Articles de revues : « Phytoplankton light absorption »

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Duarte, C. M., S. Agustí et J. Kalff. « Particulate light absorption and the prediction of phytoplankton biomass and planktonic metabolism in northeastern Spanish aquatic ecosystems ». Canadian Journal of Fisheries and Aquatic Sciences 57, n^o 1 (1 janvier 2000) : 25–33. http://dx.doi.org/10.1139/f99-184.

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Examination of particulate light absorption and microplankton metabolism in 36 northeastern Spanish aquatic ecosystems, ranging from alpine rivers to inland saline lakes and the open Mediterranean Sea, revealed the existence of general relationships between particulate light absorption and the biomass of phytoplankton and microplankton metabolism. The particulate absorption spectra reflected a dominance of nonphotosynthetic, likely detrital, particles in rivers and a dominance of phytoplankton in coastal lagoons. There was a strong relationship between the light absorbed by phytoplankton and the chlorophyll a (Chl a) concentration of the systems, which indicated an average (±SE) Chl a specific absorption coefficient of 0.0233 ± 0.0020 m2·mg Chl a-1 for these widely diverse systems. Chl a concentration was a weaker predictor of the total particulate light absorption coefficient, pointing to an important role of nonphytoplanktonic particles in light absorption. Gross production was very closely related to the light absorption coefficient of phytoplankton, whereas community respiration was strongly correlated with the total particulate light absorption coefficient, indicating the optical signatures of sestonic particles to be reliable predictors of planktonic biomass and metabolism in aquatic ecosystems.

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Asselot, Rémy, Frank Lunkeit, Philip B. Holden et Inga Hense. « Climate pathways behind phytoplankton-induced atmospheric warming ». Biogeosciences 19, n^o 1 (14 janvier 2022) : 223–39. http://dx.doi.org/10.5194/bg-19-223-2022.

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Abstract. We investigate the ways in which marine biologically mediated heating increases the surface atmospheric temperature. While the effects of phytoplankton light absorption on the ocean have gained attention over the past years, the impact of this biogeophysical mechanism on the atmosphere is still unclear. Phytoplankton light absorption warms the surface of the ocean, which in turn affects the air–sea heat and CO2 exchanges. However, the contribution of air–sea heat versus CO2 fluxes in the phytoplankton-induced atmospheric warming has not been yet determined. Different so-called climate pathways are involved. We distinguish heat exchange, CO2 exchange, dissolved CO2, solubility of CO2 and sea-ice-covered area. To shed more light on this subject, we employ the EcoGEnIE Earth system model that includes a new light penetration scheme and isolate the effects of individual fluxes. Our results indicate that phytoplankton-induced changes in air–sea CO2 exchange warm the atmosphere by 0.71 ∘C due to higher greenhouse gas concentrations. The phytoplankton-induced changes in air–sea heat exchange cool the atmosphere by 0.02 ∘C due to a larger amount of outgoing longwave radiation. Overall, the enhanced air–sea CO2 exchange due to phytoplankton light absorption is the main driver in the biologically induced atmospheric heating.

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Agustí, Susana. « Allometric Scaling of Light Absorption and Scattering by Phytoplankton Cells ». Canadian Journal of Fisheries and Aquatic Sciences 48, n^o 5 (1 mai 1991) : 763–67. http://dx.doi.org/10.1139/f91-091.

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Examination of the allometric scaling of light absorption (acell) and scattering (bcell) by 28 phytoplankton species showed that light absorption is scaled to the cross-sectional area of the cells (log acell (square micrometres per cell) = −1.06 + 2.32 log d (micrometres)) whereas light scattering is scaled to their volume (log bcell (square micrometres per cell) = −1.09 + 3.45 log d (micrometres)). The scaling of light absorption to the cross-sectional area of algal cells is explained by a decrease in intracellular chlorophyll a concentration as cell size increases, thereby avoiding inefficient light capture by photosynthetic pigments. The scaling of light scattering to cell volume conforms to the general theory for large particles (Mie theory). Light absorption by phytoplankton cells, unlike light scattering, deviates from that of nonliving particles because of the covariation between pigment content and cell size that help prevent self-shading.

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Bracher, A., M. Vountas, T. Dinter, J. P. Burrows, R. Röttgers et I. Peeken. « Quantitative observation of cyanobacteria and diatoms from space using PhytoDOAS on SCIAMACHY data ». Biogeosciences Discussions 5, n^o 6 (28 novembre 2008) : 4559–90. http://dx.doi.org/10.5194/bgd-5-4559-2008.

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Abstract. In this study the technique Differential Optical Absorption Spectroscopy (DOAS) has been adapted for the retrieval of the absorption and biomass of two major phytoplankton groups (PhytoDOAS) from data of the satellite sensor Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). SCIAMACHY measures back scattered solar radiation in the UV-Vis-NIR spectral region with a high spectral resolution (0.2 to 1.5 nm). In order to identify phytoplankton absorption characteristics in SCIAMACHY data in the range of 430 to 500 nm, phytoplankton absorption spectra measured in-situ during two different RV "Polarstern" expeditions were used. The two spectra have been measured in different ocean regions where different phytoplankton groups (cyanobacteria and diatoms) dominated the phytoplankton composition. Results show clearly different absorption characteristics of the phytoplankton groups in the SCIAMACHY spectra. Globally distributed pigment concentrations for these characteristic phytoplankton groups for two monthly periods (February–March 2004 and October–November 2005) were derived from these differential absorptions by including the information of the sensor's optical paths within the water column (i.e. light penetration depth) according to Vountas et al. (2007) derived from DOAS fits of inelastic scattering. The satellite retrieved information on cyanobacteria and diatoms distribution matches well the concentrations measured at collocated water samples with HPLC technique and concentrations derived from the global model analysis with the NOBM model (Gregg et al., 2003; Gregg and Casey, 2007). Identifying quantitative distribution of key phytoplankton groups from space allow to distinguish various biogeochemical provinces and will be of great importance for the global modelling of marine ecosystem and biogeochemical cycles addressing climate changes in the oceanic biosphere.

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Churilova, Tatiana, Natalia Moiseeva, Elena Skorokhod, Tatiana Efimova, Anatoly Buchelnikov, Vladimir Artemiev et Pavel Salyuk. « Parameterization of Light Absorption of Phytoplankton, Non-algal Particles and Coloured Dissolved Organic Matter in the Atlantic Region of the Southern Ocean (Austral Summer of 2020) ». Remote Sensing 15, n^o 3 (20 janvier 2023) : 634. http://dx.doi.org/10.3390/rs15030634.

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Climate affects the characteristics of the Southern Ocean ecosystem, including bio-optical properties. Remote sensing is a suitable approach for monitoring a rapidly changing ecosystem. Correct remote assessment can be implemented based on a regional satellite algorithm, which requires parameterization of light absorption by all optically active components. The aim of this study is to analyse variability in total chlorophyll a concentration (TChl-a), light absorption by phytoplankton, non-algal particles (NAP), coloured dissolved organic matter (CDOM), and coloured detrital matter (CDM = CDOM+NAP), to parameterize absorption by all components. Bio-optical properties were measured in the austral summer of 2020 according to NASA Protocols (2018). High variability (1–2 orders of magnitude) in TChl-a, absorption of phytoplankton, NAP, CDOM, and CDM was revealed. High variability in both CDOM absorption (uncorrelated with TChl-a) and CDOM share in total non-water absorption, resulting in a shift from phytoplankton to CDOM dominance, caused approximately twofold chlorophyll underestimation by global bio-optical algorithms. The light absorption of phytoplankton (for the visible domain in 1 nm steps), NAP, CDOM, and CDM were parametrized. Relationships between the spectral slope coefficient (SCDOM/SCDM) and CDOM (CDM) absorption were revealed. These results can be useful for the development of regional algorithms for Chl-a, CDM, and CDOM monitoring in the Southern Ocean.

