Yinxian Song

Past 140-year environmental record in the northern South China Sea: Evidence from coral skeletal trace metal variations

About 140-year changes in the trace metals in Porites coral samples from two locations in the northern South China Sea were investigated. Results of PCA analyses suggest that near the coast, terrestrial input impacted behavior of trace metals by 28.4%, impact of Sea Surface Temperature (SST) was 19.0%, contribution of war and infrastructure were 14.4% and 15.6% respectively. But for a location in the open sea, contribution of War and SST reached 33.2% and 16.5%, while activities of infrastructure and guano exploration reached 13.2% and 14.7%. While the spatiotemporal change model of Cu, Cd and Pb in seawater of the north area of South China Sea during 1986-1997 were reconstructed. It was found that in the sea area Cu and Cd contaminations were distributed near the coast while areas around Sanya, Hainan had high Pb levels because of the well-developed tourism related activities.

Coral trace metal of natural and anthropogenic influences in the northern South China Sea

The composition and concentrations of trace metals in coastal seawater have changed in parallel with variations in geochemical processes, climate and anthropogenic activities. To evaluate the response of trace metals in coastal seawater to climatic changes and human disturbances, we report annual-resolution trace element data for a Porites coral core covering ~100years of continuous growth from a fringing reef in Xiaodonghai Bay in the northern South China Sea. The results suggested that the trace metal contents in the coral skeleton demonstrated decadal to interdecadal fluctuations with several large or small peaks in certain years with remarkable environmental significances. All of the trace metals in coastal surface seawater, especially Cr and Pb (related to industrial or traffic emissions), were impacted by terrestrial inputs, except for Sr and U, which were impacted by the surface seawater temperature (SST). Moreover, Mn, Ni, Fe and Co were also contributed by weapons and military supplies during wars, and Cu, Cd and Zn were further impacted by upwelling associated with their biogeochemical cycles. Ba and rare earth element (REE) in coastal surface seawater were dominated by runoff and groundwater discharge associated with precipitation. This study provided the potential for some trace metals (e.g., REE, Ba, Cu, Cd, and Zn) in coral skeletons to be used as proxies of natural (e.g., upwelling and precipitation) and anthropogenic (e.g., war and coastal construction) variability of seawater chemistry to enable the reconstruction of environmental and climatic changes through time.

Concentration and characteristics of dissolved carbon in the Sanjiang Plain influenced by long-term land reclamation from marsh.

Since the 1960s, the marshes in the Sanjiang Plain, Northeast China, which are an important reservoir for dissolved carbon, have undergone long-term reclamation to farmland, resulting in elevated marsh loss and degradation on a large scale. This study compared the concentrations of dissolved carbon, as well as the chemical characteristics of dissolved organic carbon (DOC), in natural marshes, a degraded marsh, and drainage ditches sampled during the growing seasons between 2008 and 2010 to clarify the temporal-spatial variability of the dissolved carbon in the fluvial system influenced by the long-term reclamation. The results show that the average concentrations of total dissolved carbon (TDC) and DOC are considerably greater in the natural marshes than in the degraded marsh and drainage ditches. The average DOC concentration for the natural marshes, approximately 35.53 ± 5.15 mg L(-1), is approximately 2.39 times that in the degraded marsh (14.84 ± 4.21 mg L(-1)) and 2.77 times the average value in the ditches (12.84 ± 4.49 mg L(-1)). The dissolved inorganic carbon (DIC) exhibits increased trends in the drainage ditches compared with the natural marshes, whereas the hydrophobic fraction of DOC is present at lower concentrations in the degraded marsh and ditches. Fluorescence indices also indicate that the DOC in the degraded marsh and ditches has a simpler humification structure. In total, the long-term reclamation has led to great variability in the DOC concentration and chemical characteristics in the fluvial system. Changes in the DOC production potential and hydrological regimes due to sustained reclamation are deemed the predominant causes of this effect. The continuously decreased DOC concentration and high variability of DOC in the surface fluvial systems are inevitable if reclamation continues in the Sanjiang Plain. More importantly, the presence of tyrosine and tryptophan-like substances in the ditches indicates that there has been extensive agricultural organic pollution in the fluvial systems. This pollution could lead to more unexpected impacts on the downriver aquatic system. To avoid a destructive ecological crisis in the future, adjustment of the reclamation policy and agricultural management measures in the Sanjiang Plain is urgently needed.

Vibrational spectroscopic characterization of mudstones in a hydrocarbon-bearing depression, South China Sea: Implications for thermal maturity evaluation.

