scholarly journals Unique Authigenic Mineral Assemblages and Planktonic Foraminifera Reveal Dynamic Cold Seepage in the Southern South China Sea

2020 ◽  
Author(s):  
Pengfei Di ◽  
Yang Zhou ◽  
Niu Li
Keyword(s):  
South China Sea ◽  
South China ◽  
Planktonic Foraminifera ◽  
Southern South China Sea ◽  
China Sea ◽  
Mineral Assemblages ◽  
Authigenic Mineral

scholarly journals Unique Authigenic Mineral Assemblages and Planktonic Foraminifera Reveal Dynamic Cold Seepage in the Southern South China Sea

Minerals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 275
Author(s):  
Yang Zhou ◽  
Pengfei Di ◽  
Niu Li ◽  
Fang Chen ◽  
Xin Su ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Gas Hydrate ◽  
Planktonic Foraminifera ◽  
Southern South China Sea ◽  
Globigerinoides Ruber ◽  
Δ13c Values ◽  
Methane Seepage ◽  
Mineral Assemblages ◽  
Authigenic Mineral

Many cold seeps and gas hydrate areas have not been discovered beside the Beikan basin in the southern South China Sea (SCS), and their characteristics and histories also remain poorly known. Here we describe authigenic minerals and the carbon and oxygen isotopic composition of planktonic foraminifera Globigerinoides ruber from sediment core 2PC, recovered from the gas hydrate zone of the Nansha Trough, southern SCS, to elucidate its history of dynamic cold seepage. We infer that the occurrence of authigenic gypsum crystals and pyrite concretions, and anomalously negative δ13C values of Globigerinoides ruber, reflect paleo-methane seepage. Two major methane release events were identified, based on remarkable excursions in foraminifera δ13C at depths of 150–250 cm and 350–370 cm. Euhedral gypsum crystals and tubular pyrite concretions co-occur with extremely negative planktonic foraminifera δ13C values, indicating a shift in the sulfate methane transition zone and a change in the methane flux. Our data suggest that authigenic mineral assemblages and δ13C values of planktonic foraminifera provide a valuable tool in elucidating the characteristics of dynamic methane seepage in a marine environment.

Distribution and constraining factors of planktonic and benthic foraminifers in bottom sediments of the southern South China Sea

2020 ◽  
Author(s):  
Jian Yin ◽  
Chunlian Liu ◽  
Xiaoqiang Yang
Keyword(s):  
South China Sea ◽  
Shallow Water ◽  
South China ◽  
Planktonic Foraminifera ◽  
Cyclonic Gyre ◽  
Southern South China Sea ◽  
China Sea ◽  
Water Zone ◽  
Cluster A ◽  
Water Species

<p>Consisted of shallower Sunda Shelf, deeper Zengmu Basin, and Nansha Trough Basin, the southern South China Sea (SCS) provides an ideal scene for oceanography studies. Spreading all over nearly from 50 to 3000m at depth, a total of 93 surface sediment samples were collected to analyze the environmental factors constraining the foraminiferal distribution pattern in the southern South China Sea (SCS). Species distributions and stable isotopic compositions were combined to reveal the controlling factors, such as depth, salinity, substrate, runoff, currents, and cold seep activities. Water depth is the dominant factor controlling both assemblage composition and δ<sup>18</sup>O of benthic foraminiferal tests. The 1000 m isobath separates the sites into two clusters (Cluster A and B), which are dominated by deep-water species and shallow-water species, respectively. The sites in the deep-water zone (Cluster A) are characterized by lower absolute abundances, species richness and Shannon Index values (a measure of diversity), and higher proportions of planktonic foraminifers compared with the sites in the shallow-water zone (Cluster B). Increasing proportions of agglutinated tests with depth and rapidly decreasing proportions of planktonic foraminifera in the Nansha Trough Basin provide evidence of calcium dissolution occurring at a depth corresponding with previous reports. Oxygen stable isotopes (δ<sup>18</sup>O<sub>B</sub>) of benthic foraminifera become more positive with depth only up to 1000 m and remain constant beyond. Differences in the proportion of agglutinated and porcelaneous tests in the shallow-water zone suggest that terrestrial runoff from nearby river systems (Mekong River and northern Borneo rivers) and seasonal surface currents (SCS Southern Cyclonic Gyre and SCS Southern Anticyclonic Gyre) jointly influence the distribution patterns of foraminifera in the study area. Enrichment of planktonic δ<sup>18</sup>O is a response to cold waters brought by the SCS southern cyclonic gyre during winter. An upwelling current (Winter Natuna Off-Shelf Current) containing higher amounts of organic matter/nutrients contributes to the depleted δ<sup>13</sup>C of planktonic foraminifera and to the abnormal abundance of foraminifera at the sites within its area of influence. The dominance of the foraminifer Melonis barleeanus at sites belonging to Subcluster A1 and the stable isotope compositions of benthic foraminifera (δ<sup>18</sup>O > 0, δ<sup>13</sup>C < 0) across the sites suggest the influence of active cold seeps in the southern SCS. This research highlights the complexity of environmental variables that interact to influence the foraminiferal assemblages and geochemistry in the southern South China Sea, which could serve as a model for paleoenvironmental and palaeoceanographic reconstructions.</p>

