Climate Change Revealed By The Subfossil Chironomid Head Capsules At The Core NOW14 In Greenland

Being located in the Arctic region,Greenland has been one of the key regions for global climate change research.It not only responds sensitively to global climate change,but also directly impacts on the global climate in the northern hemisphere and then the global climate through complex sea-air-ice feedback mechanisms.The Arctic region has been one of the key areas for global climate change researches.It not only responds sensitively to global climate change,but also directly impacts on the global climate in the northern hemisphere and then the global climate through complex sea-air-ice feedback mechanisms.Among many paleoclimate reconstructed archieves,lacustrine sedimentary records have become important subjects in paleoclimate research because of the advantages of long time series and widely distributed.Biological indicators,especially some aquatic organisms(such as chironomids)are relatively sensitive to environmental changes due to their relatively narrow ecological amplitude and well preservation after death.Thus,these indicators are more welcomed by researchers who are dediacate to reconstruction of palaeolimnology and the Quaternary environment.The study of chironomid subfossil as an environmental indicator began in the early 20th century.Since the 1990s,chironomid as temperature indicator has been explored internationally and has undergone transition from qualitative description to quantitative analysis.In recent years,the importance of isotope of chironomid subfossil are highly regarded and the application of oxygen isotope index from chironomid subfossil to paleoclimate changes has just started which has broad prospects.It is imperative to expand the research to deepen the understanding of mechanism and enrich the index system of paleoclimate on lake sediments.By analyzing chironomid head capsule subfossil in lake sediments from northwestern Greenland,this paper try to prove feasibility of reconstructing paleoclimate from chironomid subfossil oxygen isotope through combination and estimated temperature based on the quantitative reconstruction of chironomid assemblage.At the same time,through the comparison between chironomid-inferred temperature and the oxygen isotope of chironomid head capsule subfossil,the paper try to analyze the mechanism of similarities and differences between the two groups of indicators.After the pre-treatment,production and identification,a total of 18 taxon of 3 families are involved in sediment samples of core NOW 14.Based on the optimum temperature values of chironomid subfossils obtained from the quantitative reconstruction using the transfer function in the previous studies,the trend of past summer(July)lake temperature can be inferred from the percentage of chironomid subfossils in NOW14.Meanwhile,the oxygen isotope smooth curves of chironomid subfossil are characterized by fluctuations which consistent with chironomid-inferred temperature,indicating that chironomid subfossil oxygen isotope can be used for palaeoclimate reconstruction in core of NOW14.The difference two group of Lowess smoothing curves between chironomid-inferred temperature and chironomid subfossil oxygen isotope is mainly found in the depths near the surface layer,and more severe amplitude of fluctuation which is reflected in curve of chironomid subfossil oxygen isotope.In this regard,this paper This paper believes that the difference mechanism resulting from the index comparison is due to the indication significance of the two groups of indicators and the complicated factors of the oxygen isotope in chironomid subfossil head capsule.Combined with the effective 210Pb dating data,this paper finds that trends in chironomid-inferred temeperature is contrary to the general global warming phenomenon since the 20th century,and the most intense and significant time period temperature conversion intensity in the whole borehole.Besides,index of 813C,C/N in NOW14 lake sediments also clearly reflect the drastic changes of ecological environment in lake.By comparison with the existing instrumental records in West Greenland,the North Atlantic Oscillation(NAO)may be an important factor to influence mechanism of climate change.