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Liew, S. C., C. K. Choo, J. W. M. Lau, W. S. Chan et T. C. Dang. « Monitoring water quality in Singapore reservoirs with hyperspectral remote sensing technology ». Water Practice and Technology 14, n^o 1 (10 janvier 2019) : 118–25. http://dx.doi.org/10.2166/wpt.2018.119.

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Abstract In this work, algorithms were developed for retrieving water quality parameters related to Singapore's reservoirs. The main constituents that affect the water reflectance (WR) – i.e. proportion of incident light reflected from the surface of water bodies after removing the surface glint component – are the suspended particles, phytoplankton and coloured dissolved organic matter (CDOM). The existing absorption spectrum model for phytoplankton in seawater is not accurate for the phytoplankton types that exist in the fresh water environment. The phytoplankton absorption spectrum was modelled by a series of Gaussian peaks from 400 to 750 nm. The peak strengths were dynamically derived from the WR measured. The phytoplankton absorption model is incorporated into a semi-empirical WR model for retrieving the absorption and backscattering coefficients of water components such as suspended sediments, CDOM and phytoplankton. The chlorophyll-a concentration and water turbidity estimated using this model correlate well with field sampling measurements, with coefficients of determination (R2) exceeding 0.8.

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Brunelle, Corinne B., Pierre Larouche et Michel Gosselin. « Variability of phytoplankton light absorption in Canadian Arctic seas ». Journal of Geophysical Research : Oceans 117, n^o C9 (3 août 2012) : n/a. http://dx.doi.org/10.1029/2011jc007345.

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Kraus, Cleber Nunes, Daniel Andrade Maciel, Marie Paule Bonnet et Evlyn Márcia Leão de Moraes Novo. « Phytoplankton Genera Structure Revealed from the Multispectral Vertical Diffuse Attenuation Coefficient ». Remote Sensing 13, n^o 20 (14 octobre 2021) : 4114. http://dx.doi.org/10.3390/rs13204114.

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The composition of phytoplankton and the concentration of pigments in their cells make their absorption and specific absorption coefficients key parameters for bio-optical modeling. This study investigated whether the multispectral vertical diffuse attenuation coefficient of downward irradiance (Kd) gradients could be a good framework for accessing phytoplankton genera. In situ measurements of remote sensing reflectance (Rrs), obtained in an Amazon Floodplain Lake (Lago Grande do Curuai), were used to invert Kd, focusing on Sentinel-3/Ocean and Land Color Instrument (OLCI) sensor bands. After that, an analysis based on the organization of three-way tables (STATICO) was applied to evaluate the relationships between phytoplankton genera and Kd at different OLCI bands. Our results indicate that phytoplankton genera are organized according to their ability to use light intensity and different spectral ranges of visible light (400 to 700 nm). As the light availability changes seasonally, the structure of phytoplankton changes as well. Some genera, such as Microcystis, are adapted to low light intensity at 550–650 nm, therefore high values of Kd in this range would indicate the dominance of Microcysts. Other genera, such as Aulacoseira, are highly adapted to harvesting blue-green light with higher intensity and probably grow in lakes with lower concentrations of colored dissolved organic matter that highly absorbs blue light (405–498). These findings are an important step to describing phytoplankton communities using orbital data in tropical freshwater floodplains. Furthermore, this approach can be used with biodiversity indexes to access phytoplankton diversity in these environments.

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Wang, S. Q., J. Ishizaka, H. Yamaguchi, S. C. Tripathy, M. Hayashi, Y. J. Xu, Y. Mino, T. Matsuno, Y. Watanabe et S. J. Yoo. « Influence of the Changjiang River on the light absorption properties of phytoplankton from the East China Sea ». Biogeosciences 11, n^o 7 (3 avril 2014) : 1759–73. http://dx.doi.org/10.5194/bg-11-1759-2014.

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Abstract. Phytoplankton light absorption properties were investigated at the surface and subsurface chlorophyll a maximum (SCM) layer in the East China Sea (ECS), a marginal sea which is strongly influenced by the Changjiang discharge in summer. Results from ECS were compared with those from the Tsushima Strait (TS) where the influence of Changjiang discharge is less. The probable controlling factors, packaging effect (cell size) and pigment composition of total chlorophyll a (Tchl a)-specific absorption coefficient (aph&ast;(λ)) were examined by the corresponding measurements of pigments identified by high-performance liquid chromatography. We observed distinct phytoplankton size structure and thereby absorption properties between ECS and TS. At the surface, mixed populations of micro-, nano- and pico-phytoplankton were recorded in ECS while pico-phytoplankton dominated in TS, generating a lower average aph&ast;(λ) in ECS than in TS. Within SCM, average aph&ast;(λ) was higher in ECS than in TS because of the dominance of nano- and micro-phytoplankton in ECS and TS, respectively. By pooling surface and SCM samples, we found regular trends in phytoplankton size-fraction versus Tchl a; and correlations between aph&ast;(λ) and Tchl a consistent with previous observations for the global ocean in TS but not in ECS. In ECS phytoplankton size-fraction was not correlated with Tchl a, which consequently caused poor relationships between aph&ast;(λ) and Tchl a. The abnormal values mainly originated from the surface low-salinity waters and SCM waters beneath them. At high Tchl a, aph&ast;(λ) of these samples was substantially higher compared to the values in TS and from the global regressions, which was attributable to the lower micro-phytoplankton fraction, and higher nano- and/or pico-phytoplankton fractions in ECS. These observations indicated that the distinct light absorption properties of phytoplankton in ECS were possibly influenced by the Changjiang discharge. Our findings imply that general bio-optical algorithms proposed based on the correlations between aph&ast;(λ) and Tchl a or the patterns in size-fraction versus Tchl a are not applicable in ECS, and need to be carefully considered when using these general algorithms in river-influenced regions.

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Behrenfeld, M. J., T. K. Westberry, E. S. Boss, R. T. O'Malley, D. A. Siegel, J. D. Wiggert, B. A. Franz et al. « Satellite-detected fluorescence reveals global physiology of ocean phytoplankton ». Biogeosciences Discussions 5, n^o 6 (5 novembre 2008) : 4235–70. http://dx.doi.org/10.5194/bgd-5-4235-2008.

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Abstract. Phytoplankton photosynthesis links global ocean biology and climate-driven fluctuations in the physical environment. These interactions are largely expressed through changes in phytoplankton physiology, but physiological status has proven extremely challenging to characterize globally. Phytoplankton fluorescence does provide a rich source of physiological information long exploited in laboratory and field studies, and is now observed from space. Here we use satellite-based fluorescence measurements to evaluate light-absorption and energy-dissipation processes influencing phytoplankton light use efficiency and demonstrate its utility as a global physiological indicator of iron-limited growth conditions. This new tool provides a path for monitoring climate-phytoplankton physiology interactions, improving descriptions of light use efficiency in ocean productivity models, evaluating nutrient-stress predictions in ocean ecosystem models, and appraising phytoplankton responses to natural iron enrichments or purposeful iron fertilizations activities.

