Fig 3 - uploaded by Helga do R. Gomes
Content may be subject to copyright.
Absorption budget for the southeastern Bering Sea through ternary plots of phytoplankton absorption (a PHY ( λ )), NAP absorption ((a PHY ( λ ))) and CDOM absorption (a CDOM ( λ )) at 412 nm, 443 nm, 560 nm and 676 nm for surface (black fi lled circles), middle 1 (black open circles), and middle 2 (black fi lled triangles) depths.
Contexts in source publication
Context 1
... examine the relative contributions of phytoplankton, NAP and CDOM absorption coefficients to total non-water absorption, the coef- ficients were displayed on a normalized ternary plot at wavebands that correspond to most ocean color sensors as well as wavebands at which the constituents show characteristic features (Fig. 3). Ex- cluding a few samples (e.g. stations near the Pribilofs), at all depths Fig. 2. Spatial distribution of the absorption budget at 443 nm for (a) surface and (b) middle 1 depths. Green, orange, and yellow represents phytoplankton, NAP, and CDOM percentage contribution, respectively, to total non-water absorption in the pie symbols. ...
Context 3
... blue to red ratio of a* PHY (λ) can be used as an indicator of Relation between chlorophyll-a and (c) quantification of package effect by a dimensionless factor at 676 nm (Q* a (676))), (d) spectral size parameter (S f ) calculated according to Ciotti et al. (2002). See Fig. 3 for symbols. phytoplankton size, with higher values (e.g., a* PHY (443)/a* PHY (676) > 3) known to be associated with smaller cells (Moore et al., 1995;Stramski & Morel, 1990). ...
Context 4
... 6. Speci fi c phytoplankton absorption (a* PHY ( λ )) (a) variability between 300 and 700 nm at surface (black solid line) and middle depths (green solid line), and (b) at 443 nm relation with chlorophyll-a. The regression fi t for surface only (dashed black line) and all depths (solid black line) are depicted. For comparison, the regression fi t from Bricaud et al. (1995) study (red solid line) is also shown. Relation between chlorophyll-a and (c) quanti fi cation of package effect by a dimensionless factor at 676 nm (Q* a (676))), (d) spectral size parameter (S f ) calculated according to Ciotti et al. (2002). See Fig. 3 for symbols.
...
Context 5
... λ ) modeled from discrete measurements of absorption without contribution from CDOM and modeled scattering. μ d was determined as the slope of the linear fi t between a T(ac-s) ( λ ) + b b(ECO) ( λ ) and K d ( λ ) obtained from BOP. Two values of μ d corresponding to the surface and middle depth samples were determined and used in the above equations. The μ d for the surface samples was 0.780 ± 0.013 (r 2 = 0.81; n = 107) and for the middle depths was 0.631 ± 0.013 (r 2 = 0.72; n = 97). μ d has been shown to vary between 0.8 to 0.65 from the surface to 1% light for b/a ratio of 4 and solar zenith angle of 30° (Bannister, 1974). The hydrographic structure, nutrients, and productivity in the Bering Sea during the in-situ sampling are described in detail else- where (Lomas et al., 2012; Mathis et al., 2010; Moran et al., 2012; Mordy et al., 2012; Stabeno et al., 2012a, 2012b). The shelf could be divided into 6 distinct zones based on hydrographic and biogeochemical characteristics. Across the shelf and the entire water column, a front extended along the 50 m isobath (inner front) while a second front was identi fi ed based on temperature at approximately the 100 m isobath (central front) on the MN and NP transects (not clear on the SL transect). These fronts divided the shelf into 3 domains – Coastal Domain, Middle Domain and the Outer Domain. Along the 70 m isobath, a broad transitional zone was present at 60 °N in hydrography (density and bottom water temperatures), nutrients and chlorophyll dividing the eastern shelf into northern shelf (60 °N and above) and southern shelf (below 60 °N). Over the northern shelf the ice melt in fl uenced the SL and MN transects creating a fresh water lens ~ 20 m deep seaward from the inner front. The spatial distributions of nutrients and productivity generally coincided with the frontal transition zones (Lomas et al., 2012; Moran et al., 2012; Mordy et al., 2012; Stabeno et al., 2012a, 2012b). Typical of the study region, the coastal domain was low in macronutrients