Phytoplankton Absorption Coefficient Research Articles

Retrieving of the biooptical characteristics of Black-Sea waters under the conditions of constant reflectance at a wavelength of 400 nm

We consider a method used for the solution of the inverse problem of biooptics of the sea according to the spectrum of upwelling radiation and propose a procedure for the correction of the data of measurement by fixing the value of reflectance at a wavelength of 400 nm. The influence of this assumption on the results of retrieving of the concentrations of admixtures in seawater is analyzed. The computed values of the concentration of chlorophyll correspond to the data of direct biological measurements, and the reconstructed spectra of the absorption coefficient of phytoplankton have local maxima typical of biological particles. The applied correction allows us to decrease the influence of measurement errors on the results of retrieving and to increase the stability of solution of the inverse problem.

Bio-optical characteristics of a phytoplankton bloom event off Baja California Peninsula (30–31°N)

A phytoplankton bloom was detected in the Southern California Current System, off the Baja California Peninsula (Mexico) on June 2003 with chlorophyll- a concentration (TChl a) of 10.13 mg m −3. Two stations (D1 and D2) were sampled on June 24, and D2 was resampled 6 days later; chlorophyll- a concentration had decreased by about one half. LAC MODIS-Chl a images were obtained and showed the spread of the bloom on the day after sampling. The phytoplankton community consisted primarily of dinoflagellate temporary cysts, mainly at the surface and at 5 m in station D1. Two Pseudo-nitzschia species ( P. australis, P. seriata) were also very abundant. Samples from the bloom had a specific phytoplankton absorption coefficient ( a ph * ( λ ) ) lower than the rest of the samples. Values varied from 0.0186 to 0.0455 m 2 mg −1 for a ph * (440) and from 0.0092 to 0.0294 m 2 mg −1 for a ph * (675), with ratios a ph * (440): a ph * (675) ranging from 0.99 to 2.20. These low ratios were associated with the combined effect of packaging, and with the relatively high ratios of fucoxanthin, peridinin, diadinoxanthin and chlorophyll- c2 to TChl a. Samples from the surface and 5 m depth at station D1 had higher ratios of Perid:TChl a (0.12–0.32) than the rest of the samples, suggesting that cysts have similar Perid:TChl a as free-living dinoflagellates. An unusual absorption spectrum with a broad maximum around 480–500 nm was associated with the high proportion of cysts and diatoms. The slope of the spectra between 443 and 488 nm was a good index to differentiate bloom samples containing high proportions of dinoflagellate temporary cysts. Further investigation of the absorption properties of dinoflagellate cysts is needed in order to detect these waters by remote sensing. Although much work is still necessary to understand and explain the bio-optical properties of a bloom, the present study is the first assessment off the Baja California coast to simultaneously consider aspects such as absorption properties, pigment composition and to include a spatial evaluation of the extension of a bloom with satellite images.

Bio-optical characteristics of the western Arctic Ocean: implications for ocean color algorithms

Global ocean color algorithms designed to estimate chlorophyll a concentration (chla) are not accurate at high latitudes. Although a regional Arctic OC4L algorithm was designed to be applicable to high northern latitudes, its applicability remains uncertain. To examine these issues, we investigated the light absorption coefficients of phytoplankton, non-algal particles (NAP), and colored dissolved organic matter (CDOM) and remote sensing reflectance, Rrs(λ), covering most of the western Arctic Ocean. A higher pigment packaging effect was identified relative to that at lower latitudes. The CDOM absorption dominated and accounted for 76% of the total non-water absorption at 443 nm and did not covary with variations in chla. This absorption is significantly higher than those in other marine environments. We also examined the backscattering coefficient of particles obtained from the inversion of Rrs(λ) and found that it covaried well with variation in NAP absorption. Our evaluation shows that when turbid waters (Rrs(670) > 0.00042 sr–1) are excluded, the performance of the OC4L is good and much better than that of the sea-viewing wide field-of-view sensor (SeaWiFS) OC4V4 and the moderate-resolution imaging spectroradiometer (MODIS) OC3M (root mean square error (RMSE) of 0.13, 0.21, and 0.22, respectively). The reason why the OC4L performs well despite strong CDOM absorption is discussed.

