In this paper, we make use of calcium carbonate-bearing sediment sequences in the Arctic-Atlantic gateway to produce a standard reference climate record for the Arctic Ocean. We present a continuous and exceptionally well-dated marine sediment record documenting the strong imprint of Arctic freshwater pulses on Earth's climate system throughout the past 0.8 m.y. Planktic foraminiferal oxygen and carbon isotope data reveal that freshwater plumes released from collapsing circum-Arctic ice sheets and ice-dammed lakes were advected to the Arctic Ocean gateway on sub-Milankovitch time scales. Given the close correspondence of Arctic freshwater pulses and strength of North Atlantic Deep Water formation as inferred from carbon isotope data, we conclude that freshening of the Arctic Ocean influenced thermohaline circulation more frequently than previously recognized. Our data show that it is critical for coupled atmosphere-ice-ocean general circulation models aimed at unraveling climate forcing factors during the Pleistocene to consider Arctic freshwater as a crucial forcing factor.