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Kiefer, Dale A., et John J. Cullen. « Phytoplankton growth and light absorption as regulated by light, temperature, and nutrients ». Polar Research 10, n^o 1 (9 janvier 1991) : 163–72. http://dx.doi.org/10.3402/polar.v10i1.6735.

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KIEFER, DALE A., et JOHN J. CULLEN. « Phytoplankton growth and light absorption as regulated by light, temperature, and nutrients ». Polar Research 10, n^o 1 (décembre 1991) : 163–72. http://dx.doi.org/10.1111/j.1751-8369.1991.tb00642.x.

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Organelli, Emanuele, Caterina Nuccio, Chiara Melillo et Luca Massi. « Relationships between phytoplankton light absorption, pigment composition and size structure in offshore areas of the Mediterranean Sea ». Advances in Oceanography and Limnology 2, n^o 2 (1 décembre 2011) : 107. http://dx.doi.org/10.4081/aiol.2011.5320.

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Phytoplankton absorption is mainly determined by pigment composition and packaging into the cell, in turn affected by pigment concentration and cell size and shape. The variations of the chlorophyll-specific absorption coefficients at two selected wavelengths (443 nm and 675 nm) were analysed for offshore areas of the Mediterranean Sea (Alboran, Algerian, Tyrrhenian, Ionian Basins and Sardinia Channel) investigated in autumn 2006, 2007 and 2008. The spatial distribution of Tchl a, accessory pigments, size structure and taxonomic composition of phytoplankton assemblages was diversified among the areas, characterized by higher contribution of photoprotective pigments in oligotrophic surface waters, while accessory chlorophylls increased in deeper layers and where microphytoplankton dominated. (443) values decreased from the oligotrophic waters to the more mesotrophic ones where microphytoplankton prevailed, while for (675) a small range of variation was observed. The differentiation of (443) was explained by the variations in the phytoplankton assemblage mean cell size, that consequently can be assumed as the main factor determining package effect. Comparison with previous parameterizations supported the existence of a Mediterranean differentiation for which the use of global models might determine inaccuracy for predicting phytoplankton absorption coefficients and thus refining ecological models.

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Letelier, Ricardo M., Angelicque E. White, Robert R. Bidigare, Benedetto Barone, Matthew J. Church et David M. Karl. « Light absorption by phytoplankton in the North Pacific Subtropical Gyre ». Limnology and Oceanography 62, n^o 4 (24 mars 2017) : 1526–40. http://dx.doi.org/10.1002/lno.10515.

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Bracher, A., M. Vountas, T. Dinter, J. P. Burrows, R. Röttgers et I. Peeken. « Quantitative observation of cyanobacteria and diatoms from space using PhytoDOAS on SCIAMACHY data ». Biogeosciences 6, n^o 5 (6 mai 2009) : 751–64. http://dx.doi.org/10.5194/bg-6-751-2009.

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Abstract. In this study the technique of Differential Optical Absorption Spectroscopy (DOAS) has been adapted for the retrieval of the absorption and biomass of two major phytoplankton groups (PhytoDOAS) from data of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) satellite sensor. SCIAMACHY measures back scattered solar radiation in the UV-Vis-NIR spectral regions with a high spectral resolution (0.2 to 1.5 nm). In order to identify phytoplankton absorption characteristics in the SCIAMACHY data in the range of 430 to 500 nm, phytoplankton absorption spectra measured in-situ during two different RV "Polarstern" expeditions were used. The two spectra have been measured in different ocean regions where different phytoplankton groups (cyanobacteria and diatoms) dominated the phytoplankton composition. Results clearly show distinct absorption characteristics of the two phytoplankton groups in the SCIAMACHY spectra. Using these results in addition to calculations of the light penetration depth derived from DOAS retrievals of the inelastic scattering (developed by Vountas et al., 2007), globally distributed pigment concentrations for these characteristic phytoplankton groups for two monthly periods (February–March 2004 and October–November 2005) were determined. This satellite information on cyanobacteria and diatoms distribution clearly matches the concentrations based on high pressure liquid chromatography (HPLC) pigment analysis of collocated water samples and concentrations derived from a global model analysis with the NASA Ocean Biogeochemical Model (Gregg et al., 2003; Gregg and Casey 2007). The quantitative assessment of the distribution of key phytoplankton groups from space enables various biogeochemical regions to be distinguished and will be of great importance for the global modeling of marine ecosystems and biogeochemical cycles which enables the impact of climate change in the oceanic biosphere to be estimated.

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Bernardo, Nariane, Enner Alcântara, Fernanda Watanabe, Thanan Rodrigues, Alisson do Carmo, Ana Carolina Campos Gomes et Caroline Andrade. « Light Absorption Budget in a Reservoir Cascade System with Widely Differing Optical Properties ». Water 11, n^o 2 (29 janvier 2019) : 229. http://dx.doi.org/10.3390/w11020229.

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Aquatic systems are complex systems due to the environmental pressures that lead to water quality parameter changes, and consequently, variations in optically active compounds (OAC). In cascading reservoir systems, such as the Tietê Cascade Reservoir System (TCSR), which has a length of 1100 km, the horizontal gradients are expressive due to the filtration process that is caused by the sequence of dams affecting the light absorption throughout the cascade. Our new observations showed that colored dissolved organic matter (CDOM) dominate two reservoirs; non-algae particles (NAP) dominate one, and phytoplankton dominates the other. The variability of light absorption along the cascade indicates the influence of watershed dynamics in the reservoirs as much as the flow driven by previous reservoirs. Despite the effect of the variability of light absorption, light absorption by phytoplankton strongly affects the total absorption in the four reservoirs in TCSR. The results obtained in this work may enable a better understanding of how the gradient pattern changes primary production and indicates a challenge in retrieving OAC concentrations using a bio-optical model for an entire cascade composed of different optical environments.

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J.W. Brewin, Robert, Stefano Ciavatta, Shubha Sathyendranath, Jozef Skákala, Jorn Bruggeman, David Ford et Trevor Platt. « The Influence of Temperature and Community Structure on Light Absorption by Phytoplankton in the North Atlantic ». Sensors 19, n^o 19 (26 septembre 2019) : 4182. http://dx.doi.org/10.3390/s19194182.

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We present a model that estimates the spectral phytoplankton absorption coefficient ( a p h ( λ ) ) of four phytoplankton groups (picophytoplankton, nanophytoplankton, dinoflagellates, and diatoms) as a function of the total chlorophyll-a concentration (C) and sea surface temperature (SST). Concurrent data on a p h ( λ ) (at 12 visible wavelengths), C and SST, from the surface layer (<20 m depth) of the North Atlantic Ocean, were partitioned into training and independent validation data, the validation data being matched with satellite ocean-colour observations. Model parameters (the chlorophyll-specific phytoplankton absorption coefficients of the four groups) were tuned using the training data and found to compare favourably (in magnitude and shape) with results of earlier studies. Using the independent validation data, the new model was found to retrieve total a p h ( λ ) with a similar performance to two earlier models, using either in situ or satellite data as input. Although more complex, the new model has the advantage of being able to determine a p h ( λ ) for four phytoplankton groups and of incorporating the influence of SST on the composition of the four groups. We integrate the new four-population absorption model into a simple model of ocean colour, to illustrate the influence of changes in SST on phytoplankton community structure, and consequently, the blue-to-green ratio of remote-sensing reflectance. We also present a method of propagating error through the model and illustrate the technique by mapping errors in group-specific a p h ( λ ) using a satellite image. We envisage the model will be useful for ecosystem model validation and assimilation exercises and for investigating the influence of temperature change on ocean colour.