but high in iron and the outer domain was high in macronutrients but low in iron. Production was high just below the pycnocline with intense subsurface chlorophyll fl uorescence maxima and subsurface supersaturation of oxygen (Stabeno et al., 2012a, 2012b). The appearance of chlorophyll fl uorescence maximum is common in the middle and outer domain (more intense in the northern shelf) of the study region during summer, where wind speeds are not ef fi cient enough in mixing the water column resulting in a two layer system observed during the study period (Stabeno et al., 2012b). The productivity was lowest in the coastal domain in both the northern and southern shelf, and highest in the middle domain of the northern shelf and middle- outer domain of the southern shelf (Lomas et al., 2012; Mathis et al., 2010; Moran et al., 2012). The surface distribution of absorption properties in the study area has been covered in detail in Naik et al. (2010). The distribution of the absorption budget in the surface and middle 1 depth clearly shows the dominance of a CDOM (443) (Fig. 2), except at stations located near the Pribilof Islands and St. Matthews Island where a PHY (443) was dominant, which is due to the enhanced production near the islands caused by interaction of tides and currents with bathymetry (Kachel et al., 2002; Stabeno et al., 2008). Patterns of a PHY (443) were similar to productivity (Lomas et al., 2012; Mathis et al., 2010; Moran et al., 2012) with the highest values near the Pribilof Islands of the southern shelf and along the central front in the middle domain, and the lowest values throughout the coastal domain. The a PHY (443) was higher in the middle depths relative to surface (ANOVA, p = 0.005) due to the in fl uence of subsurface chlorophyll maximum. Within a DG ( λ ), a CDOM ( λ ) was more dominant relative to a NAP ( λ ). Higher values of a CDOM (443) and a DG (443) (ANOVA, p = 0.007) were observed in the coastal domain of the northern shelf showing the in fl uence of Kuskokwim river runoff which is carried to the north by prevailing northern currents and constrained to the coast by the inner front. The inverse correlation between salinity and a CDOM (443) (p b 0.001) supports the contribution of river runoff to higher CDOM. The northern shelf (60 °N and above) showed a higher relative contribution from CDOM as compared to the southern shelf (below 60 N) (ANOVA, p = 0.003). The increase in contribution of a PHY (443) to total absorption was apparent going from surface samples to middle 1 depths, but the contribution of a CDOM (443) was still dominant at most stations (Fig. 2). To examine the relative contributions of phytoplankton, NAP and CDOM absorption coef fi cients to total non-water absorption, the coef- fi cients were displayed on a normalized ternary plot at wavebands that correspond to most ocean color sensors as well as wavebands at which the constituents show characteristic features (Fig. 3). Ex- cluding a few samples (e.g. stations near the Pribilofs), at all depths and wavelengths (except 676 nm) examined, a CDOM ( λ ) dominates the total non-water absorption coef fi cient followed by a PHY ( λ ) and a NAP ( λ ). This result is consistent with previous fi ndings (e.g. Belanger et al., 2006; Brown et al., 2008), where a high contribution of a CDOM ( λ ) at higher latitudes was observed. At 443 nm, where the chlorophyll-a absorption is maximum, a PHY ( λ )/ a T − W ( λ ), a NAP ( λ )/ a T − W ( λ ), and a CDOM ( λ )/ a T − W ( λ ) was 20%, 14%, and 66%, respectively for surface samples, 28%, 15%, and 57%, respectively for middle1 depth, and 19%, 16%, and 65%, respectively for middle 2 depth. The relative contribution of each component remains similar from the surface to below the chlorophyll-a maximum with the only noticeable change being the increase in a PHY (443)/ a T − W (443) and corresponding decrease in a CDOM (443)/ a T − W (443) at middle 1 depths. The CDOM contribution to total non-water absorption was generally dominant in the near ultraviolet region of the spectrum (380 nm – data not shown) and nearly null in the red region (676 nm). The highest relative contribution of a NAP ( λ ) to a T − W ( λ ) was at 560 nm and of a PHY ( λ ) to a T − W ( λ ) was at 676 nm. The relative