Partitioning total spectral absorption in phytoplankton and colored detrital material contributions

A method based on spectral information is used to derive spectral absorption coefficients of phytoplankton aφ(λ) and colored detrital material, CDM, which includes non‐algal particle and colored dissolved organic matter, aCDM(λ), from total minus water absorption coefficients measurements. This method is first validated over a dataset of more than 300 simultaneous measurements of phytoplankton, non‐algal particle, and colored dissolved organic matter absorption coefficients spectra acquired with a laboratory spectrophotometer in various oceanic and coastal European waters. The validation is presented for measurements made with a high spectral resolution (hyper‐spectral case), and a limited spectral resolution (multi‐spectral case) — the case of most devices routinely used for in situ profiling, such as the WETLabs ac‐9. In order to examine the various sources of error in the method, we test its performance considering various levels of a priori knowledge of phytoplankton absorption properties over the study area: for each site, over each region, or over a global dataset only. When the method is applied to the multi‐spectral case without introducing any “local” information on phytoplankton absorption properties, we obtain a good performance with a relative Root Mean Square Error equal to 17.8%, 14.6%, and 40.7% for aCDM(412), the CDM exponential slope, and aφ(440), respectively. Finally, the partitioning method is directly applied to in situ profiles of total minus water spectral absorption coefficient measured with an ac‐9 in various oceanic Mediterranean waters, allowing the in situ description of CDM and phytoplankton absorption coefficients with a high spatial resolution.

Spectral absorption properties of dissolved and particulate matter in Lake Erie

Spectral absorption properties of particulate and dissolved matter were determined for Lake Erie waters in order to investigate the natural variability of the absorption coefficients required as inputs to optical models for converting satellite observations of water colour into water quality information. Particulate absorption measured using the quantitative filter technique yielded absorption spectra containing a fraction that could not be attributed to phytoplankton pigments, living heterotrophs, mineral sediments, or organic detritus but were indicative of additional absorption by a fraction of dissolved organic matter present in colloidal and/or particle-bound form. Erroneously high phytoplankton absorption coefficients measured at short wavelengths using the filter technique suggested that this particle-bound DOM is removed along with phytoplankton pigments during bleaching by sodium hypochlorite and as such is mistakenly incorporated into the phytoplankton absorption signal. Observations suggest that the selective sorption of fractions of DOM onto suspended particles may be responsible for significant variability in the absorption coefficients of particulate and dissolved matter and may be an important contributor to the total spectral absorption signals in Lake Erie waters. This reservoir of coloured organic matter, which to date has not been seriously considered in the optical properties of coastal and inland waters, may produce significant uncertainties in the parameterization of optical models and the interpretation of in situ and remotely sensed aquatic colour signals.

Relationship between photosynthetic parameters and different proxies of phytoplankton biomass in the subtropical ocean

Abstract. Probably because it is a readily available ocean color product, almost all models of primary productivity use chlorophyll as their index of phytoplankton biomass. As other variables become more readily available, both from remote sensing and in situ autonomous platforms, we should ask if other indices of biomass might be preferable. Herein, we compare the accuracy of different proxies of phytoplankton biomass for estimating the maximum photosynthetic rate (Pmax) and the initial slope of the production versus irradiance (P vs. E) curve (α). The proxies compared are: the total chlorophyll a concentration (Tchla, the sum of chlorophyll a and divinyl chlorophyll), the phytoplankton absorption coefficient, the phytoplankton photosynthetic absorption coefficient, the active fluorescence in situ, the particulate scattering coefficient at 650 nm (bp(650)), and the particulate backscattering coefficient at 650 nm (bbp(650)). All of the data (about 170 P vs. E curves) were collected in the South Pacific Ocean. We find that when only the phytoplanktonic biomass proxies are available, bp(650) and Tchla are respectively the best estimators of Pmax and α. When additional variables are available, such as the depth of sampling, the irradiance at depth, or the temperature, Tchla is the best estimator of both Pmax and α.

