469, USA
5Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA

ABSTRACT: SeaWiFS (Sea-viewing Wide Field-of-view Sensor) chlorophyll data revealed strong interannual variability in fall phytoplankton dynamics in the Gulf of Maine, with 3 general features in any one year: (1) rapid chlorophyll increases in response to storm events in fall; (2) gradual chlorophyll increases in response to seasonal wind- and cooling-induced mixing that gradually deepens the mixed layer; and (3) the absence of any observable fall bloom. We applied a mixed-layer box model and a 1-dimensional physical-biological numerical model to examine the influence of physical forcing (surface wind, heat flux, and freshening) on the mixed-layer dynamics and its impact on the entrainment of deep-water nutrients and thus on the appearance of fall bloom. The model results suggest that during early fall, the surface mixed-layer depth is controlled by both wind- and cooling-induced mixing. Strong interannual variability in mixed-layer depth has a direct impact on short- and long-term vertical nutrient fluxes and thus the fall bloom. Phytoplankton concentrations over time are sensitive to initial pre-bloom profiles of nutrients. The strength of the initial stratification can affect the modeled phytoplankton concentration, while the timing of intermittent freshening events is related to the significant interannual variability of fall blooms.


KEY WORDS: Fall phytoplankton bloom · Surface forcing · Freshening · Interannual variability · Gulf of Maine · Modeling


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Cite this article as: Hu S, Chen C, Ji R, Townsend DW, Tian R, Beardsley RC, Davis CS (2011) Effects of surface forcing on interannual variability of the fall phytoplankton bloom in the Gulf of Maine revealed using a process-oriented model. Mar Ecol Prog Ser 427:29-49. https://doi.org/10.3354/meps09043

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