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A predictive model for satellite‐derived phytoplankton absorption over the Louisiana shelf hypoxic zone: Effects of nutrients and physical forcing
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| Zeitschriftentitel: | Journal of Geophysical Research: Oceans |
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| Personen und Körperschaften: | , |
| In: | Journal of Geophysical Research: Oceans, 113, 2008, C6 |
| Format: | E-Article |
| Sprache: | Englisch |
| veröffentlicht: |
American Geophysical Union (AGU)
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| Schlagwörter: |
| Zusammenfassung: | <jats:p>We investigated environmental forcing mechanisms of phytoplankton absorption near the Mississippi River delta using multiyear satellite data. An algorithm for the phytoplankton absorption coefficient (<jats:italic>a</jats:italic><jats:sub><jats:italic>ph</jats:italic></jats:sub>) was developed from in situ measurements and applied to ocean color imagery. We employed a suite of chemical and physical forcing variables, including surface currents. For satellite‐derived <jats:italic>a</jats:italic><jats:sub><jats:italic>ph</jats:italic></jats:sub> time series (2002–2004), correlation and stepwise regression analyses revealed the most important forcing variables of <jats:italic>a</jats:italic><jats:sub><jats:italic>ph</jats:italic></jats:sub> on the Louisiana shelf. Areally, Mississippi River discharge and nitrate concentration ([NO<jats:sub>3</jats:sub>]) were the two most important predictors of <jats:italic>a</jats:italic><jats:sub><jats:italic>ph</jats:italic></jats:sub> over the hypoxic zone (defined by its maximum extent). River discharge was important in a band stretching from the Mississippi River delta to the Louisiana‐Texas border. Riverine [NO<jats:sub>3</jats:sub>] and wind magnitude best predicted <jats:italic>a</jats:italic><jats:sub><jats:italic>ph</jats:italic></jats:sub> in nearshore waters, and solar radiation and SST were most important farther offshore over the hypoxic zone, indicating upwelled nutrient sources to phytoplankton. A multiple linear regression model performed well in resolving seasonal and interannual <jats:italic>a</jats:italic><jats:sub><jats:italic>ph</jats:italic></jats:sub> variability in model development years (2002–2004) (mean error of 18%, over all pixels and months) and in predicting shelf‐wide <jats:italic>a</jats:italic><jats:sub><jats:italic>ph</jats:italic></jats:sub> patterns in 2005 (mean error of 32%). Our results strongly suggest that in recent years, stratification and vertical mixing, in addition to riverine [NO<jats:sub>3</jats:sub>], play a primary role in regulating phytoplankton biomass over the hypoxic zone. As well, a springtime model experiment showed that <jats:italic>a</jats:italic><jats:sub><jats:italic>ph</jats:italic></jats:sub> over the hypoxic zone can differ by an average absolute 37% from its average scenario owing to changes solely in environmental variables other than NO<jats:sub>3</jats:sub> flux.</jats:p> |
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| ISSN: |
0148-0227
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| DOI: | 10.1029/2007jc004594 |