Retrieval of pigment concentrations and size structure of algal populations from their absorption spectra using multilayered perceptrons

Spectral absorption coefficients of phytoplankton can now be derived, under some assumptions, from hyperspectral ocean color measurements and thus become accessible from space. In this study, multilayer perceptrons have been developed to retrieve information on the pigment composition and size structure of phytoplankton from these absorption spectra. The retrieved variables are the main pigment groups (chlorophylls a, b, c, and photosynthetic and nonphotosynthetic carotenoids) and the relative contributions of three algal size classes (pico-, nano-, and microphytoplankton) to total chlorophyll a. The networks have been trained, tested, and validated using more than 3,700 simultaneous absorption and pigment measurements collected in the world ocean. Among pigment groups, chlorophyll a is the most accurately retrieved (average relative errors of 17% and 16% for the test and validation data subsets, respectively), while the poorest performances are found for chlorophyll b (average relative errors of 51% and 40%). Relative contributions of algal size classes to total chlorophyll a are retrieved with average relative errors of 19% to 33% for the test subset and of 18% to 47% for the validation subset. The performances obtained for the validation data, showing no strong degradation with respect to test data, suggest that these neural networks might be operated with similar performances for a large variety of marine areas.

Spatial variability of phytoplankton absorption coefficients and pigments off Baja California during November 2002

We have estimated the spatial variability of phytoplankton specific absorption coefficients (a* ph ) in the water column of the California Current System during November 2002, taking into account the variability in pigment composition and phytoplankton community structure and size. Oligotrophic conditions (surface Chl 0.4) were considered as phytoplankton adapted to high irradiances, and lower ratios (<0.26) as adapted to low irradiances. We found a good relationship between APP:APS and a* ph (440) for the deeper layer (DCM and below), but no clear evidence of the factors causing the variability of a* ph (440) in the upper layer.

Retrievals of a size parameter for phytoplankton and spectral light absorption by colored detrital matter from water-leaving radiances at SeaWiFS channels in a continental shelf region off Brazil

Many efforts are currently oriented toward extracting more information from ocean color than the chlorophyll a concentration. Among biological parameters potentially accessible from space, estimates of phytoplankton cell size and light absorption by colored detrital matter (CDM) would lead to an indirect assessment of major components of the organic carbon pool in the ocean, which would benefit oceanic carbon budget models. We present here 2 procedures to retrieve simultaneously from ocean color measurements in a limited number of bands, magnitudes, and spectral shapes for both light absorption by CDM and phytoplankton, along with a size parameter for phytoplankton. The performance of the 2 procedures was evaluated using different data sets that correspond to increasing uncertainties: (1) measured absorption coefficients of phytoplankton, particulate detritus, and colored dissolved organic matter (CDOM) and measured chlorophyll a concentrations and (2) SeaWiFS upwelling radiance measurements and chlorophyll a concentrations estimated from global algorithms. In situ data were acquired during 3 cruises, differing by their relative proportions in CDM and phytoplankton, over a continental shelf off Brazil. No local information was introduced in either procedure, to make them more generally applicable. Over the study area, the absorption coefficient of CDM at 443 nm was retrieved from SeaWiFS radiances with a relative root mean square error (RMSE) of 33%, and phytoplankton light absorption coefficients in SeaWiFS bands (from 412 to 510 nm) were retrieved with RMSEs between 28% and 33%. These results are comparable to or better than those obtained by 3 published models. In addition, a size parameter of phytoplankton and the spectral slope of CDM absorption were retrieved with RMSEs of 17% and 22%, respectively. If these methods are applied at a regional scale, the performances could be substantially improved by locally tuning some empirical relationships.

