ИСТИНА

The Laptev Sea surface waters with salinities varying from 3 to 30 psu allow to study optical properties of cromophoric dissolved organic matter (CDOM) along a salinity gradient. We describe the results of on-board measurements of spectral properties for surface water sampled along 130°E, from the river Lena estuary to the near-oceanic environments. Absorption spectra were measured in the wavelength range 200-650 nm. Fluorescence emission spectra were excited with wavelengths ranging from 230 to 550 nm. The specific UV absorbance index (SUVA) calculated by normalizing the absorbance at 254 nm to the DOC concentration was found similar in different locations of the Laptev Sea shelf (2.41-2.52 m2 g C-1) but increased significantly at the continental slope (5.25 m2 g C-1). The absorption slope ratio SR increased from 0.93 at the Lena Delta region to 1.07 near the continental slope, indicating distribution of terrestrial CDOM throughout the Laptev Sea shelf. CDOM fluorescence spectra typically manifested a single humic-type band with a maximum at 425-455 nm depending on the excitation wavelength. Change in excitation from 270 to 310 nm lead to the so called “blue shift” of CDOM fluorescence emission to shorter wavelengths up to 30 nm. CDOM fluorescence intensity decreased with the distance from the river Lena due to the mixing of river and marine waters. For the samples collected near the continental slope the UV protein-like fluorescence within 290-320 nm became observable indicating the presence of labile autochthonous organic matter. This study was financially supported by the Russian Foundation for Basic Research, grant №16-35-60032 mol_a_dk.