A better understanding of mineral transformations in sedimentary rocks and the controls on thermal maturity have become essential in the petroleum exploration industry in recent years. The Fushan Depression is an important hydrocarbon-bearing depression in South China Sea, which can be subdivided into three structural zones: the western, central and eastern zones. In this study, a series of mudstone samples selected from 13 drilling cores with depths ranging from 2100 to 3800 m were studied using infrared reflectance spectroscopy and X-Ray Powder Diffraction (XRD) methods. And another 10 samples have been chosen for vitrinite reflectance measurement so as to investigate the ability of using infrared spectroscopy for thermal maturity evaluations. The infrared spectra results show that quartz and silicates (e.g. illite, kaolinite, smectite) are the dominant minerals in all samples. The semi-quantitative XRD analysis reveals a clear trend in illite content as the eastern zone (mean 80.81%)>the western zone (mean 73.52%)>the central zone (mean 55.04%) as well as a contrary trend in kaolinite content. This study documents that the peak height and position of Si-O antisymmetric stretching bands at ~1025 cm(-1) and ~1000 cm(-1) have a significant correlation with the degree of kaolinite illitization, suggesting that the utility of infrared spectroscopy is a valuable tool for the study of thermal maturity in sedimentary basins. The infrared spectra and XRD results together with vitrinite reflectance data indicate that the thermal maturity in the eastern zone is anomalously high, followed by the western zone, and that in the central zone is lowest. The igneous intrusion in the eastern zone has a significant impact on thermal maturation, resulting in high degree of kaolinite illitization. By contrast, the abundance in kaolinite in the central zone represents relatively low degree of kaolinite illitization, which should be attributed to shallow burial depth.

Testing coral paleothermometers （B/Ca, Mg/Ca, Sr/Ca, U/Ca and δ18O） under impacts of large riverine runoff

Sea surface temperature (SST) proxies including B/Ca, Mg/Ca, Sr/Ca, U/Ca and δ18O were analyzed in the skeleton of a Porites coral collected from the Zhujiang River (Pearl River) Estuary (ZRE). These geochemical proxies are influenced by river runoff and this area of the northern South China Sea is strongly affected by seasonal freshwater floods. We assessed the robustness of each SST proxy through comparison with the local instrumental SST. Coral Sr/Ca shows the highest correlation with SST variations (r2=0.59), suggesting Sr/Ca is the most robust SST proxy. In contrast, coral δ18O (r2=0.46), B/Ca (r2=0.43) and U/Ca (r2=0.41) ratios were only moderately correlated with SST variations, suggesting that they are disturbed by some other factors in addition to SST. The poor correlation (r2=0.27) between SST and Mg/Ca indicates that Mg/Ca in coral skeletons is not a simple function of SST variations. This may ultimately limit the use of Mg/Ca as a coral paleothermometer.

Vibrational spectroscopic characterization of growth bands in Porites coral from South China Sea

A series of samples from different growth bands of Porites coral skeleton were studied using Raman, infrared reflectance methods. The Raman spectra proved that skeleton samples from different growth bands have the same mineral phase as aragonite, but a band at 133 cm(-1) for the top layer shows a transition from ~120 cm(-1) for vaterite to ~141 cm(-1) for aragonite. It is inferred that the vaterite should be the precursor of aragonite of coral skeleton. The positional shift in the infrared spectra of the skeleton samples from growth bands correlate significantly to their minor elements (Li, Mg, Sr, Mn, Fe and U) contents. Mg, Sr and U especially have significant negative correlations with the positions of the antisymmetric stretching band ν3 at ~1469 cm(-1). And Li shows a high negative correlation with ν2 band (~855 cm(-1)), while Sr and Mn show similar negative correlation with ν4 band (~712 cm(-1)). And Mn also shows a negative correlation with ν1 band (~1082 cm(-1)). A significantly negative correlation is observed for U with ν1+ν4 band (~1786 cm(-1)). However, Fe shows positive correlation with ν1, ν2, ν3, ν4 and ν1+ν4 bands shifts, especially a significant correlation with ν1 band (~1082 cm(-1)). New insights into the characteristics of coral at different growth bands of skeleton are given in present work.

Annual REE Signal of East Asian Winter Monsoon in Surface Seawater in the Northern South China Sea: Evidence From a Century‐Long Porites Coral Record

The East Asian winter monsoon (EAWM) plays a significant role in the Asian climate system. However, the scarcity of direct high-resolution records, especially those covering recent centuries, limits our understanding of monsoonal dynamics. Here we present a reconstruction of annual EAWM strength over the past century and a half using a Porites coral from Yongxing Island in the northern South China Sea (SCS), where the variations in the rare earth element (REE) parameters in surface seawater are dominantly controlled by the input of aeolian dust. Our record indicates that the EAWM strength weakly increased overall during the latter half of the nineteenth century but decreased during the twentieth century, especially after ~1950 Common Era. Additionally, during the past century and a half, the relationship between the EAWM and the East Asian summer monsoon, as recorded in speleothems, varied temporally and depended on the strength of the EAWM. Our findings suggest that the REE proxy of corals from the offshore SCS can be applied as an excellent indicator of the winter monsoon strength.