Optical characteristics of CDOM in meromictic water bodies (White Sea) and their relationship with salinity

Abstract

Chromophoric dissolved organic matter (CDOM) - a coloured fraction of dissolved organic matter (DOM) - is an important component of aquatic ecosystems, as it affects a spectral composition of sunlight passing through water. Optical characteristics of DOM provide information about quantity, origin and processes of transformation of DOM in aquatic systems. Inverse relation between absorption in UV range (which characterises concentration of DOM) and salinity is usually observed in coastal areas: high values of optical density correspond to low salinity and vice versa. Optical properties of DOM in two meromictic water bodies of Kandalaksha Gulf on the White Sea (lakes Yelovoe and Trekhtsvetnoe) are researched in this work. Increase of salinity with depth is observed in these unique hydrological objects: surface water is fresh or lightly salted, relict sea water is located down below. Water samples were taken with submersible pump on various depths in summer of 2026. Optical indexes, fluorescence quantum yield were calculated by spectres measured with spectrophotometer. While salinity increased with depth, optical characteristics, as a rule, were changing gradually, which characterises conservative mixing of fresh and sea water along the salinity gradient. However in some cases abnormal behavior of spectral-optical characteristics of DOM was observed. Such behavior is explained by photodiscolouration of DOM, formation of autochronous DOM or accumulation of it in bottom layer. Understanding reasons of changeability of optical properties of DOM is of key importance when solving problems like distance sounding, research of carbon cycle and ecological monitoring of coastal waters.

Speaker

Anastasia I. Deeva
Faculty of Physics, Lomonosov Moscow State University, Moscow, Russia
Russia

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