Molecular evidence for the production of labile, sulfur-bearing dissolved organic matter in the seep sediments of the South China Sea

Tingcang Hu; Min Luo; Yulin Qi; Ding He; Linying Chen; Yunping Xu; Duofu Chen

doi:10.1016/j.watres.2023.119732

Molecular evidence for the production of labile, sulfur-bearing dissolved organic matter in the seep sediments of the South China Sea

Water Res. 2023 Apr 15:233:119732. doi: 10.1016/j.watres.2023.119732. Epub 2023 Feb 12.

Authors

Tingcang Hu¹, Min Luo², Yulin Qi³, Ding He⁴, Linying Chen⁵, Yunping Xu⁵, Duofu Chen⁶

Affiliations

¹ College of Geography and Environment, Liaocheng University, Liaocheng, China.
² Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China; Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University, Shanghai, China. Electronic address: mluo@shou.edu.cn.
³ Institute of Surface-Earth System Science, College of Earth System Science, Tianjin University, Tianjin, China.
⁴ Department of Ocean Science and Hong Kong Branch of the Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), The Hong Kong University of Science and Technology, Hong Kong, China.
⁵ Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University, Shanghai, China.
⁶ Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University, Shanghai, China. Electronic address: dfchen@shou.edu.cn.

PMID: 36801578
DOI: 10.1016/j.watres.2023.119732

Abstract

Cold seeps with methane-rich fluids leaking out of the seafloor usually support massive biomass of chemosynthetic organisms and associated fauna. A substantial amount of methane is converted to dissolved inorganic carbon by microbial metabolism, and this process also releases dissolved organic matter (DOM) into pore water. Here, pore water samples from "Haima cold seeps" sediments and the non-seep reference sediments in the northern South China Sea were analyzed for optical properties and molecular compositions of pore water DOM. Our results showed that the relative abundance of protein-like DOM, H/C_wa and molecular lability boundary percentage (MLB_L%) in the seep sediments were significantly higher than those in the reference sediments, indicating that more labile DOM related to unsaturated aliphatic compounds is produced in the seep sediments. Spearman's correlation of the fluoresce and molecular data suggested that the humic-like components (C1 and C2) mainly constituted the refractory compounds (CRAM, highly unsaturated and aromatics compounds). In contrast, the protein-like component (C3) had high H/C ratios featuring high degree of DOM lability. The amount of S-containing formulas (CHOS and CHONS) was greatly elevated in the seep sediments, likely caused by abiotic and biotic sulfurization of DOM in the sulfidic environment. Although the abiotic sulfurization was proposed to have a stabilizing effect on organic matter, our results implied that the biotic sulfurization in the cold seep sediments would increase DOM lability. Overall, the labile DOM accumulated in the seep sediments is closely linked to methane oxidation, which not only support heterotrophic communities and but also likely have an impact on carbon and sulfur cycling in the sediments and the ocean.

Keywords: Cold seeps; Dissolved organic matter; Fluorescence spectrum; Fourier transform ion cyclotron resonance mass spectrometry; Sulfurization.

MeSH terms

Carbon
China
Dissolved Organic Matter*
Geologic Sediments*
Methane / metabolism
Sulfur
Water

Substances

Dissolved Organic Matter
Water
Methane
Sulfur
Carbon