Eocene - Oligocene climate change in Indonesia.

最近的研究表明，大约3400万年前，在渐新世开始时，南极洲东部首次出现了一个巨大的大陆规模的冰盖。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，目前正在辩论中。大气中温室气体的减少是一种可能性;另一种（不一定是矛盾的）想法是南大洋环流模式的变化导致了大陆的冷却。为了研究在这一事件中发生了什么，我们需要来自当时积累的沉积物的可靠记录-而不仅仅是来自南极洲本身。我们注意到了印度尼西亚爪哇岛上一处杰出的遗址。这是一个热带地区，可能是地球上海面温度最高的地方之一。爪哇地区拥有出色的微化石保存，这是必要的，因为我们希望使用微化石的地球化学技术获得对海表面温度和pH值等因素的可靠定量估计。然而，它只知道从不完整的表面露头，而连续的核心是非常可取的。我们将与印度尼西亚地质调查地质学家合作，在始新世-渐新世边界钻取两个约50米的岩心。利用取芯材料，我们将描述在这段气候变化期间海洋沉积物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，这将使我们能够估计海水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值的变化。如果二氧化碳水平下降，海洋表面的pH值应该会增加，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。海洋中碳酸盐化学的变化也可能影响了浮游生物的钙化率，这一点从我们对露头样本的初步研究中得到了暗示。由逆温室效应（或冰盖本身的反射性质）引起的全球变冷可能导致热带海洋表面温度降低，但目前热带变冷的温度或程度尚不清楚。温度变化的量将使我们能够区分反向温室效应和洋流重组对冰堆积的解释，因为前者预测印度尼西亚海道的冷却更明显。因此，我们的记录将有助于回答有关这一古老气候变化事件的一些主要悬而未决的问题。

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.