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Particulate and dissolved spectral absorption on the continental shelf of the southeastern United States
Abstract
Visible absorption spectra of particulate and dissolved materials were characterized on the continental shelf off the southeastern United States (the South Atlantic Bight), emphasizing cross-shelf and seasonal variability. A coastal front separates turbid coastal waters from clearer and seasonal variability. A coastal front separates turbid coastal waters from clearer midshelf waters. Spatial and seasonal patterns were evident in absorption coefficients for phytoplankton, detritus, and colored dissolved organic matter (CDOM); spectral shape parameters for CDOM and detritus; and phytoplankton chlorophyll-specific absorption. The magnitude of CDOM absorption reflected seaonal differences in freshwater discharge and the salinity of the midshelf waters. In the spring of 1993 (high discharge), CDOM absorption at 443 nm was >10 times that of total particulate absorption between 12 and 50 km offshore (0.28-0.69 m-1 versus 0.027-0.062 m-1) and up to 10 times the CDOM absorption measured in the previous summer (low discharge). Phytoplankton chlorophyll-specific absorption in the blue increased with distance from shore (from
... hence competing with phytoplankton for photosynthetically active radiation [6,7]. In many coastal areas, CDOM absorption is several times that of chlorophyll and confounds the retrieval of the latter from ocean colour satellite observations due to overlapping absorbance spectra at the blue wavelengths [8][9][10]. Furthermore, CDOM has proven to be a useful tracer not only for carbon but also as a proxy for mixing in a wide variety of environments [11][12][13]. ...
... In particular, during periods of weak stratification, in absence of wind forcing, vortices constrain fresh Po River waters to a southward flow along the Italian shelf [56]. In contrast, in periods of stratification, particularly in spring and summer, the Po River fresh water plume spreads across the basin to the Istrian coast to Remote Sens. 2017, 9,180 4 of 22 form a front that divides the northern basin [57,58]. The extent of Po riverine flow and wind forcing, therefore, modulate fresh water penetration in the North Adriatic [59]. ...
... Remote Sens. 2017,9, 180 ...
The performance of empirical band ratio models were evaluated for the estimation of Coloured Dissolved Organic Matter (CDOM) using MODIS ocean colour sensor images and data collected on the North-Central Western Adriatic Sea (Mediterranean Sea). Relationships between in situ measurements (2013–2016) of CDOM absorption coefficients at 355 nm (aCDOM355) with several MODIS satellite band ratios were evaluated on a test data set. The prediction capability of the different linear models was assessed on a validation data set. Based on some statistical diagnostic parameters (R2, APD and RMSE), the best MODIS band ratio performance in retrieving CDOM was obtained by a simple linear model of the transformed dependent variable using the remote sensing reflectance band ratio Rrs(667)/Rrs(488) as the only independent variable. The best-retrieved CDOM algorithm provides very good results for the complex coastal area along the North-Central Western Adriatic Sea where the Po River outflow is the main driving force in CDOM and nutrient circulation, which in winter mostly remains confined to a coastal boundary layer, whereas in summer it spreads to the open sea as well.
... Areas near the coast, sampled during September 2003, showed high a g (400) (~0.25 m -1 ) and low S (~0.011 nm -1 ). (Bricaud et al., 1981;Nelson and Guarda, 1995;Carder et al., 1999;Cannizzaro, 2004). Some extreme slope values (e.g. ...
... Away from the coast, CDOM concentrations in Cariaco were generally low (absorption coefficients at 412 nm of 0.03 m -1 ). The range of S measured was similar to that reported by other authors, both for coastal and open waters (Bricaud et al., 1981;Nelson and Guarda, 1995;Carder et al., 1999;Cannizzaro, 2004). The changes in CDOM slope from the coastal area to the open basin were likely due to different sources of CDOM, and were indicative of the mixing between riverine and autochthonous material. ...
... The changes observed in S were likely due to different sources of CDOM. The range of S observed in Cariaco in September 2003 and March 2004 was similar to that reported by other authors, both for coastal and open waters (Bricaud et al., 1981;Nelson and Guarda, 1995;Carder et al., 1999;Cannizzaro, 2004). ...
Two oceanographic cruises were conducted during September 2003 and March 2004 in the eastern half of the Cariaco Basin. Specific objectives were to examine the hydrography of the seasonal upwelling plume characteristic of this region, the spatial distribution of particles in the area, and to help determine the source and relative importance of in situ particle production vs. terrigenous particles delivered laterally from the coast.During September 2003, average surface salinities within the basin were higher (36.6) relative to Caribbean Sea waters outside the basin (35.6). Salinity patterns indicated that the Orinoco and Amazon River plumes did not enter or influenced the basin directly.The upwelling plume in March 2004 stimulated primary productivity. Beam attenuation and CDOM fluorescence profiles showed marked vertical structure in biomass of microbial populations, particularly near the oxic-anoxic interface typically located between about 250 and 300 m.
There is an increasing difference in temperature and salinity between the Cariaco Basin and the adjacent Caribbean Sea below 200 m. Inside the Basin temperatures and salinities were higher by 4Ê»C and 0.5.The influence of local rivers on the Cariaco Basin was evident during September 2003. Low salinity plumes with high beam attenuation (1m1) lined the southern margin of the Basin. The primary rivers that affected the basin were the Unare and Never.Ì Their sediment input affected the shelf near the river mouths, and a surrounding radius of up to 40 Km. Their low salinity plumes were carried northwestward toward the CARIACO time series station. In March 2004, there was minimal or no terrigenous input from local rivers. Near the Manzanares River, off the city of Cuman,Ì and near Cubagua Island, located south of Margarita Island, attenuation due to suspended particles (0.09 m-1) was observed at depth (70-150 m) during both cruises (0.09-0.15 m-1).
... La relation entre la signature spectrale du coefficient d'absorption des particules non-algales et leur origine (minérale ou organique) n'a pas été clairement établie (Nelson et Guarda, 1995 ;Sydor et Arnone, 1997 ;Gallegos et Neale, 2002 ;Siegel et al., 2002). Babin et al. (2003a) ont cependant émis l'hypothèse qu'une augmentation de cette pente indique une augmentation de la part du matériel détritique d'origine organique. ...
... (443), ainsi que la pente spectrale moyenne associée. Dans les eaux côtières, les substances jaunes ne sont pas uniquement produites par la dégradation du phytoplancton, mais elles proviennent en grande partie des apports terrigènes Nelson et Guarda, 1995;Gallegos et Neale, 2002 ;Siegel et al., 2002). Comme il a été mentionné au chapitre I (section I.A.2.b), les pentes fortes sont caractéristiques des acides fulviques d'origine continentale, alors que les pentes plus faibles sont indicatrice d'une part importante d'acides humiques . ...
Coastal waters impacted by riverine inputs play a main role in the export and burial of terrigeneous particles. Ocean colour remote remote sensing allows to retrieve surface suspended particulate matter (SPM) concentrations. To improve spatial and temporal resolutions, it can be combined with bio-optical in situ measurements and numerical modelling. The Rhône river is the main source of freshwater and particulate inputs in the Gulf of Lion (Western Mediterranean Sea). The aim of the thesis is to study the seasonal variability of the Rhône river SPM inputs and their fate at the land-ocean interface. In situ bio-optical measurements have been acquired from oceanographic vessels and ProvBio autonomous profiling floats. The SPM concentrations have been retrieved from MERIS and MODIS satellite sensors. The hydro-sedimentary model (Mars-3D) is used to simulate the hydrodynamic circulation and the sediment dynamic in the Gulf of Lion using the measured Rhône liquid and solid discharges as inputs. Regional proxys have been identified and tested to follow the dynamic of SPM within the water column from in situ bio-optical measurements. A regional algorithm has been developed to map SPM concentrations from satellite sensors measurements. The combination of these two tools shows the dependence of SPM export to Rhone river freshwater discharge and wind. During flood events, the SPM are mainly exported within surface waters. From a weak to a moderate Rhône river freshwater discharge and strong wind, SPM are tranported close to the bottom. The hydro-sedimentary model allows to better understand some processes although improvement are still required.
... Light-absorbing DOM in coastal environments-CDOM absorption typically dominates total UV absorption in seawater (DeGrandpre et al. 1996). In coastal environments, this dominance can extend into visible wavelengths (Nelson and Guarda 1995), and thus CDOM can compete with primary producers for photosynthetically available radiation, as well as contribute to error in satellite estimates of chlorophyll and primary production. In estuaries and coastal regions, CDOM exported from rivers and coastal marshes is the primary source of light-absorbing material, and thus its photochemical and biological degradation are critical determinants of the optical properties of the resident seawater. ...
... The current lack of consistency in how spectral slopes are calculated (with regard to wavelength region and computation method) makes direct comparisons across studies problematic (Coble and Brophy 1994). Nonetheless, the spectral slopes computed in this study for Satilla River CDOM (0.0137 to 0.0156) are similar to those reported in other estuaries and coastal regions, including the continental shelf of the southeastern United States into which the Satilla River drains (0.0173; Nelson and Guarda 1995) and the Middle Atlantic Bight (0.014 to 0.020; Vodacek et al. 1997). ...
Terrestrially derived dissolved organic matter (DOM) impacts the optical properties of coastal seawater and affects carbon cycling on a global scale. We studied sequential long-term photochemical and biological degradation of estuarine dissolved organic matter from the Satilla River, an estuary in the southeastern United States that is dominated by vascular plant-derived organic matter. During photodegradation, dissolved organic carbon (DOC) loss (amounting to 31% of the initial DOC) was much less extensive than colored dissolved organic matter (CDOM) or fluorescent dissolved organic matter (FDOM) loss (50% and 56% of the initial CDOM and FDOM), and analysis of kinetics suggested a reservoir of DOC that was resistant to photodegradation. In contrast, CDOM photodegra- dation closely followed first-order kinetics over two half-lives with no indication of a nondegradable component. FDOM loss was slightly biased toward fluorophores considered representative of terrestrial humic substances. Ad- ditional changes in optical properties included increases in spectral slope and shifts in fluorescence excitation/ emission maxima that were generally consistent with previous observations from field studies of photobleached DOM. Biological degradation of photobleached DOM was more rapid than that of unbleached material, and this net positive effect was evident even for extensively photodegraded material. Bacterial degradation caused shifts in the opposite direction from photochemical degradation for both spectral slope and excitation/emission maxima and thus dampened but did not eliminate changes in optical properties caused by photobleaching.
... [5] Here we report fine-scale hydrographic and optical measurements across the front south of New England during the summer 2002 as part of the New England Shelf Productivity EXperiment (NESPEX). Previous observations in this region have revealed strong cross-shelf gradients in optical properties as the influence of river discharge , with its increased load of particles and dissolved substances, decreases exponentially with distance from shore [Nelson and Guarda, 1995; DeGrandpre et al., 1996; Vodacek et al., 1997; Boss et al., 2001b]. Optical variations occur at the shelfbreak front over multiple timescales owing to the passage of internal waves, solitons, storms, and tides, and seasonal variations of vertical stratification , phytoplankton growth and freshwater discharge [Boss et al., 2001a [Boss et al., , 2001b Gardner et al., 2001; Sosik et al., 2001; Chang and Dickey, 2001; Vodacek et al., 1997; Nelson and Guarda, 1995]. ...
... Previous observations in this region have revealed strong cross-shelf gradients in optical properties as the influence of river discharge , with its increased load of particles and dissolved substances, decreases exponentially with distance from shore [Nelson and Guarda, 1995; DeGrandpre et al., 1996; Vodacek et al., 1997; Boss et al., 2001b]. Optical variations occur at the shelfbreak front over multiple timescales owing to the passage of internal waves, solitons, storms, and tides, and seasonal variations of vertical stratification , phytoplankton growth and freshwater discharge [Boss et al., 2001a [Boss et al., , 2001b Gardner et al., 2001; Sosik et al., 2001; Chang and Dickey, 2001; Vodacek et al., 1997; Nelson and Guarda, 1995]. Our data are evaluated to determine how physical processes of local mixing and upwelling influence the optical environment, and thus productivity , at the front. ...
A fine-scale survey of physical, chemical, and optical properties was done across the shelfbreak front in the Middle Atlantic Bight region south of Martha's Vineyard, Cape Cod (70.5°W) during late summer 2002. The front displayed physical and biological structure typical for this region and season: a density-compensating front with strong horizontal T and S and optical gradients, and a chlorophyll maximum layer that deepened in the seaward direction across the front, became detached beneath the shelfbreak jet, reappeared on a deeper and greater density surface on the seaward side of the shelfbreak front, and then shoaled again in the seaward direction. At times the shoreward leading edge of the chlorophyll maximum layer seaward of the front was situated beneath the chlorophyll maximum layer shoreward of the front. Hydrography on the shoreward side of the front was dominated by a bolus of cold pool water of shelf origin with minimum salinity and temperature of 33 and 10°C, respectively. The cold pool was also a pool of high CDOM absorption whose distribution coincided with the temperature and salinity across the front. The persistence of sharp horizontal T, S, and CDOM gradients indicated that advective processes exceed diffusive mixing processes at the front. CDOM in the euphotic zone showed a strong inverse relationship to temperature and, below the euphotic zone, a strong inverse relationship to salinity, indicating a terrestrial CDOM source within the cold pool and a photodegradation sink at the surface. Cross-frontal exchange of shelf CDOM and upper slope waters is inferred from the T-S properties of the CDOM pool and previously reported measurements of the mixing and circulation at this site. The chlorophyll specific absorption coefficients of discrete samples collected within the chlorophyll maximum layers, along with LPS surveys of dissolved and particulate absorption and scattering, indicate that the variability of optics at the shelfbreak front is influenced mostly by particle optics. Due to the presence of the cold pool with its high CDOM signature, the waters masses across the shelfbreak front can be considered as case 1 for particles but case 2 for dissolved materials.
