Abstract
Bohai Sea ice creates obstacles for maritime navigation and offshore activities. A better understanding of ice conditions is valuable for sea-ice management. The evolution of 67 years of seasonal ice thickness in a coastal region (Yingkou) in the Northeast Bohai Sea was simulated by using a snow/ice thermodynamic model, using local weather-station data. The model was first validated by using seasonal ice observations from field campaigns and a coastal radar (the season of 2017/2018). The model simulated seasonal ice evolution well, particularly ice growth. We found that the winter seasonal mean air temperature in Yingkou increased by 0.33 °C/decade slightly higher than air temperature increase (0.27 °C/decade) around Bohai Sea. The decreasing wind-speed trend (0.05 m/s perdecade) was a lot weaker than that averaged (0.3 m/s per decade) between the early 1970s and 2010s around the entire Bohai Sea. The multi-decadal ice-mass balance revealed decreasing trends of the maximum and average ice thickness of 2.6 and 0.8 cm/decade, respectively. The length of the ice season was shortened by 3.7 days/decade, and ice breakup dates were advanced by 2.3 days/decade. All trends were statistically significant. The modeled seasonal maximum ice thickness is highly correlated (0.83, p < 0.001) with the Bohai Sea Ice Index (BoSI) used to quantify the severity of the Bohai Sea ice condition. The freezing-up date, however, showed a large interannual variation without a clear trend. The simulations indicated that Bohai ice thickness has grown continuously thinner since 1951/1952. The time to reach 0.15 m level ice was delayed from 3 January to 21 January, and the ending time advanced from 6 March to 19 February. There was a significant weakening of ice conditions in the 1990s, followed by some recovery in 2000s. The relationship between large-scale climate indices and ice condition suggested that the AO and NAO are strongly correlated with interannual changes in sea-ice thickness in the Yingkou region.
Highlights
To understand the impact of large-scale atmosphere circulations on Bohai Sea ice, we investigated the correlations between local weather parameters, ice conditions, and large-scale atmospheric circulation indices from December to March between 1951/1952 and 2017/2018
Bohai Sea in situ observations have been used for HIGHTSI development and validation [29]
The 2017/2018 seasonal-radar-observed ice thickness was selected for HIGHTSI validation
Summary
Sea ice is an important part of the Earth environment. Sea-ice-mass balance has a profound impact on the ocean, the atmosphere, and the climate [1,2]. When sea ice is formed, the energy exchange between seawater and the atmosphere is significantly reduced, which, in turn, alters the energy balance of the upper ocean. Sea ice can act as a proxy, reflecting the regional and global climate [3]. The Bohai Sea is partially covered by sea ice during the winter. It is a southernmost sea with seasonal ice cover in the northern hemisphere. The seasonal sea-ice cover in the Bohai Sea has important ecological, Remote Sens.
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