Distributions And Sea-air Fluxes Of Volatile Halocarbons And Dimethylsulfide In The Sea Nearby The Northern End Of The Antarctic Peninsula In Summer

The ocean contains a variety of volatile active components such as dimethyl sulfide(Dimethylsulphide,DMS)and some volatile halogenated hydrocarbons(Volatile Halocarbons,VHCs).These volatile compounds not only act as a role in exchange of elements between air —sea interface,but also have important impacts on global climate change,because that they undergo a series of chemical reactions to produce new chemical products when these elements enter the atmosphere..For example,a part of DMS released by the ocean may be oxidized in the atmosphere to form cloud condensation nuclei,which affects cloud formation and solar radiation.Therefore,DMS has the potential to affect the global radiation balance and climate.VHCs are the culprit in the formation of polar ozone holes,and they are more important greenhouse gasesbecause of their ability of absorbing infrared radiation is much greater than CO2.Study for the spatial distribution of DMS and VHCs,air-sea fluxes and their influencing factors will help to deep understanding of the role of volatile active substances in the global environment,and provide a basis for building a global climate change prediction model.The Southern Ocean is the most sensitive sea area in the world due to its characteristics of the atmosphere,sea ice,high nutrients and low chlorophyll(HNLC)area etc.During the cruise of the 34 th Antarctic expedition of China from January 1 to February 3,2018,we conducted a comprehensive survey of the distribution and influencing factors of seven VHCs and DMS in the sea nearby the northern end of the Antarctic Peninsula,and the sea-air fluxes of five kind of VHCs and DMS were calculated.The main findings are as following:1.The surface temperature(T)in the sea nearby the northern end of the Antarctic Peninsula in summer is gradually decreasing from north to south,and there are some low-value areas of salinity(S)in the surface.There are “dicothermal layers” in each section.The Dissolved oxygen(DO)minimum layer is located at 1000 m.The chlorophyll(Chl-a)and total organic carbon(TOC)are higher in the upwelling area and “dicothermal layers”.There is a low salinity and oxygenenriched cold water mass in the study area.2.The distribution characteristics of the 7 VHCs in the surface water are quite different.The concentration of 7 VHCs in the Scotia Sea of the Phillip Passenage section is lower,and there is a high value area in the extension of the Phillip Ridge.The concentrations of CHCl3 and CHBr Cl2 are higher in the Powell Basin.There exist three distribution paterns in the South Orkney section and the South Shetland-South Orkney chain section: the first patern includes CH3CCl3 and CHCl3,and there is a high value area of VHCs located at the intersection with South Orkney Plateau and South Orkney Passenage;the second patern includes CCl4,CH2Br2,CHBr Cl2 and CH3 I,and there are high value areas of VHCs in the Central Basin,the bottom of the South Orkney Passenage and the east of South Orkney Plateau;the last patern only is C2Cl4,and there are high value areas in the surface and bottom layer of the South Orkney Passenage of the section.3.There were significant correlations between other 6 VHCs and various environmental factors except for C2Cl4.Thereinto,CH3CCl3 was significantly negatively correlated with T,DO and Chla,and positively correlated with S.CCl4 was only negatively correlated with S in the photiczone,and significantly negatively correlated with TOC in the south Shetland-South Orkney chain section.CHCl3 was significantly negatively correlated with T in the Philip Passenage section and a negatively correlated with Chl-a in the South Orkney section.CH2Br2 was only significantly positively correlated with DO and Chl-a,and is significantly negatively correlated with S in south Orkney section.CHBr Cl2 was significantly positively correlated with T and S,and significantly negatively correlated with DO and Chl-a in the south Shetland-South Orkney chain section.CH3 I was only significantly negatively correlated with TOC of the photiczone in the South ShetlandSouth Orkney chain section.4.The ranges of sea-air flux of CH3CCl3,CCl4,CH2Br2,CHBr Cl2 and C2Cl4 were 1.84?607.33,326.42?18740.71,0.48?409.18,1.27?118.11 and 1.37?274.72 nmol m-2d-1,respectively.It is the source for these 5 VHCs in the sea nearby the northern end of the Antarctic Peninsula in summer.5.The high-value areas of DMS are usually distributed in the surface layer of 0?30 m of each section.It probably attributed for the surface horizontal distribution of DMS that the accumulation of algae,and more DMS for cryoprotection and osmotic adjustment because of the algae metabolizing in extreme environment with low temperature and high salinity.There is a significant positive correlation between DMS and Chl-a and TOC in the euphotic zone.In the depth below the euphotic zone,DMS is significantly negatively correlated with T and S,and significantly positively correlated with DO.6.The sea-air flux of DMS ranged from 9.62 to 169.08 ?mol m-2d-1 with an average of 60.44 ?mol m-2d-1,which is close to the value in the seasonal ice zones,but much higher than other zones of the Southern Ocean.It is the source of DMS in atomothphere in the sea nearby the northern end of the Antarctic Peninsula in summer.