scholarly journals Photosynthetic Production Determines Bottom Water Oxygen Variations in the Upwelling Coastal South China Sea Over Recent Decades

2021 ◽  
Vol 9 ◽  
Author(s):  
Xiaowei Zhu ◽  
Guodong Jia ◽  
Yuhang Tian ◽  
Aibin Mo ◽  
Weihai Xu ◽  
...  
Keyword(s):  
Climate Change ◽  
South China Sea ◽  
South China ◽  
Bottom Water ◽  
Coastal Upwelling ◽  
Marine Biodiversity ◽  
Oxygen Production ◽  
Riverine Input ◽  
China Sea ◽  
Photosynthetic Oxygen

Dissolved oxygen (DO) in seawater is fundamental to marine ecosystem health. How DO in coastal upwelling areas responds to upwelling intensity under climate change is of particular interest and vital importance, because these productive regions account for a large fraction of global fishery production and marine biodiversity. The Yuedong upwelling (YDU) in the coastal northern South China Sea can be served as a study case to explore long-term responses of DO to upwelling and climate due to minor influence of riverine input. Here, bottom water DO conditions were recovered by sedimentary C28Δ22/Δ5,22 ratios of steroids in three short cores, with lower ratio value indicating higher DO concentration. The ratio records showed oscillations in varying degrees and exhibited no clear trends before ∼1980s, after which, however, there occurred a persistent decreasing trend or basically remained at lower values. Thus, inferred DO variations by the C28Δ22/Δ5,22 ratio records are not compatible with regional YDU-involved physical processes under climate change, such as southwesterly wind-induced onshore advection of reduced-oxygenated source waters from outer shelf and oceanic warming that would rather lead to less oxygenation in bottom waters in recent decades. Intriguingly, the alcohol records of n-C20:1/C28Δ5,22 and br-C15/C28Δ5,22 ratios, indicative of the relative strengths between biogeochemical oxygen consumption (i.e., by zooplankton and microbes) and photosynthetic oxygen production (i.e., by phytoplankton), changed almost in parallel with the C28Δ22/Δ5,22 records in three cores. Accordingly, we propose that net photosynthetic oxygen production outweighs source water– and warming-induced increasing deoxygenation in the study area. This study may suggest an important biogeochemical mechanism in determining bottom water DO dynamics in shallow coastal upwelling regions with minor contribution of riverine input.

scholarly journals Phytoplankton response to a plume front in the northern South China Sea

2018 ◽  
Vol 15 (8) ◽  
pp. 2551-2563 ◽  
Author(s):  
Qian P. Li ◽  
Weiwen Zhou ◽  
Yinchao Chen ◽  
Zhengchao Wu
Keyword(s):  
South China Sea ◽  
South China ◽  
Bottom Water ◽  
Coastal Upwelling ◽  
Frontal Zone ◽  
Northern South China Sea ◽  
River Estuary ◽  
Frontal System ◽  
China Sea ◽  
Plume Water

Abstract. Due to a strong river discharge during April–June 2016, a persistent salinity front, with freshwater flushing seaward on the surface but seawater moving landward at the bottom, was formed in the coastal waters west of the Pearl River estuary (PRE) over the northern South China Sea (NSCS) shelf. Hydrographic measurements revealed that the salinity front was influenced by both the river plume and coastal upwelling. On shipboard nutrient-enrichment experiments with size-fractionation chlorophyll a measurements were taken on both sides of the front as well as in the frontal zone to diagnose the spatial variations of phytoplankton physiology across the frontal system. We also assessed the size-fractionated responses of phytoplankton to the treatment of plume water at the frontal zone and the sea side of the front. The biological impact of vertical mixing or upwelling was further examined by the response of surface phytoplankton to the addition of local bottom water. Our results suggested that there was a large variation in phytoplankton physiology on the sea side of the front, driven by dynamic nutrient fluxes, although P limitation was prevailing on the shore side of the front and at the frontal zone. The spreading of plume water at the frontal zone would directly improve the growth of microphytoplankton, while nano- and picophytoplankton growths could have become saturated at high percentages of plume water. Also, the mixing of bottom water would stimulate the growth of surface phytoplankton on both sides of the front by altering the surface N∕P ratio to make it closer to the Redfield stoichiometry. In summary, phytoplankton growth and physiology could be profoundly influenced by the physical dynamics in the frontal system during the spring–summer of 2016.