Using inherent optical properties to investigate biogeochemical dynamics in a tropical macrotidal coastal system

The variability in the inherent optical properties along an estuary‐coast‐ocean continuum in tropical Australia has been studied. The study area, the Fitzroy Estuary and Keppel Bay system, is a shallow coastal environment (depth &lt; 30 m) with highly turbid waters in the estuary and blue oceanic waters in the bay and subject to macrotides. Biogeochemical and inherent optical properties (IOPs) were sampled in the near‐surface layer spatially and across the tidal phase during the dry season. These determinations included continuous measurements of spectral absorption, scattering and backscattering coefficients, together with discrete measurements of spectral absorption coefficients of phytoplankton, nonalgal particles and colored dissolved organic matter, and concentrations of phytoplankton pigments and suspended matter. Because of a large variability in the characteristics of the water components on short spatial and temporal scales, we observe a large variability in the associated optical properties. From the estuary to the bay, particle scattering and dissolved absorption decreased by 2 orders of magnitude, and nonalgal particle absorption decreased by 3 orders of magnitude. We also observed a strong variability in particle single scattering albedo and backscattering efficiency (by a factor of 6) and in specific IOPs (IOPs normalized by the relevant constituent concentration) such as suspended matter‐specific particle scattering and chlorophyll‐specific phytoplankton absorption. Superimposed on this strong spatial variability is the effect of the semidiurnal tide, which affects the spatial distribution of all measured properties. These results emphasize the need for spatially and temporally adjusted algorithms for remote sensing in complex coastal systems.

Annual variations in bio-optical properties at the ‘Estación Permanente de Estudios Ambientales (EPEA)’ coastal station, Argentina

Variations in optical properties at a coastal station (EPEA) off the North coast of Argentina (38° 28′ S 57° 41′ W) were studied in 2000–2001. Changes observed in the absorption by three components of seawater (phytoplankton, detritus, and chromophoric-dissolved-organic-matter or CDOM) were analysed in relation to changes in environmental conditions (temperature, stability of the water column, irradiance) and changes in the phytoplankton community structure. An annual cycle typical of temperate seas was observed in the stability of the water column, with a strong thermocline in summer and a vertically homogeneous regime in winter. The proportion of detritus absorption at the surface was related to these changes in stability of the water column, being larger in winter due probably to re-suspension from the bottom. Absorption by phytoplankton and CDOM were not related to temperature or the stability of the water column and there was no covariation in absorption by the three seawater components. On the other hand, absorption by phytoplankton was significantly related to the predominant cell-size. The percentage contribution of ultraphytoplankton (<5 μm) to total chlorophyll- a concentration varied between 6% and 46% throughout the year, being the highest during summer. Accordingly, the specific absorption coefficient of phytoplankton at 440 nm (absorption/chlorophyll- a) varied between 0.01 in July (when there was a bloom of the large diatom Coscinodiscus wailesii) and 0.09 m 2 mg Chla −1 in February (when Synechococcus spp. was predominant). The relationship between in situ and 1 km daily satellite estimated OC4V4 chlorophyll- a concentration showed a good correlation ( r 2 = 0.94 for 9 out of the 19 data points where an exact match up could be made). Marked variations were observed when comparing 8 day-9 km binned data with the 19 points. While some of the differences are due to the highly dynamic hydrography of this region, variations in phytoplankton composition also contribute to the difference between in situ and satellite-derived values.

