Antarctic and Southern Ocean Climate Instability during the Middle Eocene "Greenhouse" to "Icehouse" Transition

该项目将通过分析海洋钻探计划收集的不同沉积物岩心中有孔虫的镁/钙和氧同位素比值，记录下中始新世晚期南大洋水域的温度演变。始新世中期(~49~37 Ma)可能是新生代气候演化最关键的时期。深海温度降低了7摄氏度，南极洲早在42-40 Ma就出现了小冰盖。然而，最近对南大洋沉积岩心的研究表明，这种长期的冷却趋势并不是单调的。新的高分辨率氧同位素记录显示，在41.5 Ma发生了一次显著的变暖事件，被指定为中始新世气候最佳时期(MECO)。这一瞬变事件(约600 K.Y.(持续时间)被认为代表了长期冷却过程中的一次重要的气候逆转(约4摄氏度变暖)。鉴于新证据表明，始新世中期二氧化碳浓度大幅波动，这种逆转是令人信服的。因此，这次事件提供了一个独特的机会来描述高纬度气候对边界条件变化的敏感性。该项目将通过开发高分辨率稳定同位素和镁/钙数据集，记录南大洋水域在始新世晚期的温度演变。纳入了南大洋所有三个区段的地点，以解决当地与区域温度变化的问题，并确认区域信号和趋势的存在。低纬太平洋的另外一个站点将为高纬度站点提供一个比较框架。结合温度历史，这些记录还应该能够建立海水氧同位素，并通过代理，建立中始新世晚期的冰量曲线。通过提供详细的古气候框架，这项研究的更广泛的意义最终将在于它有助于证明温室气体强迫与全球气候变化之间的关系。随着始新世二氧化碳变异性的细节被确定，随着气候模型变得更加复杂，南大洋气候和南极冰盖历史的高分辨率记录将对评估二氧化碳变异性对全球气候的影响至关重要。鉴于始新世可能是大气二氧化碳以预计在未来几个世纪内发生的规模波动的最近时期，它提供了一个独特的机会来衡量气候对这一强迫范围的敏感性/不敏感性。就更广泛的影响而言，这项研究与理解全球气候变化的社会影响有关。它还将支持研究生的博士研究，并让本科生参与实践研究。

This project will document the temperature evolution of Southern Ocean waters in the late middle Eocene through analyses of the Mg/Ca and oxygen isotope ratios of foraminifera from various sediment cores collected by the Ocean Drilling Program. The middle Eocene interval (~49 to 37 Ma) is possibly the most critical period in Cenozoic climatic evolution. Deep-sea temperatures cooled by as much as 7 degrees C, and small ice sheets appeared on Antarctica as early as ~42-40 Ma. Recent work on Southern Ocean sediment cores, however, suggests that this long-term cooling trend was not monotonic. New high-resolution oxygen isotope records reveal a pronounced warming event at 41.5 Ma, designated as the Middle Eocene Climatic Optimum (MECO). This transient event (~600 k.y. in duration) is hypothesized to represent an important climatic reversal (~4 degrees C warming) in the midst of long-term cooling. This reversal is compelling in light of new evidence of wide swings in pCO2 during the middle Eocene. As such, this event provides a unique opportunity to characterize the sensitivity of high-latitude climate to changes in boundary conditions. This project will document the temperature evolution of Southern Ocean waters in the late middle Eocene through development of high-resolution stable isotope and Mg/Ca datasets. Sites from all three sectors of the Southern Ocean are included in order to address questions of local vs. regional temperature variation and to confirm the presence of regional signals and trends. One additional site in the low-latitude Pacific will provide a comparative framework for the high-latitude sites. In conjunction with a temperature history, these records should also enable the construction of a seawater oxygen isotope and, by proxy, ice-volume curve for the late middle Eocene. By providing a detailed paleoclimatic framework, the broader significance of this study will ultimately lie in its contribution to demonstrating a relationship between greenhouse-gas forcing and global climate change. As details of Eocene pCO2 variability are established, and as climate models become more sophisticated, high-resolution records of Southern Ocean climate and Antarctic ice-sheet history will be essential for assessing the impact of pCO2 variability on global climate. Given that the Eocene may have been most the recent period in which atmospheric pCO2 fluctuated on the scale projected to occur over the next few centuries, it provides a unique opportunity to gauge climate sensitivity/insensitivity to this range of forcing. In terms of broader impacts, this research is relevant to understanding the societal impacts of global climate change. It will also support a graduate student's Ph.D. research and involve undergraduates in hands-on research.