... CDOM, on the other hand, is the principal UV attenuator in natural waters (Helms et al., 2013;Kitidis et al., 2006) because its absorption increases exponentially from the PAR-to the UV-region (Bricaud et al., 1981;Helms et al., 2013;Kitidis et al., 2006;Swan et al., 2009). Particulate matter is another component that contributes to the overall UV attenuation; especially in coastal systems (Bricaud and Stramski, 1990;Mitchell et al., 2003;Nelson and Guarda, 1995), as these areas are receiving suspended particulate matter from terrestrial sources, rivers, and coastal ecosystems. In the open ocean where the origin of both CDOM and particulate matter is predominantly autochthonous, generated by phytoplankton and other organisms (Andrew et al., 2013;Twardowski and Donaghay, 2001), UV absorption by particles tends to be low, representing ~20% of total biogenous, non-water absorption (anw(λ)) in the most transparent oceanic waters (Morel et al., 2007b). ...
Oligotrophic (sub-)tropical oceans receive intense incident ultraviolet radiation (UV, 280–400 nm) and their water columns are highly transparent due to their nutrient-deficient state. This combination suggests a high potential for adverse effects on organisms, yet only few reports describe the UV exposures received in these waters and the associated impacts on marine biota. Here, we aimed to investigate the UV bio-optics of various open ocean locations and, using the Red Sea as a representative oligotrophic environment, we investigated the pattern of UV attenuation over a wide latitudinal range, quantified UV exposures in the water column, and determined impacts of UVB (280–320 nm) on indigenous phytoplankton and scleractinian corals. Globally, the lowest average downwelling diffuse attenuation coefficients (Kd) in the UV spectrum were recorded in the ultra-oligotrophic Indian Ocean Subtropical Gyre (Kd(313nm): 0.110 m-1) and South Pacific Gyre (Kd(313nm): 0.098 m-1), while aCDOM(λ) was ~1–2 orders of magnitude higher than ap(λ), In the Red Sea, UV attenuation mirrored the prevailing latitudinal gradient in nutrients, with the lowest and highest Kd(313) of 0.130 m-1 and 0.357 m-1 measured in the far north and in the south of the basin, respectively. Central Red Sea waters were most transparent to UV in late summer, i.e., a few weeks after incident irradiances and SSTs reach their annual maximum. Although, the projected increase of SST due to climate change means that extreme UV exposure and temperatures could coincide in the near future. This finding is of particular relevance since we found that Red Sea diatom species such as C. closterium are highly sensitive to UVB-induced photoinhibition and cell decay (LRD50: 11.4 kJ). Water temperature also governed the UVB sensitivity of Synechococcus sp., although this group exhibited a high resistance overall (LRD50: 57 kJ to non-detectable). For corals, we found that UVB-removal generally had little impact on the oxidative stress levels and photophysiology of S. pistillata and P. verrucosa from shallow waters, but considerably accelerated the acclimation of upward transplanted corals, which highlights that UVB is a crucial stressor that governs the photoacclimation capacity of Red Sea corals.
... CDOM, on the other hand, is the main contributor to UVR attenuation in natural waters (Helms et al., 2013;Kitidis et al., 2006) because its absorption increases exponentially from the PAR to the UV spectrum (Bricaud et al., 1981;Swan et al., 2009). Suspended particulate matter (SPM) also strongly contributes to the overall UVR attenuation, especially in coastal systems (Bricaud & Stramski, 1990;Mitchell et al., 2003;Nelson & Guarda, 1995), as these areas are receiving SPM from terrestrial sources, rivers, and coastal ecosystems. In the open ocean, the origin of both CDOM and SPM is predominantly autochthonous, generated by phytoplankton and other organisms (Andrew et al., 2013;Nelson et al., 2004;Twardowski & Donaghay, 2001). ...
Few studies have investigated ultraviolet (UV) radiation in the open ocean besides its harmful effects on organisms and influence on biogeochemical processes. Here, we assessed UV attenuation, with particular focus on UV-B, across the (sub)tropical ocean during the Malaspina 2010 Circumnavigation. Vertical UV radiometer profiles together with Chl-a concentration, and UV absorption by CDOM (aCDOM(λ)) and by suspended particulate matter (ap(λ)) were measured at 117 stations. At PAR and across UV-A and UV-B wavelengths, the lowest downwelling attenuation coefficients (Kd) during the expedition were recorded in ultra-oligotrophic regions at 5ºS–15ºS (mean Kd(305nm): 0.129 m-1, mean Kd(313nm): 0.107 m-1) in the Indian and South Pacific Oceans. The waters here were comparatively more transparent than at 5ºN–15ºN (mean Kd(305nm): 0.239 m-1, mean Kd(313nm): 0.181 m-1) where Equatorial upwelling occurs. Kd was highest near the Costa Rica Dome (Kd(313nm): 0.226 m-1) and at the confluence of the Benguela and Agulhas currents (Kd(313nm): 0.251 m-1). The contribution of ap(λ) towards non-water absorption (anw(λ)) was significantly lower at 305 nm than at 313 nm and 320 nm, suggesting the contribution of absorption by detritus and phytoplankton particles decreases compared with that of CDOM absorption as UV-B wavelength decreases. Both aCDOM(λ) and ap(λ) at UV-B wavelengths were lowest in the Indian Ocean whereas Kd was lowest in the South Pacific. This finding emphasizes that other factors besides absorption, such as scattering by reflective phytoplankton or inorganic particles, strongly influence UV-B attenuation in open ocean waters.
... The latter includes both biotic, e.g. phytoplankton, and abiotic matter (Scully & Lean 1994, Nelson & Guarda 1995, Aphalo & Albert 2012. In turn, optical properties of water are dependent on climate characteristics such as temperature, acidification, and local circulation and mixing patterns, which can all affect the levels and distribution of organic matter in the water column (Behrenfeld et al. 2006, Brewin et al. 2015. ...
Ultraviolet radiation (UVR) is an important environmental factor that can have an impact directly, or indirectly, on the health of organisms. UVR also has the potential to inactivate pathogens in surface waters. As a result, UVR can alter host-pathogen relationships. Bivalve species are threatened by various pathogens. Here, we assessed the impacts of UVR on (i) bivalves, (ii) bivalve pathogens and (iii) the bivalve host-pathogen relationship. UVR consistently impedes pathogens. However, the effect of UVR on marine animals is variable, with both positive and negative impacts. The limited available data allude to the potential to exploit natural UVR for disease management in aquaculture, but also highlight a striking knowledge gap and uncertainty relating to climate change.
... This emergence offers the capability of covering large areas on a real-time scale to directly monitor and characterize environmental pollutants entering a body of water. Addressing the problem of colored dissolved organic matter (CDOM), Nelson and Guarda [50], in the South Atlantic Bight, and Vodacek et al. [51], in the Mid-Atlantic, examined the visible absorption spectra and characteristics of particulate and dissolved materials. Both studies demonstrated that colored dissolved organic matter comes mostly from riverine runoff, and it is also widespread and abundant in natural waters, which have a significant portion of the dissolved organic matter (10-90%), and influences water-leaving radiances [52]. ...
... [17,18] . Ǐ .Ҳt-Ǽ ؕӌ ғ . ...
... The mean of (0.012 nm -1 ) in coastal waters correspondent to the overall average (0.0123 nm -1 ) value obtained in the coastal waters of European Seas 6 . The average values obtained for CWR and DWR are close to the results found in Case 1 waters 18 , and in Case 2 waters 15,16 . ...
ABSTRACT Variability in light absorption by colored dissolved organic matter ((aCDOM)), by non-algal particles ((aNAP)) and by colored detrital matter ((aCDM)) were analyzed in the coastal and deep water regions in the Black sea at the same season (Autumn) to avoid the impact of seasonal variability. The CDOM, NAP and CDM light absorption were parameterized. As result of the parameterization the two parameters were obtained (coefficient at 490 nm and slope coefficient (S):aCDOM (490) and Scdom ; aNAP(490) and Snap ; aCDM(490) and Scdm . The CDOM contributed mainly in the (490) in both coastal (79 ± 13%) and deep water (88 ± 6%) regions. High (in ~order) variability in the (490) was observed in coastal waters due to resuspension of sediments from the bottom at shallow stations. The average values were 0.010 nm-1 in coastal and 0.012 nm-1 in deep water regions. For all dataset the relationship between of aCDM(490) and Scdm was described by power function. This equation can be used for refining of the regional algorithm of aCDM(l) assessment in the Black Sea based on satellite data. The obtained in this research relative absorption of NAP and CDOM could be used for remote assessment of aNAP(l) and aCDOM(l) in the Black Sea.
... (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) Castillo and Miller, 2008;Monahan and Pybus, 1978;Nelson and Guarda, 1995). By this principle, salinity retrievals were enabled using satellite ocean colour data with increased spatial and temporal coverage of coastal and estuarine waters (Ahn et al., 2008;D'Sa, 2008;Guo et al., 2007;Shanmugam et al., 2016;Tehrani et al., 2013). ...
This study intends to develop methodologies that use high resolution satellite data from Landsat 8 (Operational Land Imager) OLI and (Thermal Infrared Sensor) TIRS sensors for characterizing spatial and temporal changes in physical and acoustical properties of coastal lagoon and estuarine waters. It employs multiple steps to achieve this possibility: a novel atmospheric correction algorithm is applied to OLI spectral data to retrieve water-leaving radiances which are key inputs for the applied models; appropriate parameterizations are developed for the OLI bands and used in conjugation with a hybrid model to produce the spectral absorption coefficients of coloured dissolved organic matter (aCDOM) and to derive surface salinity fields which inversely correspond with the aCDOM values; an efficient algorithm is employed to estimate surface water temperature using thermal infrared bands, and well-known models are employed with the satellite-derived products to determine the acoustical properties (sound attenuation and speed). Results from the above methodology were evaluated using in-situ data and Landsat 8 OLI matchup data acquired over the coastal lagoon systems (e.g., Chilika Lagoon on the coast of Bay of Bengal) during monsoon and non-monsoon seasons. The uncertainties associated with the derived products such as CDOM, salinity, temperature, sound attenuation and speed were found to be within the desirable mission goal. Recognizing the importance of the salinity gradient that plays a unique and fundamental role in defining a transitional ecosystem, spatial and temporal patterns in the structure of the salinity gradient were examined together with the CDOM patterns. High resolution OLI products exhibited a general horizontal gradient with salinity decreasing from the lagoon mouth in the eastern and central sectors to the river mouth in the northern sector and a near uniform gradient with moderate salinity in the adjacent locations (southern sector) of the lagoon. The time-series of OLI products further showed that spatial and temporal structures of the salinity are modulated by the terrestrially delivered freshwater inputs, tidal forcing at the lagoon mouth, mixing of these two waters sources, and local geomorphology. Surface water temperature products derived from the TIRS sensor for the lagoon and its adjoining locations depicted a well pronounced seasonal cycle with warmer temperatures modulated by reduced mixing and increased solar heating and stratification during non-monsoon, summer months and cooler temperatures during monsoon, winter months. The effect of salinity and temperature on the sound attenuation and sound speed was prominent in the locations of the freshwater discharge and tidal mixing regimes, where the salinity exerted a greater influence on both sound attenuation and speed despite the opposing effects of surface water temperatures. In areas of surface heating and stratification, both salinity and temperature increased causing an increase in sound attenuation and speed over the ranges found in the lagoon. These results are important for sonar performance modelling and operation of acoustic devices in such shallow water environments impacted by the terrestrial and ocean forcing factors.
... Alternatively then, some factor or factors which co-varies with salinity, such as macro-or micronutrients, trace metal toxicity, or dissolved organic carbon (DOC), must be considered as a direct or indirect control on phytoplankton species composition. We did not measure DOC, but it is known to strongly inversely correlate to salinity in the northwest Atlantic Ocean due to its primary source being riverine input (Nelson and Guarda, 1995;Vodacek et al., 1997;Vaillancourt et al., 2005). DOC may directly or indirectly influence phytoplankton community composition through non-photosynthetic carbon uptake by osmotrophic and mixotrophic phytoplankton, which are increasingly recognized as being ubiquitous in most marine algal groups, including haptophytes (Unrein et al., 2014). ...
A CHEMTAX analysis of the phytoplankton community composition is presented for the summertime northwest Atlantic Ocean from the Sargasso Sea to the New England continental shelf. To minimize the confounding influence of light intensity-related changes in internal pigment concentration (photo-acclimation), we compared CHEMTAX community composition within (but not between) five discrete optical depth layers (OL1 -5) arranged vertically throughout and beneath the euphotic zone, and extending horizontally from the oligotrophic to mesotrophic regions. CHEMTAX model results revealed a gradient of increasing proportions of eukaryotes to prokaryotes in the landward direction. The oligotrophic oceanic waters were dominated about equally by Prochlorococcus and haptophytes with Synechococcus and prasinophytes being secondarily important, while the mesotrophic slope and shelf waters were dominated by haptophytes and prasinophytes, with Prochlorococcus undetectable in shelf waters. Redundancy analysis revealed strong and significant niche separations between eukaryotic and prokaryotic phytoplankton, with the cyanobacteria more common in warmer, saltier waters, and eukaryotic species more common in fresher, colder waters. Salinity was the strongest predictor of the phytoplankton community composition in OLs 2 through 5, but in the surface OL1 temperature was the strongest predictor. There were positive significant correlations between salinity and Prochlorococcus, and negative significant correlations between salinity and all eukaryote groups: pelagophytes, chlorophytes, haptophytes, diatoms, prasinophytes, cryptophytes, and dinoflagellates, in most cases the strength of the correlation increased with depth. Other environmental variables, PO4³⁻, NO3⁻+NO2⁻, and vertical density stratification were all weak predictors of phytoplankton community composition.