A two‐component model of phytoplankton absorption in the open ocean: Theory and applications

The two‐population absorption model of Sathyendranath et al. is extended to retrieve the specific absorption coefficients (absorption per unit concentration of chlorophyll‐a) of the component populations of phytoplankton. The model relates the absorption coefficient of phytoplankton to chlorophyll‐a concentration, assuming that the assemblages of phytoplankton comprise mixtures of two populations whose proportions vary as the total concentration of cells changes. The model is applied to in situ data collected from six regions during 34 cruises. The model compares well with earlier models of phytoplankton absorption but brings the additional advantage of parameters that have clear bio‐optical and biological interpretation. Size structure of the phytoplankton populations was inferred from the values of the specific absorption coefficients. The results are consistent with pigment analyses performed on the same samples. Seasonal analysis of data from the northwest Atlantic, southeast Pacific, and the Arabian Sea showed significant changes in the spectral form and magnitude of the specific absorption coefficients of small‐ and large‐celled populations, which appear to be related to changes in species composition. The model serves thus as an optical tool to explore the large‐scale biogeography of phytoplankton.

Inherent optical properties of the Irish Sea and their effect on satellite primary production algorithms

Three cruises were conducted in the Irish Sea during May, June and July 2001 to determine the variability in inherent optical properties (IOP), photo physiological parameters and primary production (PP) and to assess the effect of IOP on satellite PP algorithms. The absorption coefficients of phytoplankton (aph), coloured dissolved organic material (aCDOM) and nonalgal particles (aNAP) were higher during May than June and July. A radiative transfer model was used to model the in-water light field based on aph (case 1) and aph, aCDOM and aNAP (case 2). When PP was compared using these light fields, there was a 46% difference in estimates. The case 2 in-water light field was coupled to a wavelength resolving satellite model of PP (PPcase2) and had a low root mean square error (RMS) (0.27 log10PP) compared with in situ PPcase2. IOP absorption, especially aCDOM, had a significant effect on the performance of this algorithm, but scattering of light by suspended particulate material had a small effect. A look-up table was generated from the in situ aph, aCDOM and aNAP measurements, which can be used in conjunction with satellite products to produce satellite maps of PP. There was <25% difference between in situ PPcase2 and the satellite PP maps, which suggests that they could be produced routinely and accurately to monitor PP in the Irish Sea and other coastal and estuarine areas.

Toward a taxon‐specific parameterization of bio‐optical models of primary production: A case study in the North Atlantic

As part of the Programme Océan Multidisciplinaire Méso Echelle (POMME) in the North Atlantic, an extensive data set of high‐pressure liquid chromatography pigment concentrations, phytoplankton absorption coefficients, primary production measurements, and P versus E curves has been acquired. This data set is analyzed with the objective of testing whether photosynthetic performances of natural phytoplankton communities are related to taxonomic characteristics. This objective is addressed in two ways. The first approach concerns the bulk photosynthetic performances of the water column: the water column photosynthetic cross section, ψ*, equals 0.088 m2 gChla−1, i.e., ∼25% higher than the average for the world ocean. Using multiple regression, size‐specific values of ψ* are subsequently derived: carbon storage by water column is more efficient with microphytoplankton (ψ* = 0.135 m2 gChla−1) than with nanophytoplankton (0.089 m2 gChla−1) or picophytoplankton (0.064 m2 gChla−1). The second (independent) approach examines the correlations between photophysiological properties and several abiotic and biotic variables. The correlations are weak, if any, between photophysiological properties and abiotic factors (temperature, nitrate concentration, and irradiance), while significant correlations are reported with biotic factors (proportion of the different phytoplankton groups, average size of the phytoplankton assemblage). Our results suggest that when large phytoplankton populations predominate at the expense of smaller ones, the specific absorption coefficient is expectedly lower, while other photophysiological properties αB, PmaxB, and Φcmax, are higher. The agreement between both independent approaches points out that large phytoplankton (essentially diatoms) are potentially more efficient in carbon storage than any other phytoplankton groups on a chlorophyll a or light absorption basis.

