Composition of the organic matter of the water, suspended matter, and bottom sediments in Nha Trang Bay in Vietnam in the South China Sea

Sipunculan worms from the Vietnamese waters are still poorly investigated, while they are well known from Chinese andTaiwanese waters of the South China Sea. During the years 2008–2010, therefore, we collected sipunculans from NhaTrang Bay in South Vietnam. Twenty species of peanut worms representing eleven genera and five families of the phylumSipuncula are recognized from more than one thousand individuals collected from various biotopes. Fifteen species arenew records for Nha Trang Bay with Nephasoma pellucidum being a new record for the South China Sea. Species accountsinclude the most important taxonomic characters as well as quantitative characteristics, distributions, and specific biotopedata. All species were illustrated in living conditions with everted introvert and tentacular apparatus. Accordingly, a key up to species level is provided.

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Petrographical and Geochemical Signatures Linked to Fe/Mn Reduction in Subsurface Marine Sediments from the Hydrate-Bearing Area, Dongsha, the South China Sea

Minerals ◽

10.3390/min9100624 ◽

2019 ◽

Vol 9 (10) ◽

pp. 624 ◽

Cited By ~ 1

Author(s):

Xi Xiao ◽

Qian-Zhi Zhou ◽

Shao-Ying Fu ◽

Qian-Yong Liang ◽

Xiang-Po Xu ◽

...

Keyword(s):

Organic Matter ◽

South China Sea ◽

Marine Sediments ◽

South China ◽

Inorganic Carbon ◽

Solid Phase ◽

The South China Sea ◽

Anaerobic Oxidation Of Methane ◽

The South ◽

China Sea

Fe and Mn oxides and (oxy)-hydroxides are the most abundant solid-phase electron acceptors in marine sediments, and dissimilatory Fe/Mn reduction usually links with the anaerobic oxidation of methane (AOM) and organic matter oxidation (OMO) in sediments. In this study, we report the results from subsurface marine sediments in the Dongsha hydrate-bearing area in the South China Sea. The petrological and geochemical signatures show that the Fe/Mn reduction mediated by AOM and OMO might occur in sediments above the sulfate-methane transition zone. X-ray diffraction and scanning electron microscopy analyses of sediments indicate that Fe(III)/Mn(IV)-oxides and authigenic carbonate minerals coexisted in the Fe/Mn reduction zone. The lower δ13C values of dissolved inorganic carbon, coupled with an evident increase in total inorganic carbon contents and a decrease in Ca2+ and Mg2+ concentrations indicate the onset of AOM in this zone, and the greater variation of PO43− and NH4+ concentrations in pore water suggests the higher OMO rates in subsurface sediments. Geochemical and mineralogical analyses suggest that the previously buried Fe(III)/Mn(IV) oxides might be activated and lead to the onset of Fe/Mn reduction induced by AOM and OMO. These findings may extend our understanding of the biogeochemical processes involved in Fe/Mn reduction in continental shelves with abundant methane, organic matter, and terrigenous metal oxides.

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