... In the coastal water of the Black Sea the overall average value of (0.011±0.002 nm -1 ) is in a good agreement with (0.0123±0.0013 nm -1 ) obtained on average for the European seas coastal waters 19 . This average value of SNAP is close to SNAP found in Case 1 waters 20 and in Case 2 waters at regional scale [21][22][23] . The ( ) spectra have an exponential spectral shape -CDOM-like spectral shape, which suggests that these two optical components may share some common chromophores 19 . ...
... the Arctic Ocean, values of detrital absorption, a d (440), varied widely (0.0016 m −1 < a d (440) < 0.22 m −1 ; Matsuoka et al. 2011), falling within the range obtained in coastal watersaround Europe(Babin et al. 2003). Values of the slope for non-algal particle absorption (S d , nm −1 ) also varied widely (0.005 nm −1 < S d < 0.017 nm −1 ), and were in the lower range of values published in the literature(Nelson and Guarda 1995;Babin et al. 2003). In the Southern Ocean, reported values of a d (440) vary within a narrower range than the Arctic Ocean (0.0001 -0.038 m −1 ;Arrigo et al. 1998;Reynolds et al. 2001), suggesting that a d (440) values in the Southern Ocean are lower than in the Arctic Ocean. ...
... Our results indicate that, despite the low and quite stable values of a CDOM (350) determined in surface waters of the Bay of Marseilles, the significant inverse linear relationship observed at both depths between a CDOM (350) and salinity illustrated a con- the potential biogeochemical influence of the Rhône River plume in this oligotrophic coastal area. Such a strong significant inverse relationship between salinity and fluorescent/absorbant CDOM is typically observed in coastal areas subjected to high river inputs (Blough et al., 1993;Green and Blough, 1994;Nelson and Guarda, 1995;Højerslev et al., 1996;Nieke et al., 1997;Vodacek et al., 1997;Seritti et al., 1998;Del 5 Castillo et al., 2000;Ferrari, 2000;Stedmon et al., 2000). By contrast, the lack of correlation between salinity and fluorescence intensities of peaks C and M at 2 m depth (excluding the maximum values, 25 November 2008) and the only weakly significant correlation observed for 5 m depth samples suggest that the Rhône River plume is not a dominant source of fluorescent CDOM in Marseilles 10 Bay. ...
Seawater samples were collected in surface waters (2 and 5 m depths) of the Bay of Marseilles (Northwestern Mediterranean Sea; 5°17′30′′ E, 43°14′30′′ N) during one year from November 2007 to December 2008 and studied for total organic carbon (TOC) as well as chromophoric dissolved organic matter (CDOM) optical properties (absorbance and fluorescence). The annual mean value of surface CDOM absorption coefficient at 350 nm [ a <sub>CDOM</sub>(350)] was very low (0.10 ± 0.02 m<sup>−1</sup>) with in comparison to values usually found in coastal waters, and no significant seasonal trend in a <sub>CDOM</sub>(350) could be determined. By contrast, the spectral slope of CDOM absorption ( S <sub>CDOM</sub>) was significantly higher (0.023 ± 0.003 nm<sup>−1</sup>) in summer than in fall and winter periods (0.017 ± 0.002 nm<sup>−1</sup>), reflecting either CDOM photobleaching or production in surface waters during stratified sunny periods. The CDOM fluorescence, assessed through excitation emission matrices (EEMs), was dominated by protein-like component (peak T; 1.30–21.94 QSU) and marine humic-like component (peak M; 0.55–5.82 QSU), while terrestrial humic-like fluorescence (peak C; 0.34–2.99 QSU) remained very low. This reflected a dominance of relatively fresh material from biological origin within the CDOM fluorescent pool. At the end of summer, surface CDOM fluorescence was very low and strongly blue shifted, reinforcing the hypothesis of CDOM photobleaching. Our results suggested that unusual Rhône River plume eastward intrusion events may reach Marseilles Bay within 2–3 days and induce local phytoplankton blooms and subsequent fluorescent CDOM production (peaks M and T) without adding terrestrial fluorescence signatures (peak C). Besides Rhône River plumes, mixing events of the entire water column injected humic (peaks C and M) CDOM from the bottom into the surface and thus appeared also as an important source of CDOM in surface waters of the Marseilles Bay. Therefore, the assessment of CDOM optical properties, within the hydrological context, pointed out several biotic (in situ biological production, biological production within Rhône River plumes) and abiotic (photobleaching, mixing) factors controlling CDOM transport, production and removal in this highly urbanized coastal area.
... The results of Kuwahara et al. [23] support other studies that show that chromophorically active concentrations of DOM and POC can significantly alter the amount of UV penetrating coral reef waters and may contribute to the regulation of intricate biogeochemical cycles surrounding benthic coral communities. Besides the attenuation caused by the water itself, CDOM is the major attenuator of UVR in oceanic and coastal waters with POC having a significant contribution also in some coastal areas [24,25]. CDOM has indeed been proposed as a mediator in climate-UVR interactions [26] as its filtering capacities are analogous to that of the ozone layer; this is CDOM absorbs more efficiently the shorter wavelengths UV-B radiation than UV-A [27]. ...
Global assessments of ultraviolet radiation (UVR) by the end of the 20th century indicated worldwide increases in UVR. While with the implement of the Montreal Protocol ozone-depleting substances are starting to decrease, studies in coral reef platforms have shown a 1% increase in UVR during the past two decades. Despite the exponential light attenuation in the water column, reef areas not exposed to a high sediment influx and other particulate and dissolved matter are continually exposed to high levels of Photosynthetically Active Radiation (PAR) and UVR. In the tropics, UVR is also enhanced due to the low solar zenith angle, shorter atmospheric path length and natural thinning of the ozone layer. Nonetheless, coral reefs and other associated marine ecosystems (i.e., mangroves and seagrasses) have thrived for millennia due to the evolution and development of UV-protecting mechanisms. In the case of reef corals, such mechanisms exist in the form of mycosporine-like amino acids (MAAs) thanks to their symbiotic relationship with unicellular photoautotrophic dinoflagellates known as zooxanthellae. Mangroves and seagrasses have a wide range of flavonoids which absorb in the UV region of the electromagnetic spectrum. Nonetheless, these organisms are still susceptible to physiological damages caused by UVR including DNA and protein damage, production of reactive oxygen species, and photo-oxidation of chlorophyll and other photosynthetic pigments. This chapter presents a summary of a series of experiments performed by researchers of the Bio-optical Oceanography Laboratory of the Department of Marine Sciences of the University of Puerto Rico aimed to study the effects of actual, lowered and enhanced levels of UVR on the shallow-water reef branching corals Acropora cervicornis and Porites furcata, the turtle grass Thalassia testudinum and the red mangrove Rhizophora mangle in La Parguera, Puerto Rico between 1997-2006. Our results show that slight increases in UVR can terminate the coral's reproductive process, reduce linear extension rates, skeletal density and photosynthetic pigments production, and increase MAAs concentrations while not necessarily affecting zooxanthellae densities within the coral tissue. Both species of macrophytes responded to ambient and increased levels of UV by changes in their photosynthetic and photoprotective pigments. Also, mangroves exposed to full solar radiation showed changes in leaf optical properties. Some of the responses observed in tropical coastal marine organisms indicate that under actual or enhanced UV scenarios most of the available energy is diverted into adaptive and survival strategies.
... Suspended Matter (TSM), and Yellow Substance (YS). The relevant SIOP coefficients were in this study obtained from ship borne data and the observed values generally fall within the ranges reported in the literature (Roesler et al. 1989, Bricaud et al. 1995, Nelson and Guarda 1995, Bowers et al. 1996, Høkedal 1999, Ferrari 2000, IOCCG 2000, Stedmon et al. 2000, Højerslev and Aas 2001, Babin et al. 2003, and Aas et al. 2005). However, the number of ship borne observations is low and the observed SIOP variability is high. ...
... The results of Kuwahara et al. [23] support other studies that show that chromophorically active concentrations of DOM and POC can significantly alter the amount of UV penetrating coral reef waters and may contribute to the regulation of intricate biogeochemical cycles surrounding benthic coral communities. Besides the attenuation caused by the water itself, CDOM is the major attenuator of UVR in oceanic and coastal waters with POC having a significant contribution also in some coastal areas [24,25]. CDOM has indeed been proposed as a mediator in climate-UVR interactions [26] as its filtering capacities are analogous to that of the ozone layer; this is CDOM absorbs more efficiently the shorter wavelengths UV-B radiation than UV-A [27]. ...
... Recent research has shown that CDOM controls the penetration and spectral distribution of solar radiation in freshwater [83,84] and marine systems, especially in regions close to the coast [48,[85][86][87][88][89][90]. The presence of CDOM can reduce UV exposure, but CDOM also attenuates the visible radiation required for photosynthesis. ...
Effects of increased UV-B on emissions of carbon dioxide and carbon monoxide (CO) and on mineral nutrient cycling in the terrestrial biosphere have been confirmed by recent studies of a range of species and ecosystems. The effects, both in magnitude and direction, of UV-B radiation on trace-gas emissions and mineral nutrient cycling are species specific and operate on a number of processes. These processes include changes in the chemical composition in living plant tissue, photodegradation (breakdown by light) of dead plant matter, including litter, release of carbon monoxide from vegetation previously charred by fire, changes in the communities of microbial decomposers, and effects on nitrogen-fixing microorganisms and plants. Long-term experiments are in place to examine UV-B effects on carbon capture and storage in biomass within natural terrestrial ecosystems. Studies in natural aquatic ecosystems have indicated that organic matter is the primary regulator of UV-B penetration. Changes in the organic matter, caused by enhanced UV-B reinforced by changes in climate and acidification, result in clarification of the water and changes in light quality that have broad impacts on the effects of enhanced UV-B on aquatic biogeochemical cycles. Increased UV-B has positive and negative impacts on microbial activity in aquatic ecosystems that can affect carbon and mineral nutrient cycling as well as the uptake and release of greenhouse and chemically reactive gases. Photoinhibition of surface aquatic microorganisms by UV-B can be partially offset by photodegradation of dissolved organic matter to produce substrates, such as organic acids and ammonium, that stimulate microbial activity. Modeling and experimental approaches are being developed to predict and measure the interactions and feedbacks between climate change and UV-B-induced changes in marine and terrestrial biogeochemical cycles. These interactions include alterations in the oxidative environment in the upper ocean and in the marine boundary layer and oceanic production and release of CO, volatile organic compounds (VOC), and reactive oxygen species (ROS, such as hydrogen peroxide and hydroxyl radicals). Climate-related changes in temperature and water supply in terrestrial ecosystems interact with UV-B radiation through biogeochemical processes operating on a wide range of time scales.
... CDOM contains humic and fulvic acids (Kowalczuk, 1999), associated with decomposition of vegetal tissue that provides a characteristic yellowish appearance. Humic and fulvic acids have been largely documented from inland sources, associated with terrigenous activity and therefore, when incorporated in the sea shows high salinity gradients (Nelson and Guarda, 1995). The origin of CDOM in coastal waters therefore may in some areas be river discharge, but in oceanic water away from the coastal zone, CDOM is probably entirely due to phytoplankton cell breakdown and zooplankton messy feeding . ...
This thesis presents a thorough critique of bio-optical models and the validity of the parameters used to describe the inherent optical properties (IOP) of the ocean that define model behaviour. The context of this critique is to assess the feasibility of coupling optical and ecosystem models so that the optical model can adequately predict the underwater light field. The study explores each step of the forward bio-optical-ecosystem model in case II waters. An available data set of optical measurements from the Irish Sea is used to evaluate the errors and uncertainty of measured optical properties, and to explore the sensitivity of the predicted radiance field to uncertainties in the model parameters.
The initialization of the bio-optical model is given by IOPs or concentrations of optically active constituents (OAC) and specific IOPs (SIOPs) derived from IOPs. Constituent concentrations and type determine optical water types. In this dataset, two distinctive water types are found in the region in different areas and seasons; chlorophyll dominated waters and mineral dominated waters. Uncertainty in IOPs and constituents are quantified in order to derive uncertainty ranges in SIOPs used in bio-optical models. Traditional SIOPs calculation significantly enlarges its apparent variability due to error propagation affecting the sensitivity of the bio-optical model. To overcome this, a new statistical method is presented which can reduce error propagation in the derivation of SIOPs from IOPs. The potential impact in reflectance of error propagation in optical modelling is studied for SIOPs obtained from both methods and a variety of water types.
Finally, predefined SIOPs values from literature are evaluated for the best optical description of the area. Real limitations are present when using literature values due to the lack of published data and in particular scattering and backscattering coefficients. Current definitions of constituent IOPs are also mismatched to those OAC found in ecosystem models and this prevents the feasibility of coupling forward optical modelling within ecosystem models. The conclusion is reached that further advances in the bio-optics field need to be made before such an approach is feasible, especially in the case of optically complex (Case II) waters.
... This relationship has also previously been reported (e.g. Nelson and Guarda, 1995;Vodacek et al., 1997). In our study, the distribution of the slope coefficient S as a function of a CDOM (375) demonstrated a robust relationship between the two parameters (Fig. 8). ...
Colored Dissolved Organic Matter (CDOM) is an important optical constituent in seawater, which significantly attenuates the violet to blue portion of visible light. Thus, CDOM reduces the radiation energy available to phytoplankton and affects remote-sensing signals. We present data from two cruises transecting the Polar Front from Atlantic to Arctic waters in the Barents Sea, in 2007 and 2008. The latter took place during the spring bloom of phytoplankton in May (0.2 < [Chl a] < 13 mg m− 3) and the former during August (max. [Chl a] < 2 mg m− 3). Absorption by CDOM at 443 nm ranged from 0.004 to 0.080 m− 1 during May and from 0.006 to 0.162 m− 1 during August. Surprisingly, CDOM absorption differed little across the Polar Front, but was higher during August than during May (P < 0.05). The slope coefficient of the absorption spectra (S) ranged from 0.008 to 0.036 nm− 1 (mean = 0.015 nm−1) including both cruises, and varied little across the Front (P > 0.05). The CDOM remote sensing product from GlobColour correlated well with sampled data (R2 = 0.73) during May. However, during August the satellite product performed poorly (R2 = 0.02) due to extensive scattering caused by coccolithophorids in the Atlantic Water. The CDOM pool was of autochthonous (marine) origin as characterized from its S vs. absorption relationship. Modeling showed that CDOM, on average, contributed equally to the light absorption as did phytoplankton (at 1 mg Chl a m− 3), and thereby reduces the amount of light available for primary production.
... Spatial changes observed in the ratio between a g (440) and a ph (440) were mainly due to the spatial changes observed in a g (440). The ratios at 443 nm in our study area are much higher than those reported for the west Florida shelf during summer (Nelson and Guarda, 1995); there they varied from 10 nearshore to about 1, approximately 100 km offshore. Similarly, the ratios in the Mississippi River plume ranged from 0.5 to 15 (Nababan, 2004 (personal communication)). ...
In situ measurements were used to study the bio-optical properties of
marine waters within the Gulf of Paria (GOP, Venezuela) and in the
Southeastern Caribbean Sea (SEC) as they are affected by the seasonal
discharge of the Orinoco River plume. The main purpose of this study was
to determine the impact of colored dissolved organic matter (CDOM) (also
known as Gelbstoff), phytoplankton, and total suspended matter (TSM) in
the color of the Orinoco River plume. This information is essential for
regional ocean color algorithms development. Salinity and silica values
indicate that the GOP and SEC waters were under the influence of the
Orinoco River plume during both seasons. This riverine influence
resulted in high values of Gelbstoff absorption, ag(λ), which
contributed to up to 90% of the total absorption at 440 nm in both the
GOP and SEC regardless of the season. Phytoplankton absorption
contributions were normally around 5%, but during the dry season these
values reached 20% in the SEC. Ratios of ag(440) to ph(440) were
extremely large, with most of the values ranging from 10 to 50. Due to
the strong absorption by Gelbstoff, light at the blue wavelengths (412
nm, 440 nm and 490 nm) was attenuated to 1% of the subsurface irradiance
in the first 5 m of the water column within the GOP, and in the first 10
m of the water column in the SEC. Furthermore, the absorption by
Gelbstoff significantly decreased the water leaving radiance
(Lw(λ)) in the blue wavelengths along the Orinoco River plume. As
ag(λ) relatively decreased from the GOP to the SEC (mean ~1.6 m-1
and mean ~0.9 m-1, respectively), a shift in the maximum peak of
Rrs(λ) spectra (Rrsmax(λ)), towards shorter wavelengths
(from ~ 580 nm to ~500 nm) was observed. Similar to Gelbstoff,
concentrations of TSM normally decreased from the stations near the
Delta to the stations in the SEC. The impact of TSM on the color of the
Orinoco plume was represented by a reduction in the magnitude of
Rrsmax(λ) of ~50% going from the waters near the Orinoco delta to
the SEC, indistinctively of the season.
... This represents the first report of the potential biogeochemical influence of the Rhône River plume in this oligotrophic coastal area. Such a strong significant inverse relationship between salinity and fluorescent/absorbant CDOM is typically observed in coastal areas subjected to high river inputs (Blough et al., 1993;Green and Blough, 1994;Nelson and Guarda, 1995;Højerslev et al., 1996;Nieke et al., 1997;Vodacek et al., 1997;Seritti et al., 1998;Del Castillo et al., 2000;Ferrari, 2000;Stedmon et al., 2000). ...
Surface waters from the Beaufort Sea in the Arctic Ocean were evaluated
for dissolved organic carbon (DOC), and optical characteristics
including UV (ultraviolet) radiation and PAR (photosynthetically active
radiation) diffuse attenuation (Kd), and chromophoric and
fluorescent dissolved organic matter (CDOM and FDOM) as part of the
MALINA field campaign (30 July to 27 August). Spectral absorption
coefficients (aCDOM (350 nm) (m-1)) were
significantly correlated to both diffuse attenuation coefficients
(Kd) in the UV-A and UV-B and to DOC concentrations. This
indicates CDOM as the dominant attenuator of both UV and PAR solar
radiation and suggests its use as an optical proxy for DOC
concentrations in this region. While the Mackenzie input is the main
driver of CDOM dynamics in low salinity waters, locally, primary
production can create significant increases in CDOM. Extrapolating CDOM
to DOC relationships, we estimate that ∼16% of the DOC in the
Mackenzie River does not absorb radiation at 350 nm. The discharges of
DOC and its chromophoric subset (CDOM) by the Mackenzie River during the
MALINA cruise are estimated as ∼0.22 TgC and 0.18 TgC,
respectively. Three dissolved fluorescent components (C1-C3) were
identified by fluorescence excitation/emission matrix spectroscopy
(EEMS) and parallel factor (PARAFAC) analysis. Our results showed an
aquatic dissolved organic matter (DOM) component (C1), probably produced
in the numerous lakes of the watershed, that co-dominated with a
terrestrial humic-like component (C2) in the Mackenzie Delta Sector.
This aquatic DOM could partially explain the high CDOM spectral slopes
observed in the Beaufort Sea.
... The majority of points that deviated from the mixing model were found at the highsalinity end of the mixing line. Field studies that present the distribution of the S in the function of a CDOM (λ) and salinity suggest that mixing is the dominant process that controls the distribution of the S values in the salinity gradient [22, 53, 56, 69]. The salinity at which a sudden increase in the spectral slope values is observed is called the inflection point [22]. ...
Dissolved organic matter (DOM) includes a broad range of organic
molecules of various sizes and composition that are released by all living and
dead plants and animals. Measuring the fraction of DOM that absorbs light (colored
or chromophoric DOM; CDOM) and fluoresces (referred to as CDOM fluorescence
or FDOM) at specific wavelengths is diagnostic of DOM source and amount. The
composition and dynamics of CDOM and FDOM across estuarine and coastal
mixing zones, eddies, upwelling, and nepheloid layers are discussed in relation to
the anomalies in physical (e.g., salinity and temperature), chemical (e.g., nutrients,
δ18O, dissolved oxygen), and biological properties (e.g., chlorophyll-a, primary
production) reported in the frontal zone. In situ observations using profiling sensors
and gliders, and remote sensing across coastal and oceanic fronts are described.
... Marginal seawaters with complex IOPs characteristics can generally be divided by hydrology parameters such as coastal fronts into coastal waters and shelf waters, for example, the division of the continental shelf of southeast US (Nelson and Guarda, 1995). The proportion of the three components independently presents temporal and spatial variations or with some co-variances reflecting variations in seawater components (Tassan, 1994;Kuwahara et al., 2000;Schofield et al., 2004). ...
The East China Sea (ECS), one of the largest continental seas, has dynamic hydrology and complex optical characteristics that make ocean color remote-sensing retrieval difficult. The distributions and proportions of the light absorption coefficients of major ocean color components based on two large-scale investigations in the ECS are presented, showing these features in typical summer and winter seasons. The absorption coefficient a
CDOM, a
NAP and a
phy of colored dissolved organic matter, non-algal particle, and pigment of phytoplankton show a decreasing trend from the coast to the outer shelf. According to the a
CDOM distribution at 440 nm, the Changjiang River plume shows an abnormal southeastward transport. An extremely high a
NAP value patch at 440 nm is present in the middle coast. The chlorophyll-a-specific phytoplankton pigment absorption (a
phy*) is much higher in winter than in summer, which may cause serious underestimated results when applying the averaged a
phy* into remote-sensing algorithms for chlorophyll concentration retrieval. The importance of phytoplankton size was evident in outer shelf waters. The absorption of a
CDOM(440) is a dominant component accounting for over half of the total seawater absorption in summer. The a
NAP(440) accounts for 64% of the absorption of the ECS coastal area in winter.
... We targeted 442 nm to compare the relative absorption of CDOM, detritus, and phytoplankton in order to determine the extent to which CDOM absorption of blue light interfered with the absorption of blue light by phytoplankton for photosynthesis. The choice of this specific wavelength was based on previous work by Nelson and Garda (1995) and Nelson et al. (1998), who used 443 nm, altered by 1 nm to match the 442 nm channel on our spectral radiometer. ...
We investigated spatial and temporal changes in spectral irradiance, phytoplankton community composition, and primary productivity in North Inlet Estuary, South Carolina, USA. High concentrations of colored dissolved organic matter (CDOM) were responsible for up to 84 % of the attenuation of photosynthetically available radiation (PAR). Green-yellow wavelengths were the predominant colors of light available at the two sampling sites: Clam Bank Creek and Oyster Landing. Vertical attenuation coefficients of PAR were 0.7–2.1 m−1 with corresponding euphotic zone depths of 1.5–6.7 m. Phytoplankton biomass (as chlorophyll a [chl a]) varied seasonally with a summer maximum of 16 μg chl a l−1 and a winter minimum of 1.4 μg chl a l−1. The phytoplankton community consisted mainly of diatoms, prasinophytes, cryptophytes and haptophytes, with diatoms and prasinophytes accounting for up to 67 % of total chl a. Changes in phytoplankton community composition showed strongest correlations with temperature. Light-saturated chl a-specific rates of photosynthesis and daily primary productivity varied with season and ranged from 1.6 to 14 mg C (mg chl a) −1 h−1 (32–803 mg C m−3 day−1). Calculated daily rates added up to an annual carbon fixation rate of 84 g C m−3 year−1. Overall, changes in phytoplankton community composition and primary productivity in North Inlet showed a strong dependence on temperature, with PAR and spectral irradiance playing a relatively minor role due to short residence times, strong tidal forcing and vertical mixing.
... The mean fall S NAP was 0.0105 6 0.0011 nm À1 , and the mean summer S NAP is slightly higher (0.0118 6 0.0008 nm À1 ; ANOVA, p < 0.01). Both averaged values for Hudson Bay are very close to those found by Bricaud et al. [1998] in Case 1 waters and Roesler et al. [1989], Nelson and Guarda [1995], Bowers et al. [1996], Ferrari et al. [2003], , and Matsuoka et al. [2011] in Case 2 waters. This shows that the mean S NAP varies little over broad geographic regions. ...
1] Previous studies have shown that the properties of optically significant water constituents (phytoplankton, suspended matter, and colored dissolved organic matter (CDOM)) in Hudson Bay are different from other Arctic regions. A new bio-optical data set collected in summer 2010 shows that this region also presents seasonal variability of the light absorption coefficients by the different constituents, with a higher relative proportion of CDOM absorption in summer than in the fall as a result of decreased phytoplankton absorption in summer. The slope of the exponential function describing nonalgal particles and CDOM spectral absorption shows little variability between fall and summer. Seasonal variability of light absorption coefficients and water optical constituents is more pronounced near the coast, while less variability is observed in the central part of the bay. Very low summertime chlorophyll-specific absorption coefficients by phytoplankton, among the lowest reported in the literature, are attributed to the high proportion of large size phytoplankton (microphytoplankton) and important packaging effect. There is also a smaller contribution of accessory pigments to total pigments in the summer than in the fall, resulting in a lower blue-to-red phytoplankton absorption ratio. These results emphasize that it is necessary to take into account the seasonal variability of light absorption properties in bio-optical models for further remote sensing applications in Hudson Bay.
... The absorption spectra of dissolved yellow substances was calculated according to the Equation (4), where S y is a shape factor (e.g., Bricaud et al., 1981 or Nelson andGuarda, 1995). a y (λ) = a y (400) e -Sy(λ-400) ...
There is presently an extensive long term data base of water quality parameters (http://www.ma.slu.se) for Lakes Vänern (1973-present), Lake Vättern (1966-present), and Lake Mälaren (1966-Present). These data were used to estimate variations in the concentrations of chloro- phyll, dissolved yellow substances, and suspended particulate inorganic material (SPIM) in the upper water layer of each lake, which were in turn used to drive a simple model of in-water optics which pre- dicted water leaving radiance reflectance. Simulations which randomly varied the optically active sub- stances based on their frequency distributions were used to produce synthetic data sets which realisti- cally simulated the variability in radiance reflectance and which could be used to examine the possible remote sensing algorithms which could be applied to each lake. Most accurate estimates of SPIM were obtained from a linear relationship with radiance reflec- tance at wavelengths greater than 600 nm (r2 value exceeding 0.9 in all lakes), The absorption of yellow substances at 420 nm (ay 420) was predictable by linear regression against a band ratio of a wavelength > 600 nm to a wavelength in the 400-580 nm range. (r2 value exceeding 0.8 in all lakes). However, in Lake Mälaren, the strongest ay algorithms were obtained when the numerator of the band ratio was within the phytoplankton pigment absorption peak between 600-700 nm. Estimation of chlorophyll de- pended on measuring a decrease in reflectance brought about by the chlorophyll absorption peak be- tween 660-680 nm. The ratio of a band at a wavelength greater than 700 nm to a band within the red chlorophyll absorption peak yields acceptable estimates of chlorophyll (r2 value exceeding 0.6 in all lakes). Simulations of radiance reflectance in the MERIS sensor bands showed that SPIM was best esti- mated from band 9 (705 nm). The concentrations of chlorophyll and ay(420) were best estimated from the band ratios 9/7 (705 nm/665 nm) and 7/3 (665 nm/490 nm) respectively. These results suggest that MERIS band 7 will play a crucial role in providing accurate estimate of chlorophyll and dissolved yellow substances in Swedish freshwaters.
... Similar S g ranges and variability have been reported for other oceanic waters (Table 3) Blough et al., 1993;Nelson and Guarda, 1995;Vodacek and Blough, 1997). Since S g is only weakly correlated with Chl (r 2 =0.09, n=385), the mean gelbstoff spectral slope, 0.019 nm -1 , is used together with the relationships in Eq. (20) to calculate a g (λ) (Eq. ...
Karenia brevis, a toxic dinoflagellate species that blooms regularly in the Gulf of Mexico, frequently causes widespread ecological and economic damage and can pose a serious threat to human health. Satellite-based ocean color imagery may provide a means for detecting and monitoring blooms, providing early alerts to coastal communities. However, a technique for discriminating K. brevis from other chlorophyll-containing algae is required. Between 1999 and 2001, a large bio-optical data set consisting of spectral measurements of remote-sensing reflectance (Rrs(lambda)), absorption (a(lambda)), and backscattering (bb(lambda)) along with chlorophyll a concentrations was collected on the central west Florida shelf (WFS) as part of the Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) and Hyperspectral Coastal Ocean Dynamics Experiment (HyCODE) programs.
Reflectance model simulations indicate that cellular pigmentation is not responsible for the factor of 3 to 4 decrease in Rrs(lambda) observed in waters containing greater than 10 4 cells 1 -1 of K. brevis. Instead, particulate backscattering coefficients measured inside K. brevis blooms are responsible for this decreased reflectivity as they were significantly lower than values measured in high-chlorophyll (>1 mg m -3), diatom-dominated waters containing fewer than 10 4 cells 1 -1 of K. brevis. A paucity of high-backscattering detritus present in K. brevis blooms caused by decreased grazing pressure perhaps due to cellular toxicity along with a general inability of K. brevis to out compete diatoms and bloom in high-nutrient, high-backscattering estuarine waters may explain this low backscattering. A classification technique for detecting high-chlorophyll, low-backscattering K. brevis blooms is developed.
In addition, a method for quantifying chlorophyll concentrations in positively flagged pixels using fluorescence line height (FLH) data obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) is introduced. Both techniques are successfully applied to Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and MODIS data acquired in late August 2001 and validated using in situ K. brevis cell concentrations.
... Light limitation, common in highly turbid and organic-rich estuarine and coastal waters, can limit primary production, and determine species composition and abundance of primary producers . Dissolved organic matter which is essentially a mixture of compounds that are produced by plant and animal decomposition, absorbs photosynthetically available radiation (PAR) 36 and indirectly controls primary production by determining the quantity and quality of light, available for photosynthesis (Nelson & Guarda 1995, Keble et al. 2005. ...
A towed, chemical sensor platform and a diver-based, automated imaging system were developed to characterize seafloor morphologies and coral architecture across centimeter to kilometer spatial scales and resolve sub-meter variability in ambient ocean chemistry across basin scale seascapes. Quantitative, thematic, water chemistry maps and benthic habitat mosaics were generated from high resolution underwater mass spectrometry and stereo, 3-D digital reef imagery. Integrated analysis of data from satellite sensors, SCUBA surveys, video sampling, and a moored observatory were used in concert to validate biogeochemical and structural comparisons of coral habitats surrounding Parque Nacional Coiba, a UNESCO World Heritage site in Pacific Panama.
... The photoreactive components of DOM are often collectively referred to as colored or chromophoric dissolved organic matter (CDOM), and are a major component of HMW-DOC (Nelson and Guarda 1995;Battin 1998). HMW-DOC is often strongly colored in systems markedly influenced by terrestrial inputs (Frimmel and Christman 1988). ...
UVirradiation of dissolved organic carbon (DOC) in the laboratory can producesmall, labile organic compounds utilizable by microbes, but few studies haveattempted to document this process in situ. 13Cnuclear magnetic resonance (NMR) was used to examine the bulk chemicalcomposition of natural and laboratory-irradiated high-molecular-weight DOC(HMW-DOC) from shaded (150 µmol m-2s-1 average light in surface water) and open (1500µmol m-2 s-1) field sitesoverone and a half years. 13C NMR revealed only small differences incarbon functional groups between laboratory irradiated and non-irradiatedHMW-DOC. However, bacterial protein productivity per cell (BPP) was enhanced innaturally irradiated samples of HMW-DOC in a field mesocosm experiment (p
... 2, which represents the surface and vertical distributions of salinity off Charleston , South Carolina, as observed during the 1984 pre- Spring Removal Experiment (pre-SPREX: Paffenhöfer et al. 1994). This evidence also was observed in recent hydrographic measurements taken on a cross-shelf transect off Savannah in the spring of 1994 (Nelson and Guarda 1995) and during a regional survey off the South Carolina coast in the summer of 1994 (Moore and Kje-C H E NFIG. 1. Continental shelf off the southeastern United States and the locations of ten rivers. ...
Physical processes that control the episodic cross-frontal transport over the inner shelf of the South Atlantic Bight were examined using a 3D primitive turbulent closure equation model. The model results showed that significant cross-frontal water exchange occurred under upwelling-favorable wind conditions through the de- tachment of isolated low-salinity lenses at the outer edge of the front. The formation of isolated lenses was a 3D feature associated with complex nonlinear processes. It depended on 1) the amount of multiple river dis- charges, 2) direction and magnitude of the wind, and 3) tidal mixing. As the total amount of river discharges increased, stronger winds were required to form the isolated lenses. When the river discharges were larger, tidal mixing tended to delay the occurrence of isolated lenses through 1) increasing the cross-shelf gradients of density and surface elevation and thus enhancing the along-shelf current and reducing the along-shelf variation of salinity, and 2) strengthening the internal stress at the bottom edge of the plume and thus slowing down the offshore water transport. The vertical salt diffusion, along-shelf and cross-shelf salt advections played a critical role in the detachment of the low-salinity water from the front. Upwelling significantly contributed to salinity increases near the coastal region in the early wind stages and the lenses' intensification in the midshelf. After the wind subsided, the eddylike circulation developed over the midshelf through adjustment of currents to surface elevation. The residence time of these eddies depended on the initial strength and location of isolated lenses. In the midshelf, where tidal mixing was relatively weak, these eddies could last about one week. In the inner shelf, where the depth was less than 20 m and tidal mixing was stronger, their lifetimes were less than one day.
The research was carried out based on the results of measuring the concentration of chlorophyll- a ( TChl - a ), spectral coefficient of light absorption by phytoplankton, non-algal particles (NAP) and colored dissolved organic matter (CDOM) in the southern part of the Sea of Azov in different seasons from 2016 to 2020. New data for the Sea of Azov on the variability of the spectral coefficient of light absorption by all optically active components have been obtained. A high (more than an order of magnitude) variability of all studied parameters was shown. The seasonal dynamics of TChl - a shows maxima in winter and summer. A relationship between the phytoplankton absorption and TChl - a has been revealed, which is described by a power function. Significant seasonal differences (two or more times) between the coefficients in the equation for parametrization of light absorption by phytoplankton were revealed. The NAP and CDOM light absorption were parametrized, the ranges of variability of the absorption
coefficient and the exponential slope were revealed, and their seasonal dynamics was shown. Annual variability of absorption coefficient of NAP and CDOM was opposite to the annual cycle of TChl - a . The NAP and CDOM absorption coefficients increased after phytoplankton blooms, when TChl - a decreased. The relative contribution of phytoplankton, NAP, and CDOM to the total absorption by particles and dissolved matter at 440 nm varied significantly over the year. The share of phytoplankton was maximum in winter and summer, while in spring and autumn the maximum contribution to absorption was made by CDOM and NAP.
Beginning systematically with the fundamentals, the fully-updated third edition of this popular graduate textbook provides an understanding of all the essential elements of marine optics. It explains the key role of light as a major factor in determining the operation and biological composition of aquatic ecosystems, and its scope ranges from the physics of light transmission within water, through the biochemistry and physiology of aquatic photosynthesis, to the ecological relationships that depend on the underwater light climate. This book also provides a valuable introduction to the remote sensing of the ocean from space, which is now recognized to be of great environmental significance due to its direct relevance to global warming. An important resource for graduate courses on marine optics, aquatic photosynthesis, or ocean remote sensing; and for aquatic scientists, both oceanographers and limnologists.
Optical properties of dissolved organic matter (DOM) were used as an indicator of the quantitative and qualitative changes occurring in marine DOM. The spatiotemporal distribution, bioavailability, and photoreactivity of chromophoric DOM (CDOM) and dissolved organic carbon (DOC) were investigated in the East China Sea (ECS) and the Yellow Sea (YS) during spring and summer using absorption spectroscopy and fluorescence excitation-emission matrix–parallel factor analysis. Over a 4-month laboratory study, we measured changes in six commonly used optical indices, including spectral slope (S275–295), slope ratio (SR: S275–295/S350–400), specific ultraviolet absorbance (SUVA254), ratio of the sum of protein-like components to the sum of humic-like components (Cprotein/Chumic), biological index (BIX), and humification index (HIX) to determine their changes following biological and photochemical degradation processes. Significant seasonal variations were observed in the spectral characteristics of CDOM in the ECS and the YS, indicating a stronger influence of the terrestrial origin and highly aromatic content of DOM in summer than in spring; this result was likely the consequence of an increase in the Changjiang River discharge, phytoplankton production, and biological activity, resulting in an increase in DOM production. Significant correlation between salinity and optical parameters (SUVA254, S275–295, S350–400, Cprotein/Chumic) indicated that water mixing strongly influenced the distributions of these optical parameters. The bioreactivity and photoreactivity of DOM varied depending on the source material, and the autochthonous protein-like DOM was more prone to biodegradation than the terrestrial DOM. The photodegradation processes acted preferentially on the CDOM than the colorless DOM. These results demonstrated that the optical parameters exhibited distinct changes during the mixing and the biodegradation and photodegradation processes and explained the seasonal distribution of DOM in the ECS and the YS.
The distribution patterns of Chromophoric Dissolved Organic Matter (CDOM) and the chemical characteristics of CDOM in the Seomjin river estuary were investigated in March, June and July 2012 in order to determine the spatial and temporal variability of CDOM along the salinity gradient considering the effects of mixing, nutrients and Chl a. The average CDOM values were 1.0 ± 0.3 m -1 , 1.3 ± 0.4 m -1 , and 1.4 ± 0.3 m -1 in March, June and July, respectively. A high concentration of CDOM (greater than 1.5 m -1 ) was found at the head of the river which decreased towards the river mouth to as low as less than 0.5 m -1 . The average concentrations of CDOM increased from the dry season (March and June) to the wet season (July), and the average slope values (S 300-500 ), which were used as indicators of CDOM characteristics and sources, were in the range of 0.013 - 0.018 ㎚ -1 . The CDOM and S 300-50 values showed that not only the concentration of CDOM but also the chemical properties of DOM clearly changed between upstream and downstream in the Seomjin river. CDOM and FDOM showed a negative correlation with salinity (R² ＞ 0.8), and CDOM was positively correlated with FDOM. Furthermore, the mixing pattern of CDOM was confirmed as conservative for all seasons. The main environmental factors influencing the concentration of CDOM was confirmed as conservative for all seasons. The main environmental factors influencing the concentration of CDOM were salinity (mixing) and water temperature, which meant the dilution of low CDOM seawater, was the controlling factor for the spatial distribution of CDOM. Increases in water temperature seemed to induce the production of CDOM during summer (June and July) through the biological degradation of DOM either by microbial activity or photo-degradation.
The main objective of the present study is to test various methods for describing the absorption spectra of coloured dissolved organic matter (CDOM) and to determine the numerical values of some optical parameters of CDOM in lakes with diverse water quality. First, the parameters of an exponential model in different spectral intervals were determined. In addition, the suitability of some other models for the approximation of CDOM spectra was estimated. Specific absorption coefficients of CDOM were calculated from the absorption coefficients and dissolved organic carbon (DOC) concentrations. The experimental initial data were differences between spectral attenuation coefficients of filtered and distilled water. Two datasets were used: 1) for 13 Estonian and 7 Finnish lakes (altogether 404 spectra between 350 and 700 nm) measured by the Estonian Marine Institute (EMI); 2) for 10 Finnish lakes (73 spectra) measured by the Finnish Environment Institute (FEI).
The spectra of CDOM absorption coefficients (aCDOM) were calculated from experimental data taking into account the correction due to scattering properties of colloids in the filtered water. The total content of CDOM in natural waters of Estonian and Finnish lakes was expressed by means of aCDOM at the wavelength of 380 nm. It varied significantly, from 0.71 to 19.5 m−1, the mean value (of all the investigated lakes) being around 6.6 m−1. Slopes of the exponential approximation varied widely, from 0.006 to 0.03 nm−1. Averaged over all lakes values of slope for the interval 380-500 nm obtained from the EMI dataset are close to those obtained from the FEI dataset: from 0.014 nm−1 (without correction) to 0.016-0.017 nm-1 (with different types of correction). These results are in good correspondence with most published data.
Attempts to describe the spectra in the region of 350-700 nm by means of hyperexponential functions (∽ exp(-αλη)) show that: (1) η < 1 (in the case of traditional exponential approximation η = 1); (2) a promising idea is to seek the best fit only for wavelengths λ > λ1, where λ1 will be chosen taking into account the real shape of aCDOM spectra.
The mean value of the specific absorption coefficient (a*CDOM) at the wavelength 380 nm obtained in this study (0.44 L mg−1 m−1) is close to the values published in the literature, if we assume that a*CDOM (380) is calculated using the data of dissolved organic matter (DOM). The optically non-active fraction of DOM in our study was high and therefore a*CDOM (380) was considerably higher (1.01 L mg−1 m−1) than a*CDOM (380).
The results of the present work could be used in the modeling of underwater light field as well as in the interpretation of radiation measurements and optical remote sensing results.
Colored dissolved organic matter plays an important role in determining the optical properties of seawater in coastal ocean. Based on the data collected at about 908 stations in China offshore, variations is investigated in the spectral absorption of colored dissolved organic matter at 440 nm (a g(440)). Higher values of a g(440) are observed in closed or semi-closed bay waters and estuarine waters. The contribution of colored dissolved organic matter to total seawater absorption at 440 nm shows the opposite distribution with that of a g(440).
