14MaB.P.澳大利亚板块对赤道太平洋影响的数值模拟

MODELING THE IMPACT OF AUSTRALIAN PLATE DRIFT ON THE EQUATORIAL PACIFIC

文章利用美国NASA的GISS海气耦合模式,研究了14MaB.P.时期与现代情景下的澳大利亚板块不同位置对赤道太平洋的影响。结果表明:14MaB.P.澳大利亚板块位置较现代偏南时,海洋次表层南赤道海水穿过印度尼西亚通道直接进入印度洋,注入赤道潜流的南赤道海水减少,使得赤道潜流主要来源于北赤道海水,造成赤道太平洋海温比现在冷,其中以赤道西太平洋海温降低幅度最大。而在海洋近表层赤道中东太平洋地区,由于进入海洋的净能量增加和西向风应力加强的共同作用,使得14MaB.P.时海温较之现代情景下要低0.2℃左右。此外,14MaB.P.澳大利亚板块较现代偏南时,赤道太平洋地区的降水量少于现代。

The Australian plate has been moving northwardly at a rate of 70km/Ma in the past 20Ma. At 14Ma ago it was located at about 10°south of its present position. Such a plate configuation made the Indonesian passage wider and might have affected climate in the Equatorial Pacific. In order to detect the possible role of Australian plate drifting in the Equatorial Pacific, we aimed at the different positions of the Australian plate between 14MaB.P. and the present in two modeling experiments. One was a controll experiment for the present-day climate, and the other was a sensitive experiment for 14MaB.P. The sole difference in these two experiments' boundary conditions is the position of the Australian plate. Two experiments were both simulated for 120 years by the GISS atmosphere-ocean model. The last 40 model years, which reached stability under respective boundary forcing, were taken as averaged climatological status.The modeling results indicate that there is a significant change in ocean circulation between the two experiments. At present EUC is composed of South Pacific water that turns eastward in New Guinea and North Pacific water. It flows toward east and then upwells in the eastern Equatorial Pacific at subsurface layer. While the Australian plate lay south and Indonesian passage became wider, most of water from south Pacific passes through the Indonesian passage and feeds into the Indian Ocean directly. Thus, at 14Ma the contribution of the south equatorial water to EUC becomes less than that at present. Because South Pacific waters are warmer than North Pacific waters, EUC which is mainly supplied by water coming from the northern Pacific results in 0.9-1.2℃colder ocean temperature in the Equatorial Pacific. When the Australian plate lay south, comparing to counterparts at present , more net heat energy enters into the surface of the Equatorial Pacific. Westward wind momentum stress becomes stronger and induces more warm water transported to the western Pacific and more cold water ascended in the eastern Pacific upwelling region. With the result of these factors co-action, surface sea temperature is about 0.2 'C lower in mid-east Equatorial Pacific and a little higher in western Equatorial Pacific than that at present. The precipitation also decreased in the Equatorial Pacific during 14MaB.P.