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The El Niño-Southern Oscillation (ENSO) is the principal climatic system in the modern Pacific Ocean, and it potentially influences the global climate. The South China Sea (SCS), in the western tropical Pacific, is significantly affected by ENSO activity. We have conducted a high-resolution oxygen isotope study of the shells of one modern and four fossil Tridacna from the Xisha Islands in the SCS. The results for the modern sample reveal that the shells of Tridacna are a good proxy of ENSO variability. We used the results of the oxygen isotope composition of four fossil Tridacna to produce high-resolution records of ENSO activity during four time slices in the Holocene. The results indicate that ENSO variability in the early Holocene was comparable to that of today, and that a minimum in the frequency and intensity of ENSO activity occurred in the mid Holocene. These findings are consistent with paleoclimatic results from corals, mollusks and sedimentary records. However, the observed extremely low frequency and moderate ENSO intensity at 4.7 ka indicate an anomalous pattern of ENSO changes within this interval of climatic transition. In addition, seasonal temperature variations during the Holocene were different from those of today and extreme seasonality may also occur during warmer periods. [ABSTRACT FROM AUTHOR]

Changes in vegetation biomass have a great impact on many aspects of the Arctic ecosystem, and historical variations of biomass in Svalbard during the Holocene remain poorly understood. In this study, we collected a palaeo-notch sediment profile in Ny-Ålesund, Svalbard, performed organic biomarker and geochemical analysis on the sediments, reconstructed the photosynthetic biomass record during the interval of 9400–2200 BP, and examined the relationship between the photosynthetic biomass changes and Holocene temperature records in the Arctic region. The photosynthetic biomass production in Ny-Ålesund experienced four development periods. It rose steadily at the beginning of the Holocene and became stabilized at a high level during the Holocene thermal maximum. However, the photosynthetic biomass dropped sharply during the mid-Holocene transition. After that, it showed a small peak during the interval of 3000–2500 BP. The historical photosynthetic biomass record is in good agreement with the temperature records: the photosynthetic biomass production increases during warmer periods, and vice versa. Therefore, temperature is likely the driving factor controlling the photosynthetic biomass production. This study improves our understanding of the terrestrial ecosystem and its responses to climate change in the Arctic. [ABSTRACT FROM AUTHOR]

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 be well-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 closely linked 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 a relatively long-term climate change record for climate conditions from mid-to-late Holocene in Svalbard. [ABSTRACT FROM AUTHOR]