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The paper presents approximate formulas 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 nine 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 analysed empirical material was characterized by a wide range of variability: the total chlorophyll a concentration (Tchla) varied between 0.3 and > 140 mg m-3, the ratio of the sum of all accessory pigment concentrations to chlorophyll a (ΣCi/Tchla) varied between 0.21 and 1.5, and the absorption coefficients aph (λ) at individual light wavelengths varied over almost three orders of magnitude. Different versions of the parameterization formulas were derived on the basis of the data gathered: a one-component parameterization in the "classic" form of a power function with Tchla as the only variable, and a two-component formula - the product of the power and exponential functions, with Tchla and ΣCi/Tchla as variables. There were distinct differences between the general version of the one-component parameterization and its variants developed for individual months of the year. In contrast to the general parameterization, both the monthly and the two-component variants enable, at least partially, the variability of pigment composition occurring throughout the year in the Baltic phytoplankton populations examined here to be taken into account. [ABSTRACT FROM AUTHOR]

This paper analyses the relationships between the light absorption coefficients at 440 nm a p (440) for particles suspended in the surface waters of the southern Baltic Sea and the concentrations of some optically significant constituents in these waters. The analysis covers two main groups of particles: phytoplankton and non-algal. For this purpose we use the extensive database of optical measurements acquired from 2006 to 2013 during 40 cruises of r/v Oceania in various regions of the southern Baltic: open waters, coastal waters, the Gulf of Gdańsk, the Pomeranian Bay and river mouths. Expressions are derived for each of these regions to describe the seasonal variations of the dependence of the light absorption coefficients for phytoplankton a ph (440) and non-algal particles a NAP (440) on concentrations of chlorophyll a ( Tchla ) and suspended particulate matter in sea water (SPM). With a knowledge of these dependences, one can determine the overall absorption coefficient for all suspended particles in any part of the Baltic Sea in particular seasons from known Tchla and SPM concentrations using the relationship a p (440) = a ph (440) + a NAP (440) = f( Tchla , SPM). These dependences reflect the characteristics of a study area and season, and their application increases the accuracy of determination of the overall absorption properties of suspended particles and their main constituents as confirmed by statistical error reduction, e.g. standard error factor falls from 1.46 to 1.38. The relationships derived in this work can be applied in the local remote sensing algorithms used for monitoring the southern Baltic. [ABSTRACT FROM AUTHOR]

The paper addresses the seasonal variability of coefficients of light absorption by suspended particulate matter a p (λ) in different regions of the Baltic Sea: open-sea waters, coastal waters, the Gulf of Gdańsk, the Pomeranian Bay and river mouths. We analysed 865 spectra of light absorption by phytoplankton a ph (λ) and non-algal particles a NAP (λ) in different seasons during 35 cruises of r/v Oceania in the southern Baltic from 2006 to 2012. Depending on season and region, we found distinct differences in the absorption properties of particles suspended in the water with respect both to the spectral shapes of the coefficients a p (λ), a ph (λ) and a NAP (λ), and to the values at the characteristic wavelength of 440 nm. The proportions of phytoplankton governing the absorption properties of the suspended matter varied from 50 to 75%, whereby the greatest spread of these proportions was found in open waters. In contrast, the greatest seasonal variability in the overall absorption coefficients a p occurred in coastal waters. The absolute values of coefficients a ph (λ) and a NAP (λ) at wavelength 440 nm in the different types of water and seasons varied respectively over three and four orders of magnitude. In river mouth waters the mean values of a ph (440) were nearly twelve times and a NAP (440) over twenty times greater than in open sea waters. The absorption properties of non-algal particles exhibited a greater regional than seasonal variability, achieving the lowest values in open and coastal waters (0.006–0.31 m −1 ), and the highest ones in river mouths (0.199–4.196 m −1 ). [ABSTRACT FROM AUTHOR]

This study presents three alternative models for estimating the absorption properties of chromophoric dissolved organic matter aCDOM(λ). For this analysis we used a database containing 556 absorption spectra measured in 2006-2009 in different regions of the Baltic Sea (open and coastal waters, the Gulf of Gdansk and the Pomeranian Bay), at river mouths, in the Szczecin Lagoon and also in three lakes in Pomerania (Poland) -- Obłęskie, Łebsko and Chotkowskie. The variability range of the chromophoric dissolved organic matter (CDOM) absorption coefficient at 400nm, aCDOM(400), lay within 0.15-8.85m-1. The variability in aCDOM(λ) was parameterized with respect to the variability over 3 orders of magnitude in the chlorophyll a concentration Chl a (0.7-119 mg m-3). The chlorophyll a concentration and aCDOM(400) were correlated, and a statistically significant, nonlinear empirical relationship between these parameters was derived (R² = 0.83). On the basis of the covariance between these parameters, we derived two empirical mathematical models that enabled us to design the CDOM absorption coefficient dynamics in natural waters and reconstruct the complete CDOM absorption spectrum in the UV and visible spectral domains. The input variable in the first model was the chlorophyll a concentration, and in the second one it was aCDOM(400). Both models were fitted to a power function, and a second-order polynomial function was used as the exponent. Regression coefficients for these formulas were determined for wavelengths from 240 to 700nm at 5nm intervals. Both approximations reflected the real shape of the absorption spectra with a low level of uncertainty. Comparison of these approximations with other models of light absorption by CDOM demonstrated that our parameterizations were superior (bias from -1.45 to 62%, RSME from 22 to 220 %) for estimating CDOM absorption in the optically complex waters of the Baltic Sea and Pomeranian lakes. [ABSTRACT FROM AUTHOR]