| The High Arctic regions are very sensitive to response and feedback to global warming, and in which permafrost thaws and alters microsites environment in tundra and stimulates microorganism activity to generate and emit greenhouse gases. In addition, major seabird colonies are typically found in high Arctic coastal areas. Seabird activity such as prey and trample transfers carbon, nitrogen and phosphorus from marine to terrestrial tundra ecosystem. Seabird activity and bird dropping affect physical and chemical properties in tundra soil, which further have important impact on the processes of sources and sinks of greenhouse gases in High Arctic. However, little research on CO2, N2O and CH4fluxes has been conducted at High Arctic tundra, such as at Svalbard, especially, effects of seabird activity on greenhouse gases in tundra. Therefore it is very important to study the influence of seabird activity and environment factors on production and emission of greenhouse gases in High Arctic tundra ecosystems During the4th and5th Chinese Arctic Research Expedition, temporal and spatial variations of greenhouse gases (CO2, N2O and CH4) fluxes and their influence factors were investigated from tundra ecosystems in Ny-Alesund, Svalbard, a Norwegian archipelago located in the High Arctic using the close chamber method. The objects of this paper were to evaluate the potential importance of CO2, N2O and CH4emissions from the tundra ecotopes affected by seabird activity and meteorological factor in the High Arctic region. Simulation experiments were designed and carried out to discuss the influence of freezing-thawing cycles on the emission rates of greenhouse gases in High Arctic tundra soil. In addition, spatial variation of CO2concentration and its isotopic compositions were and their affecting factors were also analyzed in the marine atmosphere. The main research contents are as follows:(1) Spatial and temporal variations of atmospheric of CO2, CH4and N2O concentration in NY-Alesund, High ArcticDuring the summers of2008and2009, gas samples were collected from in the different ecologic areas, including bird sanctuary tundra, including bird sanctuary, beach tundra, mining area, human activity area, etc. in Ny-Alesund, Svalbard, Norway. The concentrations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in these gas samples were determined by gas chromatography in the laboratory, the spatial and temporal variations of their concentrations were analyzed, and the factors affecting their concentrations were discussed in this study. The diurnal mean CO2and N2O concentrations in summer2008were about30ppm and25ppb higher than those in summer2009at the sites in the bird sanctuary. The mean CO2concentration at the sites in beach tundra were30ppm higher in summer2008than in summer2009while the mean N2O concentration was11ppb lower in summer2008than in summer2009. The CH4concentration in summer2008was0.7ppm lower than that in summer2009at the bird sanctuary, vice versus for the sites in the beach tundra. The interannual variation of greenhouse gases concentrations might be related to environmental conditions. High seabird activity sites showed lower CO2concentrations than medium and low seabird activity sites in bird sanctuary. Overall the mean concentration of CO2in the bird sanctuary was lower than that in the beach tundra, but higher N2O concentration occurred there, indicating that CO2uptake and N2O emission might be associated with seabird activities. The deposition of seabird guano supplied much organic carbon, nitrogen into local soils, and further stimulated tundra vegetation growth, which might increase tundra CO2sink and N2O emission. Overall the mean concentrations of CO2and CH4in Ny-Alesund were higher than the mean background concentration monitored at Zeppelin Station, whereas the mean N2O concentration was lower than background concentration. In addition, the mining area and human activity areas around the base and airport did not show evidently higher atmospheric concentrations of CO2, CH4and N2O concentrations.(2) Spatial and temporal variations of carbon dioxide, nitrous oxide and methane fluxes from High Arctic tundra in Svalbard, NorwayDuring the summers of2008and2009, net carbon dioxide, respiration rate, photosynthetic rate, net methane (CH4) and nitrous oxide (N2O) fluxes were investigated from five tundra ecotopes:bird sanctuary tundra, normal lowland tundra, non-seabird colony tundra, the tundra in abandoned coal mine and the tundra in scientific bases in Ny-Alesund (79°55’N,11°56’E) of High Arctic, Svalbard. High seabird activity sites showed large N2O and CH4emissions and CO2uptakes while low N2O and CH4emission, even high N2O and CH4uptake and high CO2emission occurred at medium and low seabird activity sites. Photosynthetic rates decreased from high seabird activity area to low seabird activity, indicating seabird activity significantly increased atmosphere CO2uptake from local tundra ecosystems. The respiration rates had no significant differences between the observation sites. Normal lowland tundra and the tundra in abandoned coal mine were the CO2sources. Overall the mean fluxes were18.3±3.6μgN2Om-2h-1and53.5±20.3μgCH4m-2h-1from tundra bird sanctuary tundra whereas non-seabird colony tundra and normal lowland tundra represented a relatively weak N2O source (8.3±13.2μgN2Om-2h-1) and strong CH4sink (-82.8±22.3μgCH4m-2h-1). Tundra soils in the tundra in abandoned coal mine and the tundra in scientific bases showed high CH4emissions due to effects of human activities, whereas high CH4uptake or low emission