Interannual Variations In Thermohaline Structure And Chlorophyll Concentration In The Euphotic Zone Around The South Shetland Islands,Antarctic During Austral Summer

The South Shetland Islands are on the south side of the Drake Passage,facing the Antarctic Peninsula via the Bransfield Strait.Surrounding waters of the South Shetland Islands hydrological circulation structure system is complex,is regarded as one of the high productivity of the southern ocean area,this area is pregnant with a large number of unique phytoplankton,zooplankton and some high trophic level predators,so has always been the hot spot of the southern ocean oceanography research area,has become an important area of the Antarctic krill fishery in recent years.Chlorophyll is a pigment that exists in phytoplankton,it can be used to evaluate phytoplankton biomass and productivity in a specific time and place,phytoplankton at the bottom of the food chain,their numbers can greatly affect the entire marine ecosystem,and moreover phytoplankton is the main component of oceanic biological pump has important influence to the global greenhouse effect.The reproduction,growth and death of marine organisms is a long-term process of development.In addition to the essential nutrients for their life,the environmental factors of their life also play a crucial role.The combination of chlorophyll concentration and hydrological structure can provide a basis for further study of global ecosystem.Abundant sunshine and nutrients exist in the ocean pervious layer,which is the most concentrated area of marine biological activities and the most productive area in the ocean.Understanding the characteristics and changes of water mass in the previous layer can not only provide basic information for oceanographic research on the Antarctic Peninsula,but also provide scientific support for the distribution and causes of pelagic marine organisms such as Antarctic krill(Euphausia superba).This study through the South Shetland Islands waters around four years from 2010 to 2013 in the previous layer of summer temperature,salt data,draw the different year levels of different layer(20m,60 m,100m and 160m)thermohaline distribution chart,CTD stance point also is divided into four sections(D1-D4),draw the different years different vertical temperature distribution in the cross section of the salt distribution chart,combed the water mass properties,distribution and interannual variability of the region characteristic.On this basis,the correlation between the chlorophyll a concentration in the four years from 2010 to 2013 and the hydrological characteristics of the sea area was further discussed.The results show that the water masses involved in the euphotic waters in the north of the South Shetland Islands are mainly Antarctic Summer Surface Water,Winter Water,Circumpolar Deep Water,Shelf Surface Water and Shelf Deep Water.The water mass structure in the deep water zone is from top to bottom: Antarctic Summer Surface Water,Winter Water and Circumpolar Deep Water.The water mass structure in the shelf area is the surface water and the deep water from top to bottom.The water temperature of surface water in the Antarctic summer gradually increases with the advance of time in the same season,while the salinity of the water group tends to be stable in the same season.The sea to the north of the South Shetland Islands is the only place for the Antarctic circumpolar current.When the Antarctic Circumpolar Current flows,its branch will be blocked by Shackleton Ridge and turn to the south.Meanwhile,a stable standing vortex will be formed on it.In terms of chlorophyll a concentration,it was concentrated in the deep water area north of the South Shetland Islands to a shallow of 100 m,and in the continental shelf area north of South Shetland Islands to a shallow of 60 m.Observed in the study area is still some high concentrations of chlorophyll,with regional division,such as in Shackleton above the ridge in vortex exists within the high concentrations of chlorophyll a density,but the concentration of chlorophyll in the vortex in did not show obvious inter-annual features,in addition,the island,near the South Shetland Islands,and Smith island there are high concentrations of chlorophyll;In terms of water mass division,the chlorophyll concentration is mostly concentrated in the Antarctic summer surface water and the winter water mass,while the chlorophyll concentration in the surrounding deep water is generally low.Among them,the concentration distribution of chlorophyll a in the Antarctic summer surface water increases to the shore with time.It is of great scientific significance to further study the biophysical interaction of the southern ocean to elucidate the complex structure of water mass and its interannual distribution with chlorophyll concentration around the South Shetland Islands.