contribution of a DG (443) was around 80% near the surface, which is slightly higher than the range (70% at 443 nm) of satellite estimates provided by Siegel et al. (2005) for the study region. The a PHY (443) and a P (443) ranged two orders of magnitude from 0.002 to 0.370 m − 1 and 0.007 to 0.420 m − 1 respectively, while a (443) and a (443) ranged one order of magnitude, 0.032 – 0.207 m and 0.057 – 0.520 m respectively, corresponding with a two orders of magnitude chlorophyll-a range of 0.04 – 32.30 mg m − 3 (Fig. 4). A non-linear relationship expressed as a power function applied between a PHY ( λ ), a P ( λ ), a DG ( λ ), and a T − W ( λ ) at 443 nm and 676 nm along with chlorophyll-a showed signi fi cant correlation, consistent with other studies (Table 2) (Bricaud et al., 2004; Cota et al., 2003). The relation between a PHY (443) and chlorophyll-a obtained for this study was similar to the Matsuoka et al. (2007) study for the Chukchi Sea and the western part of southern Beaufort Sea. For chlorophyll-a concentrations b 10 mg m − 3 , the a PHY (443) values in this study are lower than the values estimated using the middle and lower latitudes relationship of Bricaud et al. (1998) (a PHY (443) = 0.0378* chlorophyll-a 0.627 ), north polar Atlantic relationship during summer of Stramska et al. (2006) (a PHY (443) = 0.058*chlorophyll-a 0.575 ), Labrador Sea relationship of Cota et al. (2003) (a PHY (443) = 0.0402* chlorophyll-a 0.578 ) and higher than the values estimated by the western Arctic relationship of Wang et al. (2005) (a PHY (443) = 0.0151* chlorophyll-a 0.957 ). This suggests a need for a cautious approach towards generalization of bio-optical properties of polar and lower- latitude regions. The a PHY (443)/a P (443) ratio values ranged between 0.25 and 0.91, while a NAP (443)/a P (443) ranged between 0.11 and 0.75, and are within the ranges reported in literature from different regions (Bricaud et al., 1995, 2004; Cleveland, 1995). Despite this variability, a PHY (443) and a NAP (443) contributed on an average 62% and 38% respectively to a P (443), for samples at all stations and depths. The a DG (443) showed only a weak correlation with chlorophyll-a (Table 2, Fig. 4b). Within a (443), a ( λ ) showed a signi fi cant positive relation with chlorophyll-a, while a CDOM ( λ ) was poorly correlated with chlorophyll-a (Table 2). The weak correlation between a CDOM (443) and chlorophyll-a was also seen in other high northern latitudes studies (Matsuoka et al., 2007; Wang et al., 2005), which can be attributed to CDOM processes being out of phase with phytoplankton biomass or production and that most CDOM in this region is of terrestrial origin. The a T − W (443) correlated well with chlorophyll-a despite the weak correlation between a DG (443) and chlorophyll-a (Fig. 4c, Table 2). The relationships between ratios of a PHY (443), a CDOM (443) and a DG (443) to a T − W (443) and chlorophyll-a show the relative contribution of each of these components to total non-water absorption in relation to phytoplankton biomass (Fig. 5). The a PHY (443)/ a T − W (443) ratio increased with increasing chlorophyll-a with large variability at chlorophyll-a b 1 mg m − 3 (Fig. 5a). The a CDOM (443)/ a T − W (443) ratio decreased with increasing chlorophyll-a, emphasizing that as phytoplankton biomass increases, a CDOM (443) becomes less important relative to the a P (443) in a T − W (443) (Fig. 5b). The inverse relation between a DG (443)/a T − W (443) and chlorophyll-a was not as strong as between a CDOM (443)/a T − W (443) ratio and chlorophyll-a and was relatively constant up to chlorophyll-a value of 5 mg m ...
Citations
... In this way, IOPs provide the required information concerning ocean processes and characteristics that are of utmost importance from biological and bio-geochemical perspectives. In this context, remote-sensing reflectance [R rs (λ)] is intricately linked to IOPs, specifically the total spectral absorption coefficient [a t (λ)], rather than being directly associated with the optically significant constituents of seawater (Arabi, 2019;Favareto et al., 2018;Naik et al., 2013). Against this background, exploring the relationships between IOPs and R rs (λ) can boost up the quality of satellite-derived IOPs. ...
