Variable freshwater input to the Arctic Ocean during the Holocene: Implications for large-scale ocean-sea ice dynamics as simulated by a circulation model

Recent geological studies revealed that the freshwater input to the Arctic Ocean was highly variable during the Holocene. In the present study we examine the influence of changing Arctic freshwater runoff and low-saline Bering Strait inflow on large-scale ocean-sea ice dynamics by means of a general circulation model of the Arctic Ocean, the Nordic Seas, and the Atlantic. Discharge distributions used are based on paleohydrological reconstructions for the early (approx. 10 ka) and middle (about 7 ka) Holocene. Keeping all other forcing fields and topography at present-day values, we isolate the effect of a variable freshwater supply to the Arctic Ocean. The model experiments show that Arctic freshwater input is vitally important for the polar oceanic circulation, influencing the size of the Beaufort Gyre and the path of the Transpolar Drift. The results indicate that long-term Holocene variability in Arctic freshwater forcing had the potential to cause considerable variability in Arctic Ocean dynamics on a century-to-millennium scale. Moreover, a relatively warm Bering Strait inflow exerts a strong influence on polar sea ice. It is likely that a gradual increase in the influx during the early Holocene slowly affected the polar climate by melting some ice and decreasing the surface albedo in the eastern Arctic. The effect of Arctic freshwater forcing on the Atlantic thermohaline circulation (THC) is small in our experiments. We conclude that changes in the Arctic Ocean freshwater input alone only played a minor role for potential variations in the THC during the Holocene.