Beginning systematically with the fundamentals, the fully-updated third edition of this popular graduate textbook provides an understanding of all the essential elements of marine optics. It explains the key role of light as a major factor in determining the operation and biological composition of aquatic ecosystems, and its scope ranges from the physics of light transmission within water, through the biochemistry and physiology of aquatic photosynthesis, to the ecological relationships that depend on the underwater light climate. This book also provides a valuable introduction to the remote sensing of the ocean from space, which is now recognized to be of great environmental significance due to its direct relevance to global warming. An important resource for graduate courses on marine optics, aquatic photosynthesis, or ocean remote sensing; and for aquatic scientists, both oceanographers and limnologists.
More than 1500 water samples were taken from the Kattegat, the Skagerrak and adjacent waters. The value of the absorption coefficient of yellow substance at 310 nm was found to vary from 0.06 to 7.4 m-1 in the open coastal waters, with a mean value of 1.3 m-1. The corresponding wavelength-averaged value (250-450 nm) of the semilogarithmic spectral slope of the coefficient ranges from 0.008 to 0.042 nm-1, and the mean value is 0.023 nm-1. Closer to river discharges, as in the fjords, the values of the slope seem to be more constant at around 0.0175 ± 0.0015 nm-1. In this area the slope must then be known in order to compare absorption at different wavelengths or to model the yellow substance absorption.
This chapter presents a discussion on chromophoric dissolved organic matter (DOM) in the coastal environment. Over the past decade, there has been a renewed interest in the properties and distribution of the major light-absorbing constituent of the DOM pool in natural waters (the 0.2 μm fraction). This material—referred in the past by various names such as Gelbstoff, yellow substance, gilvin, and humic substances) has more recently been provided the name chromophoric dissolved organic matter (CDOM). This designation more clearly highlights that this material absorbs not only visible light but also light in the UV-A (wavelengths from 315–400 nm) and UV-B (wavelengths from 280–315 nm), which are also part of the surface solar spectrum. By this definition—absorption at wavelengths over the range of surface solar radiation—CDOM represents only a portion of the total DOM pool. Although both “CDOM” and “humic substances” refer to the chemically complex, light-absorbing material produced by the decay of plant and algal matter, the use of “CDOM” is restricted to the material that is present in natural waters. However, the use of “humic substances” refers to material that is extractable from natural waters. This discrimination is necessary because the extracted materials are not always representative of those found in the original waters.
Dissolved organic matter (DOM) can be degraded by sunlight into a variety of photoproducts that stimulate the growth and activity of microorganisms in aquatic environments. All biologically labile photoproducts identified to date fall into one of four categories: (1) low-molecular-weight (MW) organic compounds (carbonyl compounds with MW of 20% of the bacterial carbon demand. Likewise, 30% of the bacterial nitrogen demand can be met by photodegradation of the nitrogen components of DOM, a process likely to be of particular importance in nitrogen-limited systems. When considered on a depth-integrated basis around the globe, at least 1.0
Relationships between optical and physical properties were examined on the basis of intensive sampling at a site on the New England continental shelf during late summer 1996 and spring 1997. During both seasons, particles were found to be the primary source of temporal and vertical variability in optical properties since light absorption by dissolved material, though significant in magnitude, was relatively constant. Within the particle pool, changes in phytoplankton were responsible for much of the observed optical variability. Physical processes associated with characteristic seasonal patterns in stratification and mixing contributed to optical variability mostly through effects on phytoplankton. An exception to this generalization occurred during summer as the passage of a hurricane led to a breakdown in stratification and substantial resuspension of nonphytoplankton particulate material. Prior to the hurricane, conditions in summer were highly stratified with subsurface maxima in absorption and scattering coefficients. In spring, stratification was much weaker but increased over the sampling period, and a modest phytoplankton bloom caused surface layer maxima in absorption and scattering coefficients. These seasonal differences in the vertical distribution of inherent optical properties were evident in surface reflectance spectra, which were elevated and shifted toward blue wavelengths in the summer. Some seasonal differences in optical properties, including reflectance spectra, suggest that a significant shift toward a smaller particle size distribution occurred in summer. Shorter timescale optical variability was consistent with a variety of influences including episodic events such as the hurricane, physical processes associated with shelfbreak frontal dynamics, biological processes such as phytoplankton growth, and horizontal patchiness combined with water mass advection.
The optics of chromophoric dissolved organic matter (CDOM) in the Greenland Sea were investigated and compared to results from earlier studies in the Southeastern North Sea. Absorption at 375 nm (a375) in the Greenland Sea varied from 0.77 m-1 to the detection limit of our instrument (0.05 m-1), with the highest values found during summer. The spectral slope coefficient (S) ranged from 8.2 to 26.4 μ m-1 with the highest values occurring during winter. Seasonal variations in the in situ production and degradation of CDOM where shown to be responsible for the trends seen. A negative correlation between S and a375 was evident in the Greenland Sea and differed noticeably from that found in coastal waters. The differing S-a375 behavior of CDOM known to be of terrestrial origin allowed the development of an algorithm for the differentiation between marine and terrestrial organic matter. The behavior of marine CDOM was modeled by S = 7.4 + 1.1/a375.
Dissolved and suspended materials in the ocean modify the in-water light field by absorbing and scattering photons. Direct measurement of inherent optical properties of individual optical constituents is difficult since the constituents themselves cannot all be separated. A model was developed to resolve in situ phytoplankton absorption from a measured in situ total absorption spectrum which includes water, dissolved organics, particulate detritus, and phytoplankton. The model was tested on a set of absorption spectra obtained from the productive waters around the San Juan Islands, Washington. Results indicate that the model can predict the spectral shape of phytoplankton absorption (rz > 0.9) and total photon absorption by phytoplankton with ~27% error. Total photon absorption can be used to estimate phytoplankton absorption of light energy for improved primary production predictions, given submarine light field measurements or model calculations. Although developed for high chlorophyll waters, the model parameters are easily modified for vario&Casc 1 optical domains.
A three-component model of ocean colour is presented, that takes into account contributions of phytoplankton, non-chlorophyllous particles and dissolved organic matter. The model is based on theoretical considerations and is validated by comparison with observed reflectance spectra. It is then used to address the problem of estimating chlorophyll concentration in coastal (case 2) waters by remote sensing. Principal component analysis is carried out on a large number of reflectance spectra simulated using the model. The results indicate the possibility of chlorophyll retrieval in at least some case 2 waters. Retrieval becomes difficult in waters where the signal from small quantities of chlorophyll is drowned in the noise from large quantities of non-chlorophyllous particles and dissolved organic matter. Non-chlorophyllous particles are the most easy to recover, while dissolved organic matter appears to be the most difficult. The non-linearity of the system limits the possibility of a single algorithm to cover all ranges of variation. It appears possible to pass from full spectral data to five selected wavelengths without any loss in the retrieval efficiencies. The use of 400 nm-channel data in the algorithm, in addition to the data from the usual 440, 520 and 550nm channels, considerably increases the possibility of distinguishing phytoplankton from dissolved organic matter.
A major objective of biological oceanography today is to quantify the mean and the variance of phytoplankton production on a global basis. Synoptic satellite sensing of the world's ocean is essential to this effort which requires contemporaneous sea surface data to provide complete water column information. Toward these objectives we present a spectrally dependent bio-optical model for the computation of in situ phytoplankton production. Using this model we show that in situ phytoplankton production can be accurately estimated from measurements of incident spectral irradiance and phytoplankton pigment concentrations. We also present estimates of photosynthetically absorbed radiation as a function of wavelength for a natural phytoplankton population. These complete spectral data provide insight into the wavelength-dependent utilization of radiant energy by phytoplankton and the influence of phytoplankton on the optical properties of the water column. We show that the model can be used for shipboard observations and that it may be especially useful for predicting production rates from data provided by untended buoys.
Absorption coefficients of total particulate (biogenous) matter were determined in the mesotrophic waters of the Peruvian upwelling and the oligotrophic waters of the Sargasso Sea. A method based on spectral criteria was used to partition these coefficients into absorption by living algal cells and by nonalgal (mainly detrital) material. This method was tested by independently measuring absorption by nonalgal material for samples from the Sargasso Sea.
The average Chl‐specific absorption coefficients measured in the Sargasso Sea are significantly higher than in the Peruvian upwelling and also higher in the surface layer than in the deep Chl maximum layer. These systematic variations appear to be mainly due to differences in sizes and intracellular pigment concentrations of the cells, inducing differences in the amplitude of the package effect.
Spectral measurements of downwelling and upwelling daylight were made in waters different with rcspcct to turbidity and pigment content and from these data the spectral val- ues of the reflectance ratio just below the sea surface, R( x ), were calculated. The experi- mental results are interpreted by comparison with the theoretical R(h) values computed from the absorption and back-scattering coefficients. The importance of molecular scattering in the light back-scattering process is emphasized. The R(X) values observed for blue waters are in full agreement with computed values in which new and realistic values of the absorp- tion coefficient for pure water are used and presented. For the various green waters, the chlorophyll concentrations and the scattering coefficients, as measured, are used in compu- tations which account for the observed R(X) values. The inverse process, i.e. to infer the content of the water from R( x ) measurements at selected wavelengths, is discussed in view of remote sensing applications.
The variability of the absorption ( a *), attenuation ( c *) and scattering ( b *) coefficients per unit of chl a concentration has been investigated in the range 34.0–740 nm for nine species of phytoplankton from diverse classes. The experimental results are compared to the predictions of a previously presented model. Using the a *(λ) values, the size distribution of the suspension and the central value of the refractive index as input parameters, the model provides the spectral values of the efficiency factors for attenuation and scattering. This model, developed for sphencal homogeneous cells, accounts for the large variations observed for c * and b *, whilst the ‘package effect’ accounts for those of a *. For the studied species, the influence of the cell shape and of the internal structures on c * and b * does not appear crucial. From the theory/experiment comparison, a bulk refractive index can be deduced for each phyloplankter. This index is shown to be consistent with the water content and dry matter composition of the different algal classes as deduced from published data, and more surprisingly to covary with the intracellular chl a concentration of cells.
A reflectance model developed to estimate chlorophyll a concentrations in the presence of marine colored dissolved organic matter, pheopigments, detritus, and bacteria is presented. Nomograms and lookup tables are generated to describe the effects of different mixtures of chlorophyll a and these degradation products on the R(412):R(443) and R(443):R(565) remote-sensing reflectance or irradiance reflectance ratios. These are used to simulate the accuracy of potential ocean color satellite algorithms, assuming that atmospheric effects have been removed. For the California Current upwelling and offshore regions, with chlorophyll a not greater than 1.3 mg/cu m, the average error for chlorophyll a retrievals derived from irradiance reflectance data for degradation product-rich areas was reduced from +/-61 percent to +/-23 percent by application of an algorithm using two reflectance ratios rather than the commonly used algorithm applying a single reflectance ratio.
Synechococcus WH7803 responded to growth irradiance between 30 and 2,000 µEinst m‒2 s‒1 by adjusting the cellular concentration of β-carotene but not zeaxanthin, β-carotene decreased from 0.68 to 0.15 fg cell‒1 with increasing light intensity and maintained a constant molar ratio with Chl a (0.24 β-carotene: 1 Chl a). The zeaxanthin concentration remained at 1.8 fg cell‒1. The responses of the two carotenoids are consistent with previous evidence that zeaxanthin and β-carotene are embedded in different membranes of the cell and that the bulk of carotenoids in cyanobacteria do not serve as photosynthetic light-harvesting pigments. In cells grown in high light, the concentration of zeaxanthin was significantly higher than either Chl a or phycoerythrin, indicating that a significant percentage of absorbed light was not photosynthetically active. The constant amount of zeaxanthin per cell may serve as a useful tool in quantifying Synechococcus abundance and growth in natural waters.
Abstract
Synechococcus WH7803 responded to growth irradiance between 30 and 2,000 µEinst m‒2 s‒1 by adjusting the cellular concentration of β-carotene but not zeaxanthin, β-carotene decreased from 0.68 to 0.15 fg cell‒1 with increasing light intensity and maintained a constant molar ratio with Chl a (0.24 β-carotene: 1 Chl a). The zeaxanthin concentration remained at 1.8 fg cell‒1. The responses of the two carotenoids are consistent with previous evidence that zeaxanthin and β-carotene are embedded in different membranes of the cell and that the bulk of carotenoids in cyanobacteria do not serve as photosynthetic light-harvesting pigments. In cells grown in high light, the concentration of zeaxanthin was significantly higher than either Chl a or phycoerythrin, indicating that a significant percentage of absorbed light was not photosynthetically active. The constant amount of zeaxanthin per cell may serve as a useful tool in quantifying Synechococcus abundance and growth in natural waters.
Data from 2872 hydrographic stations have been used to determine the oceanographic climatology of the southeastern US continental shelf waters. The data were sorted by each degree of latitude and by depth into three zones (0-20 m, 21-40 m, 41-60 m). Inner shelf water temperatures were similar to adjacent land air temperatures, while outer shelf temperatures were moderated by the Gulf Stream. Minimum and maximum water temperatures occurred in Georgia and South Carolina inner shelf water. Bottom temperatures were unusually low off Florida in the summer probably because of shelf break upwelling. Surface salinity was lowest adjacent to the rivers and reached minimums in the spring at the time of high runoff. An exception to this occurred in the fall, when strong southward winds apparently advected low salinity coastal water southward and offshore flow was restricted. Heat flux was calculated from changes in monthly mean depth-averaged inner shelf water temperatures. Heating occurred from March through July with maximum rates of 103 W m/sup -2/. Cooling occurred from October through February with maximum rates of -90 W m/sup -2/. Bulk stratification was estimated from the difference in near-surface and near-bottom monthly mean density. In the spring, stratification increases in inner shelf areas because of decreasing winds and increasing heat flux and runoff. By summer the whole shelf is highly stratified reflecting the contrast between high surface water temperatures and cooler bottom waters. Highest bulk stratification is found over the outer shelf. Stratification decreased with the approach of fall with the associated cooling and high winds. Mean flow at midshelf was northward and appears to be produced by an along-shelf slope of sea level of oceanic origin. 36 references, 12 figures, 1 table.
