Despite a growing interest in the paleoclimate evolution of the Holocene period in the Siberian sector of the Arctic Ocean relatively few data are available about the marine conditions from the shallow Siberian shelf seas. Within the frame of the joint Russian-German projects "Laptev Sea" and "SIRRO" high-resolution records from the Kara and Laptev seas have been studied for their palynological content in order to reconstruct sea-surface conditions and freshwater input from the large Siberian rivers during the Holocene.Holocene dinoflagellate cyst assemblages from both the Kara and Laptev Sea indicate the presence of a marine thermal optimum in the early Holocene. The onset occurred in the Laptev Sea shortly after the transition to the Holocene while sediment cores studied so far from the inner Kara Sea do not span this period. A long-term cooling in the mid and late Holocene is recognised in both shelf seas but, obviously, major steps did not occur synchronously. The records are characterised by few sub-millennia oscillations suggesting that conditions were relatively stable in the later part of the Holocene. Chlorococcalean algae reflect a variable freshwater input during the Holocene that was related to the post-glacial sea-level rise and retreat of the estuaries of the large rivers, Ob, Yenisei and Lena to their present position.