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Maske, H., et M. Latasa. « Solar ultraviolet radiation dependent decrease of particle light absorption and pigments in lake phytoplankton ». Canadian Journal of Fisheries and Aquatic Sciences 54, n^o 3 (1 mars 1997) : 697–704. http://dx.doi.org/10.1139/f96-321.

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The ultraviolet (UV) spectral component of daylight on a clear day at mid-latitudes can significantly reduce phytoplankton pigments within a daylight period. Phytoplankton samples from Redberry Lake, Saskatchewan, dominated by cyanobacteria were incubated in quartz bottles under optical long band-pass filters (cutoff wavelength 420-305 nm) in daylight in June. After incubation, samples were filtered, and in vivo particle light absorption (380-700 nm) and pigment concentrations were measured. Solar ultraviolet-B irradiance (UV-B; 280-320 nm) was measured radiometrically. On sunny days the samples that were exposed to daylight UV light showed a relative decrease in particle absorption and pigment concentration after the incubation compared with samples exposed only to visible daylight. No such decrease was observed during an overcast day. The UV-B data did not show a clear relation with the degree of pigment reduction, suggesting that other environmental factors or the state of adaptation partially controlled the pigment decrease of phytoplankton under UV-B exposure. Neither specific spectral components of the absorption spectrum nor specific pigments were more easily degraded than others by solar UV light, although the ratio of zeaxanthin to chlorophyll a probably increased in cyanobacteria as a result of UV exposure.

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Nelson, NB, BB Prezelin et RR Bidigare. « Phytoplankton light absorption and the package effect in California coastal waters ». Marine Ecology Progress Series 94 (1993) : 217–27. http://dx.doi.org/10.3354/meps094217.

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Behrenfeld, M. J., T. K. Westberry, E. S. Boss, R. T. O'Malley, D. A. Siegel, J. D. Wiggert, B. A. Franz et al. « Satellite-detected fluorescence reveals global physiology of ocean phytoplankton ». Biogeosciences 6, n^o 5 (8 mai 2009) : 779–94. http://dx.doi.org/10.5194/bg-6-779-2009.

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Abstract. Phytoplankton photosynthesis links global ocean biology and climate-driven fluctuations in the physical environment. These interactions are largely expressed through changes in phytoplankton physiology, but physiological status has proven extremely challenging to characterize globally. Phytoplankton fluorescence does provide a rich source of physiological information long exploited in laboratory and field studies, and is now observed from space. Here we evaluate the physiological underpinnings of global variations in satellite-based phytoplankton chlorophyll fluorescence. The three dominant factors influencing fluorescence distributions are chlorophyll concentration, pigment packaging effects on light absorption, and light-dependent energy-quenching processes. After accounting for these three factors, resultant global distributions of quenching-corrected fluorescence quantum yields reveal a striking consistency with anticipated patterns of iron availability. High fluorescence quantum yields are typically found in low iron waters, while low quantum yields dominate regions where other environmental factors are most limiting to phytoplankton growth. Specific properties of photosynthetic membranes are discussed that provide a mechanistic view linking iron stress to satellite-detected fluorescence. Our results present satellite-based fluorescence as a valuable tool for evaluating nutrient stress predictions in ocean ecosystem models and give the first synoptic observational evidence that iron plays an important role in seasonal phytoplankton dynamics of the Indian Ocean. Satellite fluorescence may also provide a path for monitoring climate-phytoplankton physiology interactions and improving descriptions of phytoplankton light use efficiencies in ocean productivity models.

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Schuback, Nina, et Philippe D. Tortell. « Diurnal regulation of photosynthetic light absorption, electron transport and carbon fixation in two contrasting oceanic environments ». Biogeosciences 16, n^o 7 (4 avril 2019) : 1381–99. http://dx.doi.org/10.5194/bg-16-1381-2019.

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Abstract. Understanding the dynamics of marine phytoplankton productivity requires mechanistic insight into the non-linear coupling of light absorption, photosynthetic electron transport and carbon fixation in response to environmental variability. In the present study, we examined the variability of phytoplankton light absorption characteristics, light-dependent electron transport and 14C-uptake rates over a 48 h period in the coastal subarctic north-east (NE) Pacific. We observed an intricately coordinated response of the different components of the photosynthetic process to diurnal irradiance cycles, which acted to maximize carbon fixation, while simultaneously preventing damage by excess absorbed light energy. In particular, we found diurnal adjustments in pigment ratios, excitation energy transfer to reaction centre II (RCII), the capacity for non-photochemical quenching (NPQ), and the light efficiency (α) and maximum rates (Pmax) of RCII electron transport (ETRRCII) and 14C uptake. Comparison of these results from coastal waters to previous observations in offshore waters of the subarctic NE Pacific provides insight into the effects of iron limitation on the optimization of photosynthesis. Under iron-limited, low-biomass conditions, there was a significant reduction of iron-rich photosynthetic units per chlorophyll a, which was partly offset by higher light absorption and electron transport per photosystem II (PSII). Iron deficiency limited the capacity of phytoplankton to utilize peak midday irradiance for carbon fixation and caused an upregulation of photoprotective mechanisms, including NPQ, and the decoupling of light absorption, electron transport and carbon fixation. Such decoupling resulted in an increased electron requirement (Φe,C) and decreased quantum efficiency (ΦC) of carbon fixation at the iron-limited station. In both coastal and offshore waters, Φe,C and ΦC correlated strongly to NPQ, albeit with a significantly different slope. We discuss the implications of our results for the interpretation of bio-optical data and the parameterization of numerical productivity models, both of which are vital tools in monitoring marine photosynthesis over large temporal and spatial scales.

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Sun, Xuerong, Fang Shen, Robert J. W. Brewin, Mengyu Li et Qing Zhu. « Light absorption spectra of naturally mixed phytoplankton assemblages for retrieval of phytoplankton group composition in coastal oceans ». Limnology and Oceanography 67, n^o 4 (8 mars 2022) : 946–61. http://dx.doi.org/10.1002/lno.12047.

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Russell, Dierssen et Hochberg. « Water Column Optical Properties of Pacific Coral Reefs Across Geomorphic Zones and in Comparison to Offshore Waters ». Remote Sensing 11, n^o 15 (25 juillet 2019) : 1757. http://dx.doi.org/10.3390/rs11151757.

