LIGHT ABSORPTION BY PHYTOPLANKTON, NON-ALGAL PARTICLES AND COLORED DISSOLVED ORGANIC MATTER IN THE SEA OF AZOV IN JANUARY AND APRIL 2016 Churilovaa T., Efimovaa T., Moiseevaa N., Georgievaa E., Suslinb V., Krivenkoa O. a
MHI
Kovalevsky Institute of Marine Biological Research RAS, 2 Nakhimov, Sevastopol, 299011, Russian Federation; b Marine Hydrophysical Institute RAS, 2 Kapitanskaya Str., Sevastopol, 299011, Russian Federation IBSS
e-mails:
[email protected]
Standard algorithms of remote assessment of chlorophyll a concentration in upper layer of the Sea of Azov do not provide correct estimations (Saprigin, 2011). To transform correctly satellite data to chlorophyll a concentration and other water quality and productivity indicators it is required to develop regional algorithms based on knowledge about the variability of light absorption by all in-water optically active components, their relative contribution to total light absorption and their link with chlorophyll a concentration. The Sea of Azov bio-optical data are extremely limited, and in particular there is no available information about light absorption by phytoplankton, non-algal particles (NAP) and colored dissolved organic matter (CDOM). The aim of the current research is to investigate variability of light absorption coefficients by phytoplankton (ππβ π ), by NAP (πππ΄π π ) and CDOM (ππΆπ·ππ π ), chlorophyll a concentrations in the Sea of Azov in January and April 2016. The water sampling was conducted during two cruises of RV βProfessor Vodyanitskyβ in January (PV 83) and April 2016 (PV 84). Chlorophyll a and phaeopigment concentrations were determined by spectrophotometrically method (Jeffrey, Humphrey, 1975; Lorenzen, 1967). CDOM light absorption coefficients were measured in accordance with NASA protocol (Mitchell et al, 2003). Particulate absorption was determined by the filter pad technique (Yentsch, 1962; Mitchell, Kiefer, 1988). Optical measurements were carried out with a dual-beam spectrophotometer (Lambda 35, Perkin Elmer) equipped with an integrating sphere. Particulate absorption (ap(Ξ»)) was separated on light absorption by phytoplankton pigments (aph(Ξ»)) and by non-algal particles (aNAP(Ξ»)) (Tassan, Ferrari, 1995). Spectral distribution of aCDOM(Ξ») and aNAP(Ξ») was described with exponential function.
Fig. 1. Map of the stations carried out in the sea of Azov in January (filled symbols) and in April (open symbols) 2016.
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y(January) = 0.037 x 0.660, r2=0.97 y (April) = 0.050 x0.73, r2=0.91 y= 0.0378 x 0.627 (Bricaud et al., 1995) y= 0.045 x 0.82 (Churilova et al., 2017)
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Fig. 2. Spectra of light absorption by phytoplankton pigment (ππβ π ), non-algal particles (πππ΄π π ), colored dissolved organic matter (ππΆπ·ππ π ) in January (blue line) and in April (green line) 2016
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Fig. 3. Relationship between phytoplankton light absorption coefficients at 440 nm ( ππβ (440) ) and chlorophyll a concentrations in sum with phaeopigments (Chl-a) in the Sea of Azov in January (blue) and April (green) in comparison with the data obtained in global ocean (red) (Bricaud et al, 1995) and in the Black Sea in winter (purple) (Churilova et al, 2017).
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Fig. 4. Dependence of chlorophyll a specific light absorption coefficients of phytoplankton at wavelength ~ β β 440 nm (ππβ (440)) and ~ 678 nm (ππβ (678)) and their ratio (R) of chlorophyll a concentration (Chl-a) in January (blue symbols) and in April (green symbols) 2016 in comparison with global ocean data (red line) disrobed in (Bricaud et al, 1995).
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Fig. 5. Relationship between colored dissolved organic matter light absorption coefficients (ππΆπ·ππ π ) at 440 nm ( ππΆπ·ππ 440 ) and slope coefficients of spectra distribution of ππΆπ·ππ π (ππΆπ·ππ ) in January (blue symbols) and April (green symbols) 2016.
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Fig. 6. Contribution of the phytoplankton light absorption ( ππβ 440 ), non-algal particles ( πππ΄π 440 ) and colored dissolved organic matter (ππΆπ·ππ 440 ) in total light absorption (ππ‘ππ‘ ) at 440 nm in January (blue symbols) and in April (green symbols) 2016.
CONCLUSIONS: For the first time, biooptical studies were carried out in the Sea of Azov and new data were obtained on the light absorption by phytoplankton pigments, suspended and colored dissolved organic matter in the Sea of Azov. These data could be used as a basis for the development of regional algorithms for remote assessment of Chl-a and aCDM in optically complex waters of the Sea of Azov. Acknowledge: This research was funded by Russian Academy of Science (grants β ΠΠΠΠ-Π18-118020790229-7 and ΠΠΠΠ-Π18-118012690119-7) and partly supported by the Russian Foundation for Basic Research (projects β 18-05-80025 and β 17-05-00113).
