Articles | Volume 12, issue 4
Ocean Sci., 12, 1013–1032, 2016
Ocean Sci., 12, 1013–1032, 2016

Research article 26 Aug 2016

Research article | 26 Aug 2016

Parameterization of the light absorption properties of chromophoric dissolved organic matter in the Baltic Sea and Pomeranian lakes

Justyna Meler1, Piotr Kowalczuk1, Mirosława Ostrowska1, Dariusz Ficek2, Monika Zabłocka1, and Agnieszka Zdun1 Justyna Meler et al.
  • 1Institute of Oceanology Polish Academy of Sciences, Powstańców Warszawy 55, 81-712 Sopot, Poland
  • 2Institute of Physics, Pomeranian University of Słupsk, Bohaterów Westerplatte 64, 76-200 Słupsk, Poland

Abstract. 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 Gdańsk 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 400 nm, aCDOM(400), lay within 0.15–8.85 m−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 700 nm at 5 nm 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.

Short summary
Three alternative models for estimation of absorption of chromophoric dissolved organic matter (CDOM) have been formulated. The models were based on empirical database containing measurements from different regions of the Baltic Sea and three Pomeranian lakes in Poland. An assumption regarding continuum of inherent optical properties in marine and estuarine waters and freshwater has been proved and enabled the accurate estimation of CDOM absorption in various environments.