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During the passage of a cold front in March 2002, bio-optical properties examined in coastal waters impacted by the Mississippi River indicated that westward advective flows and increasing river discharge containing high concentrations of nonalgal particles contributed significantly to surface optical variability. A comparison of seasonal data from three cruises indicated spectral models of absorption and scattering to be generally consistent with other coastal environments, while their parameterization in terms of chlorophyll (Chl) a concentration showed seasonal variability. The exponential slope of the colored dissolved organic matter (CDOM) averaged 0.0161 [+ or -] 0.00054 [nm.sup.-1] and nonalgal absorption averaged 0.011 [nm.sup.-1] with deviations from general trends observed due to anomalous water properties. Although the phytoplankton specific absorption coefficients varied over a wide range [0.02 to 0.1 [m.sup.2] [(mg Chl).sup.-1] at 443 nm] being higher in offshore surface waters, values of phytoplankton absorption spectra at the Sea-Viewing Wide Field-of-View Sensor (Sea WiFS) wave bands were highly correlated to modeled values. Particulate scattering characteristics were similar to observations for other coastal waters, while backscattering ratios were on average lower in phytoplankton-dominated surface waters (0.011 [+ or -] 0.003) and higher in low Chl near-bottom waters (0.0191 [+ or -] 0.0045). Average percent differences in remote sensing reflectance [R.sub.rs] derived from modeled and in-water radiometric measurements were highest in the blue wave bands (52%) and at locations with more stratified water columns. Sea WiFS estimates of Chl and CDOM absorption derived using regional empirical algorithms were highly correlated to in situ data. OCIS codes: 010.4450, 290.1350, 120.0280.

We introduce a sediment-induced light attenuation algorithm into the biogeochemical model of the Regional Ocean Modeling System (ROMS). A fully coupled ocean-atmospheric-sediment-biogeochemical simulation is carried out to assess the impact of sediment-induced light attenuation on primary production in the northern Gulf of Mexico during Hurricane Gustav in 2008. The new model shows a better agreement with satellite data on both the magnitude of nearshore chlorophyll concentration and the distribution of offshore bloom. When Gustav approaches, resuspended sediments shift the inner shelf ecosystem from a nutrient-limited one to light-limited. One week after Gustav's landfall, accumulated nutrient and favorable optical environment induces a post-hurricane algal bloom in the top 20 m of water column, while the productivity in the lower column is still light-limited due to unsettled sediment. Corresponding with the elevated offshore NO3 flux (38.71 mmol N/m/s) and decreased chlorophyll flux (43.10 mg/m/s), the post-hurricane bloom in the outer shelf is resulted from the cross-shelf nutrient supply instead of the lateral dispersed chlorophyll. Sensitivity tests indicate sediment light attenuation efficiency affects primary production when sediment concentration is moderately high. [ABSTRACT FROM AUTHOR]

Phytoplankton taxonomy, pigment composition and photo-physiological state were studied in Galveston Bay (GB), Texas (USA) following the extreme flooding associated with Hurricane Harvey (August 25-29, 2017) using field and satellite ocean color observations. Percentage of chlorophyll a (Chl a) in different phytoplankton groups were determined from a semi-analytical IOP (inherent optical property) inversion algorithm. The IOP inversion algorithm revealed the dominance of freshwater species (cyanobacteria and green algae) in the bay following the hurricane passage (September 29, 2017) under low salinity conditions associated with the discharge of floodwaters into GB; 2 months after the hurricane (October 29-30, 2017), under more seasonal salinity conditions, the phytoplankton community transitioned to an increase in small sized groups such as haptophyte and prochlorophyte. Sentinel-3A OLCI-derived Chl a obtained using a red/NIR band ratio algorithm for the turbid estuarine waters was highly correlated (R² > 0.90) to HPLC-derived Chl a concentrations. A Non-Negative Least Square (NNLS) inversion model was then applied to OLCI-derived Chl a maps of GB to obtain spatiotemporal distributions of phytoplankton diagnostic pigments; results appeared consistent with extracted phytoplankton taxonomic composition derived from the IOP inversion algorithm. OLCI-derived diagnostic pigment distributions also exhibited good agreement with HPLC measurements, with mean R² ranging from 0.39 for violaxanthin to 0.98 for Chl a. Environmental factors (e.g. floodwaters) combined with phytoplankton taxonomy also strongly modulated phytoplankton physiology in the bay as indicated by measurements of photosynthetic parameters with a Fluorescence Induction and Relaxation (FIRe) system. Phytoplankton in well-mixed waters (mid-bay area) exhibited maximum PSII photochemical efficiency (FV/FM) and low effective absorption cross section (δPSII), while the areas adjacent to the shelf (likely nutrient-limited) showed low FV/FM and elevated values. Overall, the approach using field and ocean color data combined with inversion models allowed, for the first time, an assessment of phytoplankton response to a large hurricane-related floodwater perturbation in a turbid estuarine environment based on its taxonomy, pigment composition and physiological state. [ABSTRACT FROM AUTHOR]

Abstract: Estuaries have been recognized as important sources of carbon dioxide (CO2) to the atmosphere; however, contributions of these systems to regional and global carbon budgets are not well constrained due to limited information on seasonal and spatial variability. In this study, we use satellite remote sensing to obtain seasonal pCO2 distribution and air‐sea CO2 fluxes in Apalachicola Bay, a national estuarine research reserve located in the northern Gulf of Mexico that receives seasonally varying dissolved organic matter‐rich waters from the Apalachicola River. A combination of time series (2005–2016) and seasonal field observations (2015–2016) of pH and biophysical variables were used to develop seasonal pH‐pCO2 relationships for obtaining surface pCO2 estimates and air‐sea CO2 fluxes from Visible and Infrared Imaging Radiometer Suite (VIIRS) ocean color data. Monthly and seasonal maps of pCO2 and air‐sea CO2 fluxes showed a general trend of higher fluxes in winter and summer corresponding to high river flow and warm water temperatures. However, CO2 fixation via photosynthesis and low water temperatures contributed to lower fluxes to the atmosphere in spring and fall, respectively. Throughout the study period, Apalachicola Bay was a net source of CO2 with large seasonal and spatial variability and a mean annual CO2 flux to the atmosphere of 3.4 ± 3.1 mol·m−2·year−1 (9.4 ± 8.5 mmol·m−2·day−1), consistent with fluxes reported for other estuaries. This study demonstrates the critical role that satellite observations can play to improve the estuarine contributions to the global carbon flux estimates. [ABSTRACT FROM AUTHOR]