In this study, the absorption coefficients of phytoplankton community (aPh(λ)), Colored Dissolved Organic Matter (CDOM) [aCDOM(λ)], and Non-Algal Particles (NAP) [aNap(λ)] were analyzed in the northern Persian Gulf, a Mediterranean-type semi-enclosed marginal sea, through seven cruise expeditions conducted from May 2018 to February 2022. The highest and lowest aPh(443) values were observed in the shallow area (depth ≤20 m) during the wet season (November–April) (0.043 ± 0.004 m-1) and within the deep area (depth >20 m) through the dry season (July–September) (0.024 ± 0.003 m-1), respectively. The chlorophyll-specific absorption (a*Ph(λ)) values increased from the deep to shallow areas as well as the wet to dry seasons. A significant difference was further detected in a*Ph(λ) magnitude at the blue (443 nm) and red (675 nm) wavelengths, with the mean values of 0.0124/0.0223 m2 mg−1 and 0.0069/0.0135 m2 mg−1 in the wet/dry seasons, respectively. The mean values of aCDOM(443) in the shallow area during the wet season (0.10 ± 0.001 m-1) were significantly larger than those in the deep area during the dry season (0.06 ± 0.002 m-1). Similarly, aNAP(443) decreased from the shallow (0.056 ± 0.021 m-1) to deep areas (0.019 ± 0.011 m-1), and from the wet (0.035 ± 0.020 m-1) to dry (0.029 ± 0.015 m-1) seasons. The statistical analysis revealed that the differences in aCDOM(λ) and aNAP(λ) spectral distribution were not statistically significant for the duration of the wet and dry seasons, whereas significant differences were observed in the shallow and deep samples. During both wet and dry seasons, the magnitude of the blue-green absorption spectra was dominated by CDOM, but the red bands were associated with phytoplankton dominated samples. The ratio of aCDOM(λ)/a*Ph(λ) was utilized as an index for uncertainty assessment to estimate Chl-a concentrations by the National Aeronautics and Space Administration (NASA) standard Chl-a algorithms for the Moderate Resolution Imaging Spectrometer (MODIS; OC3M) and Sentinel-3 Ocean and Land Color Instrument (OLCI) (OLCI; OC4v6). The results additionally demonstrated that the satellite-derived Chl-a was overestimated due to higher aCDOM(λ) and underestimated owing to lower a*Ph(λ) at the low (<0.5 mg m−3) and high (>3 mg m−3) concentrations of Chl-a, respectively. The study findings established that the red bands should be considered for tuning or developing new Chl-a algorithms in the Persian Gulf.
... Currently, there has not been a great deal of situ bio-optical and above-water remote sensing research in the Bering Sea carried out in the 21st century. However, the results obtained in the eastern part of the Bering Sea by Naik et al. [21,22] should be noted. In the works [23,24], the data represented the central and eastern parts of the Bering Sea. ...
This study aimed to assess the applicability of global bio-optical algorithms for the estimation of chlorophyll-a (chl-a) concentration (C) and develop regional empirical bio-optical algorithms for estimating C and colored dissolved organic matter (CDOM) content (D) from ocean remote sensing reflectance spectra in the western part of the Bering Sea in the late summer period. The analysis took into account possible problems with the different relative contributions of phytoplankton and CDOM to water-leaving radiance and possible errors associated with the atmosphere correction procedure for ocean color satellite data. Shipborne remote sensing measurements obtained using an above-water hyperspectral ASD HandHeld spectroradiometer, satellite measurements collected via MODIS and VIIRS radiometers, and in situ measurements of C and D in seawater were used. The simulated values of the different multispectral satellite radiometers with daily or 2-day global coverage, obtained by applying the corresponding spectral response functions to ship hyperspectral data, were also analyzed. In this paper, a list of recommended regional bio-optical algorithms is presented. Recommendations are given depending on the possible quality of atmospheric correction and the purpose of use. To obtain more precise estimations of С, OC3/OC4-like algorithms should be used. If the atmosphere correction is poor, then use OC2-like algorithms in which spectral bands in the 476–539 nm range should be used to estimate C and bands near 443 nm to estimate D; however, in the last case, this will provide only the order of magnitude. To estimate more independent fields of C and D, it is necessary to use a spectral range of 501–539 nm for chl-a and bands near 412 nm in the case of modern satellite radiometers (e.g., OLCI or SGLI), for which this band is not the first. Additionally, we showed that global bio-optical algorithms can be applied with acceptable accuracy and similar recommendations.
... It should be noted that the standard algorithm for coastal areas may yield significantly overestimated absolute values of Chl due to the effect of relatively high concentrations of colored dissolved OM (CDOM) (Kopelevich et al., 2008). It is known that for the eastern shelf of the Bering Sea, the standard algorithm overestimates low Chl values and underestimates high values (Naik et al., 2013(Naik et al., , 2015. Here, the overestimation of low values (below 0-5 mg/m 3 ) is associated precisely with the effect of CDOM (Naik et al., 2013). ...
... It is known that for the eastern shelf of the Bering Sea, the standard algorithm overestimates low Chl values and underestimates high values (Naik et al., 2013(Naik et al., , 2015. Here, the overestimation of low values (below 0-5 mg/m 3 ) is associated precisely with the effect of CDOM (Naik et al., 2013). In absolute terms, the difference between Chl measured in situ and estimated from satellite data can reach 4-4.5 mg/m 3 in May and June with a median value below 0.5 mg/m 3 and usually does not exceed 2 mg/m 3 in July-October with a median close to 0 mg/m 3 (Naik et al., 2013). ...
... Here, the overestimation of low values (below 0-5 mg/m 3 ) is associated precisely with the effect of CDOM (Naik et al., 2013). In absolute terms, the difference between Chl measured in situ and estimated from satellite data can reach 4-4.5 mg/m 3 in May and June with a median value below 0.5 mg/m 3 and usually does not exceed 2 mg/m 3 in July-October with a median close to 0 mg/m 3 (Naik et al., 2013). Naik et al. (2015) found that the average ratio between the measured and estimated (using the OC3M algorithm) Chl values was almost 2.3. ...
is study characterizes the spatiotemporal variability of chlorophyll-a in the Bering Sea and adjacent Pacific Ocean based on 2003–2019 MODIS data. Average long-term seasonal variations of the chlorophyll-a concentration are described, and the typical times of phytoplankton bloom in various parts of the
given area are found. Interannual variability of spring bloom times is analyzed for three regions: the western
part of the sea northeast of the Kamchatka Strait, the northern part of the sea near Cape Navarin, and the
central part of the sea. The first two of these regions have similar average long-term characteristics. We have
shown that the interannual variability of the onset of spring bloom times vary between these two regions with
an amplitude of around 2 months. The western part of the sea is characterized by a shift in bloom to earlier
periods (March–April), while the spring bloom in the northern region shifts to May–June. Unlike these two
regions, the spring bloom is much less pronounced in the central part of the sea; it usually starts in May–June
and may last for several weeks. In this case, the chlorophyll-a concentration can be relatively high in August–
October as well. In some years, the fall bloom can be even more pronounced by intensity (with a peak of the
chlorophyll-a concentration) than the spring bloom. This situation is more typical for the open Pacific
Ocean, rather than for the Bering Sea. For the entire water area under consideration, we have compared the
course of spring bloom in 2010 and 2015 to reveal that the spatial development of bloom in different years can
also vary significantly. The interannual differences in its onset in different regions of the sea are most likely
associated with the features of physical processes that control the formation of stable water stratification
(spring ice melting and solar heating under weak wind impact) and can also be associated with the variability
of currents.
... However, distinct trends in the SW suggest differences in pigment packaging and/or change in pigment composition (Bricaud et al., 1995) that is consistent with the phytoplankton taxa reported in past work Arrigo et al., 1999Arrigo et al., , 2000Smith et al., 2014), and as observed in the phytoplankton absorption spectra (Figure 10); further, higher a * phy 443 also suggest better light adaptation by diatoms in the SW. The a * phy 443 versus chlorophyll relationship shows similarity to other high latitude regions (e.g., Naik et al., 2013), but is lower than the fit reported by Bricaud et al. (1995), which was obtained for middle and lower latitude waters ( Figure 11C). These differences in the a * phy λ in the blue and other wavelengths including the green band has been shown to lead to underestimations in satellite derived chlorophyll (Arrigo et al., 1998b;Dierssen and Smith, 2000), as also demonstrated in our study ( Figure 11D). ...
The Ross Sea, one of the most productive regions in the Southern Ocean, plays a significant role in deep water formation and carbon cycling. Dissolved organic carbon (DOC) concentrations and chromophoric dissolved organic matter (CDOM) absorption and fluorescence (FDOM) properties were studied in conjunction with biophysical properties during austral summer. Elevated values of both DOC (mean 47.82 ± 5.70 μM) and CDOM (absorption coefficient at 325 nm, a cdom 325: mean 0.31 ± 0.18 m –1 ) observed in the upper shelf waters in the southwest (SW), north of the Ross Ice Shelf (RIS), the northwest and along a transect inward of the shelf break, suggested in situ production and accumulation linked to the productive spring/summer season. However, regional differences were observed in CDOM with a cdom 325 higher (0.63 ± 0.19 m –1 ) and its spectral slope S 275 – 295 lower (24.06 ± 2.93 μm –1 ) in the SW compared to other regions (0.25 ± 0.08 m –1 and 28.92 ± 2.67 μm –1 , respectively). Similarly, the specific UV absorption coefficient or SUVA 254 determined at 254 nm was greater (1.85 ± 0.55 m ² mg –1 C) compared to other regions (1.07 ± 0.24 m ² mg –1 C), indicating CDOM of greater molecular weight and aromaticity in the SW. Phytoplankton absorption spectra indicated the shallow mixed layer of SW Ross Sea to be dominated by diatoms (e.g., Fragilariopsis spp. ), a preferential food source for grazers such as the Antarctic krill, which in large numbers have been shown to enhance CDOM absorption, a likely source in the SW. Excitation-emission matrix (EEM) fluorescence combined with parallel factor analysis (PARAFAC) retrieved one protein-like and two humic-like FDOM fractions commonly observed in the global ocean. In contrast to a cdom 325 which was uncorrelated to DOC, we observed weak but significant positive correlations between the humic-like FDOM with salinity and DOC, high value of the biological index parameter BIX and an instance of increasing FDOM with depth at a location with sinking organic matter, suggesting autochthonous production of FDOM. The absorption budget showed a relatively higher contribution by CDOM (70.7 ± 18.3%) compared to phytoplankton (22.5 ± 15.2%) absorption coefficients at 443 nm with implications to ocean color remote sensing. This first study of DOM optical properties provides additional insights on carbon cycling in the Ross Sea.
