We evaluated the relationships between water masses and pico- and nano-phytoplankton and bacterial abundance in the Chukchi Sea. The abundance of picoplankton ranged from 0.01 ~ 103 cells.mL1 （100 m, station R05） to 2.21 x 103 cells.mL-1 （10 m, station R05） and that of nanoplankton ranged from 0.03 x 103 cells.mL-I （100 m, station R07） to 2.21 ~ 104 cells.mLq （10 m, station R05）. The lowest abundance of bacteria in the whole water column （0.21 x 106 cells.mLq） was at 100 m at station R17, and the highest （9.61 x 106 cells.mLL） was at 10 m at station R09. Melting sea ice affected the physical characteristics of the Chukchi Sea by reducing salinity of the surface mixed layer, resulting in greater hydrodynamic stability of the water column. These changes were accompanied by increased bacterial abundance. The warm Pacific water brought nutrients into the Chukchi Sea, resulting in greater abundance of bacteria and nano-phytoplankton in the Chukchi Sea than in other regions of the Arctic Ocean. However, the abundance of pico-phytoplankton, which was related to chlorophyll a concentration, was higher in Anadyr water than in the other two water masses. The structures ofpico- and nanoplankton communities coupled with the water masses in the Chuk- chi Sea can serve as indicators of the inflow of warm Pacific water into the Chukchi Sea.
In vivo fluorescence has a wide application in analyzing microalgae, including assessing phytoplankton biomass, rates of primary production and physiological status. This study describes a preliminary investigation on the joint application of the three kinds of fluorescence analysis in the physiological study of microalgae. Flow cytometry and fluorescence spectrometry were used to obtain the in vivo static fluorescence information of pigments, and a Pulsed-Amplitude-Modulation chlorophyll fluorometer was used to detect the dynamic fluorescence of chlorophyll. The validity of the joint application was proved by analyzing two labora- tory cultured Arctic microalgae, Pseudo-nitzschia delicatissima （Bacillariophyceae） and Thalassiosira sp. The higher value of minimum fluorescence yield in dark-adapted state （Fo）, actual photochemical efficiency of PSll （ФPSII）, and electron transport rate （ETR） exhibited positive results in a higher cell abundance and chlorophyll a content of P. delicatissima; whereas higher fl-carotene content of Thalassiosira sp. played an important role in the protection of photosynthesis.
