The tropical rain belt of South America during Plio-Pleistocene cooling

研究了上新世南美洲大气环流增强的时间和热带辐合带（ITCZ）的位置。上新世变冷涉及到与赤道太平洋温度变化有关的大气环流的加强。上新世太平洋海温记录表明，纬向海温梯度和经向海温梯度的增加分别增强了大气Walker环流和Hadley环流。大西洋和太平洋之间的地表水交换受到海洋盐度差异的限制，表明中美洲海道的最终关闭发生在4.7 ~ 4.2 Ma之间。这次关闭对赤道太平洋环流和东赤道太平洋冷舌的发展产生了强烈影响。CAS的关闭也影响了ITCZ的纬度位置，但模式和资料显示的方向相反。本研究旨在利用厄瓜多尔海上ODP站点1239的海洋沉积物，对上新世三个关键时期南美洲赤道西部和安第斯山脉西部的植被变化进行孢粉学记录。我们的目标是南美洲西北部气候和陆地水文的变化记录，这些变化与ITCZ在4.7 - 4.2之间的早期移位和3.6 - 1.7 Ma之间的Walker环流增强时间有关。第一年我们接近上新世早期。我们可以证明，在CAS闭合期间，ITCZ向南移动与证实其向南移动假设的数据一致。

The proposal focusses on the timing of the atmospheric circulation intensification and the position of the Intertropical Convergence Zone (ITCZ) over South America during the Pliocene. Pliocene cooling involves the intensification of the atmospheric circulation related to temperature changes in the Equatorial Pacific Ocean. Pliocene sea surface temperature (SST) records of the Pacific indicate that increases of the zonal and meridional SST gradients intensified the atmospheric Walker and Hadley circulations, respectively. Restriction of the surface water exchange between the Atlantic and Pacific oceans recorded by the salinity divergence between oceans indicates that the final closure of the Central American Seaway (CAS) occurred between 4.7 and 4.2 Ma. The closure had a strong impact on the circulation in the Equatorial Pacific and the development of the eastern Equatorial Pacific cold tongue. Closure of the CAS also influenced the latitudinal position of the ITCZ, but models and data indicate shifts in opposite directions. The proposal aims at a palynological record of Pliocene vegetation change in west equatorial South America and the western Andean Cordillera for three key periods of the Pliocene using marine sediments of ODP Site 1239 offshore of Ecuador. We aim at a record of changes in climate and terrestrial hydrology of northwest South America related to an early shift of the ITCZ between 4.7 and 4.2 and the timing of the intensification of the Walker circulation between 3.6 and 1.7 Ma. In the first year we approached the early Pliocene period. We could demonstrate that the ITCZ shifted southwards in line with the data confirming the hypothesis of its southward shift during CAS closure.