During March 1979 spectral absorptance for the suspended particles of the coastal waters of Baja California was determined by measuring the diffuse transmittance of filters containing the particles with a simply designed spectrophotometer. The absorptancc for the upper water of 20 stations varied by over an order of magnitude, but the spectra were generally similar in shape and indicated that phytoplankton pigments were the dominant absorbers. A region of major spectral change was found between 400 and 435 nm, where a shift in maxirnal absorptance toward shorter wavelengths was correlated with increased concentrations of phcopigmcnts relative to chlorophyll. A multivariate analysis of the data yielded two spectra for the specific absorptance in units of rn". mg pigment ' of those particles containing chlo- rophyll and those containing pheopigments. The specific absorptancc for chlorophyll-con- taining particles is compared with previous measurements in the field and laboratory; the specific absorptance for pheopigment-containing particles has not been measured before.
Methods are described for the measurement of spectral absorption coefficients, fluorescence excitation, and fluorescence yields for pigmented particles retained on filters. The corrections required for absorption coefficients include determining increased optical pathlength while corrections for fluorescence include determining system spectral variability, mean fight level and reabsorption. The empirical technique is consistent with and validated by theoretical relationships for light transmission and fluorescence of absorbing particulate material embedded in a medium with intense scattering. These methods were applied to a study of photoadaptation in several phytoplankton species and revealed variations in the blue for chlorophyll a specific absorption (a~h(~.)) and fluorescence excitation (F*(k)) of greater than 3- and 10-fold, respectively. Variations in the spectral shapes and the magnitude of a~h(Z) and F*(Z) with photoadaptation are determined largely by the effect of pigment absorption in discrete particles, sometimes referred to as the sieve or package effect. A model is presented expressing F*(Z) in terms of a*(Z) which predicts large variability in F*(k) due to cell size and cellular pigmentation and which may help reconcile the previously reported, but unexplained variations in F*(~,). Spectral variations in the fluorescence yield appear to be caused by variations in the fraction of light absorbed by photosystem II which fluoresces as compared to photosystem I or photoprotective pigments which do not fluoresce. The techniques presented provide a rapid, reproducible, and simple approach for routine analysis, particularly for field applications where particle densities are too low for direct analysis of absorption spectra.
The spectral irradiance distribution at five stations on lakes and at sea was measured with a portable underwater spectral irradiance meter. Chlorophyll a concentration and the absorption coefficient of the water were concurrently measured. From measured spectral irradiance distributions, radiant energy absorbed per unit volume was computed. At these stations, the effect of upward irradiance on total quanta absorbed by the water was negligibly small for all layers. The relative contributions of phytoplankton, detritus, dissolved organic matter, and pure water to the total absorbed quanta were also computed by taking into consideration the spectral dependency of each component: the contribution of quanta absorbed by the water was negligibly small for all layers. The relative contributions of phytoplankton, detritus, dissolved organic matter, and pure water to the total absorbed quanta were also computed by taking into consideration the spectral dependency of each component: the contribution of quanta absorbed by phytoplankton was about 3-10% in clear water and about 30-40% in the plankton-rich water.
Marine humic and fulvic acids were concentrated from about 1,400 liters of seawater from the Gulf of Mexico, and specific absorption coefficients were measured for each from 240 to 675 nm. Spectral absorption coefficients were then calculated for Gulf of Mexico stations where earlier data on humic and fulvic acid concentrations were available. Marine humic and fulvic acid values have low molecular weights consistent with extrapolations from soil-derived curves of their specific absorption coefficients vs. molecular weight. Marine fulvic and humic acids appear to account for most if not all water color or GelbstoK in the offshore regions of the Gulf of Mexico. Based on a remote-sensing reflectance model, it appears that the increase in the Gelbstoff: chlorophyll ratio for waters adjacent to and downstream from regions ‘of high primary productivity accounts for much of the deviation found for such waters from the global chlorophyll algorithm of the Coastal Zone Color Scanner.
Absorption spectra of several phytoplankton species were decomposed, after correction for the particle effect, to estimate in vivo absorption properties of the major light-harvesting pigments in algae. A Gaussian shape is suitable, theoretically and empirically, to represent the absorption spectra of individual photosynthetic components. The Gaussian parameters agreed well with the expected pigment compositions of 3 groups of algae, and the peak heights were linearly correlated with the concentrations of any one of the 4 major pigments measured in the samples. The linear relationship did not vary with phytoplankton species. We present here the first estimates of the 'true' in vivo specific absorption coefficients of 4 major pigments, after correction for particle effect. The results are used to reconstruct the in vivo absorption spectrum of a multi-species sample.
An extensive series of optical absorption spectra were recorded for waters in the eastern Caribbean Sea, the Gulf of Paria, and the Orinoco River Estuary during the high-flow period of the Orinoco River in the Fall of 1988. Evidence for high levels of dissolved, colored organic matter (COM) was found throughout the eastern Caribbean, with these levels increasing substantially at stations nearer the Gulf of Paria and the Orinoco River. The dependence of the absorption at 300 nm (a300) on salinity exhibited conservative mixing behavior for transects through the Gulf of Paria. In contrast, transects through the Orinoco Estuary revealed that a300 remained approximately constant or slightly increased with increasing salinity up to 27°/00 after which it decreased linearly with increasing salinity. This nonconservative behavior was not produced by COM release from suspended particulate matter at higher salinity, nor did it appear to originate from the sediment. Below 30°/00, the slopes of the log-linearized absorption spectra were independent of salinity (0.0140 nm-1). At higher salinities, the slopes apparently increased, suggesting that the COM is modified. Based on specific absorption coefficients measured for COM isolated from this area, COM input by the Orinoco River is estimated to be ~2.5×1012 g C/yr, which represents about 1% of the total global transport of dissolved organic carbon to the ocean. This input is likely to influence substantially the carbon cycle, photochemical properties, and optical characteristics of the waters in this region.
Natural fluorescence, dissolved silica and salinity were investigated as possible tracers to distinguish between piedmont river and coastal plain river waters discharged into the ocean off North Carolina and Georgia. In the Georgia study area, dissolved silica was not suitable for use as a tracer because silica concentrations were variable and did not mix conservatively with seawater. In the North Carolina study area, dissolved silica concentrations exhibited too much short-term variability for tracer use. In both areas, natural fluorescence was a suitable tracer. Additional investigations relevant to tracer application were made of the method for determining natural fluorescence; these include dependence on temperature of analysis, pH dependence, sample storage effect, sensitivity, correlation with total organic carbon and possible interferences from chlorophyll a, lignin sulfonates, detergents, petroleum and iron.
The nearshore frontal zone off the coast of Georgia was found to be an area of high phytoplankton and bacterioplankton abundance and activity. Phytoplankton and bacterioplankton populations on the seaward side of the frontal zone had significantly higher photosynthetic and heterotrophic potentials than the nearshore side of the front. Phytoplankton species composition changed across the front, verifying that the front is a barrier to cross shelf mixing. Nearshore, large chain forming diatoms dominated, while smaller single cell diatoms and cyanobacteria dominated the seaward side of the front. Increased bacterioplankton activity was found associated with phytoplankton photosynthetic activity. Light appeared to be the major factor controlling photosynthesis across the frontal zone. Nitrogen, phosphorus and silica were present in similar concentrations, well above levels that would limit photosynthesis, on both sides of the front. Therefore the outflow of nutrients from rivers or estuaries did not influence primary production directly.
Monthly cruises were conducted for one year to examine temporal and spatial variability in nutrients, chlorophyll, and the relative rate of photosynthesis of the <10 μm and total size fraction along a cross-shelf transect off Savannah, Georgia. Additionally, an upwelling event on the outer shelf was examined in some detail to determine its effect on primary production, phytoplankton species composition, nutrient and chlorophyll concentrations. Our results show that chlorophyll concentrations are always high (1.9–8.0 μ l−1) close to shore with little cruise-to-cruise variability. At offshore stations (>20–30 km) nutrients and chlorophyll concentrations were generally low (nitrate <0.1 μm, chlorophyll <1.0 μg l−1). The outer shelf (c. 100 km offshore), however, exhibited considerable variability. When we found upwelling at the shelf break, chorophyll a concentrations at the surface were as high as 6.0 μg l−1. At other times surface chlorophyll at the same locations averaged 0.1–0.2 μg l−1 with nitrate concentrations <0.1 μm. Phytoplankton >10 μm dominated the near shore stations. The <10 μm fraction dominated the phytoplankton of the mid and outer shelf, except during upwelling when diatoms such as Skeletonema costatum and Asterionella japonica were found in high abundance. Our study shows that phytoplankton abundance exhibits little seasonal variability in the Georgia Bight, but that upwelling events induce high frequency (days to weeks) variability on the outer shelf.
Absorption and total scattering coefficients of four phytoplankton species grown in batch cultures were measured simultaneously. Backscattering coefficients were obtained by using an integrating sphere. These coefficients are transformed into specific coefficients, i.e. related to a unit of concentration in chlorophyll a, and also into dimensionless efficiency factors characteristic of the cells. The specific coefficients differ noticeably from one species to another. Total scattering and backscattering coefficients are clearly depressed near and inside the absorption bands. These minima can be interpreted by combining the theory of anomalous dispersion with Mie‐Lorentz theory applied to polydisperse suspensions. The backscattering efficiency (ratio of backseattering to total scattering) of algal cells appears to be very low (typically <0.1%). These different results must be taken into consideration when interpreting and modeling the optical properties of seawater, particularly ocean color. They also must be considered when modeling photosynthesis, since the variations in the light‐harvesting ability of the cells intervene directly in the quantum yield estimate.
A provisional analysis of satellite ocean color imagery and in situ profiles of spectral irradiance and Chl a fluorescence partitions the Northeast Pacific Ocean into four geographically and bio-optically distinct provinces the California Current system, the Alaskan gyre, the east central North Pacific central gyre, and the subarctic front. Within each province in a given 2-month period (June-July 1985 and October-November 1982), a family of regression equations was found to accurately predict the vertical profiles of irradiance attenuation and normalized Chl a fluorescence from K490 - the surface diffuse attenuation coefficient which can be estimated from remotely sensed ocean color. -from Authors
We present four lines of evidence consistent with the suggestion of Gieskes and Kraay that the < 1‐ µ m particles observed in North Atlantic seawater associated with the carotenoid zeaxanthin are cyanobacteria ( Synechococcus spp.). First, four quite different clones of marine Synechococcus contain zeaxanthin as their main carotenoid (50–80% of total carotenoids). Second, none of the other ultraplankters we have yet studied contains more than traces of zeaxanthin, though they contain other pigments potentially useful as chemosystematic markers. Third, none of these other “diagnostic” carotenoids was reported by Gieskes and Kraay. Fourth, the latitudinal gradient of zeaxanthin reported correlates well with our observations of the abundance of Synechococcus, but not of other ultraplankters in the North Atlantic. The circumstantial evidence is strong and merits direct confirmation.
Spectral values of absorption of light by dissolved organic matter were measured in samples originating from diverse parts of the ocean, quite different with respect to pigment and par- ticle content. The use of llO-cm cells and then of lo-cm cells, with a highly sensitive spec- trophotometer, allowed measurement throughout the UV-visible range (200-700 nm) even for the low concentrations of yellow substance encountered in the open sea. The concentra- tion appears influenced predominantly by natural and industrial land discharges. In oceanic waters, it remains low and seems to be related to the biological activity averaged over a long period rather than to the local and temporary phytoplankton content. However, even at such low concentrations, yellow substance in the open sea may have an effect on absorption and hence on ocean color similar to that of low or moderate algal biomass. The spectral depen- dence law of absorption appears to vary within a restricted range, and an average law can be considered representative of rapid measurements at one selected wavelength.
The magnitude and variability of the maximal quantum yield of photosynthesis were examined in the northwestern Sargasso Sea in April 1985. Maximal quantum yield was calculated from light-limited photosynthetic rates and spectrally-weighted absorption coefficients. The absorption by total particulates collected on a glass fiber filter was partitioned into two components, one associated with living phytoplankton and one associated with other absorbing particles. Two types of maximal quantum yield were calculated: one from the absorption by total particulates and one from the absorption by the phytoplanktonic component alone. Maximal quantum yield calculated from absorption by total particulates was low [0.014 to 0.071 mol C (mol photons)-1] and decreased as the proportion of absorption due to the non phytoplanktonic particles increased. The phytoplanktonic maximal quantum yield was higher [0.033 to 0.102 mol C (mol photons)-1] and varied by a factor of two over a period of two weeks during and following a spring bloom. Use of the phytoplanktonic component of absorption to calculate maximal quantum yield allowed analysis of changes in maximal quantum yield as a function of changes in phytoplankton physiology rather than changes in the amount of absorption by particulate detritus. The pattern of variation in quantum yield was related to nitrogen flux; these data suggest that maximal quantum yield can be predicted from environmental conditions on a regional or seasonal basis.
Rates of degradation of phytoplankton chlorophylls and carotenoids under visible light exposure were determined in laboratory experiments. Killed phytoplankton cells and copepod fecal pellets were used as sources of pigments. Chlorophylls, pheopigments and carotenoids were analyzed by HPLC. Experiments included aerated and N2 bubbled treatments (light and dark), and in one experiment, killed phytoplankton cells were aged in darkness for 5 days in the presence of an active bacterial population prior to exposure to light. Pigment bleaching in solution was also examined. Pigment degradation was light- and oxygen-dependent and showed apparent first-order kinetics with respect to light exposure. The chlorophylls, pheopigments and major carotenoids bleached at similar rates. Pigments in killed cells bleached faster than the pigments contained in copepod fecal pellets, perhaps due to a higher effective light dose for the smaller particles and to differences in the structural organization of pigments in killed cells versus fecal pellets. Light-dependent degradation of pigments in aerated organic solutions varied with solvent composition. In pure acetone, carotenoids and chlorophylls bleached at similar rates. In acetone:water mixtures, carotenoids were considerably more stable than chlorophylls. A sensitized mechanism of pigment photooxidation could account for the apparent coupling of light-dependent degradation of different pigment types in detrital particles and in acetone solution. In detrital particles such as fecal pellets, sensitized photooxidations may be enhanced by the localized concentration of detrital pigments and other lipophilic material within hydrophobic microenvironments.
