Xuebo Yin

Human impact overwhelms long-term climate control of weathering and erosion in southwest China

During the Holocene there has been a gradual increase in the influence of humans on Earth systems. High-resolution sedimentary records can help us to assess how erosion and weathering have evolved in response to recent climatic and anthropogenic disturbances. Here we present data from a high-resolution (similar to 75 cm/k.y.) sedimentary archive from the South China Sea. Provenance data indicate that the sediment was derived from the Red River, and can be used to reconstruct the erosion and/or weathering history in this river basin. Accelerator mass spectrometry C-14 dating provides direct age control and reveals coherent variations in clay mineralogy, geochemistry, and terrigenous flux, indicative of strong chemical weathering and physical erosion during the mid-Holocene warm period (6400-4000 cal [calibrated] yr B.P.), followed by weakening from ca. 4000-1800 cal yr B.P., and renewed intensification since 1800 cal yr B.P.. Comparison with climatic records from China indicates that precipitation and temperature controlled both physical erosion and chemical weathering intensity before 1800 cal yr B.P.. However, weathering proxies in the offshore sediment indicate recent increased soil erosion. We suggest that enhanced human activity (deforestation, cultivation, and mining) since the end of the Chinese Han Dynasty (220 CE) has overwhelmed the natural climatic controls on erosion in the Red River.

Geochemical records in the South China Sea: implications for East Asian summer monsoon evolution over the last 20 Ma

Abstract We reconstruct past changes in the East Asian summer monsoon over the last 20 Ma using samples from Ocean Drilling Program (ODP) Site 1146 of Leg 184 in the northern South China Sea based on the major (Al, Ca, Na, K, Ti, etc.) and trace element (Rb, Sr, and Ba) geochemistry of terrigenous sediments. This study and combined review suggests that the long-term evolution of the East Asian summer monsoon is similar to that of the Indian summer monsoon, but distinct from the East Asian winter monsoon. Generally, the Asian summer monsoon intensity has decreased gradually from its maximum in the Early Miocene. In contrast, the Asian winter monsoon shows a phased enhancement since 20 Ma bp. Moreover, our study shows that the long-term intensities of the Asian summer and winter monsoons may have different forcing factors. Specifically, the winter monsoon is strongly linked to phased uplift of Tibetan plateau and to Northern Hemispheric Glaciation. In contrast, global cooling since 20 Ma bp may have largely reduced the amount of water vapour held in the atmosphere and thus weakened the Asian summer monsoon.

Trace metals in the surface sediments of the intertidal Jiaozhou Bay, China: Sources and contamination assessment

The major (Al) and trace metal (Cu, Pb, Zn, Cr, Cd, and As) concentrations in 29 surface sediment samples from the intertidal Jiaozhou Bay (JZB) are evaluated to assess the contamination level. The results show that the overall sediment quality in the area has been obviously impacted by trace metal contamination. The geoaccumulation index and the enrichment factor values indicate that no Cr or Cu contamination has occurred on the whole, only a few stations have been polluted by As, and some areas have been polluted by Cd, Pb, and Zn. Principal component analysis suggests that the Cu, Pb, Zn, and Cd are derived from anthropogenic inputs and that Cr, As, Cu, and Zn are influenced by natural weathering processes. Cu and Zn may originate from both natural and anthropogenic sources. The contamination in the northeastern JZB is higher than that in other areas of the bay.

Seasonal variability and flux of particulate trace elements from the Yellow River: Impacts of the anthropogenic flood event

In this study, the suspended particulate matter (SPM) of the Yellow River (Huanghe) was collected biweekly at the outlet and analyzed for particulate trace element contents. The seasonal variations of the trace elements were primarily controlled by hydrological processes, which determined different sources of the SPM. Moreover, As, Co, Cr, and Ni primarily originated from lithogenic sources, whereas Cd, Cu, Pb and Zn were influenced by anthropogenic activities. The Yellow River has suffered moderate to considerable ecological risk during the late stage of Water and Sediment Regulation (WSR). Using the discharge-weighted contents method, the annual trace element fluxes were estimated, with ca. 30% of the annual fluxes occurring within the short WSR period (6% of one year). More specifically, 75% of the Cd flux was from an anthropogenic source, which likely posed a significant threat to the estuary and the adjacent coastal ecosystems.

