High resolution oxygen isotope and grayscale records of a medieval fossil giant clam(Tridacna gigas) in the South China Sea: physiological and paleoclimatic implications

Mollusks are well known for their detailed recording of paleoenvironmental and paleoclimatic changes in their carbonate shells. In this study, we constructed 18-year blue color intensity and oxygen isotope profiles of a14C dated （AD 990±40） fossil giant clam,Tridacna gigas, from Shidao Island, South China Sea. Theδ18O profile of theT. gigas specimen displayed regular annual cycles and was probably controlled by seasonal variations of the climatic parameters. The blue color intensity profile showed good agreement with theδ18O series, and both had 18 clear annual cycles in accordance with the 18 visually identified annual growth bands. The annual shell growth rate determined from the blue color intensity and oxygen isotope profiles indicated that the annual shell increment of theTridacna specimen was stable after the onset of sexual ma-turity. Spectral analysis of theδ18O and blue color intensity time series suggested that the El Ni？o-Southern Oscillation （ENSO） period observed in the instrumental temperature and precipitation records of the South China Sea during the past 50 years also existed in medieval times. Our results showed that fossil giant clams could provide a good archive of historical intra-seasonal to decadal climate variations.

Relocation of the Yellow River Estuary in 1855 AD Recorded in the Sediment Core from the Northern Yellow Sea

Relocation of the Yellow River estuary has significant impacts on not only terrestrial environment and human activities, but also sedimentary and ecological environments in coastal seas. The responses of regional geochemical characteristics to the relocation event, however, have not been well studied. In the present study, we performed detailed geochemical elemental analyses of a sediment core from the northern Yellow Sea and studied their geochemical responses to the 1855AD relocation of the Yellow River estuary. The results show that TOC/TN, Co/A1203, Cr/A1203, Ni/A1203 and Se/A1203 ratios all decreased abruptly after 1855 AD, and similar decreases are observed in the sediments of the mud area southwest off the Cheju Island. These abrupt changes are very likely caused by the changes in source materials due to the relocation of the Yellow River estuary from the southern Yellow Sea to the Bohai Sea, which the corresponding decreasing trends caused by the changes in main source materials from those transported by the Liaohe River, the Haihe River and the Luanhe River to those by the Yellow River. Because the events have precise ages recorded in historical archives, these obvious changes in elemental geochemistry of sediments can be used to calibrate age models of related coastal sea sediments.

Potential Applications of X-ray Fluorescence Core Scanner in Elemental Analyses of the Muddy Sediments on the Coastal Shelves of China and in Ecological Study

Large areas of muddy sediments on the coastal shelves of China provide important samples for studying climate and ecological changes. Analysis of a large number of such samples, which is essential for systematic study on environmental information recorded in mud areas because of complicated sedimentary environment and variable sedimentary rate, requires a fast and economical method. In this study, we investigated the potential of X-ray fluorescence core scanner （XRFS）, a fast analytical instrument for measuring the elemental concentrations of muddy sediments, and observed a significant correlation between the element concentrations of muddy sediments determined by regular X-ray fluorescence spectrometer （XRF） and XRFS, respectively. The correlations are mainly determined by excitation energy of elements, but also influenced by solubility of element ions. Furthermore, we found a striking link between A1 concentrations and marine-originated organic carbon （MOC）, a proxy of marine primary productivity. This indicates that MOC is partly controlled by sedimentary characteristics. Therefore, XRFS method has a good potential in fast analysis of a large number of muddy sediment samples, and it can also be used to calibrate MOC in ecological study of coastal seas.

