Over the last decades the western Arctic Ocean has undergone unprecedented environmental changes. However, long-term marine phytoplankton in situ observations are still rare and therefore insufficient to fully characterize evolutionary trends. This study investigate diatom flux and composition in sediment trap material collected in the Northwind Ridge, western Arctic Ocean from August 2008 to September 2009. Our data show that Chaetoceros resting spores are the predominant species accounting for >40% of the diatom composition. The sea ice diatom group, which includes Fossula arctica, Fragilariopsis cylindrus and F. oceanica, dominates the rest of the assemblage throughout the observation period. While the diatom fluxes in winter are extremely low, higher values are found in summer, with summer 2009 flux values being twice as high as in 2008. High total mass and diatom fluxes in summer 2009 are attributed to the intertwined effect of a weakened Beaufort Gyre, strengthened Pacific Water Inflow (PWI) and distribution pattern of the sea ice. Enhanced values of coastal diatoms and terrigenous proxies in summer 2009 are in agreement with intensified PWI. Sea ice diatoms and sea ice biomarker IP 25 fluxes are both high during the sea ice melting season and significantly correlated (r 2 = 0.64, p < 0.01). Our data also suggest that sea ice diatoms are prone to selective dissolution in the water column and sediments, implying biases on diatom assemblages and subsequently on paleoceanographic reconstructions.