Elemental and isotopic compositions of the hydrothermal sulfide on the East Pacific Rise near 13°N

The mineralogical, elemental, and isotopic characteristics of a hydrothermal sulfide sample from one dredge station (12°42.30′N, 103°54.48′W, water depth 2655 m) on the East Pacific Rise near 13°N were analyzed. The hydrothermal sulfide was composed mainly of sphalerite, chalcopyrite, and pyrite and was a Zn-rich sulfide; in layer ep-s-1, goethite formed by secondary oxidation was found. The concentrations of rare elements, such as Li (0.15×10−6–0.30×10−6), Be (0.01×10−6–0.05×10−6), Zr (73.8×10−9–1344×10−9), Nb (8.14×10−9–64.7×10−9), Hf (2.54×10−9–28.0×10−9), and Ta (0.203×10−9–1.21×10−9), were far lower in the hydrothermal sulfide than in the ocean crust, whereas the content of Au was higher and the contents of Co, Ni, Sr, Cs, Ba, Bi, and U were low. The correlations between Zn and Cr, Cd and Ga, Cu and P, P and In (R2 > 0.8) were positive, whereas those between Zn and Fe, Cu, and Ba (R2 > 0.8) were distinctly negative. From low-temperature mineral assemblages to high-temperature mineral assemblages, the spatial distributions of dispersive and rare elements (e.g. In, Li, Cs) in the hydrothermal sulfide displayed corresponding variations. The variations observed in some elements (e.g., Cd, Cs, P) are controlled by Zn, Fe, and Cu sulfides, respectively. Seafloor weathering accounts for the enrichment of V, Mn, and rare earth elements (REE) in the henna sulfide-oxidation layer that bears the secondary oxide mineral, leading to identical REE patterns for this layer (ep-s-1) and seawater. Seafloor weathering also distinctly affects the correlations between the element ratios of the hydrothermal sulfide. From high-temperature mineral assemblages to low-temperature mineral assemblages, Fe content and δ34S value of the hydrothermal sulfide increase gradually, and Zn content and lead isotopic ratios decrease gradually on the contrary, which indicate the influences of seawater on elements and the sulfur and lead isotopic compositions enhance gradually during the formation of hydrothermal sulfides.

One hundred-year sedimentary record of heavy metal accumulation in the southeastern Liaodong Bay of China

Integrated analyses of grain size, 210Pb stable isotope, and heavy metals were performed to characterize the sedimentary core LDC30 collected from the southeastern Liaodong Bay of China and investigate the 100-year history of heavy metal accumulation. The aluminum-normalized enrichment factors and the excess metal fluxes (MFxs) indicated that the metal accumulation in the southeastern Liaodong Bay occurred in three stages: a pre-industrial stage (prior to 1960s) with natural accumulation, an initial industrial stage (1960–1990) with slowly elevated accumulation, and an industrialized stage (post-1990s) with accelerated accumulation. A moderate enrichment of Cd and Pb (up to 4.1- and 2.6-fold over the baseline, respectively) and a slight enrichment of Cr, Cu, Ni, and Zn (up to 1.3-fold) were measured in the recent sediments. Multivariate analysis demonstrated that the Cr, Cu, Ni, and Zn were from the natural origin, whereas Cd and Pb from the anthropogenic origin. The MFxs of Cd and Pb showed a drastically increasing trend since 1990s, which could result from the intensive application of fertilizers and combustion of fossil fuels.

Geochemistry of rare earth elements in the mid-late Quaternary sediments of the western Philippine Sea and their paleoenvironmental significance

Based on a δ18O chronology, rare earth elements (REE) and other typical elements in sediments from core MD06-3047 in the western Philippine Sea were analyzed to constrain the provenances of the sediments and investigate quantitative changes in the Asian eolian input to the study area over the last 700 ka. Among the competing processes that might affect REE compositions, sediment provenance is the most important one. Provenance analysis suggests that the study sediments have two provenance end-members; local volcanic sources are dominant, and eolian dust from the Asian continent has a smaller contribution. During glacial periods, eolian input to the western Philippine Sea was enhanced. In contrast, material supply from local volcanics increased during interglacial periods. Changes in eolian input to the study area were probably related to the strength of the East Asian winter monsoon (EAWM) as well as aridity in the Asian continent on an orbital time scale, and were partly influenced by local control factors on shorter time scales. Therefore, we propose that the present study expands the application of the REE-based method for quantitatively estimating the eolian component from the mid-latitude northern Pacific to the low-latitude western Pacific. Additionally, the study preliminarily confirms the influence of EAWM-transported eolian material on sedimentation in the western Philippine Sea since 700 ka.

