上新世海道变化对中国气候的影响

气候记录显示晚新生代全球气候在上新世3~4Ma发生明显变化, 这一转变与海道变化触发的全球变冷密切相关。对于这一时期, 以往数值模拟研究较多关注热带海道(中美海道和印尼海道), 而白令海峡打开的气候效应往往被忽略。本文利用挪威地球系统模式, 模拟了白令海峡打开和热带海道关闭／收缩对中国气候的影响。白令海峡和热带海道的变化, 都可以引起全球大部分地区的气候响应; 但白令海峡打开的气候影响主要集中在中高纬地区, 对热带气候的影响并不显著; 而热带海道的变化可以引起全球大范围地区的温度降低, 导致热带太平洋表面温度升高, 使得热带太平洋东西之间的温度梯度加强, 热带太平洋厄尔尼诺-南方涛动年代际变率加强。对于上新世中国区域气候而言, 热带海道的变化比白令海峡打开的作用更加重要, 热带海道关闭/收缩可以引起我国东北和西南地区的气候响应, 而白令海峡打开对我国气候的影响几乎可以忽略。

Impact of changes in seaways on Chinese climate during Pliocene

Remarkable global cooling happened since the Pliocene about 3~4Ma ago. This cooling was often linked to changes in seaways during this period. Previous modelling studies focused mainly on the changes in tropical seaways, including the closing of Central America Seaway and the narrowing of Indonesian Seaway, but paid less attentions to changes in high latitude seaways, for example the opening of the Bering Strait. With the Norwegian Earth System model, this study simulates the climate effects due to the changes in the tropical seaways and the Bering Strait. These simulations demonstrate that the changes in the tropical seaways and the Bering Strait cause surface climate responses in most global regions. The opening of the Bering Strait causes the climate responses mainly in mid- and high-latitudes. The closing/narrowing of the tropical seaways leads to cooling in most regions, but warming in the tropical Pacific. Regionally, the closing/narrowing of the tropical seaways plays a more important role in Chinese climate evolution during the Pliocene, in relative to the opening of the Bering Strait. The closing/narrowing of the tropical seaways causes climate responses in Northeast and Southwest China. In Northeast China, the annual temperature decreases about 0.2~0.6℃, and the annual precipitation decreases by 100mm. In Southwest China, the annual temperature increases about 0.2~0.6℃, and the annual precipitation decreases more than 100mm. In contrast, the climate responses due to the opening of the Bering Strait are insignificant in China. The importance of tropical seaways on the regional climate in China is linked to the modification of tropical ocean temperature. The closing/narrowing of the tropical seaways, which intensifies the temperature gradient between the east and the west tropical Pacific and enhances ENSO variability, leads to the stronger regional climate responses in China, in relative to the opening of Bering Strait.