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Temperature seasonality, the difference between summer and winter temperature, has significant influences on global terrestrial and marine ecosystems. However, most of proxy-based climate records are of limited temporal resolution and thus insufficient to quantify the past temperature seasonality. In this study, high-resolution Sr/Ca ratios of modern (live-caught) and fossil (dead-collected) Tridacna gigas shells from the South China Sea (SCS) were used to reconstruct the seawater temperature seasonality during the late Holocene. The averaged seawater temperature seasonality around 2165 ± 75 BC (4.46 ± 1.41°C, derived from the data of 18 yr) were similar to the seasonality of recent decade (4.41 ± 0.82°C during AD 1994–2005), but the temperature seasonality around AD 50 ± 40 (3.69 ± 1.37°C, derived from the data of 48 yr) and AD 990 ± 40 (3.64 ± 0.87°C, derived from the data of 11 yr) was significantly lower than that during AD 1994–2005. The reduced seasonality around AD 990 ± 40 was attributable to the unusually warm winter during the medieval times, probably caused by the weakening of East Asian Winter Monsoon. Our study highlighted the potential of T. gigas shells in providing high-resolution seasonality climate information during the late Holocene. [ABSTRACT FROM AUTHOR]

The large-scale syntheses of global mean temperatures in IPCC fourth report suggested that the Northern Hemisphere temperature in the second half of the 20th century was likely the highest in at least the past 1,300 years and the 1990s was likely the warmest decade. However, this remains debated and the controversy is centered on whether temperatures during the recent half century were higher than those during the Medieval Climate Anomaly (MCA, AD 800-1300) and the Roman Warm Period (RWP, BC 200-AD 400), the most recent two natural warm periods of the late Holocene. Here the high resolution sea surface temperatures (SSTs) of two time windows around AD 990 (±40) and AD 50 (±40), which located in the MCA and RWP respectively, were reconstructed by the Sr/Ca ratio and δO of Tradacna gigas shells from the northern South China Sea. The results suggested that the mean SSTs around AD 990 (±40) and AD 50 (±40) were 28.1 °C and 28.7 °C, 0.8 °C and 1.4 °C higher than that during AD 1994-2005, respectively. These records, together with the tree ring, lake sediment and literature records from the eastern China and northwest China, imply that the temperatures in recent decades do not seem to exceed the natural changes in MCA, at least in eastern Asia from northwest China to northern SCS. [ABSTRACT FROM AUTHOR]

• Onshore deposits of the 1000-year-old tsunami were identified in Dongshan Bay, northeastern South China Sea. • This study further north is mutually corroborated with previous studies in the SCS. • This research provides examples and methods for the study of onshore tsunami deposits. A giant tsunami occurred in the South China Sea (SCS) approximately a thousand years ago, and various types of tsunami deposits were identified on the Xisha Islands, coastline of South China and Badoc Island, the Philippines. However, little is known about the extent of the affected SCS coastlines and the history of other giant tsunamis. Here, we identify tsunami deposits in the coastal sediment of Dongshan Bay, northeastern SCS. The tsunami deposit contains marine shell debris and coarse quartz grains, distinct from the muddy deposits in the upper and lower layers. Geochemical proxies, including Sr/Ba, Ca, Ti, Ca/Ti, and total organic carbon, indicate the marine intrusion of the event deposit. Radiocarbon ages of shells of the event layer are 970–1179 and 1137–1462 cal. yr BP (2σ range of calibrated 14C age). We suggest that the event layer was possibly deposited by the 1000-year-old tsunami. We found onshore tsunami deposits further north than previous studies, providing a new research example of onshore tsunami deposits and a reference for tsunami deposit research and tsunami disaster prevention. [ABSTRACT FROM AUTHOR]

The Dongdao Island of Xisha Islands is an epitome of the island eco-system of South China Sea, and red-footed booby ( Sula sula ) and Pissonia grandis are typical species of the island community. However, a large herbivore ‘urus’ (actually cattle) is now threatening the survival of other species. We analyzed the lithology, as well as organic carbon and nitrogen concentration and isotopes of the sediment core DY2 sampled from the ‘Cattle Pond’ of Dongdao Island, Xisha Islands. Combined with the isotope results of modern cattle and seabird droppings, we identified the eco-geological characteristic of the ‘urus’. According to the AMS 14 C dating of the lumpy cattle excreta and charcoal on the interface layer, we determined the landing time of ‘urus’ and identified a population booming after the landing as shown in the isotope profiles. The ‘urus’, actually cattle, is a special species in the whole island eco-system, but it could disrupt the offshore ecosystem irreversibly; therefore ‘urus’ population needs to be controlled on a proper level. This research proposed a possible method to study the history of invasive species. [ABSTRACT FROM AUTHOR]

