From Greenhouse to Icehouse: Past changes in southern hemisphere vegetation and the evolution of the Antarctic ice sheet

极地地区在我们理解未来比现在更温暖的世界中的环境变化方面发挥着关键作用。南极过去的植被和气候，以及其高度敏感和动态的冰盖的演变，很难受到地质数据的约束。现有的为数不多的远场数据和更少的近场记录表明，从渐新世到中新世，南极洲出现了大规模的冰盖堆积，在大气中二氧化碳浓度接近现代的晚新生代温暖时期，冰盖部分甚至完全坍塌。大约3000万年前南极绕极流(ACC)的爆发恰逢全球海洋环流发生重大变化，大气中二氧化碳浓度显著下降，在此过程中，南极洲从“温室环境”转变为冰沙漠。今天，ACC管理着海洋和大气之间的热量和碳交换，尽管这种大洋流是地球气候系统的关键组成部分，但关于它的起源、演变和对全球环境的影响仍存在许多争议。PHD项目将使用选定的海洋和陆地记录中的花粉、孢子和甲藻化石来重建新生代植被和陆地气候。该项目将把重点放在南美洲、南极洲和澳大拉西亚的关键地区，这些地区靠近德雷克海峡和塔斯曼门。两个大洋门户的构造变化是始新世晚期以来ACC发育的主要控制因素。为了提高我们对控制ACC演化的主要事件和过程的时间安排的了解，该项目将侧重于选定的地质时间间隔，其中包括地球气候演化的关键门槛，例如始新世-渐新世和渐新世-中新世的过渡。

The polar regions play a key role in our understanding of environmental change in a future warmer-than-present world. The past vegetation and climate of Antarctica and the evolution of its highly sensitive and dynamic ice sheet are poorly constrained by geological data. The few existing far-field data, and even fewer proximal records, indicate a major ice-sheet build-up in Antarctica from the Oligocene to the Miocene, with partial or even complete ice-sheet collapses during warm Late Cenozoic intervals with near-modern atmospheric CO2-concentrations. The onset of the Antarctic Circumpolar Current (ACC) about 30 million years ago coincided with major changes in global ocean circulation and a significant decline in atmospheric carbon dioxide concentration during which Antarctica transformed from a "greenhouse environment" into an ice desert. Today the ACC regulates the exchange of heat and carbon between the ocean and the atmosphere, and although this large ocean current is a key component of Earth's climate system, many controversies exist about its origin, evolution and impact on the global environment. The PhD project will use fossil pollen, spores and dinoflagellates from selected marine and terrestrial records to reconstruct Cenozoic vegetation and terrestrial climate. The project will focus on key regions in South America, Antarctica and Australasia, which are closely located to the Drake Passage and Tasman Gateway. Tectonic changes in both ocean gateways were a major control for the development of the ACC since the late Eocene. In order to improve our understanding about the timing of the main events and processes controlling the evolution of the ACC, the project will focus on selected geological time intervals that include critical threshold in Earth's climate evolution, such as the Eocene-Oligocene and Oligocene-Miocene transitions.