Stable isotopes in modern planktonic foraminifera: Sediment trap and plankton tow results from the South China Sea

2011 ◽  
Vol 79 (1-2) ◽  
pp. 15-23 ◽  
Author(s):  
Hui-Ling Lin ◽  
David Der-Duen Sheu ◽  
Yih Yang ◽  
Wen-Chen Chou ◽  
Guo-Wei Hung
Keyword(s):  
Stable Isotopes ◽  
South China Sea ◽  
South China ◽  
Sediment Trap ◽  
Planktonic Foraminifera ◽  
The South China Sea ◽  
The South ◽  
China Sea

Contrasting Characteristics of Convection over the Northern and Southern South China Sea during SCSMEX

2006 ◽  
Vol 134 (4) ◽  
pp. 1041-1062 ◽  
Author(s):  
Paul E. Ciesielski ◽  
Richard H. Johnson
Keyword(s):  
South China Sea ◽  
South China ◽  
Kelvin Wave ◽  
Southern South China Sea ◽  
Rainy Period ◽  
Stratiform Rain ◽  
China Sea ◽  
Convective Systems ◽  
Early Afternoon ◽  
Dominant Feature

Abstract Observations from two enhanced sounding arrays during the May–June 1998 South China Sea Monsoon Experiment (SCSMEX) are used to determine and contrast the properties of convection over the northern and southern South China Sea (SCS). A regression analysis between SST data and monthly rainfall indicates that the ENSO signal exerted a strong influence on the rainfall distribution over the SCS during SCSMEX. This resulted in wetter-than-normal conditions along the south China coast and northern SCS, and generally drier-than-average conditions elsewhere, particularly over the Philippine Islands. The monsoon onset as determined by a shift in the low-level winds from easterly to southwesterly over the SCS occurred around mid-May. Over the southern enhanced sounding array (SESA), the onset was characterized by a rainy period associated with the passage of a convectively coupled Kelvin wave. This was followed by a weeklong break and then several episodic rain events with increasingly higher rain rates. Rainfall over the northern enhanced sounding array (NESA), which was largely out of phase with SESA rainfall events, occurred primarily during two 10-day periods separated by a weeklong break. Convective characteristics over the SESA, deduced primarily from heat and moisture budget profiles, indicate a high stratiform rain fraction consisting of alternating periods with decaying mesoscale systems that organized near the western Borneo coastline and shallower convective clouds. In contrast, NESA-averaged profiles were indicative of deep convection with a relatively small stratiform rain fraction, which was confirmed with radar analyses during the onset convective period. The diurnal cycle of convection is a dominant feature throughout much of the SCS. Over both budget regions, early morning (0500–0800 LT) convective systems were frequently initiated near the coasts, then gradually dissipated during the course of the day as the midlevel steering currents moved the systems away from the coastline. These decaying convective systems resulted in an early afternoon (1400 LT) rainfall peak over both sonde arrays.

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