Seasonal variation of absorption by particles and colored dissolved organic matter (CDOM) in Funka Bay, southwestern Hokkaido, Japan

Between November 2000 and October 2001, the seasonal variation in absorption by particles (phytoplankton and detritus) and colored dissolved organic matter (CDOM) was measured in Funka Bay (a subarctic coastal region of Japan). In autumn–winter, chlorophyll a concentration (Chl a) near the euphotic zone remained very low (<1.0 mg m −3) but markedly increased in spring (16.8 mg m −3). Chlorophyll-specific absorption coefficient for phytoplankton ( a ∗ ph( λ)) was high during summer and low during the spring bloom. This is because the package effect was greater during the spring bloom due to the presence of large diatoms, while small phytoplankton dominated during summer. Absorption at 440 nm by CDOM was higher than that of phytoplankton and detritus, except during the spring bloom, and the relative contribution of CDOM absorption to the total absorption coefficient was >50%. CDOM and detritus absorption did not increase with increasing Chl a, but it showed a time lag between the spring bloom. It is suggested that phytoplankton degradation started after the spring bloom; detritus absorption increased and, then, CDOM absorption increased. River runoff was not a significant influence in Funka Bay, therefore, CDOM production may be mainly related to microbial activity.

Spectral absorption coefficient of phytoplankton and its relation to chlorophyll a and remote sensing reflectance in coastal waters of southern China

The spectral absorption coefficient of phytoplankton in coastal waters of southern China is investigated. Large variations in the absorption coefficient of phytoplankton are found. The absorption coefficient of phytoplankton at 443 nm ranged from 0.006 m−1 to 0.484 with an average value of 0.067 m−1 The chlorophyll-specific absorption coefficient of phytoplankton is also a bio-optical variable, with a spectrally averaged value of 0.025 m2˙mg−1. The variations of chlorophyll-specific absorption coefficient are mainly attributed to pigment composition of phytoplankton and package effect. The chlorophyll-specific absorption coefficient of phytoplankton decreases with the increasing of chlorophyll a concentration. This relationship can be described by a power law function, with the parameters and the coefficient of determination r2 as functions of wavelength, but the parameters describing the relationships in present study differed from that in Case 1 waters, thus the regional adjustment of model parameters was of particular significance for improving the accuracy of bio-optical algorithms for estimation of Chl-a concentration and primary production from remotely sensed data. Regression analysis of reflectance (Rrs) ratio and absorption coefficient of phytoplankton (aph) indicates a close correlation between them, which means that it is possible to sretrieve absorption coefficient of phytoplankton using ocean color remote sensing data in optically complex coastal waters.

New tools for the study of oceanic eddies: Satellite derived inherent optical properties

Satellite study of oceanic eddy formation, propagation, interactions, and fate was first conducted by sea surface temperature derived at infrared wavelengths. For visible wavelength ocean color reflectances, it is shown that recent radiative transfer model inversions provide additional characteristics of eddies: their constituent absorption and backscattering inherent optical properties. The chromophoric dissolved organic matter absorption coefficient has the highest contrast and is therefore the most visually evident inherent optical property (while the phytoplankton absorption coefficient and backscattering coefficients are respectively less discernible). For use as an analytical tool, comparisons suggests that the chromophoric dissolved organic matter absorption coefficient has a ∼10× higher contrast (i.e., ∼5% vs. 50%) in the Middle Atlantic Bight making eddy events detectable over longer time periods than with SST imagery. Example imagery illustrates the application of chromophoric dissolved organic matter and phytoplankton absorption coefficient inherent optical properties to the visual injection of dissolved and particulate organic carbon into the deep ocean by a Gulf Stream ring.