A modified opal-glass technique was developed for the determination of the specific absorption spectrum of natural phytoplankton. Glass fiber filters were used to collect suspended particles. The absorption spectrum was determined before and after the extraction of pigments by methanol. This technique was evaluated using phytoplankton cultures and seawater samples containing various kinds of particles other than phytoplankton cells. Specific absorption coefficients of phytoplankton (kc) were estimated from the spectrum of the modified opal-glass technique where the specific absorption coefficients determined directly in the original suspension were applied for correction. Averaged specific absorption coefficients (kc) were also derived.
Concurrent measurements of the spectral absorption coefficient and photosynthetic pigmentation of natural particulates were performed to determine the principal pigments responsible for the absorption of spectral irradiance in seawater. The spectral absorption coefficient, Ap(λ), was then analyzed by taking the second and fourth derivatives with respect to wavelength. The wavelength and magnitude of these derivative values provide useful information regarding the identification and quantification of phytoplankton pigments responsible for a given spectral signature. Linear relationships were examined and established between derivative values at selected wavelengths and concentrations of the major tetrapyrrole pigments, specifically chlorophylls a, b, and c. The correlation between derivative values near 526 nm and concentrations of photosynthetic carotenoids was poor and presumably caused by the broad absorption spectra of these pigments. A comparison of the measured particulate absorption coefficient with the absorption coefficient "reconstructed" for the phytoplankton component revealed that detritus can be a major source of light absorption. The method described here provides a rapid means of obtaining estimates of photosynthetic pigment concentrations in natural samples where absorption can be strongly influenced by detrital matter.
Visible light-dependent changes in the visible and near-ultraviolet spectral absorption (250750 nm) of phytodetritus (killed and disrupted phytoplankton and copepod fecal pellets) were determined in laboratory experiments, as were spectral changes due to the growth of bacteria. Bacteria carbon and nitrogen content were estimated. Results of the laboratory studies are compared to field measurements of particulate spectral absorption in waters from the South Atlantic Bight off the southeastern U.S. The correction for pathlength amplification of filtered particulate samples () is also examined. Light-dependent changes in the spectral absorption of phytodetritus are principally due to the bleaching of chlorophylls, pheopigments, and carotenoids. With bleaching of these pigments the residual phytodetrital absorption is due to more light-stable chromophores which absorb in the violet to near-ultraviolet. In the visible region, detrital-type absorption appears to represent the longer wavelength tails of absorption spectra which reach maxima in the ultraviolet. Extension of the spectral measurements to 250 nm revealed two general patterns. Biological macromolecules associated with phytoplankton, fresh phytodetritus and bacteria contribute to a broad maximum in absorption centered around 260 nm (likely due to nucleic acids and the aromatic amino acids of proteins). In the turbid near-shore waters of the South Atlantic Bight, detrital-type absorption showed a rather featureless, steady increase in absorption with decreasing wavelength, similar to typical DOM spectra, which may be due to relatively refractory particulate geomacromolecules (i.e., complex organics such as fulvic acids). Some near-surface field samples also indicated the presence of uv-photoprotective pigments associated with the phytoplankton community. Detrital type spectral absorption in the visible may be contributed by a variety of chromophores, some portion of which may be contained in heterotrophic organisms. The nature of the chromophores and particle types which constitute detrital-type absorption may differ between coastal and open ocean waters.
Spectral absorption coefficients and fluorescence quantum efficiencies were determined for humic substances from a variety of sources. Specific absorption coefficients kh, for humic substances at wavelengths λ from 300 to 500 nm can be closely described by the relation AeB(450-λ), where A and B are constants. When the kh values are in units of liter (mg organic carbon)−1meter−1 and wavelength λ is in nanometers, mean values of A and B for aquatic humus in the 12 water bodies studied were 0.6±0.3 and 0.014±0.001, respectively. Spectral absorption coefficients of dissolved organic matter in blackwater rivers, of the “yellow substance” in the sea, and of fulvic acids extracted from soils are very similar. Fluorescence quantum yields of humic substances were low and more variable than the absorption coefficients, ranging from 0.0005 to 0.012 with excitation at 350 nm (average of 0.0045±0.0038 for 6 waters). Fluorescence spectra for the humic substances were remarkably similar with maximum emission at 430 to 470 nm. Results of this study can be used to compute photolysis rates of pollutants as a function of depth in natural water bodies.
The concentration and distribution of particulate trace metals in waters of the South Atlantic Bight are controlled by cross-shelf advection of continentally derived inorganic detritus from nearshore sources and in situ biogenic particle production. Particulate trace metal flux across the outer continental shelf is mostly in organic particles. The flux of trace metals in terrigenous particles across the South Atlantic Bight is approximately as efficient as particle transport to the North Atlantic from the St. Lawrence discharge system. With the exception of Fe, the cross-shelf transport of trace metal in terrestrially derived particles is considerably less than the soluble transport of trace metals delivered to the South Atlantic Bight by rivers. The relative importance of particulate fluxes follows the order Fe>Mn>Pb>Co>Zn>Ni>Cd>Cu.
Primary production rates and concentrations of photosynthetic pigments were measured on 5 days during March and April 1987, at 26°N, 155°W in the North Pacific subtropical gyre. The primary production measurements were carried out using on-deck incubators with blue and blue-violet filters which simulated both the intensity and spectral characteristics of submarine light. Dawn-to-dusk production rates averaged 777±219 mg C m−2. The quantum requirements implied by photosynthetic rates measured near the base of the euphotic zone approached the theoretical minimum of 8 Ein mol−1C if the chlorophyll a-specific absorption coefficient () was assumed to equal 16 m2 g−1 Chl a. Both the absorption characteristics of extracted pigments and of particulate material collected on glass fiber filters indicated that was constant and equal to 16.0±1.6 m2 g−1 Chl a over the depth of the euphotic zone if submarine light were assumed to have the same spectral characteristics as surface light. When the spectral characteristics of submarine light were properly modeled, was found to increase by about a factor of three between the surface and approximately the 14% light level and to equal 44±7 m2 g−1 Chl a throughout the lower 75% of the euphotic zone. The dramatic difference in the ability of phytoplankton to absorb equal quantum fluxes of white and blue light implies that areal primary production rates can be underestimated by about a factor of two in the open ocean if incubations are conducted using surface light attenuated with neutral density filters.
A 3 year field study was conducted to investigate patterns, magnitude and variability of primary production; the abundance, biomass and composition of producers and consumers; and the relative importance of physical and chemical variables associated with these parameters, in inner shelf waters of the South Atlantic Bight. Discrete interval, time series and continuous measurements were made along a transect and at two process-oriented stations during summer and winter 1985–1988. A quasi-permanent density front constrains low salinity (<34‰) waters to within ca 10 km of the coast. These waters contain abundant autotrophic and heterotrophic communities. Primary production is high, 6–7 × 102gC m−2 year−1, and is apparently subsidized by rapid nutrient recycling in the water column, sediments and adjacent salt marshes. Silicate is notable for its excess concentrations year-round and supports substantial diatom productivity. Correlation analyses suggest that Si strongly influences phytoplankton biomass, whereas growth rates are coupled to availability of light and NH4. Despite evidence of considerable variability in primary production over daily to interannual scales, plankton biomass is relatively constant. Experimental studies suggest a tight coupling between primary producers and microconsumers, and support the hypothesis that substantial fractions of primary and secondary production are recycled within the water column.
A phycocyanin-rich cyanobacterium belonging to the genus Synechocystis has been adapted and grown under differing irradiances (PAR), ranging from 16 to 1450 μE m−2 s−1, and differing spectral compositions (“white”, “blue” and “green”). Chlorophyll-specific as well as carbon-specific spectral absorption and scattering coefficients were determined for all conditions. Due to drastic changes in chlorophyll and phycocyanin content per cell in response to the radiative level imposed to the culture, these coefficients undergo extreme variations, in a range wider than the inter-specific range already reported for eucaryotic algae. The optical dimensionless efficiency factors have been computed and used to calculate the bulk refractive index (in the range 1.05–1.06 with respect to the index of water). The optical properties of this picoplanktonic species is typical of “small” optical particles, with a scattering efficiency increasing towards the blue, and a backscattering efficiency increasing towards the red end of the spectrum. Superimposed on this pattern are features associated with the presence of pigments, including the phycocyanin signature. Although the cellular pigment concentrations are high (particularly at low irradiances), the package effect remains negligible. Thus Synechocystis is well suited for harvesting light, even if the presence of biliprotein appears to be useless in regards to the spectral quality of the light available in the deep layers of the euphotic zone.
Variability in concentration and type of marine particles is the dominant source of optical variability in the oceans. As part of the Optical Dynamics Experiment (ODEX) spectral absorption coefficients and fluorescence excitation were measured for marine particles sampled at stations in the California Current and the Eastern edge of the North Central Pacific Gyre. Chlorophyll a normalized fluorescence spectra [F∗ (λ)] or chlorophyll a plus phacopigment normalized absorption coefficients [] were analysed with regard to their spectral shapes and magnitudes.Comparison of absorption samples indicates large variability vertically (mixed layer vs deep euphotic zone), horizontally (nearshore vs central gyre) and seasonally (autumn vs spring). When compared to spectra for detritus and for healthy cultures, it is apparent that a variable fraction of the particulate absorption in he ocean is due to detrital components. The effects of absorption by discrete particles may also result in variations in the magnitude and spectral shape of . F∗ (λ) exhibited less variability than . Because F∗ (λ) appears to be a property of phytoplankton only, the principle causes of variability are photoadaptation and possible taxonomic changes in the phytoplankton crop.Because the origin of particulate organic material (POM) for these regions can be assumed to be derived from in situ biogenic processes, the deviation of field spectra from those observed for cultures must in large part bee to the previous history of biolgical dynamics within a particular water mass. Data presented here indicate that in situ or remote optical sensors may be capable of supplying information on algal physiology and ecosystem characterization including the extent of photoadaptation and the accumulation of small detrital particles derived from grazing.
Spectral absorption of phytoplankton from cultures and natural samples was measured on filters with various optical setups including collimated and diffuse irradiation and measurements of wetted filters within an integrating sphere. In suspensions within an integrating sphere, specific absorption coefficients for laboratory cultures varied by a factor of only two.
Measurements on filters yielded values dependent on filter load. Specific absorption coefficients derived from measurements of sample filters were considerably higher than values obtained from suspensions in an integrating sphere due to increased diffuseness of irradiance and to pathlength amplification by filter‐particle and particle‐particle interactions. Measured absorption of phytoplankton in the blue can be increased greatly by absorption of detritus, evident from absorption spectra of depigmented samples on filter. After subtracting detrital absorption, absorption spectra of phytoplankton are qualitatively similar to the corresponding quantum‐corrected fluorescence excitation spectra. The detritus‐corrected ratio of absorption at 440 vs. 675 nm shows average values between 1 and 1.5.
Comparison with published values shows that specific in vivo absorption coefficients of phytoplankton are mostly overestimated as a result of the methodology applied. In the blue region of the spectrum, overestimation of phytoplankton absorption in field samples is possible if detrital absorption is neglected.
The contributions of detrital particles and phytoplankton to total light absorption are retrieved by nonlinear regression on the absorption spectra of total particles from various oceanic regions. The model used explains more than 96% of the variance in the observed particle absorption spectra. The resulting absorption spectra of phytoplankton are then decomposed into several Gaussian bands reflecting absorption by phytoplankton pigments. Such a decomposition, combined with high-performance liquid chromatography data on phytoplankton pigment concentrations, allows the computation of specific absorption coefficients for chlorophylls a, b, and c and carotenoids. The spectral values of these in vivo absorption coefficients are then discussed, considering the effects of secondary pigments which were not measured quantitatively. We show that these coefficients can be used to reconstruct the absorption spectra of phytoplankton at various locations and depths. Discrepancies that do occur at some stations are explained in terms of particle size effect. These coefficients can be used to determine the concentrations of phytoplankton pigments in the water, given the absorption spectrum of total particles.
A time sequence of surface pigment images of the South Atlantic Bight (SAB), derived from the Nimbus 7 CZCS for the period between November 1978 and October 1979, was correlated with in situ observations of hydrographic parameters, fresh-water discharge, sea level, coastal winds, and currents in order to couple physical processes and the spatial and temporal variability of the surface pigment fields. A definite seasonal modulation of the surface pigment fields was found, with the concentrations in the Georgia Bight being highest in summer, and those north of Cape Romain highest in winter. This phase difference was found to be the result of variations in wind fields, Gulf Stream-shelf interactions, and fresh-water discharge patterns. At some locations (e.g., near Charleston) the alongshore band of high pigment concentrations increased in width throughout the year; at other locations (near Jacksonville), the alongsore band exhibited a minimum width in the summer and a maximum width in the fall of 1979.
An assessment is presented of the state-of-the-art of remote, (satellite-based) Coastal Zone Color (CZCS) Scanning of color variations in the ocean due to phytoplankton. Attention is given to physical problems associated with ocean color remote sensing, in-water algorithms for the correction of atmospheric effects, constituent retrieval algorithms and application of the algorithms to CZCS imagery. The applicability of CZCS to both near-coast and mid-ocean waters is considered, and it is concluded that while differences between the two environments are complex, universal algorithms can be used for the case of mid-ocean waters, and site-specific algorithms are adequate for CZCS imaging of the near-coast oceanic environment. A short description of CVCS and some sample photographs are provided in an appendix.