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.

该项目将通过对海洋钻井程序收集的各种沉积物核心的有孔虫的Mg/Ca和氧同位素比的分析来记录中始新世晚期的南方海水的温度演化。始新世间隔（〜49至37 mA）可能是培根气候进化中最关键的时期。深海温度的冷却多达7度C，而小型冰盖早在〜42-40 MA上出现在南极洲。然而，最近在南洋沉积物核心上的工作表明，这种长期冷却趋势不是单调的。新的高分辨率氧同位素记录显示出一个明显的变暖事件在41.5 MA，被指定为始新世中间气候最佳（MECO）。假设这个瞬态事件（持续时间〜600 K.Y.）代表长期冷却中重要的气候逆转（约4度C变暖）。鉴于中始新世中，PCO2宽阔的摇摆的新证据，这种逆转令人信服。因此，此事件提供了一个独特的机会来表征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的同位素和MG/CA数据集来记录始新世中期南方海水的温度演变。包括来自南洋三个部门的地点，以解决当地与区域温度变化的问题，并确认存在区域信号和趋势。低纬度太平洋地区的另一个地点将为高纬度位点提供比较框架。结合温度史，这些记录还应使海水氧同位素以及冰卷曲线的中期始新世晚期构建。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在证明温室加气强迫与全球气候变化之间的关系方面做出的贡献。随着始新世PCO2变异性的细节，随着气候模型变得越来越复杂，南方海洋气候和南极冰上历史的高分辨率记录对于评估PCO2变异性对全球气候的影响至关重要。鉴于始新世可能是最近几个世纪内大气PCO2波动的最新时期，它为衡量气候敏感性/对这种强迫范围的不敏感提供了独特的机会。就更广泛的影响而言，这项研究与了解全球气候变化的社会影响有关。它还将支持研究生博士学位。研究并参与本科生的动手研究。