Eocene - Oligocene climate change in Indonesia.

最近的研究表明，东南极大陆规模的巨大冰盖最早出现在大约3400万年前，接近渐新世的开始。冰盖突然出现的原因，以及随之而来的全球气候的重大变化，目前仍在争论之中。大气温室气体的减少是一种可能性；另一种(不一定相互矛盾的)想法是，南大洋环流模式的变化导致了大陆的降温。为了研究这次事件中发生了什么，我们需要可靠的记录，记录当时积累的沉积物--而不仅仅是南极洲周围的沉积物。来自印度尼西亚爪哇的一个杰出的历史遗迹引起了我们的注意。这是一个热带地区，可能是地球上海面温度最高的地区之一。爪哇地区有很好的微化石保存，这是必要的，因为我们想要使用微化石的地球化学技术获得对海洋表面温度和pH值等因素的可靠定量估计。然而，它只能从不完整的地表露头中得知，而连续的岩芯是非常可取的。我们将与印度尼西亚的地质调查地质学家合作，在始新世-渐新世界线上钻探两个~50m的岩心。利用岩心材料，我们将描述在这段气候变化期间海洋浮游和海底化石组合的变化，并利用这些信息来确定沉积物的年龄。我们将分析海面和海底有孔虫的氧同位素比率，这将使我们能够估计海水的温度和同位素组成的变化。对硼同位素比率的类似分析将揭示海洋pH的变化。如果二氧化碳水平下降，表层海洋的pH值应该会上升，从而影响我们的硼同位素记录。我们将能够判断这些变化是突然的还是渐进的。正如我们对露头样品的初步研究所暗示的那样，海洋碳酸盐化学的变化也可能影响了浮游生物的钙化率。由反向温室效应(或冰帽本身的反射性质)引起的全球变冷可能会导致热带地区海面温度下降，但目前还不知道热带变冷的温度或程度。温度变化的大小将使我们能够区分反向温室效应和洋流重组对冰层形成的解释，因为前者预测印尼海道将出现更明显的降温。因此，我们的记录将有助于回答关于这一古老的气候变化事件的一些重大悬而未决的问题。

Recent research has shown that a great continent-scale ice cap on East Antarctica first appeared about 34 million years ago, near the beginning of the Oligocene epoch. The causes of the sudden appearance of the ice cap, and the major change in global climate that accompanied it, are currently under debate. A reduction in atmospheric greenhouse gases is one possibility; another (not necessarily contradictory) idea is that changes in southern ocean circulation patterns caused a cooling of the continent. To study what happened during the event we need reliable records from sediments that accumulated at that time - and not just from around Antarctica itself. An outstanding site of the right age from Java, Indonesia, has come to our attention. This is a tropical site that would have had among the highest sea-surface temperatures on the planet. The Java locality has excellent microfossil preservation, which is necessary as we want to obtain reliable quantitative estimates of factors such as sea surface temperature and pH using geochemical techniques using the microfossils. However it is only known from incomplete surface outcrops, whereas a continuous core is highly desirable. We will drill two ~50m cores across the Eocene - Oligocene boundary in collaboration with geological survey geologists from Indonesia. Using the cored material, we will describe changes in the marine planktonic and sea floor fossil assemblages through this interval of climate change, and use that information to establish the age of the sediments. We will analyze the oxygen isotope ratios of sea surface and sea-floor foraminifera, which will enable us to estimate changes in the temperature and isotopic composition of seawater. Similar analyses of the boron isotope ratio will reveal the changing pH of the ocean. If declining carbon dioxide levels occurred, the surface ocean pH should have increased, affecting our boron isotope record. We will be able to tell if those changes were sudden or gradual. Changes in the carbonate chemistry of the ocean may also have affected the calcification rates of planktonic organisms, as is hinted from our pilot study of outcrop samples. Global cooling caused by a reverse greenhouse effect, (or by the reflective nature of the ice cap itself), might have cause sea surface temperature reduction in the tropics, but at present the temperatures or the extent of tropical cooling are not known. The amount of temperature change will allow us to distinguish between the explanations of a reverse greenhouse effect and ocean current reorganization for the ice build-up, as the former predicts more pronounced cooling in the Indonesian seaway. Hence our record will help answer some of the major outstanding questions about this ancient climate change event.