Abstract
Abstract. We introduced a sediment-induced light attenuation algorithm into a biogeochemical model of the Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) modeling system. A fully coupled ocean–atmospheric–sediment–biogeochemical simulation was carried out to assess the impact of sediment-induced light attenuation on primary production in the northern Gulf of Mexico during the passage of Hurricane Gustav in 2008. When compared with model results without sediment-induced light attenuation, our new model showed a better agreement with satellite data on both the magnitude of nearshore chlorophyll concentration and the spatial distribution of offshore bloom. When Hurricane Gustav approached, resuspended sediment shifted the inner shelf ecosystem from a nutrient-limited one to a light-limited one. Only 1 week after Hurricane Gustav's landfall, accumulated nutrients and a favorable optical environment induced a posthurricane algal bloom in the top 20 m of the water column, while the productivity in the lower water column was still light-limited due to slow-settling sediment. Corresponding with the elevated offshore NO3 flux (38.71 mmol N m−1 s−1) and decreased chlorophyll flux (43.10 mg m−1 s−1), the outer shelf posthurricane bloom should have resulted from the cross-shelf nutrient supply instead of the lateral dispersed chlorophyll. Sensitivity tests indicated that sediment light attenuation efficiency affected primary production when sediment concentration was moderately high. Model uncertainties due to colored dissolved organic matter and parameterization of sediment-induced light attenuation are also discussed.
Highlights
Light, nutrients and temperature play a vital role in photosynthesis and marine ecosystems
A recent numerical model study simulated a substantial increase in near-bottom oxygen consumption due to resuspended particulate organic matter (POM) remineralization during moderate resuspension events (Moriarty et al, 2018). These past studies and the new finding of this study suggest that particulate matter dynamics might substantially contribute to bottom oxygen depletion and hypoxia development following a hurricane passage
We introduced a sediment-induced light attenuation algorithm to the Regional Ocean Modeling System (ROMS) biogeochemical model
Summary
Nutrients and temperature play a vital role in photosynthesis and marine ecosystems. The vertical structure of light availability in an aquatic environment is mainly modulated by the shading effects of chlorophyll, colored dissolved organic matter (CDOM), detritus and sediment (Cloern, 1987; Devlin et al, 2008; Ganju et al, 2014; McSweeney et al, 2017; Schaeffer et al, 2011). Along the Louisiana–Texas shelf in the nGoM, suspended sediment concentration (SSC) in the water column exhibits strong seasonality, i.e., high in the winter and spring seasons due to strong sediment resuspension and high fluvial sediment discharge, while largely reduced in summer and fall owing to the relatively low river inputs and weak resuspension (Zang et al, 2019).
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