Ocean Temperatures Through Early Cenozoic Climate Maxima Across a Latitudinal Transect from the North to the South Pacific - A Multi-Proxy In Situ Approach

地球过去气候的记录为我们未来的气候提供了重要线索。 例如，始新世早期（56 至 4900 万年前）的特点是大气中温室气体含量高于现代，全球平均气温也高得多。这个时期可能是 21 世纪或 22 世纪的一个很好的类比。到那时，气候模型预测，温室气体排放将产生比地球至少 3500 万年以来所经历的更温暖的环境。 过去所有温暖气候时期的一个共同特征是高纬度地区异常温暖。然而，当前的气候模型无法重现这些温暖的极地温度。古气候记录和模型模拟之间的这种分歧给气候研究带来了重大挑战。古气候数据是否有偏差，气候模型是否不准确，或者两者兼而有之？目前，由于缺乏可靠的古气候数据，气候模型的测试受到限制。例如，过去海面温度的许多记录都是基于浮游有孔虫化石壳的同位素和化学成分。这些微生物生活在整个海洋表面，它们的壳保存在海底沉积物中。然而，这些化石化学记录可能会因数百万年的沉积过程而退化。高分辨率显微成像现在可以识别化石有孔虫壳内保存较好的区域。最近的分析发展使得测量这些微小区域的化学成分成为可能。 拟议的研究将利用这些新方法重新评估始新世早期温暖时期太平洋赤道到极地的海面温度梯度。这些数据将为数据模型不匹配提供新的线索，并有助于提高气候模型的准确性。该研究将支持一名研究生。该项目的成果将在科学推广展览中重点展示，向非科学家介绍古气候研究。我们准确模拟地球历史上温暖气候的能力为我们了解地球大气系统提供了最重要的测试之一。特别令人感兴趣的是始新世早中期（56 至 4900 万年前），这是温室气体水平最后一次超过约 600 ppm CO2（现代为 412 ppm，每年增加超过 2 ppm）。这一时期的一个令人费解的特征是高纬度地区异常温暖，同时伴随着相对凉爽的热带气温和微弱的纬度温度梯度。然而，即使是当前的气候模型也无法模拟这样的气候状况。这种数据模型不匹配可能部分是由古气候档案的成岩改变引起的。经过数百万年的沉积物，成岩作用可能会改变有孔虫壳的原始同位素和化学成分，这些沙粒大小的海洋微化石是迄今为止地球过去气候最重要的记录者。在过去的几年里，人们发现这些有孔虫壳内的微小（仅几十微米）区域比其余材料保存得更好。原位（“就地”）分析方法的最新发展和改进与高分辨率成像相结合，现在可以识别和分析有孔虫壳内这些保存较好的区域。通过使用这些新兴的现场技术，我们的目标是重新评估南太平洋纵断面早始新世气候最大值的经向温度梯度。因此，我们将重点关注气候建模界最感兴趣的三个时间间隔：(1) 始新世早期气候最佳期（~53 – 51 Ma）； (2) 古新世-始新世热最大值 (PETM, ~56 Ma), (3); PETM 之前评估预热背景条件的时期。最先进的成像方法将与用于氧同位素分析的二次离子质谱 (SIMS)、用于测定镁/钙 (Mg/Ca) 比率的电子探针微量分析 (EPMA) 以及用于穿过有孔虫室壁的多元素深度剖析（成岩作用的化学“指纹”）的激光烧蚀 ICP-MS 结合使用，以识别有孔虫壳内保存完好的区域。原位数据将与传统的氧同位素测量相结合，以评估先前发表的古记录的潜在偏差。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Records of Earth’s past climate hold important clues to our future climate. For example, the early Eocene (56 to 49 million years ago) was characterized by higher-than-modern atmospheric greenhouse gas levels and much warmer mean global temperatures. This period may be a good analog for the 21st or 22nd century. By that time, climate models predict that greenhouse gas emissions will produce warmer conditions than the Earth has experienced for at least 35 million years. One common feature of all past periods of warm climate is the exceptional warmth of high latitude regions. However, current climate models fail to reproduce these warm polar temperatures. This disagreement between paleoclimate records and model simulations poses a major challenge in climate research. Are the paleoclimate data biased, are the climate models inaccurate, or both? Testing of climate models is currently limited by the scarcity of robust paleoclimate data. For instance, many records of past sea surface temperature are based on the isotopic and chemical composition of fossil shells of planktic foraminifera. These microorganisms live throughout the surface ocean and their shells are preserved in seafloor sediments. However, these fossil chemical records can be degraded by sedimentary processes acting over millions of years. High-resolution microscopic imaging now allows for the identification of better-preserved areas within fossil foraminifera shells. And recent analytical developments make it possible to measure the chemistry of these tiny areas. The proposed study will use these new methods to re-assess equator-to-pole sea surface temperature gradients in the Pacific Ocean during the early Eocene warm period. These data will shed new light on the data-model mismatches and help improve the climate models’ accuracy. The study will support a graduate student. The project results will be highlighted in a science outreach display to introduce paleoclimate studies to non-scientists.Our ability to accurately simulate warm climates in Earth history provides one of the most important tests of our understanding of the Earth’s atmospheric system. Of particular interest is the early to middle Eocene 56 to 49 million years ago) which is the last time that greenhouse gas levels exceeded ~600 ppm CO2 (modern 412 ppm, increasing more than 2 ppm/year). A puzzling feature of this time is the exceptional warmth of high-latitude regions associated with relatively cool tropical temperatures and a weak latitudinal temperature gradient. However, even current climate models fail to simulate such a climate regime. This data-model mismatch may be partially caused by diagenetic alteration of paleoclimate archives. After millions of years in the sediment, diageneses may alter the original isotopic and chemical composition of foraminifer shells, sand-grain-sized marine microfossils that are – by far – the most important recorders of the Earth’s past climate. Within the past years, it was found that minute (just tens of microns) domains within these foraminifer shells are better preserved than the remaining material. Recent developments and improvements of in situ (‘in place’) analytical approaches in combination with high-resolution imaging now allows for the identification and analysis of these better-preserved domains within foraminifer shells. By using these new and emerging in situ technologies, we aim to re-asses meridional temperature gradients through early Eocene climate maxima across a South Pacific longitudinal transect. Thereby, we will focus on three time intervals that are of highest interest for climate modeling community: (1) The Early Eocene Climate Optimum (~53 – 51 Ma); (2) The Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma), (3); The period just before the PETM to assess to pre-warming background conditions. State-of-the-art imaging approaches to identify better preserved domains within foraminifer shells will be used in combination with Secondary Ion Mass Spectrometry (SIMS) for oxygen isotope analysis, Electron Probe Microanalysis (EPMA) for the determination of Magnesium/Calcium (Mg/Ca) ratios, and Laser-Ablation ICP-MS for multielement depth profiling through foraminifer chamber walls (chemical ‘fingerprinting’ of diagenesis). The in situ data will be paired with conventional oxygen isotope measurements to assess the potential bias of previously published paleorecords.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.