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Measurements of light absorption coefficients by particles suspended in seawater (ap(λ)), by phytoplankton (aph(λ)) and detritus (ad(λ)) were carried out in the southern Baltic Sea for the original seawater samples and four size fractions: pico-particles (0.2–2 µ m), ultra-particles (2–5 µ m), nano-particles (5–20 µ m) and micro-particles (20–200 µ m). Chlorophyll a (Chl a) and suspended particulate matter (SPM) concentrations were determined. The proportions of particles from the size classes in the ap (443), aph (443) and ad (443) were determined. Pico- and ultra-particles had the largest contribution to the total particle absorption – an average of 38 % and 31 %. Particles of 5–20 µ m accounted for approximately 20 % of ap (443) and aph (443) and 29 % of ad (443). The contribution of particles > 20 µ m averaged 5 %–10 %. In total SPM contribution of micro-particles averaged 17 %; nano-, ultra- and pico-particles averaged 29 %, 26 % and 27 %, respectively. In total Chl a , the proportions of pico- and ultra-particles averaged 35 % each, nano-particles 16 % and micro-particles 15 %. Temporal and spatial variability of particles contributions in size classes were observed. The average chlorophyll-specific and mass-specific light absorption coefficients, i.e., light absorption coefficients normalized to Chl a or SPM, were determined for all size fractions. The chlorophyll-specific coefficients ap(Chla)(λ) , ad(Chla)(λ) and aph(Chla)(λ) , ± standard deviations, do not allow clear separation of the individual fractions. For mass-specific coefficients, ap(SPM)(λ) , ad(SPM)(λ) and aph(SPM)(λ) , it is possible to distinguish between large particles (20–200 µ m) and small and medium particles (0.2–20 µ m). These results will allow monitoring of suspended matter in size classes in optically complex waters of southern Baltic Sea. [ABSTRACT FROM AUTHOR]

Measurements of light absorption coefficients by particles suspended in seawater (ap (λ)), by phytoplankton (aph(λ)) and detritus (ad (λ)) were carried out in the Baltic Sea waters. Measurements were performed for the original (unfiltered) seawater samples and the four selected size fractions: pico-particles with diameters (0.2–2 μm), ultra-particles with diameters (2–5 μm), nano-particles with diameters (5–20 μm) and micro-particles (20–200 μm). Chlorophyll a (Chla) concentrations and total suspended particulate matter (SPM) concentrations were determined. The proportions of particles from the size classes (micro, nano, ultra and pico) in the total light absorption by particles, phytoplankton and detritus were determined. Particles with sizes < 5 μm (i.e. pico and ultra-particles) had the largest contribution to the total particles absorption – an average of 38 % and 31 %. Particles of 5–20 μm accounted for approximately 20 % of all particles and phytoplankton and 29 % of the detritus. The contribution of large particles > 20 µm averaged 5–10 %. The average chlorophyll-specific and mass-specific light absorption coefficients, i.e. light absorption coefficients normalized to Chla and to SPM concentration, were determined for all size fractions. The determined average chlorophyll-specific light absorption coefficients ap(Chla)(λ), ad(Chla)(λ) and aph(Chla)(λ), along with standard deviations, do not allow clear separation of the individual fractions. For mass-specific light absorption coefficients, ap(SPM)(λ), ad(SPM)(λ) and aph(SPM)(λ), it is possible to distinguish between large particle fractions (microplankton – 20–200 μm) and small and medium particle fractions (0.2–20 μm). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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]

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]

A number of methods for indirectly estimating the size structure of the phytoplankton population in the Baltic Sea were analysed. These analyses were based on ~1000 samples of phytoplankton pigment concentrations and light absorption coefficients taken from surface waters, mainly in the southern Baltic Sea. Standard reference methods of diagnostic pigment analysis (DPA), originally developed for open ocean conditions, were employed to determine the proportions of pico-, nano- and microplankton groups in the population. A new preliminary modification of DPA, better adapted to the specific nature of the phytoplankton population in the Baltic Sea, is also proposed. Specific relationships between diagnostic pigments and chlorophyll a concentration are taken into account. The accuracies of different methods potentially useful in remote sensing observations of the Baltic Sea were examined. Several standard methods based on the total abundance of phytoplankton known from the literature were compared with the two new proposed variants. One with the newly developed typical Baltic pattern of change, representing the average relationship between the chlorophyll a concentration and the percentage contributions of the various size groups, and the other based on spectral absorption properties. The comparison indicated that if the standard methods known from the literature were applied to Baltic data, the estimates would be encumbered with significant errors, both systematic (up to ±30%) and statistical (up to 24%). It was also shown that the systematic errors of such estimates could be substantially reduced by applying one of the two preliminary variants of the methods proposed here. • Methods for estimating the phytoplankton population size structure were compared. • Standard literature methods are subject to significant systematic errors. • Preliminary modified calculation methods for the Baltic Sea are proposed. • Modified version of the diagnostic pigment analysis method for Baltic phytoplankton • New pattern of changes in the proportions of size groups with chlorophyll a [ABSTRACT FROM AUTHOR]

The paper presents the modelling results of selected characteristics of water-leaving light in an optically complex nearshore marine environment. The modelled quantities include the spectra of the remote-sensing reflectance Rrs(λ) and the hue angle α, which quantitatively describes the colour of water visible to the unaided human eye. Based on the latter value, it is also possible to match water-leaving light spectra to classes on the traditional Forel-Ule water colour scale. We applied a simple model that assumes that seawater is made up of chemically pure water and three types of additional optically significant components: particulate organic matter (POM) (which includes living phytoplankton), particulate inorganic matter (PIM), and chromophoric dissolved organic matter (CDOM). We also utilised the specific inherent optical properties (SIOPs) of these components, determined from measurements made at a nearshore location on the Gulf of Gdańsk. To a first approximation, the simple model assumes that the Rrs spectrum can be described by a simple function of the ratio of the light backscattering coefficient to the sum of the light absorption and backscattering coefficients (u = bb/(a + bb)). The model calculations illustrate the complexity of possible relationships between the seawater composition and the optical characteristics of an environment in which the concentrations of individual optically significant components may be mutually uncorrelated. The calculations permit a quantitative interpretation of the Forel-Ule scale. The following parameters were determined for the several classes on this scale: typical spectral shapes of the u ratio, possible ranges of the total light absorption coefficient in the blue band (a(440)), as well as upper limits for concentrations of total and organic and inorganic fractions of suspended particles (SPM, POM and PIM concentrations). The paper gives examples of practical algorithms that, based on a given Rrs spectrum or some of its features, and using lookup tables containing the modelling results, enable to estimate the approximate composition of seawater. [ABSTRACT FROM AUTHOR]