Characteristics of chromophoric and fluorescent dissolved organic matter in the Nordic Seas

• Published in: Ocean Science
• Main Authors: A. Makarewicz, P. Kowalczuk, S. Sagan, M. A. Granskog, A. K. Pavlov, A. Zdun, K. Borzycka, M. Zabłocka
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2018
• Subjects: Geography. Anthropology. Recreation; G; Environmental sciences; GE1-350; Norwegian Sea; Nordic Seas; Sea ice; Spitsbergen
• Online Access: https://doi.org/10.5194/os-14-543-2018; https://doaj.org/article/78d74c459b3342799d023ad911362cf1

Optical properties of chromophoric (CDOM) and fluorescent dissolved organic matter (FDOM) were characterized in the Nordic Seas including the West Spitsbergen Shelf during June–July 2013, 2014, and 2015. The CDOM absorption coefficient at 350 nm, a CDOM (350) showed significant interannual variation ( T test, p < 0.00001). In 2013, the highest average a CDOM (350) values ( a CDOM (350) = 0.30 ± 0.12 m −1 ) were observed due to the influence of cold and low-salinity water from the Sørkapp Current (SC) in the southern part of the West Spitsbergen Shelf. In 2014, a CDOM (350) values were significantly lower ( T test, p < 0.00001) than in 2013 (average a CDOM (350) = 0.14 ± 0.06 m −1 ), which was associated with the dominance of warm and saline Atlantic Water (AW) in the region, while in 2015 intermediate CDOM absorption (average a CDOM (350) = 0.19 ± 0.05 m −1 ) was observed. In situ measurements of three FDOM components revealed that fluorescence intensity of protein-like FDOM dominated in the surface layer of the Nordic Seas. Concentrations of marine and terrestrial humic-like DOM were very low and distribution of those components was generally vertically homogenous in the upper ocean (0–100 m). Fluorescence of terrestrial and marine humic-like DOM decreased in surface waters (0–15 m) near the sea ice edge due to dilution of oceanic waters by sea ice meltwater. The vertical distribution of protein-like FDOM was characterized by a prominent subsurface maximum that matched the subsurface chlorophyll a maximum and was observed across the study area. The highest protein-like FDOM fluorescence was observed in the Norwegian Sea in the core of warm AW. There was a significant relationship between the protein-like fluorescence and chlorophyll a fluorescence ( R 2 = 0.65, p < 0.0001, n = 24 490), which suggests that phytoplankton was the primary source of protein-like DOM in the Nordic Seas and West Spitsbergen Shelf waters. Observed variability in selected spectral indices (spectral slope coefficient, S 300–600 ...