The Climate And Ecology Changes In Larsemann Hills, Antarctica And The In-situ Observation Of Trace Gases In Polar Regions

The polar regions, especially the Antarctica, far from and hardly influenced by the human activities, are considered to be the sensitive and core research areas of the global climate variations. The reconstruction and retrieving of the past climate, environment and ecology of polar regions, as well as the high-accuracy monitoring of trace gases under the modern climate background, would contribute to revealing the evolution regulations and controlling factors of the earth’s ecological environment, and consequently providing the scientific evidences of predicting the possible climate and environment trends in the future.In this thesis, we chose the lacustrine deposits at East Antarctic ice-free area as the research object and discussed the character of millennium scale climate change and the respond to the ecological system to retrieve the past climate condition. On the other hand, we chose the Larsemann Hills in East Antarctic and the Ny-Alesund in Arctic as the main study areas for the modern climate research. The trace gases such as ozone, bromine oxide and nitrogen dioxides were observed continuously using passive differential optical absorption spectroscopy. A Large number of first-hand data was got and the feature of the trace gases variations was discussed.The main research contents and results are listed as follows:1. The eco-geological research of the lacustrine deposits at Larsemann Hills, East AntarcticThe chronology of the lake sediment core collected from Mochou lake, Larsemann Hills (69°22.3’S,76°22.0’E) was established on the basis of AMS14C dating. Furthermore, the high-resolution records of lake biomass were retrieved from the loss on ignition at550℃, lithology, grain size, magnetic susceptibility and geochemical element indexes. Statistical analysis such as cluster analysis and factor analysis was performed to reconstruct the continuous and high-resolution records of lake productivity. The relationship between the climate variation and eco-response for the past6720cal. a BP was also discussed.Results showed that the source of the Mochou lake sediments were composed of the sedentary product of local bedrock, the deposits of the algae residues and a few droppings of penguin or other seabirds. According to the statistical analysis of element geochemistry, the assemblage of eight elements, including Cu, Zn, Hg, As, Se, Co, Ni, S, was considered to be the geochemical marker of the penguin droppings, which indicated the penguin (seabirds) populations at the area of Mochou lake. While the other ten variates including TC, TN, LOI550℃, Si, Ti, Ga, P, Ca, Mg, Mn were closely related with the organic content and bedrock content, which indicated the variation trend of the lake productivity.There had been a small size of penguins at the Larsemann Hills before6720cal. a BP and a rapid increase of the penguin’s population was observed after about3500cal. a BP. The paleoclimate of mid-late Holocene was also experienced several alternations. During the periods of6720-6100cal. a BP,5400-4750cal. a BP,4600-4350cal. a BP,4200-3650cal. a BP and3400-3140cal. a BP, the results showed relatively high biomass, which were consistent with the warm and humid climate and high lake productivity. While pronounced low biomass periods were occurred at6100-5400cal. a BP,4750-4600cal. a BP,4350-4200cal. a BP and3650-3400cal. a BP with cold and arid climate as well as low lake productivity. It was notable that some150-years-spanned rapid cooling events were found during the warm climate period at5400-3650cal. a BP, which were rarely reported from other ice-free regions of East Antarctic.By comparing with the solar activity index and the climatic indicator retrieved from ice core of East Antarctic inland, the climate change of Larsemann Hills, East Antarctic was obviously forced by the solar activity and consistent with the ice core records at long time scale, while showed diverse character at short time scale.2. The monitoring and research of ozone, bromine oxide and nitrogen dioxides column densities in polar regionsSince the discovery of "Antarctic Ozone Hole", the reason, mechanisms and the recovery of the ozone hole have been the focus of people’s attention for a long time. The in-situ observations of ozone, bromine oxide and nitrogen dioxides column densities were performed by ground-based passive DOAS (Differential Optical Absorption Spectroscopy) at Larsemann Hills, East Antarctic (69°22’24" S,76°22’14" E) and Ny-Alesund, Arctic (78°54’26"N,11°53’9"E) during summer, respectively. The application of DOAS techniques at polar regions was discussed, as well as the vertical distribution, mechanism and sources of three trace gases.1) The Slant Column Densities (SCD) of stratospheric ozone were observed by zenith-sky DOAS pattern. The Vertical Column Densities (VCD) were then retrieved by linear fitting of air mass factor (AMF) and differential SCD subtracting Fraunhofer Reference Spectrum.The ozone results at Larsemann Hills (from Dec10th,2008to Feb19th,2009) showed that there was no obvious "ozone hole" during the monitoring period with the lowest level at219DU. The ozone VCD had greatly decreased at Dec20th to25th2008and Jan27th to Feb1st2009with a daily variation of60DU.During the monitoring period (from Jul12th to Aug17th,2010) at Ny-Alesund, Arctic, ozone VCD stabilized at about300DU but decreased rapidly and kept low level during late August. It was probably because as the frequent atmospheric dynamic processes like polar vortex occurred during summer, the exchange of the stratosphere and tropopause happened frequently and diffused rapidly, which caused the severe fluctuation of the total ozone column.By comparing the ozone column results of different monitoring patterns, the passive DOAS showed good correlation with the satellite board OMI measurements, which confirmed the validity of the applying of DOAS technology in polar regions. Furthermore, with much higher spacial resolution, the ground-based passive DOAS technique is the supplement and confirmation of the satellite observation at circumpolar latitudes.2) The bromine oxide column densities in Larsemann Hills, East Antarctic and the nitrogen dioxides column densities in Ny-Alesund, Arctic were observed by multi-axis DOAS pattern respectively. The tropospheric differential SCD at four off-axis angles were obtained by extracting spectrums at five different angles (90°,5°,10°,15°/30°,20°) and subtracting stratospheric column densities. Then the variation trend of VCD and mixing ratios of the trace gases could be calculated.The BrO results at Larsemann Hills, East Antarctic (from Dec10th,2008to Feb.19th,2009) suggested the dSCD diurnal variation with a "W" pattern and no obvious difference of the four off-axis elevation angles, which indicated that the concentration of BrO was very low and uniformly distributed. The BrO VCD showed a typical "high at noon while low at twilight" diurnal pattern. According to the AMF Box Model, the average mixing ratio of BrO was9.64pptv during the monitoring period. The main source of BrO was composed of the photo degradation product of man-made brominated hydrocarbon and the chemical release at the surface of acid sea salt. The NO2results at Ny-Alesund, Arctic (from Jul5th to Aug1st,2011) showed a typical tropospheric pattern as the differential SCD decreased when elevation angle increased. According to the AMF Box Model, the average mixing ratio of NO2during the measurement period was4.09ppbv. The occurrence of high NO2concentration might be related to the fossil fuel combustions of the vessels and the abnormal fluctuation at twilight might be influenced by the atmospheric photochemical reactions at sea surface.The ground-based multi-axis DOAS showed much higher spacial and temporal resolutions than satellite measurements, especially in the aspect of sensitivity at short time scale and limited area. There will be very big development perspective for applying of DOAS in polar regions.