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Despite the traditional view of coral reefs occurring in oligotrophic tropical conditions, water optical properties over coral reefs differ substantially from nearby clear oceanic waters. Through an extensive set of optical measurements across the tropical Pacific, our results suggest that coral reefs themselves exert a high degree of influence over water column optics, primarily through release of colored dissolved organic matter (CDOM). The relative contributions of phytoplankton, non-algal particles, and CDOM were estimated from measurements of absorption and scattering across different geomorphic shallow-water reef zones (<10 m) in Hawaii, the Great Barrier Reef, Guam, and Palau (n = 172). Absorption was dominated at the majority of stations by CDOM, with mixtures of phytoplankton and CDOM more prevalent at the protected back reef and lagoon zones. Absorption could be dominated by sediments and phytoplankton at fringing reefs and terrestrially impacted sites where particulate backscattering was significantly higher than in the other zones. Scattering at three angles in the backward direction followed recent measurements of the particulate phase function. Optical properties derived from satellite imagery indicate that offshore waters are consistently lower in absorption and backscattering than reef waters. Therefore, the use of satellite-derived offshore parameters in modeling reef optics could lead to significant underestimation of absorption and scattering, and overestimation of benthic light availability. If local measurements are not available, average optical properties based on the general reef zone could provide a more accurate means of assessing light conditions on coral reefs than using offshore water as a proxy.

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Kim, G. E., M. A. Pradal et A. Gnanadesikan. « Quantifying the biological impact of surface ocean light attenuation by colored detrital matter in an ESM using a new optical parameterization ». Biogeosciences 12, n^o 16 (28 août 2015) : 5119–32. http://dx.doi.org/10.5194/bg-12-5119-2015.

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Abstract. Light attenuation by colored detrital material (CDM) was included in a fully coupled Earth system model (ESM). This study presents a modified parameterization for shortwave attenuation, which is an empirical relationship between 244 concurrent measurements of the diffuse attenuation coefficient for downwelling irradiance, chlorophyll concentration and light absorption by CDM. Two ESM model runs using this parameterization were conducted, with and without light absorption by CDM. The light absorption coefficient for CDM was prescribed as the average of annual composite MODIS Aqua satellite data from 2002 to 2013. Comparing results from the two model runs shows that changes in light limitation associated with the inclusion of CDM decoupled trends between surface biomass and nutrients. Increases in surface biomass were expected to accompany greater nutrient uptake and therefore diminish surface nutrients. Instead, surface chlorophyll, biomass and nutrients increased together. These changes can be attributed to the different impact of light limitation on surface productivity versus total productivity. Chlorophyll and biomass increased near the surface but decreased at greater depths when CDM was included. The net effect over the euphotic zone was less total biomass leading to higher nutrient concentrations. Similar results were found in a regional analysis of the oceans by biome, investigating the spatial variability of response to changes in light limitation using a single parameterization for the surface ocean. In coastal regions, surface chlorophyll increased by 35 % while total integrated phytoplankton biomass diminished by 18 %. The largest relative increases in modeled surface chlorophyll and biomass in the open ocean were found in the equatorial biomes, while the largest decreases in depth-integrated biomass and chlorophyll were found in the subpolar and polar biomes. This mismatch of surface and subsurface trends and their regional dependence was analyzed by comparing the competing factors of diminished light availability and increased nutrient availability on phytoplankton growth in the upper 200 m. Understanding changes in biological productivity requires both surface and depth-resolved information. Surface trends may be minimal or of the opposite sign than depth-integrated amounts, depending on the vertical structure of phytoplankton abundance.

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Naik, Puneeta, et Eurico J. D’Sa. « Phytoplankton light absorption of cultures and natural samples : comparisons using two spectrophotometers ». Optics Express 20, n^o 5 (13 février 2012) : 4871. http://dx.doi.org/10.1364/oe.20.004871.

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Effler, Adam Joseph Peter, Feng Peng, Steven W. Effler, Christopher M. Strait, MaryGail Perkins et Kimberly L. Schulz. « Light absorption by phytoplankton and minerogenic particles in Cayuga Lake, New York ». Inland Waters 5, n^o 4 (1 octobre 2015) : 433–50. http://dx.doi.org/10.5268/iw-5.4.807.

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Ferrari, Giovanni M., et Stelvio Tassan. « A METHOD USING CHEMICAL OXIDATION TO REMOVE LIGHT ABSORPTION BY PHYTOPLANKTON PIGMENTS ». Journal of Phycology 35, n^o 5 (octobre 1999) : 1090–98. http://dx.doi.org/10.1046/j.1529-8817.1999.3551090.x.

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Greg Mitchell, B., et Dale A. Kiefer. « Chlorophyll α specific absorption and fluorescence excitation spectra for light-limited phytoplankton ». Deep Sea Research Part A. Oceanographic Research Papers 35, n^o 5 (mai 1988) : 639–63. http://dx.doi.org/10.1016/0198-0149(88)90024-6.

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Kim, G. E., M. A. Pradal et A. Gnanadesikan. « A new parameterization for surface ocean light attenuation in Earth System Models : assessing the impact of light absorption by colored detrital material ». Biogeosciences Discussions 12, n^o 5 (2 mars 2015) : 3905–42. http://dx.doi.org/10.5194/bgd-12-3905-2015.

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Abstract. Light limitation can affect the distribution of biota and nutrients in the ocean. Light absorption by colored detrital material (CDM) was included in a fully coupled Earth System Model using a new parameterization for shortwave attenuation. Two model runs were conducted, with and without light attenuation by CDM. In a global average sense, greater light limitation associated with CDM increased surface chlorophyll, biomass and nutrients together. These changes can be attributed to the movement of biological productivity higher up the water column, which increased surface chlorophyll and biomass while simultaneously decreasing total biomass. Meanwhile, the reduction in biomass resulted in greater nutrient availability throughout the water column. Similar results were found on a regional scale in an analysis of the oceans by biome. In coastal regions, surface chlorophyll increased by 35% while total integrated phytoplankton biomass diminished by 18%. The largest relative increases in modeled surface chlorophyll and biomass in the open ocean were found in the equatorial biomes, while largest decreases in depth-integrated biomass and chlorophyll were found in the subpolar and polar biomes. This mismatch of surface and subsurface trends and their regional dependence was analyzed by comparing the competing factors of diminished light availability and increased nutrient availability on phytoplankton growth in the upper 200 m. Overall, increases in surface biomass were expected to accompany greater nutrient uptake and therefore diminish surface nutrients, but changes in light limitation decoupled trends between these two variables. Understanding changes in biological productivity requires both surface and depth-resolved information. Surface trends may be minimal or of the opposite sign to depth-integrated amounts, depending on the vertical structure of phytoplankton abundance.

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Gorai, T., T. Katayama, M. Obata, A. Murata et S. Taguchi. « Low blue light enhances growth rate, light absorption, and photosynthetic characteristics of four marine phytoplankton species ». Journal of Experimental Marine Biology and Ecology 459 (octobre 2014) : 87–95. http://dx.doi.org/10.1016/j.jembe.2014.05.013.

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Wang, Shengqiang, Joji Ishizaka, Toru Hirawake, Yuji Watanabe, Yuanli Zhu, Masataka Hayashi et Sinjae Yoo. « Remote estimation of phytoplankton size fractions using the spectral shape of light absorption ». Optics Express 23, n^o 8 (14 avril 2015) : 10301. http://dx.doi.org/10.1364/oe.23.010301.

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Churilova, T., V. Suslin, H. M. Sosik, T. Efimova, N. Moiseeva, S. Moncheva, V. Mukhanov, O. Rylkova et O. Krivenko. « Phytoplankton light absorption in the deep chlorophyll maximum layer of the Black Sea ». European Journal of Remote Sensing 52, sup1 (24 octobre 2018) : 123–36. http://dx.doi.org/10.1080/22797254.2018.1533389.

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Sosik, Heidi M., et B. GREG Mitchell. « Light absorption by phytoplankton, photosynthetic pigments and detritus in the California Current System ». Deep Sea Research Part I : Oceanographic Research Papers 42, n^o 10 (octobre 1995) : 1717–48. http://dx.doi.org/10.1016/0967-0637(95)00081-g.

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Moiseeva, N. A., T. Ya Churilova, T. V. Efimova, V. A. Artemiev et E. Yu Skorokhod. « Spectral bio-optical properties of water of Atlantic sector of Antarctic ». Marine Biological Journal 5, n^o 4 (30 décembre 2020) : 69–78. http://dx.doi.org/10.21072/mbj.2020.05.4.06.

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Studies of variability of spectral bio-optical properties of water of Atlantic sector of Antarctic were carried out during the 79th cruise of the RV “Akademik Mstislav Keldysh” (11.01.2020–04.02.2020). Chlorophyll a and phaeopigment concentration varied in the layer studied from 0.1 to 1.8 mg·m−3, except for two stations with content reaching 2.2 and 4.4 mg·m−3. The relationship was revealed between light absorption coefficient by phytoplankton and chlorophyll a concentration at a wavelength, corresponding to spectrum maxima: aph(438) = 0.044 × Ca1.2, r2 = 0.84 (n = 117); aph(678) = 0.021 × Ca1.1, r2 = 0.89 (n = 117). Spectral distribution of light absorption coefficient by non-algal particles and colored dissolved organic matter was described by exponential function. Absorption parameterization coefficients were retrieved: (1) light absorption coefficient by non-algal particles (0.001–0.027 m−1) and by colored dissolved organic matter (0.016–0.19 m−1) at a wavelength of 438 nm; (2) spectral slope coefficients of these components (0.005–0.016 and 0.009–0.022 nm−1, respectively).

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Sein, Dmitry V., Anton Y. Dvornikov, Stanislav D. Martyanov, William Cabos, Vladimir A. Ryabchenko, Matthias Gröger, Daniela Jacob, Alok Kumar Mishra et Pankaj Kumar. « Indian Ocean marine biogeochemical variability and its feedback on simulated South Asia climate ». Earth System Dynamics 13, n^o 2 (13 avril 2022) : 809–31. http://dx.doi.org/10.5194/esd-13-809-2022.

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Abstract. We investigate the effect of variable marine biogeochemical light absorption on Indian Ocean sea surface temperature (SST) and how this affects the South Asian climate. In twin experiments with a regional Earth system model, we found that the average SST is lower over most of the domain when variable marine biogeochemical light absorption is taken into account, compared to the reference experiment with a constant light attenuation coefficient equal to 0.06 m−1. The most significant deviations (more than 1 ∘C) in SST are observed in the monsoon season. A considerable cooling of subsurface layers occurs, and the thermocline shifts upward in the experiment with the activated biogeochemical impact. Also, the phytoplankton primary production becomes higher, especially during periods of winter and summer phytoplankton blooms. The effect of altered SST variability on climate was investigated by coupling the ocean models to a regional atmosphere model. We find the largest effects on the amount of precipitation, particularly during the monsoon season. In the Arabian Sea, the reduction of the transport of humidity across the Equator leads to a reduction of the large-scale precipitation in the eastern part of the basin, reinforcing the reduction of the convective precipitation. In the Bay of Bengal, it increases the large-scale precipitation, countering convective precipitation decline. Thus, the key impacts of including the full biogeochemical coupling with corresponding light attenuation, which in turn depends on variable chlorophyll a concentration, include the enhanced phytoplankton primary production, a shallower thermocline, and decreased SST and water temperature in subsurface layers, with cascading effects upon the model ocean physics which further translates into altered atmosphere dynamics.

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Ruiz, Maria Guillermina, Vivian Alicia Lutz, Valeria Segura, Carla Florencia Berghoff et Rubén Mario Negri. « The color of EPEA : Variability in the in situ bio-optical properties in the period 2000 - 2017 ». Marine and Fishery Sciences (MAFIS) 33, n^o 2 (20 octobre 2020) : 205–25. http://dx.doi.org/10.47193/mafis.3322020301105.

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The “Estación Permanente de Estudios Ambientales” (EPEA, 38°28´ S 57°41´ W, Argentina) is an ecological time series of in situ observations started in 2000 aiming to assess changes in the marine environment and plankton communities under a global change scenario. Bio-optical properties are studied at EPEA since the color of the ocean undergoes temporal fluctuations, both for natural and anthropogenic causes. Here we assessed whether bio-optical properties at EPEA have changed during 2000-2017, identifying the occurrence of special events and inter-annual trends in these properties. An increasing trend in chlorophyll a concentration, possibly due to an increase in the smaller fraction of phytoplankton was observed. Although the absorption coefficient of phytoplankton did not follow a significant trend, it represented the occurrence of special events of high biomass suggesting that satellite information should be useful for the study site. The specific absorption coefficient of phytoplankton and the blue to red absorption ratio showed high values in summer and low in winter, according to the probable dominance of different size cells and their expected acclimation to the light regime. These results emphasize the relevance of periodic bio-optical in situ observations in understanding coastal ecosystems in a context of climate change.

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van de Poll, W. H., G. Kulk, K. R. Timmermans, C. P. D. Brussaard, H. J. van der Woerd, M. J. Kehoe, K. D. A. Mojica, R. J. W. Visser, P. D. Rozema et A. G. J. Buma. « Phytoplankton chlorophyll <i>a</i> ; biomass, composition, and productivity along a temperature and stratification gradient in the northeast Atlantic Ocean ». Biogeosciences 10, n^o 6 (25 juin 2013) : 4227–40. http://dx.doi.org/10.5194/bg-10-4227-2013.

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Abstract. Relationships between sea surface temperature (SST, > 10 m) and vertical density stratification, nutrient concentrations, and phytoplankton biomass, composition, and chlorophyll a (Chl a) specific absorption were assessed in spring and summer from latitudes 29 to 63° N in the northeast Atlantic Ocean. The goal of this study was to identify relationships between phytoplankton and abiotic factors in an existing SST and stratification gradient. Furthermore, a bio-optical model was used to estimate productivity for five phytoplankton groups. Nutrient concentration (integrated from 0 to 125 m) was inversely correlated with SST in spring and summer. SST was also inversely correlated with near-surface (0–50 m) Chl a and productivity for stratified stations. Near-surface Chl a and productivity showed exponential relationships with SST. Chl a specific absorption and excess light experiments indicated photoacclimation to lower irradiance in spring as compared to summer. In addition, Chl a specific absorption suggested that phytoplankton size decreased in summer. The contribution of cyanobacteria to water column productivity of stratified stations correlated positively with SST and inversely with nutrient concentration. This suggests that a rise in SST (over a 13–23 °C range) stimulates productivity by cyanobacteria at the expense of haptophytes, which showed an inverse relationship to SST. At higher latitudes, where rising SST may prolong the stratified season, haptophyte productivity may expand at the expense of diatom productivity. Depth-integrated Chl a (0–410 m) was greatest in the spring at higher latitudes, where stratification in the upper 200 m was weakest. This suggests that stronger stratification does not necessarily result in higher phytoplankton biomass standing stock in this region.

