Eocene - Oligocene climate change in Indonesia.

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.