A sediment sequence from the eastern Laptev Sea shelf (Siberian Arctic, Russia) has been studied for dinoflagellate cysts in order to reconstruct sea-surface conditions during the late Holocene. Variability of assemblage composition and derived sea-surface temperature estimates indicate that the neoglacial cooling was not a gradual climate change from 2510 to 900 cal. yr BP. Relatively stable conditions, with temperatures that were warmer than today, were punctuated by a few cooling events in summer on centennial time-scales. During these events temperatures reached modern values. This suggests that modern conditions may have been established abruptly within a short period in the past 1000 yr, which is not documented in our record. Copyright © 2001 John Wiley & Sons, Ltd.