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Peperzak, L., H. J. van der Woerd et K. R. Timmermans. « Disparities between <i>Phaeocystis</i> ; in situ and optically-derived carbon biomass and growth rates : potential effect on remote-sensing primary production estimates ». Biogeosciences Discussions 11, n^o 4 (29 avril 2014) : 6119–49. http://dx.doi.org/10.5194/bgd-11-6119-2014.

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Abstract. The oceans play a pivotal role in the global carbon cycle. Unfortunately, the daily production of organic carbon, the product of phytoplankton standing stock and growth rate cannot be measured globally by discrete oceanographic methods. Instead, optical proxies from Earth-orbiting satellites must be used. To test the accuracy of optically-derived proxies of phytoplankton physiology and growth rate, standard ex situ data from the wax and wane of a Phaeocystis bloom in laboratory mesocosms were compared with hyperspectral reflectance data. Chlorophyll biomass could be estimated accurately from reflectance using specific chlorophyll absorption algorithms. However, the conversion of chlorophyll (Chl) to carbon (C) was obscured by the observed increase in C : Chl under nutrient-limited growth. C : Chl was inversely correlated (r2 = 0.88) with Photosystem II quantum efficiency (Fv/Fm), the in situ fluorometric oceanographic proxy for growth rate. In addition, the optical proxy for growth rate, the quantum efficiency of fluorescence &varphi; was linearly correlated to Fv/Fm (r2 = 0.84), but not – as by definition – by using total phytoplankton absorption, because during nutrient-limited growth the concentrations of non-fluorescent light-absorbing pigments increased. As a consequence, none of the three proxies (C : Chl, Fv/Fm, φ) was correlated to carbon or cellular phytoplankton growth rates. Therefore, it is concluded that although satellite derived estimates of chlorophyll biomass may be accurate, physiologically-induced non-linear shifts in growth rate proxies may obscure accurate phytoplankton growth rates and hence global carbon production estimates.

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Michel-Rodriguez, Monica, Sebastien Lefebvre, Muriel Crouvoisier, Xavier Mériaux et Fabrice Lizon. « Underwater light climate and wavelength dependence of microalgae photosynthetic parameters in a temperate sea ». PeerJ 9 (4 octobre 2021) : e12101. http://dx.doi.org/10.7717/peerj.12101.

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Studying how natural phytoplankton adjust their photosynthetic properties to the quantity and quality of underwater light (i.e. light climate) is essential to understand primary production. A wavelength-dependent photoacclimation strategy was assessed using a multi-color pulse-amplitude-modulation chlorophyll fluorometer for phytoplankton samples collected in the spring at 19 locations across the English Channel. The functional absorption cross section of photosystem II, photosynthetic electron transport (PETλ) parameters and non-photochemical quenching were analyzed using an original approach with a sequence of three statistical analyses. Linear mixed-effects models using wavelength as a longitudinal variable were first applied to distinguish the fixed effect of the population from the random effect of individuals. Population and individual trends of wavelength-dependent PETλ parameters were consistent with photosynthesis and photoacclimation theories. The natural phytoplankton communities studied were in a photoprotective state for blue wavelengths (440 and 480 nm), but not for other wavelengths (green (540 nm), amber (590 nm) and light red (625 nm)). Population-detrended PETλ values were then used in multivariate analyses (partial triadic analysis and redundancy analysis) to study ecological implications of PETλ dynamics among water masses. Two wavelength ratios based on the microalgae saturation parameter Ek (in relative and absolute units), related to the hydrodynamic regime and underwater light climate, clearly confirmed the physiological state of microalgae. They also illustrate more accurately that natural phytoplankton communities can implement photoacclimation processes that are influenced by in situ light quality during the daylight cycle in temporarily and weakly stratified water. Ecological implications and consequences of PETλ are discussed in the context of turbulent coastal ecosystems.

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Suggett, David J., Hugh L. MacIntyre et Richard J. Geider. « Evaluation of biophysical and optical determinations of light absorption by photosystem II in phytoplankton ». Limnology and Oceanography : Methods 2, n^o 10 (7 août 2004) : 316–32. http://dx.doi.org/10.4319/lom.2004.2.316.

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Stæhr, PA, S. Markager et K. Sand-Jensen. « Pigment specific in vivo light absorption of phytoplankton from estuarine, coastal and oceanic waters ». Marine Ecology Progress Series 275 (2004) : 115–28. http://dx.doi.org/10.3354/meps275115.

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Finkel, Z. V., et A. J. Irwin. « Light absorption by phytoplankton and the filter amplification correction : cell size and species effects ». Journal of Experimental Marine Biology and Ecology 259, n^o 1 (avril 2001) : 51–61. http://dx.doi.org/10.1016/s0022-0981(01)00225-8.

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Wang, Guifen, Wenxi Cao, Yuezhong Yang, Wen Zhou, Sheng Liu et Dingtian Yang. « Variations in light absorption properties during a phytoplankton bloom in the Pearl River estuary ». Continental Shelf Research 30, n^o 9 (mai 2010) : 1085–94. http://dx.doi.org/10.1016/j.csr.2010.02.010.

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Aiken, Jim, James Fishwick, Gerald Moore et Katharine Pemberton. « The annual cycle of phytoplankton photosynthetic quantum efficiency, pigment composition and optical properties in the western English Channel ». Journal of the Marine Biological Association of the United Kingdom 84, n^o 2 (avril 2004) : 301–13. http://dx.doi.org/10.1017/s0025315404009191h.

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Phytoplankton photosynthetic quantum efficiency (PQE), pigments, absorption characteristics, species composition (converted to phytoplankton carbon, Cph) and other variables were measured at an offshore site in the western English Channel throughout 2001, using an opportunistic weekly sampling schedule. The variation of chlorophyll-a (Chla) and other phytoplankton pigments followed the classical seasonal cycle, driven by incident light, patterns of stratification and nutrient availability. Phytoplankton and pigment concentrations were low in the winter, rising to a peak in the spring ‘bloom’, with episodic blooms throughout the summer, an autumn bloom and a decline to the winter minimum. Surface layer Chla and total pigment (Tpig) concentrations were highly correlated for the whole year, yet it was observed that the fraction of Chla in Tpig (Chla/Tpig) was not constant and had a distinct seasonal pattern, low in winter and higher in spring, summer and autumn blooms. Chlorophyll-a/Tpig was linearly correlated with recent ambient light fluxes and maximum PQE (PQEm) throughout most of the year, though more significantly within seasonal periods. Chlorophyll-a and Tpig were both linearly correlated to Cph and the Chla/Cph ratio was significantly correlated with both Chla/Tpig and PQEm. Also the optical absorption ratios, a674/a443 and a674/a490 were significantly correlated with PQE and Chla/Tpig, indicating probable optical signatures for these two parameters. The seasonal cycle of measurements of photosynthetic quantum efficiency provided a bench-mark against which all the photosynthetically-driven seasonal changes of biological properties can be understood, in terms of incident solar radiation and nutrient availability. We conclude that phytoplankton synthesize Chla preferentially to other pigments or carbon compounds in conditions beneficial to growth. The PQEm, the ratios of Chla/Tpig, Chla/Cph and a674/a443 are greater when plants are growing actively. In periods of nutrient sufficiency, PQEm, Chla/Tpig and a674/a443 are all linear functions of the mean total photon flux for the recent few days. Photosynthetically driven changes in Chla synthesis, cause observed changes of Chla/Tpig and Chla/Cph ratios.

