Holocene Climatic Changes And Environmental Events In Typical Areas Of Arctic,Antarctic And Coastal China Regions

Global warming is one of the most important publics’ concern among all the global environmental problems and the temperature in the Arctic is rising at a speed twice the global average,a phenomenon known as Arctic amplification.Global warming will also generate a series of disasters and previous studies have shown that frequent extreme environmental events in the mid-latitude is closely related to Arctic amplification.Studying past is the key to predict future.Therefore,in order to cope better with global climate change and minimize the impact of climate change on China,we need to reconstruct historical climate changes in Svalbard and extreme environmental events in coastal China.In addition,intensified human activities in polar regions have led to environmental pollution issues and little is known about current pollution status in the polar regions.Centering on the above issues,our research team collected several materials,including sediment cores,Tridacnidae and ancient wood,from polar regions and coastal China,discussed the Holocene climate changes in the Arctic and coastal China,and assessed the environmental pollution status in both Arctic and Antarctica.The following points will be discussed in this study.1.Mid-to-late Holocene climate change and its ecological responses in SvalbardThe Arctic region is very 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.Palaeo-notch sediments could withstand glaciers and be well-preserved after deposition,and thus be regarded as a ideal material for palaeoclimatic research.In this study,multiple weathering indices were determined for palaeo-notch sediment from London Island,they all showed consistent weathering conditions,and they were closely linked to climate changes,in line with TOC results.Our reconstructed climate record is consistent with ice rafting record from North Atlantic and glacier activity from Greenland,Iceland and Svalbard.In addition,C/N atomic ratios and carbon isotope indicate that organic matter in the sediment is mainly derived from lacustrine algae.We estimated the relative organic matter contribution from allochthonous and autochthonous sources,used multiple geochemical proxies to reconstruct palaleoproductivity variations,and investigated their link to climatic records from surrounding regions.Changes in the reconstructed palaeoproductivity are consistent palaeoclimatic records from the surrounding regions.Thus palaeoproductivity variations on the Blomstrandhalv(?)ya are mainly driven by climate changes;palaeoproductivity increase during warmer periods,and vice versa.2.Total photosynthetic biomass record between 9400 and 2200 BP in Ny-AlesundChanges in vegetation biomass have a great impact on many aspects of the Arctic ecosystem.However,historical variations of biomass in Svalbard during the Holocene remain poorly understood.In this study,we performed organic biomarker and geochemical analysis on palaeo-notch sediment profile(YN)in Ny-Alesund,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-Alesund 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(HTM).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.3.Glacial deposits during the LIA recorded in palaeo-notch sedimentThe middle unit of palaeo-notch sediment profile YN contains a large number of gravels,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 AD and 1900 AD,the middle unit is deposited between 2219 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 new evidence for larger glaciers during the LIA than that during the Younger Dryas in western Spitsbergen.4.AD 1257 Samalas volcanic eruption event recorded in Xisha IslandsThe contents of Ti,A1 and Fe2O3 in DY6 collected from Dongdao Island,South China Sea(SCS),were determined to be much higher than those in the three major sediment end-members(coral sand,guano and plants),and their likely sources include terrigenous dust and volcanic ash.At 61 cm(～AD 1300),the contents of Ti,A1 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,implying a possible material input from volcanic eruptions.The documented great Samalas volcanic eruption at AD 1257 in Indonesia is likely the candidate for this volcanic eruption.5.Mid-to late Holocene carbon isotopic record of Tridacnidae and its controlling mechanismThe carbon isotopic fractionation process in biogenic carbonate is very complex.In this study,5 Tridacnidae samples were collected from the South China Sea and analyzed in detail to study seasonal variations.The high-resolution SV3C records exhibited cyclic variations,likely related to seasonality in environmental parameters(e.g.,primary productivity,salinity,nutrient,DIC).57 Tridacnidae were collected and analyzed to study the millennium-scale changes of Tridacnidae δ13C during the mid-to late Holocene.The Tridacnidae δ13C over the period 500-5500 BP is statistically significantly correlated with solar activity,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 the oceanic δ13C Suess effect.This study improves our understanding about the seasonal and long-term variations of δ13C in Tridacnidae.6.An extreme ecological event between 5600-5900 BP in Zhoushan ArchipelagoA 3.3-m-thick,74.5-m-long ancient wood layer was discovered in Zhoushan Archipelago,East China Sea.The analysis results of sporopollen and seeds indicated that the vegetation types represented by the ancient wood layer is the subtropical evergreen and deciduous broad leaved mixed forest,similar with those in Hemudu site.The distribution of the ancient woods and well-preserved ancient wood stumps indicated that these ancient woods were native and not transported from other places.The ancient plants as well as their leaves,fruits and seeds were all preserved well,indicating a sudden deposition event.As inferred from the radiocarbon dating results and palaeoclimatic records,the ancient wood layer was likely caused by the coaction of the rapid sea level rise and strong storm surges,which became more frequent and intensive during the period 5900-5600 yr BP due to intensified summer monsoon winds,strong winter monsoon winds and very low ENSO activity.7.Assessment of heavy metal contamination in the AntarcticFildes Peninsula,with a high density of scientific stations,has been significantly impacted by anthropogenic activities.However,the contamination from penguins,a biovector that transports pollutants from ocean to land,has seldom been assessed.In this study,32 lacustrine surface sediment samples on Fildes Peninsula and 8 lacustrine surface sediment samples on Ardley Island were collected to determine Cu,Zn,Pb,Ni,Cr,Cd,Co,Sb,Hg and P levels.The results showed that the heavy metal contents on Ardley Island are significantly higher than those on Fildes Peninsula.The contaminants on Fildes Peninsula are mainly derived from anthropogenic activities,while the contaminants on Ardley Island are related to biomagnification in the food chain.The results indicated that the impact of penguin-transported contamination on Antarctic environment outweighs human activities near scientific stations in some areas.Therefore,more attention should be paid to the impacts of Antarctic animals on the Antarctic environment.8.Assessment of heavy metal contamination in the ArcticNy-Alesund has been significantly impacted by anthropogenic activities(e.g.coal mining,scientific research,cruise ship tourism)over the past 100 years.However,the study of heavy metal contamination in Ny-Alesund currently mainly focus on surface soil or surface fjord sediments and little is known about the history and pollution status of heavy metal contamination over the past 100 years.In this study,we collected a palaeo-notch sediment profile YN,analyzed the contents of six typical heavy metals(Cu,Pb,Cd,Hg,As,Se)in the sediments,and assessed the historical pollution status in Ny-Alesund using the pollution load index,geoaccumulation index and enrichment factor.The results showed that the contents of heavy metals over the past 100 years increased rapidly.In addition,heavy metals Pb,Cd,Hg and Se are much more polluted than other metals and show a clear signal of enrichment.The contamination is linked to gas-oil powered generators,coal mining,research station,cruise ship tourism and long-range transport of pollutants.