... As reservoirs are often primary sources for agricultural, urban and industrial uses, they are critical for economic and social development. Previous studies addressing these limitations have generally focused on one reservoirs; consequently, results of these past studies lack regional perspectives and were inadequate to provide a wider view on the variability of OACs across eco-regions Naik et al., 2013;Shi et al., 2013). According to the Ecological Environment Bulletin in 2017 from Ministry of Ecology and Environment of the People's Republic of China, 23% of the monitoring lakes or reservoirs were eutrophic and 67% of the monitoring important reservoirs or lakes were mesotrophic. ...
Reservoirs were critical sources of drinking water for many large cities around the world, but progress in the development of large-scale monitoring protocols to obtain timely information about water quality had been hampered by the complex nature of inland waters and the various optical conditions exhibited by these aquatic ecosystems. In this study, we systematically investigated the absorption coefficient of different optically-active constituents (OACs) in 120 reservoirs of different trophic states across five eco-regions in China. The relationships were found between phytoplankton absorption coefficient at 675 nm (aph (675)) and Chlorophyll a (Chla) concentration in different regions (R2:0.60-0.82). The non-algal particle (NAP) absorption coefficient (aNAP) showed an increasing trend for reservoirs with trophic states. Significant correlation (p < 0.05) was observed between chromophoric dissolved organic matter (CDOM) absorption and water chemical parameters. The influencing factors for contributing the relative proportion of OACs absorption including the hydrological factors and water quality factors were analyzed. The non-water absorption budget from our data showed the variations of the dominant absorption types which underscored the need to develop and parameterize region-specific bio-optical models for large-scale assessment in water reservoirs.
... Overestimation of Q* a (675) values was also observed by Kerkar et al. (2020) in this region earlier, accompanied with a negative relationship between Q* a (675) and Chl-a which has been attributed to package effect supported by other studies (Alcântara et al., 2016). The Q* a overestimation has been associated with uncertainties in the pathlength amplification factor and has been observed in previously published literature (Naik et al., 2013;Alcântara et al., 2016). In the present study, overestimation of Q*a (values shown in Table 2) could potentially be explained by the aforementioned methodological limitation, or the biological noise often encountered in cases where lower optical densities are observed (Alcântara et al., 2016). ...
Knowledge of Southern Ocean carbon cycling is limited by a paucity of phytoplankton primary productivity (PP) and spectral absorption data in this globally-important region. We measured ¹³C-based PP in the Southern Ocean during austral summer 2016, examining its link with spectral absorption coefficients and phytoplankton size structure derived from an absorption-based global model. Phytoplankton productivity was assessed at both coastal (60°S-69°S) and frontal stations (40°S-60°S), characterized by silicate- replete and -depleted water masses respectively (indicated by measured nutrient ratios) to capture a range of phytoplankton growth conditions. Bio-optical relationships were used as indicators of phytoplankton community size structure and to assess the extent of cellular pigment packaging - a phenomenon reported previously for phytoplankton cells in this region. Blue-Red (B/R) ratios of phytoplankton absorption (aph) spectra indicated that microplankton (more prone to “package effects”) were the dominant size class at most sites sampled. Overall, PP was better explained by aph (R² = 0.85) than total chlorophyll-a (R² = 0.64) in surface waters. The a*ph (675)-chlorophyll-a relationship explained package effects more effectively in frontal regions (R² = 0.63) than stations further south (R² = 0.30). The global absorption-based model captured smaller (pico, nano) size classes but failed to identify larger microplankton, underscoring the need for region-specific algorithm modifications. Our findings improve existing understanding of spatio-temporal trends in PP and bio-optical variability within the ISSO – knowledge that is essential to improve capacity to retrieve PP from satellite-based models in this important region.
... Ранее для большого массива океанических данных была установлена зависимость между Ca и aph(λ), которая описывается степенной функцией [16,17]. Коэффициенты этой степенной зависимости различны как для разных акваторий [18,19], так и для одной акватории в разные сезоны [20,21]. ...
