Reconstruction Of Long-term Sea Ice Changes In Arctic Barents-Kara Sea And Analysis Of Its Association With Strong Cold Waves In Chinese History

The connection between the rapid retreat of the Arctic sea ice and the weather and climate in the mid-latitudes in the context of current global warming is a scientific hotspot and also a difficulty.The East Asia region,including China,is one of the regions frequently affected by the rapid changes of the Arctic weather and climate system.The scientific community generally agrees that the Arctic Barents-Kara Sea region is a key sea area that affects the extreme cold events to happen in the winter and spring of China,but there still are many controversies existing regarding its patterns and mechanisms.One of the reasons for this is the lack of understanding of the long-term changes of sea ice in this critical area,as well as correlation analysis with the historical climate in China.Using high-resolution ice core and tree ring proxies for sea ice extent(SIE),a robust time series of autumn SIE over the Barents-Kara(B-K)sector of the Arctic during 1289-1993 was reconstructed.After intercomparing the results and statistical parameters of different methods,SIE time series were synthesized into a more robust series using the weighted average method,which used the explained variances as the weights.The results shows that the autumn B-K SIE was large from the end of the 13 th century to the end of 18 th century,with large variations and a slightly expanding trend overall.This reflects significant multidecadal oscillations under the Little Ice Age(LIA)background.The B-K SIE began to decrease at the end of the 18 th century,and a shrinking trend became significant during the second half of the 19 th century,which lasted into the 1930s-1940 s.The 1930s-1940 s was a period with a relatively low SIE in the BK Sea,and the SIE had a short period of expansion from the 1940s-1970 s.However,the B-K SIE has continuously and significantly shrank since the 1970 s.The reduction in the B-K SIE since the end of the 18 th century has been unprecedented in both duration and speed over the last 700 years.The B-K SIE has retreated significantly since the 1970 s,with a speed 6.18 times greater than the former mean retreating speed.The industrial revolution may be a dominant factor for this result.The Arctic SIE in recent years may be the lowest it has been over the last millennium.Based on the historical documents related to cold events,a time series of the winter extreme cold index of China during 1289-1993 was reconstructed.Using the reconstructed BK SIE sequence and winter extreme cold index sequence,combining with the winter Siberian High Index(SHI)and NAO index sequence,the changes in Arctic B-K SIE and its relationship with extreme cold weather and climate events in China were analyzed under different climatic backgrounds.The results show that the correlation between the autumn SIE of the B-K Sea and the extreme winter cold events in China was significant during the instrumental period(1981-2017),and the “bridge effect” of the Siberian High and NAO was also significant,i.e.when the autumn B-K SIE is low,the NAO shifts to negative phase in the winter and Siberian high strengthens,causing more severe cold waves to attack China.During the reconstruction period(1289-1911),more extreme cold winters occurred in China during low SIE periods than high SIE periods.However,by comparison with NAO and Siberian high index(SHI)sequences,it is found that the relationships between B-K SIE,NAO,SHI and extreme cold events in China are not that stable as the instrumental period,the "bridge effect" doesn't exist.The extreme winter cold events in China occurred more frequently during the periods when the autumn B-K SIE is low especially in the significant SIE dropping periods,such as the post-1970 s.However,in the periods with more winter cold events happening in China,the BK SIE is not always at a low level.This may be caused by the internal variability of the climate system leading to the adjustment of the atmospheric circulation,resulting in a negative NAO transformation and stronger Siberian high,which is conducive to cold air mass accumulation and dumping southward,thus causing more extreme cold events happening in China.After quantitative analysis on the number of the extreme cold years in China during the low B-K SIE periods,it's found that the percentage of extreme cold events happening in low SIE periods is higher than in the high SIE periods,and it is even more obvious in the period since the industrial revolution,especially during this period of 1981-2017.It shows that there is a significant correlation between the autumn B-K SIE and winter extreme cold events in China.Large scales of human activities since the industrial revolution have caused not only the global warming and the sharply reduction of the Arctic sea ice,but also more frequent extreme winter cold events to happen in the mid-latitudes of the Northern Hemisphere.