occurred in the soils of normal lowland tundra and bird sanctuary tundra. The mean N2O fluxes from the tundra in abandoned coal mine and the tundra in scientific bases were one order of magnitude higher than those from normal lowland tundra and bird sanctuary tundra, indicating that human activities significantly increased N2O emissions from tundra soils. NEE were positively related to air temperature and ground temperature, with no significant correlation with precipitation and air humidity. The mean TN, NH4+-N, NO3--N, TP and TS concentrations in the soils of High seabird activity sites are one to two orders of magnitude higher than those in the soils of non-seabird colony tundra, indicating seabird activity was the strongest soil physical and chemical processes. Soil TC and soil water regime were important factors affecting CH4fluxes from tundra soils in High Arctic. A strong positive correlation between N2O flux and the contents of soil TN, NH4+-N and NO3--N in bird sanctuary tundra further confirms that seabird guano N inputs and atmospheric N (as NH3) deposition are the predominant factors controlling the spatial variability of tundra N2O fluxes. The N2O fluxes showed a significant positive correlation with soil NH4+-N contents (r=0.66, p<0.001) at all the observation sites although the fluxes weakly correlated with soil total nitrogen (TN) contents (r=0.35, p=0.09), indicating that NH4+-N content acted as a strong predictor for N2O emission rates in tundra soils.(3) Impact of freezing-thawing cycles on emission rates of greenhouse gases from tundra soil in the ArcticIn this study, normal tundra soil of Arctic, moss, normal tundra soil of Antartic, bird sanctuary tundra soil, seabird ornithogenic, Seal colony tundra soil and Penguin guanos were collected from six tundra regions in Arctic and Antarctic, and experimentally subjected to three freezing-thawing cycles (FTCs). We investigated the effects of FTCs on the emissions of three GHGs N2O, CO2and CH4, with special focus on the effects of freezing temperature, frequency and water content. The GHG emission rates were extremely low in frozen tundra soils. However, there was a fast increase in the emission rates of three GHGs following thawing. The emission rates and their variations were different from different experimental processes and different tundra soils. The greenhouse gases emission rates were higher during FTCs when the freezing temperature was at-20℃than-10℃. Furthermore, accumulated greenhouse gases fluxes were higher from5FTCs than3FTCs with different emission rates in each FTCs. CO2and CH4emission rates from the soils impacted by penguin guano were two or three orders of magnitude higher than those from other tundra soils. N2O emissions fluxes were one order of magnitude from bird sanctuary tundra soil and Seal colony tundra soil larger than those from others. Added0,2,5,10and20ml deionized water to tundra soil and experienced3FTCs, the variation of CH4fluxes was smallest. However, CO2emissions rates decreased with adding more water into tundra soil. The variation of N2O emission rates increased with adding more water into tundra soil. Fluxes of greenhouse gases and its variation were affected by soil physical and chemical properties during freeze-thaw cycle. Greenhouse gases emission rates from tundra soil were significantly affected by freeze-thaw cycles in Arctic and Antarctic, especially C cycle of penguin activity tundra area and N cycle of the seal activity tundra area.(4) Stable isotopes of carbon dioxide in the marine atmosphere along a hemispheric course from China to AntarcticaDuring the24th Chinese Antarctic Expedition, the air samples were collected at10:00and22:00(local times) along the north-south track of the ship "Xuelong" from Shanghai Harbor, China to Antarctica. Carbon dioxide (CO2) concentrations and its isotopic compositions were measured in these samples. Mean CO2concentration at22:00(419.4±27.1ppm) was higher than that at10:00(392.7±20.0ppm), whereas δ13C-CO2values at22:00(-8.58±0.47%o) were lower than those at10:00(-8.23±0.49%o) in the marine atmosphere, indicating that the13C/12C ratio of the CO2might be associated with the photosynthetic uptake and respiration activity of terrestrial or marine organisms during the diurnal cycle. Overall the mean δ13C-and δ18O-CO2were-8.39±0.51‰and0.03±1.39‰, respectively, in the atmosphere from30°N to69°S. Atmospheric δ13C-and δ18O-CO2averaged-8.08±0.83%o and-0.49±0.66%o on Millor Peninsula of East Antarctica. A small but progressive increase in δ13C values with increasing latitudes southward was in good agreement with the expected trend. The enhanced CO2concentrations occurred in the atmosphere close to Eurasia continent, Philippines, Malaysia and Indonesia, and the δ13C oscillations in the atmosphere of33°N-30°S agreed well with anthropogenic pollution from the adjacent countries. In the range of30°S-50°S, atmospheric CO2concentrations were generally low with a relatively stable value of δ13C and δ18O. A great difference of δ13C occurred between10:00and22:00following the pronounced change of CO2concentrations in the range of50°S-70°S, and atmospheric CO2was significantly depleted in13C in the Antarctic Convergence Zone. The δ13C significantly negatively correlated with δ18O-CO2, and they showed a significant negative and positive correlation with CO2concentrations. Our results indicated that the isotopic compositions of CO2in the marine atmosphere might be a sensitive indicator for the strength of CO2source and sink from the ocean. |
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