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Wrigley, TJ, JM Chambers et AJ McComb. « Nutrient and gilvin levels in waters of coastal-plain wetlands in an agricultural area of Western Australia ». Marine and Freshwater Research 39, n^o 5 (1988) : 685. http://dx.doi.org/10.1071/mf9880685.

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The Peel-Harvey catchment lies on a sandy coastal plain, largely cleared for agriculture, and drains into a eutrophic estuarine system. Sixty-eight wetlands in the catchment had total phosphorus concentrations of 0.4-7.8 mg I-1, the high values being atrributed to agricultural activity. Conductivity was 150-8770 �S cm-1, pH 4.1-9.3. Waters contained high concentrations of gilvin, up to 262 g440 m-1 with a mean ratio of 6.2. Particulate material contributed little to light absorption at lower wavelengths (400-450 nm) but governed absorbance at 600-700 nm. Wetlands with the largest concen- trations of gilvin were located in the grey Bassendean sands, leachates from which had gilvin levels up to 748 g440 m-1. NO phytoplankton blooms were observed, and it is suggested that high gilvin levels and the consequent reduction in light penetration are important in maintaining low phytoplankton biomass in these lakes.

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Mercado, Jesús M., et Francisco Gómez-Jakobsen. « Seasonal variability in phytoplankton light absorption properties : Implications for the regional parameterization of the chlorophyll a specific absorption coefficients ». Continental Shelf Research 232 (janvier 2022) : 104614. http://dx.doi.org/10.1016/j.csr.2021.104614.

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Zheng, Guangming, et Dariusz Stramski. « A model based on stacked-constraints approach for partitioning the light absorption coefficient of seawater into phytoplankton and non-phytoplankton components ». Journal of Geophysical Research : Oceans 118, n^o 4 (avril 2013) : 2155–74. http://dx.doi.org/10.1002/jgrc.20115.

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Meler, Justyna, Sławomir B. Woźniak, Joanna Stoń-Egiert et Bogdan Woźniak. « Parameterization of phytoplankton spectral absorption coefficients in the Baltic Sea : general, monthly and two-component variants of approximation formulas ». Ocean Science 14, n^o 6 (11 décembre 2018) : 1523–45. http://dx.doi.org/10.5194/os-14-1523-2018.

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Abstract. This paper presents approximate formulas (empirical equations) for parameterizing the coefficient of light absorption by phytoplankton aph(λ) in Baltic Sea surface waters. Over a thousand absorption spectra (in the 350–750 nm range), recorded during 9 years of research carried out in different months of the year and in various regions of the southern and central Baltic, were used to derive these parameterizations. The empirical material was characterized by a wide range of variability: the total chlorophyll a concentration (Tchl a) varied between 0.31 and 142 mg m−3, the ratio of the sum of all accessory pigment concentrations to chlorophyll a (∑Ci/Tchla) ranged between 0.21 and 1.5, and the absorption coefficients aph(λ) at individual light wavelengths varied over almost 3 orders of magnitude. Different versions of the parameterization formulas were derived on the basis of these data: a one-component parameterization in the “classic” form of a power function with Tchl a as the only variable and a two-component formula – the product of the power and exponential functions – with Tchl a and ∑Ci/Tchla as variables. We found distinct differences between the general version of the one-component parameterization and its variants derived for individual months of the year. In contrast to the general variant of parameterization, the new two-component variant takes account of the variability of pigment composition occurring throughout the year in Baltic phytoplankton populations.

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Carvalho, Melissa, Aurea Maria Ciotti, Sônia Maria Flores Gianesella, Flávia Marisa Prado Saldanha Corrêa et Rafael Riani Costa Perinotto. « Bio-Optical Properties of the Inner Continental Shelf off Santos Estuarine System, Southeastern Brazil, and their Implications for Ocean Color Algorithm Performance ». Brazilian Journal of Oceanography 62, n^o 2 (juillet 2014) : 71–87. http://dx.doi.org/10.1590/s1679-87592014044506202.

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Optical characterizations of coastal water masses are important tools for a better understanding of physical and biochemical processes and aid the optimization of ocean color algorithms. In this study we present three optical classes of water observed during October/2005 and March/2006 on the inner continental shelf adjacent to Santos Bay (Brazil), based on remote sensing reflectance. ANOVA indicated a crescent estuarine influence in classes 1 to 3. Class 3 presented the highest chlorophyll-a and nutrient concentration and highest light absorption coefficients. Colored dissolved organic matter (CDOM) dominated the light absorption in all classes and was strongly correlated to salinity in October/2005 due to the influence of the La Plata plume. The results indicated that CDOM dynamics in the Santos inner shelf are very complex. The performance of global chlorophyll algorithms was significantly smaller for October/2005 than for March/2006. As inconsistent changes in light absorption spectra by phytoplankton were detected between samplings, the results show that future bio-optical algorithms for this region must be optimized preferentially considering CDOM optical parameters.

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Mai, Guangming, Xingyu Song, Xiaomin Xia, Zengling Ma, Yehui Tan et Gang Li. « Photosynthetic Characteristics of Smaller and Larger Cell Size-Fractioned Phytoplankton Assemblies in the Daya Bay, Northern South China Sea ». Microorganisms 10, n^o 1 (23 décembre 2021) : 16. http://dx.doi.org/10.3390/microorganisms10010016.

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Cell size of phytoplankton is known to influence their physiologies and, consequently, marine primary production. To characterize the cell size-dependent photophysiology of phytoplankton, we comparably explored the photosynthetic characteristics of piconano- (<20 µm) and micro-phytoplankton cell assemblies (>20 µm) in the Daya Bay, northern South China Sea, using a 36-h in situ high-temporal-resolution experiment. During the experimental periods, the phytoplankton biomass (Chl a) in the surface water ranged from 0.92 to 5.13 μg L−1, which was lower than that in bottom layer (i.e., 1.83–6.84 μg L−1). Piconano-Chl a accounted for 72% (mean value) of the total Chl a, with no significant difference between the surface and bottom layers. The maximum photochemical quantum yield (FV/FM) of Photosystem II (PS II) and functional absorption cross-section of PS II photochemistry (σPS II) of both piconano- and micro-cells assemblies varied inversely with solar radiation, but this occurred to a lesser extent in the former than in the latter ones. The σPS II of piconano- and micro-cell assemblies showed a similar change pattern to the FV/FM in daytime, but not in nighttime. Moreover, the fluorescence light curve (FLC)-derived light utilization efficiency (α) displayed the same daily change pattern as the FV/FM, and the saturation irradiance (EK) and maximal rETR (rETRmax) mirrored the change in the solar radiation. The FV/FM and σPS II of the piconano-cells were higher than their micro-counterparts under high solar light; while the EK and rETRmax were lower, no matter in what light regimes. In addition, our results indicate that the FV/FM of the micro-cell assembly varied quicker in regard to Chl a change than that of the piconano-cell assembly, indicating the larger phytoplankton cells are more suitable to grow than the smaller ones in the Daya Bay through timely modulating the PS II activity.

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