In this study, eight Tridacnidae specimens of three different species ( Tridacna gigas , Tridacna derasa and Hippopus hippopus ) were collected from Xisha Islands of South China Sea. The Sr/Ca ratio, which has been widely used as sea surface temperature (SST) proxy in coral samples, was determined on these specimens using ICP-OES to examine their potential for paleoclimate reconstruction. While within-species differences were found to be insignificant, the mean Sr/Ca ratios of the three species (2.24 ± 0.1, 1.77 ± 0.1 and 1.91 ± 0.14 mmol/mol for modern T. gigas , T. derasa and H. hippopus specimens, respectively) are statistically different. Species identification, therefore, is necessary before using Tridacnidae Sr/Ca ratios as paleoclimate recorders. While the relationship between local SST and Sr/Ca ratios of H. hippopus was unclear, the Sr/Ca profiles of modern T. gigas and T. derasa specimens are significantly correlated to local SST, implying that they can be used as SST proxies. The range of Sr/Ca ratios measured in this study is comparable to the Tridacnidae Sr/Ca measurements obtained in previous studies from other areas, but there are also substantial differences in detail, indicating that calibration for regional differences is also needed before paleoclimate reconstruction is attempted. In addition, although the mean Sr/Ca values of T. gigas , T. derasa and coral samples in Xisha Islands were significantly different, their Sr/Ca-SST calibration slopes were comparable, pointing to a similar thermodynamic fractionation and highlighting the potential of the combination of Tridacnidae and coral samples for paleo-SST seasonality reconstruction. [ABSTRACT FROM AUTHOR]

Abstract: We collected three ornithogenic coral sand sedimentary profiles from Jinyin Island, Jinqing Island and Guangjin Island of Yongle archipelago, South China Sea and reconstructed the deposition flux of anthropogenic Hg over the past 700years in the study area. On the whole, the anthropogenic Hg flux is relatively low; it remained at a low level before the Industrial Revolution with a small peak at about 1450–1550 AD, which may record the enhanced metallurgy activity in Ming Dynasty of China. During the 20th century, the deposition flux of anthropogenic Hg increased rapidly, but two troughs occurred during the periods around 1940s and 1970s, corresponding to the economic depression caused by World War II, Civil War in China (1945–1949), and the Culture Revolution (1966–1976) in China. Since the 1970s the deposition flux of anthropogenic Hg has been persistently increasing, apparently the result of fast economic development in East and Southeast Asia countries around South China Sea. [Copyright &y& Elsevier]

The carbon isotopic fractionation process in biogenic carbonate is very complex, and the mechanism for seasonal and long-term variations in biogenic carbonate δ13C remains a matter of debate. In this study, 5 Tridacnidae samples were collected from the South China Sea and analyzed in detail to study seasonal variations. The high-resolution δ13C records exhibited cyclic variations, likely related to seasonality in environmental parameters (e.g., Chl-a concentration, salinity, SST, rainfall). 57 Tridacnidae were collected and analyzed to study the millennium-scale changes of Tridacnidae δ13C during the mid- to late Holocene and the controlling mechanism. The Tridacnidae δ13C over the period 500–5500 BP is statistically significantly correlated with solar activity (TSI and sunspot number), likely attributed to the presence of symbiotic zooxanthellae within Tridacnidae 's mantle lobes. Solar activity could significantly affect the metabolic activity of zooxanthellae, Tridacnidae 's microenvironment, and thus Tridacnidae 's δ13C composition. The decoupling between the Tridacnidae δ13C and solar activity over the past 200 years is most likely due to increased amount of anthropogenic CO 2 and the oceanic δ13C Suess effect. This study improves our understanding about the seasonal and long-term variations of δ13C in Tridacnidae. • The first mid- to late Holocene Tridacnidae δ13C record in South China Sea was reconstructed. • Mid- to late Holocene carbon isotopic records of Tridacnidae is linked to solar activity. • Potential controlling mechanism of long-term Tridacnidae δ13C composition was proposed. [ABSTRACT FROM AUTHOR]