scholarly journals Study on Sedimentary Records of Paleoclimate and Paleoenvironmental Evolution of the Dongsha Atoll of South China Sea in Recent 70 Thousand Years

2020 ◽  
Vol 206 ◽  
pp. 02002
Author(s):  
Li tengfei
Keyword(s):  
Organic Matter ◽  
South China Sea ◽  
South China ◽  
Sediment Layer ◽  
Red Tides ◽  
Low Oxygen ◽  
Sediment Grain Size ◽  
China Sea ◽  
Marine Biomass ◽  
Dongsha Atoll

The Dongsha Atoll of South China Sea are located on the western reef terrace of Dongsha Atoll, where a large amount of terrigenous clastic materials and marine biomass are accumulated, which play an important role in the global material cycles. In recent years, the water level in this area has been on the decrease along with the frequent occurrence of floods, red tides, low-oxygen conditions and warmer waters as a result of worsening global ecology. In this paper, accelerated mass spectrometer (AMS) 14C was used to analyse the sediments in Dongsha Atoll of South China Sea, and studied the organic matter deposition in this area in the past 70,000 years combined with sediment grain size, geochemistry and other indicators, which revealed the influence of paleoclimate environment and climate change on the development of this area. The results showed that the environment and climate are essential to the distribution of particles, which can be divided into three layers from bottom to top, i.e., calcium-rich layer, organic matter layer and fine-grained sediment layer. Al2O3, K2O, TFe2O3 and MgO contribute 58.84% to the total variance, indicating that the composition plays a decisive role in the content of major elements in the region. Turbidity sediments have been widely distributed in different areas of the region since last glacial period, among which turbidity occurred most frequently in the period 200,000 years ago when the sea level was relatively low. This study provided a theoretical basis for the evolution of climate and environment in the South China Sea.

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

Minerals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 624 ◽  
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.

The standing stock and CaCO3 contribution of Halimeda macroloba in the tropical seagrass-dominated ecosystem in Dongsha Island, the main island of Dongsha Atoll, South China Sea

2020 ◽  
pp. 1-9
Author(s):  
Jaruwan Mayakun ◽  
Chen-Pan Liao ◽  
Shao-Lun Liu
Keyword(s):  
Growth Rate ◽  
South China Sea ◽  
South China ◽  
Standing Stock ◽  
Dry Weight ◽  
Carbonate Production ◽  
China Sea ◽  
Carbonate Budget ◽  
Marine Carbonate ◽  
Dongsha Atoll

Abstract Calcareous green alga in the genus Halimeda are important contributors to the marine carbonate budget. Dongsha Island is located in the northernmost South China Sea and is a seagrass-dominated ecosystem with intermixed Halimeda macroloba patches, making it an excellent system to better examine the extent of carbonate contribution by H. macroloba in such an ecosystem. To this end, we examined the standing stock and actual CaCO3 contribution of H. macroloba in the seagrass-dominated ecosystem (herein Dongsha Island) and compared them with those in Halimeda-dominated ecosystems. The density, growth rate, calcification rate and CaCO3 content of H. macroloba at four life stages were investigated. The mean density of H. macroloba was around 8.82 ± 1.57 thalli m−2 and the estimated standing stock was 61,740 to 72,730 thalli. Thalli produced 1 to 2 new segments day−1, giving a growth rate of 0.003 ± 0.001 g dry weight thallus−1 day−1. Calculated algal biomass and annual areal production were 0.03 g m−2 and 9.66 g m−2 year−1. In each square metre of this area, H. macroloba produced 8.82 to 17.64 new segments day−1, accumulating 0.002 ± 0.001 g CaCO3 thallus−1 day−1 or around 6.44 g CaCO3 m−2 year−1. Mean CaCO3 content was 0.32 ± 0.05 g thallus−1. As expected, the growth rate and CaCO3 production of H. macroloba in Dongsha Island were lower than in other studies from Halimeda tropical ecosystems. Overall, this work provides the baseline of carbonate production of H. macroloba in Dongsha Island and relevant systems where the ecosystem is dominated by seagrasses.

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

Oceanology ◽  
2011 ◽  
Vol 51 (6) ◽  
pp. 959-968 ◽  
Author(s):  
V. I. Peresypkin ◽  
A. V. Smurov ◽  
N. A. Shulga ◽  
E. S. Safonova ◽  
T. G. Smurova ◽  
...  
Keyword(s):  
Organic Matter ◽  
South China Sea ◽  
Bottom Sediments ◽  
South China ◽  
Suspended Matter ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Nha Trang Bay

Crown-of-thorns starfish outbreak at oceanic Dongsha Atoll in the northern South China Sea

2019 ◽  
Vol 49 (6) ◽  
pp. 2495-2497 ◽  
Author(s):  
James Davis Reimer ◽  
Hiroki Kise ◽  
Hin Boo Wee ◽  
Chen-Lu Lee ◽  
Keryea Soong
Keyword(s):  
South China Sea ◽  
South China ◽  
Northern South China Sea ◽  
China Sea ◽  
Dongsha Atoll
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