Inversion of bio-optical properties in the coastal upwelling waters of the northern South China Sea

2014 ◽  
Vol 85 ◽  
pp. 73-84 ◽  
Author(s):  
Junfang Lin ◽  
Wenxi Cao ◽  
Guifen Wang ◽  
Wen Zhou ◽  
Zhaohua Sun ◽  
...  
Keyword(s):  
Optical Properties ◽  
South China Sea ◽  
South China ◽  
Coastal Upwelling ◽  
Northern South China Sea ◽  
China Sea

A Marine Biodiversity Project in the South China Sea: Joint Efforts Made in the SCS Workshop Process

2011 ◽  
Vol 26 (1) ◽  
pp. 119-149 ◽  
Author(s):  
Yann-huei Song
Keyword(s):  
Economic Development ◽  
South China Sea ◽  
South China ◽  
The South China Sea ◽  
Marine Biodiversity ◽  
Marine Resources ◽  
The South ◽  
China Sea ◽  
Current State ◽  
Made In

AbstractThe South China Sea (SCS) is one of the world’s richest marine biodiversity areas, with abundant and diverse marine resources. In recent years, however, due to rapid economic development and population growth, marine biodiversity in the SCS is being lost. Beginning in 1991, the participants in the Informal Workshop on Managing Potential Conflicts in the South China Sea (the SCS Workshop) agreed to recommend to the relevant governments to explore areas of cooperation in the SCS, which include the study of marine biodiversity. As a result, in March 2002, a joint biodiversity project was carried out around the undisputed Indonesian Islands of Anambas in the SCS. Other joint biodiversity projects have also been proposed, but with no progress. This article studies the joint efforts made by the participating authorities in the SCS Workshop process to understand better the current state of marine biodiversity in the SCS.

scholarly journals Long term changes in the ecosystem in the northern South China Sea during 1976–2004

2008 ◽  
Vol 5 (5) ◽  
pp. 3737-3779 ◽  
Author(s):  
X. Ning ◽  
C. Lin ◽  
Q. Hao ◽  
C. Liu ◽  
F. Le ◽  
...  
Keyword(s):  
Climate Change ◽  
South China Sea ◽  
South China ◽  
Northern South China Sea ◽  
Seawater Temperature ◽  
Climate Trend ◽  
Redfield Ratio ◽  
China Sea ◽  
N Limitation

Abstract. Physical and chemical oceanographic data were obtained by seasonal monitoring along Transect N in the northern South China Sea (nSCS) during 1976–2004. Fluctuations of DIN (dissolved inorganic nitrogen), seawater temperature (SST and Tav – average temperature of the water column), N:P ratio and salinity (Sav and S200 – salinity at the 200 m layer) exhibited an increasing trend, while those of T200, DO, P, Si, Si:N and SSS exhibited a decreasing trend. The annual rates of change in DIN, DO, T and S revealed pronounced changes, and the climate trend coefficients Rxt, which was defined as the correlation coefficient between the time series of an environmental parameter and the nature number, were 0.38 to 0.89 and significant (p≤0.01 to 0.05). Our results also showed that the ecosystem has obviously been influenced by the positive trends of both SST and DIN, and negative trends of both DO and P, e.g. before 1997, DIN concentrations in the upper layer were very low and N:P ratios were less than half of the Redfield ratio of 16, indicating potential N limitation. However, after 1997, all Si:P ratios were >22 and the Nav:Pav was close to the Redfield ratio, indicating potential P limitation, and therefore N limitation has been reduced after 1997. Ecological investigation shows that there have been some improved responses of the ecosystems to the long-term environmental changes in the nSCS, and chlorophyll-a concentration, primary production, phytoplankton abundance, benthic biomass, cephalopod catch and demersal trawl catch have increased. But phosphorus depletion in upper layer may be related to the shift in the dominant species from diatoms to dinoflagellates and cyanophytes. The ecosystem response was induced by not only anthropogenic activities, but also global climate change, e.g. pronounced responses to ENSO. The effects of climate change on the nSCS were mainly through changes in the monsoon winds, and physical-biological oceanography coupling processes.

scholarly journals The Current Environmental Situation and Green Solutions for Vietnam's East Sea

2019 ◽  
Vol 4 (9) ◽  
pp. 70-74
Author(s):  
Thi Minh Hao Dong ◽  
Huu Cuong Le ◽  
Thanh Hai Truong
Keyword(s):  
Climate Change ◽  
South China Sea ◽  
South China ◽  
Natural Capital ◽  
Action Plan ◽  
The South China Sea ◽  
East Sea ◽  
The South ◽  
China Sea ◽  
The Impact

The South China Sea, including the Vietnam Sea, is witnessing significant changes under the impact of both nature and man. These are the impacts of climate change and ocean change with "extreme" signs such as increasing storms, coastal floods, sea level rise, sea acidification, pollution and environmental incidents, ... occur thicker, more intense and irregular. Especially serious degradation of the environment and biodiversity of the sea, increasing environmental incidents, including oil spills, ... due to human impact. Especially the large-scale destruction of coral reefs, seagrass beds in island clusters off the South China Sea has been happening at a worrying rate. The destructive fishing activities of humans in the South China Sea have caused ecosystem degradation and the extinction of some species, such as sea turtles, some sharks and another species. Other fish, especially the giant mussel, the consequence is a decrease in the natural capital of the sea, leading too prolonged "ecological disturbances". The reserves of seafood in the Spratly region (of Vietnam) and the West Sea in the East Sea have decreased by about 19% compared to before 2017. Therefore, the improvement of marine environment quality, including biodiversity conservation and major marine ecosystems are to preserve marine natural assets, contributing to the implementation of Vietnam's green growth strategy and action plan. This is the path that Vietnam has chosen to both grow marine economy, adapt to climate change, and protect the environment both in the short and long term, towards sustainable development.

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