Purpose. The purpose of the work is to evaluate accuracy of the satellite products for the coastal waters near Sevastopol, generated by the standard algorithms based on the MODIS and VIIRS (installed at the artificial Earth satellites Aqua and Terra, and at Suomi NPP, respectively) data.
Methods and Results. In situ sampling was carried out at the station (44°37’26" N and 33°26’05" E) located at a distance of two miles from the Sevastopol Bay. The chlorophyll a concentration was measured by the spectrophotometric method. The spectral light absorption coefficients by optically active components were measured in accordance with the current NASA protocol. The spectroradiometers MODIS and VIIRS Level-2 data with spatial resolution 1 km in nadir around the in situ station (44°37’26"±0°00’32" N and 33°26’05"±0°00’54" E) were used. The satellite products were processed by the SeaDAS 7.5.3 software developed in NASA. The research showed that the standard NASA algorithms being applied to the MODIS and VIIRS data, yielded incorrect values of the optically active components’ content in the Black Sea coastal waters near Sevastopol as compared to the data of in situ measurements in the same region: the satellite-derived “chlorophyll a concentration” was on average 1.6 times lower in spring, and 1.4 times higher in summer; the contribution of phytoplankton to total light absorption at 443 nm was underestimated in 8.7 times; the light absorption by colored detrital matter was overestimated in 2.2 times.
Conclusions. The NASA standard algorithms are inapplicable to calculating bio-optical indices in the coastal waters of the Black Sea near Sevastopol since they provide incorrect values of the satellite products (Ca-s, aph-s(443) and aCDM-s(443)). Operative ecological monitoring based on satellite data requires development of a regional algorithm taking into account the seawater optical features in the region and in the coastal zone, in particular.
... Ранее для большого массива океанических данных была установлена зависимость между Ca и aph(λ), которая описывается степенной функцией [16,17]. Коэффициенты этой степенной зависимости различны как для разных акваторий [18,19], так и для одной акватории в разные сезоны [20,21]. ...
Цель. Цель работы − оценить точность спутниковых продуктов для прибрежных вод Севастополя,
восстановленных стандартными алгоритмами по данным спектрорадиометров MODIS,
установленных на искусственных спутниках Земли Aqua и Terra, и VIIRS на спутнике Suomi NPP.
Методы и результаты. Отбор проб in situ проводился на станции, расположенной на расстоянии
двух миль от бухты Севастопольской в точке с координатами 44° 37' 26" с. ш. и 33° 26' 05" в. д.
Для определения концентрации хлорофилла а использовали спектрофотометрический метод.
Спектральные показатели поглощения света оптически активными компонентами измеряли
в соответствии с современным протоколом NASA. Использовались данные MODIS и VIIRS 2-го
уровня с пространственным разрешением 1 км вокруг станции. Обработку спутниковых данных
проводили при помощи программного обеспечения SeaDAS 7.5.3, разработанного NASA.
Исследование показало, что содержание оптически активных компонентов в прибрежных водах
Севастополя по данным MODIS и VIIRS при использовании стандартных алгоритмов определяется
некорректно: в сравнении с данными измерений in situ значения концентрации хлорофилла а
в среднем весной меньше в 1,6 раза, а летом – больше в 1,4 раза; вклад пигментов фитопланктона
в общее поглощение света на длине волны 443 нм в среднем меньше в 8,7 раза; поглощение
света окрашенным растворенным органическим веществом в сумме с неживой взвесью в среднем больше в 2,2 раза.
Выводы. Стандартные алгоритмы NASA не применимы для расчета биооптических показателей вод
(концентрация хлорофилла a, показатель поглощения света пигментами фитопланктона и показатель
поглощения света окрашенным растворенным органическим веществом в сумме с неживой взвесью)
в прибрежном районе Черного моря вблизи Севастополя. Чтобы использовать спутниковые данные
для экологического мониторинга, необходимо развивать региональный алгоритм, учитывающий
оптические особенности вод в этом районе, в частности в сложной прибрежной зоне.
... Numerous rivers discharge from the Alaska mainland into the eastern Bering Sea, supplying freshwater rich with CDOM and suspended sediment. These optically unique water sources affect water clarity over the eastern Bering Sea shelf (Naik et al., 2013). From October-May, strong winds and weak cross-shelf density gradients allow advection of fluvial water sources over the middle and outer shelf (Danielson et al., 2011). ...