Responses of Primary Productivity to Current and Climate Changes in the Mud Area to the Southwest of Cheju Island During the Past 800 Years

The biogenic silica (BSi) ,total organic carbon (TOC) ,total nitrogen (TN) and grain size were analyzed with a gravity core (3250-6) collected from the mud area in the north East China Sea.The average deposition rate of the upper core was about 0.078cm yr1based on the results of 210Pbex.The mean grain size increased with depth in general.The frequency distribution of grain size showed that two marked changes of deposition environment occurred at 30 cm and 50 cm depths (about 1550 AD and 1300 AD,respectively) .The variations of BSi and TOC indicated two distinct major periods of primary productivity over the past 800 years:a stage of low primary productivity corresponding to weak upwelling and low nutrient input below 30 cm depth (about 1200-1550 AD) ,and a stage of high primary productivity with strong currents and upwelling above 30 cm depth (about 1550-1950 AD) .The stage with high primary productive appeared to be due to the northward-expanded muddy area caused by strong Asian Winter Monsoon and enhanced Yellow Sea Warm Current in winter.In conclusion,the BSi and TOC in the muddy sediments,the symbols of marine primary productivity,can be then used to investigate the evolution history of currents and relative climate change in the offshore areas.

From sea to land: assessment of the bio-transport of phosphorus by penguins in Antarctica

In Antarctica, the marine ecosystem is dynamically interrelated with the terrestrial ecosystem. An example of the link between these two ecosystems is the biogeochemical cycle of phosphorus. Bio- vectors, such as penguins, transport phosphorus from sea to land, play a key role in this cycle. In this paper, we selected three colonies of penguins, the most important seabirds in Antarctica, and computed the annual quantity of phosphorus transferred from sea to land by these birds. Our results show that adult penguins from colonies at Ardley Island, the Vestfold Hills, and Ross Island could transfer phosphorus in the form of guano at up to 12 349, 167 036, and 97 841 kg/a, respectively, over their breeding period. These quantities are equivalent to an annual input of 3.96× 10^9-1.63 × 10^10 kg of seawater to the land of Antarctica. Finally, we discuss the impact of phosphorus on the ice-flee areas of the Antarctica.

An Introduction to the Special Issue

Shelf seas are important systems supporting China’s rapid economic and societal developments.However,the Yellow Sea(YS)and the East China Sea(ECS)environments have undergone dramatic changes recently,which have profoundly impacted their ecosystem health.Being within the Asian monsoon-dominated region,the environment of the YS and the ECS is influenced by oceanic processes such as the intrusion of the Kuroshio Current(KC)and by human activities of China’s rapidly developed coastal regions.Thus,the YS and the ECS are ideal regions to understand and to distinguish the influences

Organic geochemical characterization on a seal excrement sediment core from Fildes Peninsula,Western Antarctica

Organic geochemical analysis was performed on a sediment core HN1 from Fildes Peninsula on King George Island, Western Antarctica. Short-chain n-alkanes were the main components of the aliphatic hydrocarbons present, and they were likely to be from algae and bacteria; n-C23 was likely derived from moss. Fecal sterols and phytol dominated the alcohol composition, and may have come from seal feces and vegetation, respectively. The fluctuations in their concentrations generally have responded to historical changes in the ecosystems near the region. The even-carbon fatty acids, such as n-Cl6, n-Cl8 and t/-C24, dominated the alkenoic acid composition, which mainly originated from bacteria, moss and zooplankton. The low concentrations of unsaturated fatty acids showed a predominance of C16：1 and C18：1 unsaturated acids, and demonstrated that the sediment was well preserved and had a simple and stable source of organic materials.

Higher sea surface temperature in the northern South China Sea during the natural warm periods of late Holocene than recent decades

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 past1,300 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 d18O 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.

Ecosystem evolution of seal colony and the influencing factors in the 20th century on Fildes Peninsula,West Antarctica

As the topmost predator in Antarctica,the seal is a unique indicator of Antarctic environment and climate changes.In this study,we collected a sediment core from the Fildes Peninsula of West Antarctica,and used cholesterol,cholestanol,epicoprostanol,coprostanol,and seal hair numbers as the proxy indicators of seal population size and phytol as of general vegetation,and we reconstructed the 20th century history of variation of the seal population and vegetation abundance on this island.The sealing industry in the early 20th century caused the dramatic decline of seal population,and the ban of seal hunting since the 1960s led to its recovery of seal population.The seal population during the past century was primarily controlled by human activities and krill density.The reconstructed relation between seal population and vegetation abundance may offer new insights into Antarctic environment and ecology.