Spatial Distributions Of Biogenic Elements And Their Influencing Factors In The East Indian Ocean In Spring

To better understand the spatial and temporal distributions of biogenic elements and theirs influencing factors in the East Indian Ocean, vertical profiles of temperature, salinity, dissolved oxygen, inorganic nutrients, chlorophyll and other elements were investigated, along four transects with 88 stations in total, in the upper water(0~300 m) in the tropical East Indian Ocean in spring of 2013. And the formation mechanism of oxygen minimum, primary nitrite maximum(PNM) and subsurface chlorophyll maximum(SCM) were discussed. The results are summarized as the following:(1) Water stratification was prevalent and prominent thermo-haloclines were formed at depth of 80~120 m in the East Indian Ocean in spring. Pycnocline was deepest near the equator and the depth of pycnocline became shallower gradually away from the equator to the south and north.(2) There were prevalent chemoclines(pH, DIC,DO, NO3--N, PO43--P, SiO32--Si)which appeared simultaneously with pycnocline in the East Indian Ocean in spring,and there was high degree of coincidence between the chemoclines and pycnocline.DIC and nutrient concentration increased rapidly below the chemoclines duo to decomposition of organic matter; At the same time, there was oxygen maximum in the subsurface(about 200 m) duo to consumption of oxygen during decomposition of organic matter.(3) The phenomenon of SCM and PNM existed universally in the East Indian Ocean in spring. The SCM and PNM which appeared with patch distribution pattern usually located in the upper boundary of the pycnocline and nutricline.The light,nutrients and pycnocline affected the depth and value of SCM. PNM was mainly resulted from the incomplete reduction of nitrate by phytoplankton.