... Over the northern middle and outer shelf, high near-surface water clarity allows light to penetrate through the mixed layer and into the nutrient-rich waters below, where primary production can continue throughout the summer (Mordy et al., 2012;Stabeno et al., 2012aStabeno et al., , 2012b. However, substances other than chlorophyll-a may also affect light transmission through the pycnocline, as concentrations of nonalgal particulate and CDOM can be higher in subsurface layers than in the mixed layer (Naik et al., 2013). ...
Biophysical processes that affect subsurface water clarity play a key role in ecosystem function. However, subsurface water clarity is poorly monitored in marine ecosystems because doing so requires in-situ sampling that is logistically difficult to conduct and sustain. Novel solutions are thus needed to improve monitoring of subsurface water clarity. To that end, we developed a sampling method and data processing algorithm that enable the use of bottom trawl fishing gear as a platform for conducting subsurface water clarity monitoring using trawl-mounted irradiance sensors without disruption to fishing operations. The algorithm applies quality control checks to irradiance measurements and calculates the downwelling diffuse attenuation coefficient, Kd, and optical depth, ζ– apparent optical properties (AOPs) that characterize the rate of decrease in downwelling irradiance and relative irradiance transmission to depth, respectively. We applied our algorithm to irradiance measurements, obtained using bottom-trawl-mounted archival tags equipped with a photodiode collected during NOAA’s Alaska Fisheries Science Center annual summer bottom trawl surveys of the eastern Bering Sea continental shelf from 2004 to 2018. We validated our AOPs by quantitatively comparing surface-weighted Kd from tags to the multi-sensor Kd(490) product from the Ocean Colour Climate Change Initiative project (OC-CCI) and qualitatively evaluating whether tag Kd was consistent with patterns of subsurface chlorophyll-a concentrations predicted by a coupled regional physical-biological model (Bering10K-BESTNPZ). We additionally examined patterns and trends in water clarity in the eastern Bering Sea. Key findings are: 1) water clarity decreased significantly from 2004 to 2018; 2) a recurrent, pycnocline-associated, maximum in Kd occurred over much of the northwestern shelf, putatively due to a subsurface chlorophyll maximum; and 3) a turbid bottom layer (nepheloid layer) was present over a large portion of the eastern Bering Sea shelf. Our study demonstrates that bottom trawls can provide a useful platform for monitoring water clarity, especially when trawling is conducted as part of a systematic stock assessment survey.
... The blue to red ratio of a * ph is used as proxy of phytoplankton size, where higher values (> 3) of a * ph (443)/a * ph (676) are associated with smaller cells (Lohrenz et al. 2003). All the stations in the study area, exhibited predominance of relatively smaller size phytoplankton and hence less or no package effect as reported elsewhere by Naik et al. (2013), which corroborates our observations discussed in previous sections. The moderate relationship of radiometer-derived K d (490) with in situ Chl-a and a ph (490) (Fig. 11c, d) indicates that the factors other than phytoplankton biomass (such as a nph , a CDOM and TSM) also influence the light attenuation in the water column. ...
The Southern Ocean (SO), in spite of its major contribution to global primary productivity (PP), remains underexplored in this aspect. Light being the most limiting parameter affecting primary production, it is crucial to study the ambient light field to understand PP and associated processes. The current study makes a dual effort to present PP estimates as well as understand the bio-optical variability in the Indian sector of the Southern Ocean (ISSO). Results suggest that PP was highest at Sub-Tropical Front (STF) and lowest at Polar Front-2 (PF2). Most PP profiles were characterized by subsurface maxima, indicating probable photoinhibition or micronutrient limitation at surface layer. Strong correlation between measured and satellite-based integrated PP (R2 = 0.94, RMSE = 77.48, p < 0.01) indicated the efficacy of global models in their original formulation in bio-optically complex SO waters. The maximum photochemical efficiency of phytoplankton (Fv/Fm) measured by fast repetition rate fluorometry varied from 0.1–0.4, implying reduced phytoplankton photosynthetic efficiency in ISSO. The ratio between remote sensing reflectance (Rrs)-derived phytoplankton absorption (aph) at blue-red band (B/R ratio) indicated dominance of smaller phytoplankton in surface and larger phytoplankton at subsurface. Higher Chl-a specific phytoplankton absorption (a*ph
) than phytoplankton absorption (aph) suggested an adaptation of dominant phytoplankton species to low light, yet a better light harvest efficiency. However, low contribution of aph suggested a strong influence of non-phytoplankton materials to the total absorption budget. We therefore infer that, the surrounding physical environment in terms of nutrients and bio-optical variability modulated phytoplankton size class and thereby productivity more critically in the surface than in the deeper layers of ISSO.
