• Yuhong Wang

      Articles written in Journal of Earth System Science

    • Anaerobic oxidation of methane in coastal sediment from Guishan Island (Pearl River Estuary), South China Sea

      Zijun Wu Huaiyang Zhou Xiaotong Peng Nan Jia Yuhong Wang Linxi Yuan

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      The concentrations of CH4, SO$^{2−}_{4}$, 𝛴 CO2 and the carbon isotope compositions of 𝛴 CO2 and CH4 in the pore-water of the GS sedimentary core collected from Guishan Island (Pearl River Estuary), South China Sea,were determined. The methane concentration in the pore-water shows dramatic changes and sulfate concentration gradients are linear at the base of the sulfate reduction zone for the station. The carbon isotope of methane becomes heavier at the sulfate-methane transition (SMT)likely because of the Raleigh distillation effect; 12CH4 was oxidized faster than 13CH4 and this caused the enrichment of residual methane 𝛿13C and 𝛿13C-𝛿 CO2 minimum. The geochemical profiles of the pore-water support the existence of anaerobic oxidation of methane (AOM), which is mainly controlled by the quality and quantity of the sedimentary organic matter. As inferred from the index of 𝛿13C-TOC value and TOC/TN ratio, the organic matter is a mix of mainly refractory terrestrial component plus some labile alga marine-derived in the study area. A large amount of labile organic matter (mainly labile alga marine-derived) is consumed via the process of sedimentary organic matter diagenesis, and this reduces the amount of labile organic matter incorporated into the base of the sulfate reduction zone. Due to the scarcity of labile organic matter, the sulfate will in turn be consumed by its reaction with methane and therefore AOM takes place.Based on a diffussion model, the portion of pore-water sulfate reduction via AOM is 58.6%,and the percentage of 𝛴 CO2 in the pore-water derived from AOM is 41.4%. Thus, AOM plays an important role in the carbon and sulfur cycling in the marine sediments of Pearl River Estuary.

    • A great volcanic eruption around AD 1300 recorded in lacustrine sediment from Dongdao Island, South China Sea

      Zhongkang Yang Nanye Long Yuhong Wang Xin Zhou Yi Liu Liguang Sun

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      The contents of Ti, Al and Fe₂O₃ in a lacustrine sediment core (DY6) collected from Dongdao Island, South China Sea (SCS), were determined to be much higher than those in the three major sediment endmembers (coral sand, guano and plants), and their likely sources include terrigenous dust and volcanic ash. At 61 cm (~AD 1300), the contents of Ti, Al and Fe₂O₃ have an abnormally high spike, which cannot be explained by terrigenous dust. The Sr and Nd isotope compositions at 61 cm are in excellent agreement with those in volcanic materials, but they are significantly different from those in terrigenous dust, implying a possible material input from historical volcanic eruptions in the lacustrine sediment DY6. The documented great Samalas volcanic eruption at AD 1257 in Indonesia is likely the candidate for this volcanic eruption.

    • Mid-to-late Holocene climate change record in palaeo-notch sediment from London Island, Svalbard

      Zhongkang Yang Liguang Sun Xin Zhou Yuhong Wang

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      The Arctic region is very sensitive to climate change and important in the Earth’s climate system. However, proxy datasets for Arctic climate are unevenly distributed and especially scarce for Svalbard because glaciers during the Little Ice Age, the most extensive in the Holocene, destroyed large quantities of sediment records in Svalbard. Fortunately, palaeo-notch sediments could withstand glaciers and bewell-preserved after deposition. In this study, we reconstructed a mid-to-late Holocene record of climate changes in a palaeo-notch sediment sequence from London Island. Multiple weathering indices were determined, they all showed consistent weathering conditions in the study area, and they were closelylinked to climate changes. Total organic carbon (TOC) and total nitrogen (TN) were also determined, and their variation profiles were similar to those of weathering indices. The climate change record in our sediment sequence is consistent with ice rafting record from North Atlantic and glacier activity from Greenland, Iceland and Svalbard, and four cold periods are clearly present. Our study provides arelatively long-term climate change record for climate conditions from mid-to-late Holocene in Svalbard.

    • Evidence for glacial deposits during the Little Ice Age in Ny-Alesund, western Spitsbergen

      ZHONGKANG YANG WENQING YANG LINXI YUAN YUHONG WANG LIGUANG SUN

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      The glaciers act as an important proxy of climate changes; however, little is known about the glacial activities in Ny-Alesund during the Little Ice Age (LIA). In the present study, we studied a 118-cm-high palaeo-notch sediment profile YN in Ny-Alesund which is divided into three units: upper unit (0–10 cm), middle unit (10–70 cm) and lower unit (70–118 cm). The middle unit contains many gravels and lacks regular lamination, and most of the gravels have striations and extrusion pits on the surface. The middle unit has the grain size characteristics and origin of organic matter distinct from other units, and it is likely the glacial till. The LIA in Svalbard took place between 1500 and 1900 AD, the middle unit is deposited between 2219 yr BP and AD 1900, and thus the middle unit is most likely caused by glacier advance during the LIA. Glaciers during the LIA likely overran the sampling site, removed part of the pre-existing sediments, and contributed to the formation of diamicton in the middle unit. This study provides evidence for glacial deposits during the LIA in Ny-Alesund and improves our understanding about historical glacier dynamics and ice-sheet margins during the LIA in western Spitsbergen.

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