Low-Latitude Paleoceanography and Phytoplankton Productivity Through the Eocene/Oligocene Transition (IODP Expedition 320)

目前我们生活的这个由极地冰盖主导的星球，在我们星球的大部分历史中都不是典型的。南极洲目前的冰盖生长阶段大约始于2300万年前（一个被称为始新世/渐新世边界过渡的间隔）。从温暖的无冰气候到凉爽的冰川气候的转变是一个意义深远的事件，但其发生的原因尚不清楚。地质观测和气候模型都支持对这种转变的一个很好的解释是，大气中的二氧化碳下降到足够低的水平，使气候降温，并在南极洲大陆上开始结冰。二氧化碳的减少可能是由于风化过程的增强或海洋浮游生物活动的增加而发生的。在这一时期，南极洲周围的海洋浮游生物的产量有所增加，但我们不知道这种情况是否发生在世界海洋的更广泛地区，特别是在最大的海洋栖息地太平洋。该项目将通过考察将于2009年3月至5月由“综合海洋钻探计划”钻探的新沉积物岩心，调查在始新世/渐新世边界的赤道太平洋是否发生了这种浮游生物生产力触发因素。首席研究员和PDRA都是这次探险队320的船上科学家，他们将在岩心被发现后立即对其进行检查。通过量化浮游生物化石的丰度并检查它们的组成，我们将能够确定生产力水平，并评估太平洋浮游生物是否可能对全球二氧化碳的减少做出了贡献，并最终导致了当时发生的气候转变。

The current polar ice-sheet dominated planet that we live on is not typical of most of our planet's history. The current phase of ice-sheet growth on Antarctica began around 23 million years ago (an interval known as the Eocene/Oligocene boundary transition). This switch from warm, ice-free climates to cooler, glacial climates was a profound event but the reasons why it happened are still unclear. One good explanation for this switch, which has support from both geological observations and climate models, is that atmospheric CO2 dropped low enough to cool the climate and to initiate ice-growth on the Antarctica continent. This decline in CO2 may have occurred through enhanced weathering processes or through the increased activity of oceanic plankton. An increase in the productivity of oceanic plankton has been documented from around Antarctica at this time, but we do not know whether this occurred over wider areas of the world ocean, and in particular in the largest oceanic habitat, the Pacific. This project will investigate whether this plankton productivity trigger occurred in the Equatorial Pacific at the Eocene/Oligocene boundary, by examining new sediment cores that will be drilled by the Integrated Ocean Drilling Program in March - May 2009. The Principal Investigator and named PDRA are both Shipboard Scientists on this Expedition 320 and will examine the cores as soon as they are recovered. By quantifying the abundances of the plankton fossils and examining their composition, we will be able to determine the levels of productivity and assess whether Pacific plankton may have contributed to global CO2 drawdown and ultimately to the climate transition that occurred at this time.