Effect of Santa Ana winds on bio-optical properties off Baja California

The effect of Santa Ana winds on bio-optical properties (absorption coefficients of particles, detritus and phytoplankton) off Baja California (Mexico) was evaluated using data obtained during four cruises in January, April, August and October 1999. Meteorological data from a station at Todos Santos Bay and satellite-derived wind data indicated three Santa Ana events during October 1999, with low relative humidity, high air temperature and persistent ENE winds. The absorption coefficient of detritus (adT) in surface samples was ten-fold higher in October because of the inorganic material wind-driven by the Santa Ana events that occurred from 9 to 11 and from 17 to 20 October, 1999. The absorption coefficients of particles (ap) and phytoplankton (aɸ) in the euphotic zone were higher in the April survey as a result of higher phytoplankton abundance. The ap, a and Kd values in the euphotic zone were fitted to chlorophyll using a power function, with an explained variance of 37%, 72% and 16%, respectively. On excluding the October adT surface values, chlorophyll explained 82% of the changes in the absorption coefficients (ap and aɸ), and 87% of the Kd variability. Approximately 80% of the chlorophyll concentration can be explained by the water column spectral reflectance relationship: Rrs(443)/Rrs(555). According to our results, regional chlorophyll estimates from water column bio-optical information were not greatly affected by wind-borne dust transported during the October 1999 Santa Ana events.

Natural variability of phytoplanktonic absorption in oceanic waters: Influence of the size structure of algal populations

The spectral absorption coefficients of phytoplankton in oceanic waters were previously shown to vary with chlorophyll a concentration according to nonlinear relationships with a great deal of noise. We analyzed this biological noise on a data set of 596 simultaneous absorption and high‐pressure liquid chromatography (HPLC) pigment measurements acquired within the surface layer (first optical depth) from various regions of the world's oceans. We observed systematic deviations from the average relationships for some oceanic areas and also seasonally within given areas. Using the detailed HPLC measurements, the influences of pigment composition and package effect (the two main sources of variability in algal absorption for a given chlorophyll a concentration) were explicitly separated for each sample. It was found that while the pigment composition experiences large variations, even within a restricted chlorophyll range, it is often not (at least within the first optical depth) the dominant source of the biological noise. Instead, these deviations mostly result from variability in the pigment packaging effect (for a given chlorophyll a concentration) due to variations in algal community size structure. This conclusion is fully confirmed by an independent approach, which consists of estimating a “size index” of algal populations from the relative concentrations of taxonomic pigments.

Bio-optical model for Chesapeake Bay and the Middle Atlantic Bight

Retrievals of bio-optical properties from satellite measurements in Case 2 waters depend on algorithms that account for multiple constituents affecting spectral quality of the upwelling light flux. Semi-analytical (SA) models are suitable for this purpose, but must be parameterized with in situ data, particularly in estuarine and coastal waters. We examined spatial and temporal variability of bio-optical properties in Chesapeake Bay and the adjacent Middle Atlantic Bight (CB/MAB) to parameterize and validate the Garver/Siegel/Maritorena (GSM01) model. Several years (1996–2002) of data on inherent and apparent optical properties confirmed high scattering and strong absorption by dissolved and particulate components that did not co-vary. These data, consisting of the chlorophyll (chl a)-normalized phytoplankton absorption coefficient, a ph *( λ), and the spectral slope of absorption due to dissolved and detrital materials, S cdm, were used to optimize model parameters of GSM01 and produce a version of the model tuned for CB/MAB we have designated GSM01-CB. Performance of GSM01-CB was measured against the globally optimized version of GSM01 and the empirical algorithm, OC4v.4, using both in situ and satellite-derived radiances from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) as inputs to the model. GSM01-CB outperformed OC4v.4 in retrieving chl a in CB, and both SA models outperformed OC4v.4 in MAB. GSM01 and GSM01-CB also returned reasonable estimates of other bio-optical products, including the absorption coefficient for dissolved and detrital materials, a cdm(443), and the particulate backscatter coefficient, b bp(443). We present alternatives to the parameterization of GSM01-CB to account for interannual variability of a ph *( λ) in CB using empirical relationships with key variables that regulate phytoplankton dynamics in the estuary (i.e., freshwater flow and nutrient loading), and to include regional gradients of S cdm in MAB.