Collaborative Research: P2C2--The Oligocene-Miocene Boundary: Carbon-Dioxide (CO2) Sensitivity and Ice Sheet Hysteresis

该项目是对2300万年前发生在渐新世-中新世边界的一次极端的、短暂的气候振荡的研究。该事件的特征是底栖有孔虫稳定氧同位素组成（delta18O）的15万年振荡，通常被认为反映了南极冰盖的快速前进和后退，以及全球碳循环的扰动和海洋和陆地系统中生物影响的证据。这次事件的规模和持续时间都不寻常，与我们对冰盖行为的理解明显矛盾。研究人员将使用过去气候和大气环流模型模拟的替代测量来解决四个首要问题：事件的主要驱动因素是什么：碳循环动力学和大气二氧化碳（CO2）轨道？从温度和冰体积的变化来看，这次事件的规模有多大？考虑到当时接近现代的大气二氧化碳水平，北半球冰盖是否已经增长，如果是这样，它们对底栖三角洲18o信号的影响是什么？如果二氧化碳水平一直像代理记录显示的那样低，那么以极地为中心的陆地冰盖怎么会经历这样的变化呢？更广泛的影响包括研究生指导，参与一个关注过去气候历史的重要暑期学校，以及气候历史本科教育模块的发展。

The project is a study of an extreme, short-lived climate oscillation that occurred at the Oligocene-Miocene boundary about 23 million years ago. The event is characterized by a 150,000-year oscillation in the stable oxygen isotope composition (delta18O) of benthic foraminifera, generally thought to reflect a rapid advance and retreat in the Antarctic ice sheet, as well as a perturbation in the global carbon cycle and evidence of biotic impacts in marine and terrestrial systems. The magnitude of the event and its short duration are unusual and in apparent contradiction to our understanding of ice sheet behavior. The researchers will use proxy measurements of past climate and general circulation model simulations to address four overarching questions: What were the primary drivers of the event: carbon cycle dynamics and atmospheric carbon dioxide (CO2), orbits? What was the magnitude of the event in terms of temperature and ice volume change? Could Northern Hemispheric ice sheets have grown, given near-modern atmospheric CO2 levels at the time, and if so, what is their impact on the benthic delta18O signal? How can a polar-centered, terrestrial ice sheet experience such variability if CO2 levels remained as low as suggested by proxy records? The broader impacts include graduate student mentoring, participation in an important summer school focused on past climate history, and the development of undergraduate education modules for climate history.