Significant anaerobic production of fluorescent dissolved organic matter in the deep East Sea (Sea of Japan)

Abstract

The distribution of fluorescent dissolved organic matter (FDOM) in the East Sea (Sea of Japan) was examined by excitation‐emission matrix spectroscopy with parallel factor analysis (PARAFAC). Humic‐like FDOM (FDOMH) increased with depth and was significantly correlated with Apparent Oxygen Utilization (AOU), indicating that FDOMH in the deep water is mainly produced by oxidation of organic matter. In addition, a surprisingly large excess of FDOMH relative to that expected from the observed AOU was found from 1000 m to the bottom (up to 3500 m). Based on the high‐resolution geographical distribution and characteristics of FDOM in the East Sea, we conclude that this excess likely originates from anaerobic FDOMH production in subsurface bottom sediments. This FDOMH flux accounts for 8–15% of the total FDOM production in the water column. Our results suggest that anaerobic activities in subsurface sediments are an important hidden source of FDOM in the ocean.

Black Sea dissolved organic matter dynamics: Insights from optical analyses

“…Sediments have been identified as a source of CDOM and FDOM in the Baltic Sea and Sea of Japan, as evidenced by their correlation with AOU changing in the respective basin's deep waters (Kowalczuk et al ; Kim and Kim ). In the AOL, the relationships between FDOM and CDOM with ACM are consistent with depth, suggesting that sediments are not a direct source of FDOM.…”

“…For humic-like samples, Hayase and Shinozuka (H and S) reported values from five station in fluorescence units (flu), Yamashita and Tanoue (Y and T) reported values from the mesopelagic northern and southern hemispheres (MNH and MSH, respectively) and abyssal waters in normalized fluorescence units (N.FI.U. ), Jørgensen et al (2011) reported values from two components in RU, and Kim and Kim (2016) reported values from two components in intermediate and deep waters in quinine sulfate units (QSU). "NR" denotes the y-intercepts from previous studies that were not reported.…”

Significant Seasonal Change in Optical Properties by atmospheric humic-like substances (HULIS) in Water-Soluble Organic Carbon Aerosols

“…The spectral characteristics of component 1 (C1; Ex/Em = 305/416 nm) refer to humic substances, which are assigned to peak M, while component 3 (C3; Ex/Em = 365/484 nm) is 15 associated with terrestrial humic substances, which are assigned to peak C (Table S1) (Birdwell and Engel, 2010;Coble, 2007). Component 2 (C2; Ex/Em = 290/340 nm) represents a protein-like (tryptophan-like) component, which is assigned to peak T and is mostly originated from autochthonous biological production (Table S1) (Birdwell and Engel, 2010;Coble, 2007;Kim and Kim, 2016). However, C2 and C3 seem to be highly influenced by the most abundant and dominant fluorophore C1 because of its high intensity and large spectral area compared to other two components.…”

“…It has been widely accepted that photochemical degradation is an important process for the efficient removal of 5 chromophoric dissolved organic matter (CDOM) that absorbs and fluoresces at certain wavelengths of light under solar radiation in aquatic ecosystems, which alters absorption in the UV region, spectral shape, and CDOM composition (Kim and Kim, 2016;Helms et al, 2013;Mladenov et al, 2009). The humic selective photochemical degradation of aerosol WSOC was resulted in greater reduction in the optical properties and WSOC content in total carbon pool (Birdwell and Engel, 2010;Helms et al, 2013).…”

“…The PARAFAC model was performed in the MATLAB R2013a program using the DOMFluor toolbox in order to determine the fluorescent components in WSOC (Stedmon and Bro, 2008;Kim and Kim, 2016). The number of unique components was identified from the combined EEM data of aerosol samples and the results were validated by split-half analysis and analysis using random initialization (Stedmon and Bro, 2008).…”