Genesis of anhydrite in hydrothermally altered basalt from the East Pacific Rise near 13°N

This study reports the occurrence of anhydrite in hydrothermally altered pillow basalt (12°50.55′N, 103°57.62′W, water depth 2 480 m), which may have been produced in the basalt during seawater-basalt interaction in the laboratory. The existence of anhydrite in the altered basalt indicates extensive high-temperature hydrothermal alteration at the surface of seafloor pillow basalt. Microprobe analysis shows significant chemical zoning in the hydrothermally altered pillow basalt, in which Ca, Si and Al contents decrease and P, Fe, Mn, Cr and S contents increase from fresh basalt to altered basalt. The negative correlation between Rb-Sr and Li-Sr, and negative correlation between Li-Ca and Rb-Ca in the high-temperature vent fluids show that these fluids underwent anhydrite precipitation before fluid jetting due to mixing with seawater in the sub-seafloor. Based on these observations, we show that not all Ca in the anhydrite comes from basalt in the reaction zone, and that the basalts on the seafloor or in the upflow zone may also provide Ca for anhydrite.

Component characteristics of organic matter in hydrothermal barnacle shells from Southwest Indian Ridge

In 2008–2009, hydrothermal barnacle and sediment samples were collected from the Southwest Indian Ridge during a survey of the China Ocean Mineral Resources R&D Association (COMRA). Samples were analyzed by gas chromatography-mass spectrometer (GC-MS), revealing the main organic constituents of hydrothermal barnacle and sediment to be fatty acids and alkylbenzenes. N-alkanes which possessed obvious even carbon advantage were also detected in hydrothermal sediment. The high concentrations of aromatic compounds might be the result of macromolecular thermal alteration. Microorganism in the submarine hydrothermal ecosystem, especially those related to sulfur metabolism, might be the source of the high concentrations of fatty acids detected in these samples. In high temperature and high pressure hydrothermal environments, n-alkanes which possessed obvious even carbon advantage might originate from thermal alteration of carboxylic acids and other lipid compounds.

Factors affecting the rare earth element compositions in massive sulfides from deep-sea hydrothermal systems

To reconstruct the evolution of ore-forming fluids and determine the physicochemical conditions of deposition associated with seafloor massive sulfides, we must better understand the sources of rare earth elements (REEs), the factors that affect the REE abundance in the sulfides, and the REE flux from hydrothermal fluids to the sulfides. Here we examine the REE profiles of 46 massive sulfide samples collected from seven seafloor hydrothermal systems. These profiles feature variable total REE concentrations (37.2-4092 ppb) and REE distribution patterns (La-CN/Lu-CN ratios = 2.00-73.8; (Eu/Eu*) CN ratios = 0.34-7.60). The majority of the REE distribution patterns in the sulfides are similar to those of vent fluids, with the sulfides also exhibiting light REE enrichment. We demonstrate that the variable REE concentrations, Eu anomalies, and fractionation between light REEs and heavy REEs in the sulfides exhibit a relationship with the REE properties of the sulfide-forming fluids and the massive sulfide chemistry. Based on the sulfide REE data, we estimate that modern seafloor sulfide deposits contain approximately 280 t of REEs. According to the flux of hydrothermal fluids at mid-ocean ridges (MORs) and an average REE concentration of 3 ng/g in these fluids, hydrothermal vents at MORs alone transport more REEs (>360 t) to the oceans over the course of just 2 years than the total quantity of REEs in seafloor sulfides. The excess REEs (i.e., the quantity not captured by massive sulfides) may be transported away from the systems and become bound in sulfate deposits and metalliferous sediments.