Flow cytometry investigation of picoplankton across latitudes and along the circum Antarctic Ocean

Using a flow cytometer （FCM） onboard the R/V Xuelong during the 24th Chinese Antarctic cruise, picoplankton community structure and biomass in the surface water were examined along the latitude and around the Antarctic Ocean. Salinity and temperature were automatically recorded and total Chl a was determined. Along the cruise, the abundance of Synechococcus, Prochlorococ- cus, pico-eukaryotes and heterotrophic bacteria ranged in 0.001-1.855~ 10s ind./L, 0.000-2.778×108 ind./L, 0.002-1.060×108 ind./L and 0.132-27.073×108 ind./L, respectively. Major oceanic distri- bution of Synechococcus and Prochlorococcus appeared between latitudes 30°N and 30°S. Prochlorococcus was mainly influenced by water temperature, water mass combination and freshwater inflow. Meanwhile, Synechococcus distribution was significantly associated with landing freshwater inflow. Pico-eukaryotes and heterotrophic bacteria were distributed all over the oceans, but with a relatively low abundance in the high latitudes of the Antarctic Ocean. Principal Component Analysis showed that at same latitude of Atlantic Ocean and Indian Ocean, picoplankton distribution and constitution were totally different, geographical location and different water masses combination would be main reasons.