The melting of sea ice affects the ocean heat absorption in the form of positive feedback, and plays an important role in the changes of the Arctic environment and economic activities in the Arctic region. Based on the daily sea ice concentration data of the Arctic Ocean from 1979 to 2018, the estimation method of sea ice retreat onset dates in the Arctic marginal sea was improved by comprehensively considering the factors such as sea ice conditions and so on in different seas. Comparative analyses of different methods show that this improved method can reflect the changes of ice conditions in different sea areas and different years, and can eliminate some influences of weather disturbance on the estimation of retreat onset, so as to avoid premature estimation results. By using this method, it is found that the retreat onset dates of every Arctic marginal sea are generally advanced. The advanced trends of retreat onset dates are generally the same as advanced trends of melt onset dates. However, different sea areas have different degrees of advancement. The Kara Sea and the Chukchi Sea have the strongest trend of early retreating, reaching 9 d/(10 a), while the East Siberian Sea has the weakest trend, only 4 d/(10 a). The difference of retreat onset dates gradually increases between these regions. There are significant interannual variations in the retreat onset dates, the standard deviations of each marginal sea are about 15 d. In the past decade, the difference between the earliest and the latest retreating reaches 50 d, which appeared in the Beaufort Sea.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |