This MS sheds a light on the role and fate of diatoms over a course of a spring bloom in the Arctic Ocean, based on the estimates of their mortality, senescent rate, and the population with fast sinking rate.These estimations were designed to test a hypothesis in which Si-depletion triggers (1) senescence of diatoms and (2) selective sinking of the dying population.Because of intense CO2-sequation in the Arctic Ocean, this hypothesis is valuable to be tested, but the results in this study unlikely support this hypothesis.For example, high % living diatoms in the upper layer was achieved at Stns 6, 7 and 8 with low silicic acid concentration, but this result doesn't meet (1).It could be explained, at least partly, by rapid selective sinking of dead populations as shown in Fig. 5. But, low % living diatoms at Stn. 4 with high silicic acid concentration was resulted from shift of equilibrium point between mortality rate and sinking rate toward