Study On The Spatial Distribution,Differences And Control Factors Of Bacterial Abundance And Production In The Southern And Arctic Oceans

Using the data of 5th and 32nd CHIN ARE,this projcet studies the bacterial abundance and production in Arctic and Antarctic Oceans,including Chukchi,Nordic and northwestern Weddell Seas and shows the space distributions of these two parameters.Together with environmental and biological factors like temperature,salinity,nutrients and Ch1 ?,we speculate different response mechanisms of bacterial abundance and production in different sampling areas.Comparing distributions and fractions of Ch1 ? with bacterial production,we calculate microbial carbon demand balance and autotrophic or heterotrophic statuses in Chukchi and northwestern Weddell Seas.At last,we compare and illustrate the difference between bacterial abundance and production in these three sampling areas.Here are the main conclusions:(1)Chukchi Sea:In summer,bacterial abundance ranges from 0.56 to 6.41 ×108 cells dm-3 in upper 100 m,with an average of 2.25×108 cells dm-3.The Chukchi shelf has a significantly higher bacterial abundance than the north marginal area.Bacterial production is between 0.042 and 1.92 mg C m3 d-1,averaging on 0.60 mg C m-3 d-1.Integrated bacterial production is between 11.04 and 53.47 mg C m-2 d-1 and averages on 29.61 mg C m-2 d-1.Bacterial abundance has positively significant correlations with temperature and Ch1 a,while bacterial production only with bacterial abundance and Ch1 ?.Bacterial community suffers from a moderate bottom-up control in the whole Chukchi Sea.However,this effect weakens in Chukchi shelf compared to the whole sampling area,while turns to top-down control in the northern marginal sea.The whole Chukchi Sea is heterotrophic,which means that the DOC provided by photosynthesis of phytoplankton does not meet bacterial growth demand.The reason caused this is that phytoplankton community is not at bloom during our sampling period.The gross primary production is rather low.On the contrary,bacterial activities are at high levels.The different heterotrophic statuses at each sampling stations are considered to be correlated with fractions of Ch1 ?.(2)Nordic Seas:Bacterial abundance in the upper 100 m has a range of 0.75 to 15.12 ×108 cells dm-3,with an average of 3.31 ×108 cells dm-3.Bacterial production at station BB03 and BB08 is from 0.13 to 0.79 mg C m-3 d-1 and 0.20 to 0.84 mg C m-3 d-1 respectively,with an average of 0.46 mg C m-3 d-1.Integrated bacterial production is 34.16 and 53.64 mg C m-2 d-1,respectively.Bacterial abundance has a positively significant correlation with Ch1 ?.At the same time,bacterial production has positively significant correlations with sumCh1 ?as well as picoChl a.As a result of higher seawater temperature and a moderate bottom-up control,the environmental factors like temperature have an unobvious influence on bacterial abundance and production.Predations by protists and the unevenly active bacterial community makes the uncoupling relationship between bacterial abundance and production.(3)Northwestern Weddell Sea:Bacterial abundance has a range of 0.20 to 3.34 ×108 cells dm-3 in the upper 100 m,and averages on 1.03 ×108 cells dm-3.Bacterial production is between 0.06 and 2.42 mg C m-3 d-1,with an average of 0.44 mg C m-3 d-1.In the euphotic zone,integrated bacterial production is between 7.45 and 75.50 mg C m-2 d-1,averaging on 27.88 mg C m-2 d-1.The upper water column of northwestern Weddell Sea has a heterotrophic status.Microbial carbon demand balance in euphotic zone ranges from-64.01 to 223.66 mg C m-2 d-1.Among the bacterial production stations,4 are autotrophic with positive microbial carbon demand balance.They are located in the west and east of sampling area,dominated by Bellinsgauzen Sea and Weddell Surface Water.The rest 5 stations are heterotrophic and have negative microbial carbon demand balance,which are mainly controlled by Weddell-Scotia Confluence.The main influential factors on microbial carbon demand balance are the spatially different distribution and fraction of Ch1 ?.The autotrophic stations have significantly higher concentrations of Ch1 ?,and mainly dominated by microChl a,while nano and pico Ch1 ? predominate at heterotrophic ones.In the whole sampling area,bacterial abundance is positively correlated with temperature while bacterial production is positively correlated with temperature as well as Ch1 ?.At autotrophic stations,bacterial abundance has no correlations with other environmental and biological factors.However,both bacterial abundance and production have positive correlations with temperature.In addition,bacterial production also positively correlates with sumChl a at heterotrophic stations.A strong top-down control is found in northwestern Weddell Sea,which implies predation has a significant influence on bacterial abundance.(4)Differences between the Southern and Arctic Oceans:There is a significant difference in bacterial abundance caused by temperature between Nordic and Chukchi seas,while not in production.Bacterial communities are affected by moderate bottom-up control in both areas.Phytoplankton communities at bacterial production stations in both Nordic and Chukchi Seas are dominated by pico-phytoplankton and micro-ones have very small fraction.In Chukchi Sea,nitrogen limitation is the main reason that restricts the development of phytoplankton community,while in Nordic Seas,it is silicateBoth bacterial abundance and production are significantly different between Nordic Sea,Chukchi Sea and Weddell Sea.But between Nordic and Weddell Seas,only bacterial abundance has the significant difference.The main reasons caused the difference of bacterial abundance are temperature and control type;while for production,they are temperature and Ch1 ?.In addition,nitrogen limitation in Chukchi Sea makes a contribution to the dominance of pico-phytoplankton;while in northwestern Weddell Sea,nutrients have a poor restriction.The autotrophic stations are dominated by micro-phytoplankton and nano and pico-phytoplankton predominate at heterotrophic stations.