Vertical distribution of pH in the top ~10 m of deep-ocean sediments: Analysis of a unique dataset

Frontiers in Marine Science

Marine Science

Yi Sui¹  Hongbin Wang²  Changgao Shao³  Louis Legendre⁴  DanLing Tang⁵ 

[1] Department of Oceanography, Dalhousie University, Halifax, NS, Canada;Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangdong Remote Sensing Center for Marine Ecology and Environment (GDRS), Guangzhou, China;Qingdao Institute of Marine Geology, China Geological Survey, Qingdao, China;Sanya Institute of South China Sea Geology, Guangzhou Marine Geological Survey, China Geological Survey, Sanya, China;Academy of South China Sea Geological Science, China Geological Survey, Sanya, China;Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangdong Remote Sensing Center for Marine Ecology and Environment (GDRS), Guangzhou, China;Sorbonne University, CNRS, Laboratoire d’Océanographie de Villefranche, LOV, Villefranche-sur-Mer, France;Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangdong Remote Sensing Center for Marine Ecology and Environment (GDRS), Guangzhou, China;

关键词: sediment pH;    Northern South China Sea;    ~10 m sediment cores;    ancient ocean;    diagenetic processes;   

DOI  :  10.3389/fmars.2023.1126704

 received in 2022-12-18, accepted in 2023-02-21,  发布年份 2023

来源: Frontiers

【 摘 要 】

We analyze, for the first time in the oceanographic literature, pH over the top ~10 m of the sediment (down to 11.9 m) in a deep-sea environment, together with the oxidation/reduction potential and concentrations of solid organic carbon (OC) and CaCO3. A total of 1157 sediment cores were collected from years 2000 to 2011 over >300,000 km2 in the South China Sea, at water depths up to 3702 m. We found that there were marked downward pH increases in the upper 2 m of the sediment (first 20-40 ka, corresponding to the geochemically active period). In deeper, older sediment (up to 200 ka), pH was generally less variable with depth but not uniform, and solid OC may have been consumed down to ≥10 m depth. This reflected interactions between in situ geochemical diagenetic processes, which tended to create vertical variations, and vertical diffusion of ions, which tended to even out vertical variability. In other words, there were slow diagenetic geochemical processes in the sediment layer below 2 m, and the effects of these in situ processes were partly offset by vertical diffusion. Overall, our study identified a previously unknown consistent pH difference between the upper 2 m of the sediment and the underlying layer down to ≥10 m, and suggested combinations of geochemical diagenetic processes and vertical diffusion of ions in the porewater to explain it. These results provide a framework for further studies of pH in the top multi-meter layer of the sediment in the World Ocean.

【 授权许可】

Unknown   
Copyright © 2023 Shao, Tang, Legendre, Sui and Wang