Abstract
Data on the light absorption by seawater and its components are needed in many theoretical and practical aspects of marine science and engineering. However, up to now, there is a lack of such data for the northeastern part of the Black Sea. This article presents the data on light absorption measured by a portable integrated cavity absorption meter (ICAM) spectrophotometer in the Gelendzhik region of the Black Sea during field studies in June 2017 and 2018, together with other bio-optical and oceanographic data from in situ measurements and satellite observations. In 2018, the elevated values of the colored dissolved organic matter (CDOM) absorption in the surface layer were observed concurrently with high values of salinity, contradicting the idea of river runoff being the main CDOM source. The vertical profiles of salinity differed in 2017 and 2018, especially in shallow waters; in the upper layer, the salinity increased from 17.1 psu in 2017 to 17.8 psu in 2018, while the values of CDOM absorption increased from 0.10 to 0.16 m−1. The analysis of available hydrometeorological data pointed to intensive vertical mixing due to the strong wind forcing as a main factor in increasing values of both salinity and the CDOM absorption in the surface layer in 2018.
Highlights
This work is aimed at studying the inter-annual variability of the light absorption properties of seawater in the surface layer of the northeastern part of the Black Sea
The seawater absorption properties depend on the content of optically active components of seawater, such as the colored dissolved organic matter (CDOM), phytoplankton pigments, detritus and other particles, and the seawater itself
One can see the pronounced inter-annual variability of the bio-optical parameters compared with the seasonal variability of the climatic values
Summary
The problem was practically solved with the idea of using the integrating sphere to collect the scattered light at the photodetector such that the losses were caused only by absorption This idea was implemented in a laboratory seawater light absorption meter “Volna” [1], which provided the first mass data on spectral light absorption by seawater and its components from measurements in the Atlantic and Pacific Oceans in 1971, as well as in the Baltic Sea [2]. First measurements of spectral absorption by seawater components, including CDOM, at a modern level, were carried out at the beginning of this century; recently, they were aimed at developing satellite algorithms for the separate determination of absorption by chlorophyll and yellow substance [12,13]. The yellow substance absorption coefficient ag is used, which is calculated from satellite data [14] The results of these studies are presented in References [15,16,17]. A detailed description of the measurement procedure and calculation is given in Reference [23]
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