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

始新世中期“温室”向“冰库”转变期间南极和南大洋气候不稳定

• 批准号: 0338337
• 负责人: James Zachos
• 金额: $ 9.73万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-06-15 至 2006-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0338337&HistoricalAwards=false
• 关键词: Antarctic; Southern; Ocean; Climate; Instability

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.

该项目将通过分析大洋钻探计划收集的各种沉积物岩心中有孔虫的Mg/Ca和氧同位素比率，记录南大洋沃茨在始新世晚期的温度演变。始新世中期（~49 ~ 37 Ma）可能是新生代气候演化最关键的时期。深海温度下降了7摄氏度，南极洲早在42-40 Ma就出现了小冰盖。然而，最近对南大洋沉积物岩心的研究表明，这种长期冷却趋势并不是单调的。新的高分辨率氧同位素记录揭示了一个明显的变暖事件在41.5马，被指定为中始新世气候最佳（MECO）。该瞬态事件（约600 k.y.在持续时间）被假设为代表一个重要的气候逆转（约4摄氏度变暖）在长期冷却的中间。这种逆转是令人信服的，根据新的证据，在始新世中期的pCO 2大幅波动。因此，这一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Mg/Ca数据集，记录南大洋沃茨在中始新世晚期的温度演变。南大洋所有三个部分的站点都包括在内，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。在低纬度太平洋的另一个站点将为高纬度站点提供一个比较框架。结合温度的历史，这些记录也应该使建设的海水氧同位素，并通过代理，冰量曲线中始新世晚期。通过提供一个详细的古气候框架，这项研究的更广泛的意义将最终在于它的贡献，证明温室气体强迫和全球气候变化之间的关系。随着始新世pCO 2变化的详细信息的建立，以及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对于评估pCO 2变化对全球气候的影响至关重要。考虑到始新世可能是大气pCO 2在未来几个世纪预计发生的规模上波动的最近时期，它提供了一个独特的机会来衡量气候对这一范围的强迫的敏感性/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学位。研究并让本科生参与实践研究。