Benthic fluxes of dissolved organic carbon from gas hydrate sediments in the northern South China Sea.

Chia-Wei Hung,David J Burdige,Chuang-Yi Ho,Chin-Chang Hung,Hsin-Hung Chen,Kuo-Hao Huang,Yung-Yen Shih,Chau-Chang Wang,Yu-Shih Lin

doi:10.1038/srep29597

Abstract

Hydrocarbon vents have recently been reported to contribute considerable amounts of dissolved organic carbon (DOC) to the oceans. Many such hydrocarbon vents widely exist in the northern South China Sea (NSCS). To investigate if these hydrocarbon vent sites release DOC, we used a real-time video multiple-corer to collect bottom seawater and surface sediments at vent sites. We analyzed concentrations of DOC in these samples and estimated DOC fluxes. Elevated DOC concentrations in the porewaters were found at some sites suggesting that DOC may come from these hydrocarbon vents. Benthic fluxes of DOC from these sediments were 28 to 1264 μmol m−2 d−1 (on average ~321 μmol m−2 d−1) which are several times higher than most DOC fluxes in coastal and continental margin sediments. The results demonstrate that the real-time video multiple-corer can precisely collect samples at vent sites. The estimated benthic DOC flux from the methane venting sites (8.6 × 106 mol y−1), is 24% of the DOC discharge from the Pearl River to the South China Sea, indicating that these sediments make an important contribution to the DOC in deep waters.

Highlights

Effects of mud volcanoes and gassy sediments on the concentration of Dissolved organic carbon (DOC) in the deep ocean, we collected bottom water and porewater samples to measure DOC concentrations using a real-time video multiple corer (V Corer) in the northern South China Sea (NSCS) in 2014, and used these results to evaluate the DOC flux across the sediment-water interface at these sites
The lowest bottom water DOC concentrations were observed at background site BKG-1 and MV6 (Table 1)
The DOC concentration in the bottom water at another background site is 107 μM, higher than other regions, suggesting that it could be a combination of high DOC emission water and deep sea water in the NSCS

Summary

Introduction

Effects of mud volcanoes and gassy sediments on the concentration of DOC in the deep ocean, we collected bottom water and porewater samples to measure DOC concentrations using a real-time video multiple corer (V Corer) in the NSCS in 2014, and used these results to evaluate the DOC flux across the sediment-water interface at these sites. The use of a real-time video multiple-corer to take samples from gas hydrate sediments offers distinct advantages over other types of sampling devices (e.g., piston or gravity cores), since it provides direct visual evidence that one is sampling a venting site. Scientists have been studying gassy sediments in the South China Sea for over 10 years (see, for example, Yang et al.17), but they have seldom observed high methane or DOC fluxes due to the use of traditional piston or gravity coring without real-time video

Methods

Results

Conclusion