Effects of North Atlantic summer marine heatwaves on Arctic sea ice freeze-up delay: modulation by atmospheric teleconnections

Since the early 21st century, the Arctic sea ice melting season has significantly lengthened, primarily due to delayed freeze onset (FO). We identify the northern Chukchi and East Siberian Seas as the FO key area with the most significant interannual variability in Arctic FO and link it to extreme ocean events, particularly marine heatwaves (MHWs) in North Atlantic. The results show that, in July, intense and persistent MHWs occurred near southeast Greenland Island (seGI), which served as a strong near-surface heat source, with warm air masses ascending up to 300 hPa. This facilitated the development of planetary-scale wave activity flux (WAF) in August. The WAF over seGI, together with the WAF from the Pacific side, resulted in a strengthened anticyclonic circulation prevailed over the FO key area in September. The abnormal descending warm airflow caused by anticyclonic circulation resulted in a two-week delay in FO in its key area compared to the climatology. Unlike general warm sea surface temperature, MHW-induced anomalous heat release can reach the higher atmospheric level (300hPa), which is less affected by disturbances from lower and higher atmosphere, more accessibly impacting the Arctic sea ice.