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Light absorption by phytoplankton in the southern Baltic and Pomeranian lakes: mathematical expressions for remote sensing applications

Meler J., Ostrowska M., Ficek D., Zdun A.

Oceanologia

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2017

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No. 59 (3)

195--212

EN

The absorption properties of phytoplankton in surface waters of the Baltic Sea and coastal lakes are examined in the context of their relationships with the concentration of the main photosynthetic pigment, chlorophyll a. The analysis covers 425 sets of spectra of light absorption coefficients aph (λ) and chlorophyll a concentrations Chla measured in 2006–2009 in various waters of the Baltic Sea (open and coastal waters, the Gulf of Gdańsk and the Pomeranian Bay, river mouths and the Szczecin Lagoon), as well as in three lakes in Pomerania, Poland (Obłęskie, Łebsko and Chotkowskie). In these waters the specific (i.e. normalized with respect to Chla) light absorption coefficient of phytoplankton aph*(λ) varies over wide ranges, which differ according to wavelength. For example, aph*(440) takes values from 0.014 to 0.124 mg−1 m2, but aph*(675) from 0.008 to 0.067 mg−1 m2, whereby Chla ranges from 0.8 to 120 mg m−3. From this analysis a mathematical description has been produced of the specific light absorption coefficient of phytoplankton aph*(λ), based on which the dynamics of its variability in these waters and the absorption spectra in the 400–700 nm interval can be reconstructed with a low level of uncertainty (arithmetic statistical error: 4.09–10.21%, systematic error: 29.63–51.37%). The relationships derived here are applicable in local remote sensing algorithms used for monitoring the Baltic Sea and coastal lakes and can substantially improve the accuracy of the remotely determined optical and biogeochemical characteristics of these waters.

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Seasonal variability in the optical properties of Baltic aerosols

Zdun A., Rozwadowska A., Kratzer S.

Oceanologia

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2011

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No. 53 (1)

7-34

EN

A five-year dataset of spectral aerosol optical thickness was used to analyse the seasonal variability of aerosol optical properties (the aerosol optical thickness (AOT) at wavelength λ=500 nm, AOT(500) and the Angström exponent for the 440-870 nm spectral range, α(440, 870)) over the Baltic Sea and dependence of these optical properties on meteorological factors (wind direction, wind speed and relative humidity). The data from the Gotland station of the global radiometric network AERONET (Aerosol Robotic Network, http://aeronet.gsfc.nasa.gov) were taken to be representative of the Baltic Sea conditions. Meteorological observations from Farosund were also analysed. Analysis of the data from 1999 to 2003 revealed a strong seasonal cycle in AOT(500) and α(440, 870). Two maxima of monthly mean values of AOT(500) over the Baltic were observed. In April, an increase in the monthly mean aerosol optical thickness over Gotland most probably resulted from agricultural waste straw burning, mainly in northern Europe and Russia as well as in the Baltic states, Ukraine and Belarus. During July and August, the aerosol optical thickness was affected by uncontrolled fires (biomass burning). There was a local minimum of AOT(500) in June. Wind direction, a local meteorological parameter strongly related to air mass advection, is the main meteorological factor influencing the variability of aerosol optical properties in each season. The highest mean values of AOT(500) and α(440, 870) occurred with easterly winds in both spring and summer, but with southerly winds in autumn

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Inherent optical properties of suspended particulate matter in the southern Baltic Sea

Woźniak S.B., Meler J., Lednicka B., Zdun A., Stoń-Egiert J.

Oceanologia

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2011

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No. 53 (3)

691-729

EN

The inherent optical properties (IOPs) of suspended particulate matter and their relations with the main biogeochemical characteristics of particles have been examined in the surface waters of the southern Baltic Sea. The empirical data were gathered at over 300 stations in open Baltic Sea waters as well as in the coastal waters of the Gulf of Gdańsk. The measurements included IOPs such as the absorption coefficient of particles, absorption coefficient of phytoplankton, scattering and backscattering coefficients of particles, as well as biogeochemical characteristics of suspended matter such as concentrations of suspended particulate matter (SPM), particulate organic matter (POM), particulate organic carbon (POC) and chlorophyll a (Chl a). Our data documented the very extensive variability in the study area of particle concentration measures and IOPs (up to two orders of magnitude). Although most of the particle populations encountered were composed primarily of organic matter (av. POM/SPM = ca 0.8), the different particle concentration ratios suggest that the particle composition varied significantly. The relations between the optical properties and biogeochemical parameters of suspended matter were examined. We found significant variability in the constituent-specific IOPs (coefficients of variation (CVs) of at least 30% to 40%, usually more than 50%). Simple best-fit relations between any given IOP versus any constituent concentration parameter also highlighted the significant statistical errors involved. As a result, we conclude that for southern Baltic samples an easy yet precise quantification of particle IOPs in terms of the concentration of only one of the following parameters - SPM, POM, POC or Chl a - is not achievable. Nevertheless, we present a set of best statistical formulas for a rough estimate of certain seawater constituent concentrations based on relatively easily measurable values of seawater IOPs. These equations can be implemented in practice, but their application will inevitably entail effective statistical errors of estimation of the order of 50% or more.