Effects Of Sea Animal Activity And Glacial Retreat On Soil Greenhouse Gas Fluxes In The Antarctica

Global climate change is an indisputable fact,mainly driven by the increasing concentrations of greenhouse gases(GHG)in the atmosphere.CO2,CH4 and N2O are the most important greenhouse gases and the main contributors to the global warming while soils are important sources and sinks for these three gases.The Antarctic region is not only a key area for regulating the global climate,but also one of the most sensitive regions to global climate change,in particular the Antarctic Peninsula and the sub-Antarctic islands owning large ice-free area.Thus,research of the soil greenhouse gas fluxes is of great significance for estimation of regional and global greenhouse gas budgets and formulation of the strategy for adapting climate change.There are large number of sea animals such as penguins and seals living in the Antarctica and sub-Antarctica in particular.Due to climate change and human activities,the number of sea animals in the Antarctic region is increasing,and the signs of penguin colony expansion and migration are significant.It has been reported that sea animal colonies are emission hotspots for greenhouse gases.However,most of the reported studies focus on the magnitude of the soil GHG fluxes in the sea animal colonies while the spatial variability and the controls in these regions are still unclear.Furthermore,with the recession of the glacier,more and more areas are exposed for soil development and sea animal activity,which may form new GHG emission hotspots.However,studies considering the expansion of sea animals(mainly penguin)which occupies the fresh glacial retreat area and thus generates new greenhouse gases emission hotspots are rare.This leads to the existing studies about the soil GHG fluxes in the Antarctica not only being lack in the coverage of land surface types but also being insufficient in the research depth,makes it impossible to estimate the soil GHG budget in these regions and seriously affects the accuracy and application values of current global GHG budget.In response to the above questions,three transects on South Georgia,sub-Antarctica are selected and field measurements and laboratory incubations are used to determine the magnitude and spatial pattern of the three major soil greenhouse gases-CO2,CH4 and N2O fluxes in the present study.The first transect is conducted at the Maiviken Bay including three sites away from an Antarctic fur seal(Arctocephalus gazella)colony.The other two transects are at the Saint Andrews Bay:transect within the world biggest King penguin(Aptenodytes patagonicus)colony and transect along the glacier retraction zone with the early exposure area occupied by the King penguin.Field CO2 and CH4 fluxes are measured at the 9 sites of the transects at the Maiviken Bay and within the King penguin colony and intact soil cores of 95 sampling plots of all the 14 sites for the three transects are collected for the laboratory GHG fluxes incubation.To explore the internal control factors and the underlying mechanism for the spatial variability of the greenhouse gas fluxes,soil physical and chemical properties,the community abundance and composition of the soil bacteria and methanotrophs are analyzed and nutrient addition incubations were conducted in the laboratory.The main conclusions of this study are as follows:(1)The upland bare areas are unknown large methane sinks with the methane uptake rates of-154 to-13 ?g CH4 m-2 h-lon the islands like South Georgia in the Antarctica and sub-Antarctica.Because of the extreme cold environment on the South Georgia,soil development is weak in the upland bare area.The lower contents of soil water and nutrients are suitable for the development of Type ? methanotrophs,making soils in this region the huge sinks for the atmosphere methane.Furthermore,it is likely that these islands may be net methane sinks due to the wide distribution of the barren soils and dry uplands in these regions.(2)Colonies of sea animal are hotspots for GHG emissions and the density and intensity are the controls.Emission rates of CO2,CH4 and N2O in Antarctic flur seal and King penguin colonies are 113-2756 mg CO2 m-2 h-1,-1-19 ?g CH4 m-2 h-1 and 38-14564?g N2O m-2 h-1 and 29-11550 mg CO2 m-2 h-1,1-14100 ?g CH4 m-2 h-1 and 0-29545 ?g N2O m-2 h-1,respectively.Soil CO2 and N2O fluxes show no differ while CH4 uptake rates are inhabited as compared to that of the upland Bare control area.In the sea animal colonies,soils receive a large amount of water,carbon,nutrients and even bacteria from other regions by the deposition of excreta,changing soil environment,enhancing soil respiration and N2O emission and inhabiting soil methane uptake.The more the sea animals,the higher the soil GHG fluxes within the colonies.(3)Significant influence of soil exposure time on the soil GHG fluxes along the glacier retreat zone is observed.The early exposure area colonized by the sea animals are found new GHG emission hotspots.In the glacier retreat zone,the longer the soil exposure time,the better the soil and vegetation development and the higher the contents of soil moisture and nutrients.Furthermore,soil physical and chemical properties in the penguin activity area are further better as compared to the fresh exposed area.Thus,abilities of soil to emit CO2 and uptake methane from the atmosphere are limited by the exposure time while the expansion of sea animal colonies accelerates the soil development in the early exposed areas,inhibiting the methane uptake and stimulating CO2 and N2O emissions.(4)Soil moisture and labile carbon are limiting factors for soil respiration while soil moisture is the main limiting factor for the soil methane uptake in the Antarctic region.In the Antarctica,soil development is limited by the dry and cold climate and content of soil moisture and labile carbon are lower in areas without sea animal activities,making them the limiting factor for the soil respiration and methane uptake.The innovations of this paper are:(1)Controls and the underlying mechanism for the spatial variability of soil GHG fluxes are determined,improved the relevant research.(2)soils in the upland bare area on the South Georgia island are found to be huge methane sinks,providing new data for the estimation of the region and global GHG budgets.