Fig. 4: Mechanisms of Russian pan-Arctic river heat discharges on Arctic sea ice changes.

a During the mid-Holocene, the intensified early summer solar insolation resulted in mid- and high-latitude Asian positive temperature anomalies and enhanced the river runoff that originated from reinforced permafrost, land snow/ice thawing, and river basin precipitation. Meanwhile, the increased precipitation and associated heat content were mainly from the lower latitudes due to the enhanced meridional moisture gradient, which could have been transported by the intensified East Asian summer monsoon (EASM) and the polar vortex, including the westerlies. As a result, the increased river heat discharge enhanced the loss of Arctic sea ice in early summer and strengthened the absorption of solar energy inputs. b During the late Holocene, the opposite conditions prevailed. In the Arctic Ocean, the blue areas represent the loss of sea ice in early summer, while the white regions point to sea ice cover in early summer.