Reconstructing last interglacial sea level based on models and observation from the Bahamas

今天的主要冰盖正在萎缩，因此导致全球海平面上升。了解它们未来融化的程度和速度对公共卫生、沿海基础设施和经济稳定都是一个紧迫的问题。这个研究项目将调查主要冰盖对适度变暖的影响程度。这个项目将通过重建地球历史上最近一段时间的海平面来解决这个问题，当时由于地球轨道的自然和周期性变化，全球平均气温比工业化前略高（+1-2摄氏度）。这一时期，也就是最后一次间冰期，大约发生在12.5万年前。关于全球海平面有多高以及海平面是否在这一漫长暖期结束时突然上升（冰盖崩塌）存在争议。这段时间内海平面变化的幅度和速度对于改进下个世纪海平面上升的预测都很重要。海平面将根据巴哈马的地质记录重建最后一次间冰期的海平面。末次间冰期海洋沉积物和化石珊瑚的当前高度测量将与古冰盖和海平面变化模型相结合，以推断过去这一关键暖期海平面的响应和演变。这项工作将提高对未来海平面变化预测的准确性，并将为海平面研究领域的新研究者提供支持。为了提高我们对未来海平面上升的理解，我们可以求助于记录极地冰盖对长期变暖反应的地质历史时期。末次间冰期（LIG, ~ 128 - 116 ka）是这种方法的主要目标，因为当时的温度相对于今天略有升高。对这一时期的全球平均海平面和冰损失的重建表明，这一时期的全球平均海平面更高，然而，冰融化的确切幅度和时间仍然存在争议。改善这些重建的一个主要障碍是，目前对自LIG以来固体地球向上或向下移动的程度的了解有限，因此对当地重建的海平面与过去全球平均水平的偏差有多大。通常使用模式预测来修正这一分量，然而，由于对地球内部结构和过去冰盖演变的不完全了解，模式是不确定的。该项目旨在通过将巴哈马的海平面观测与固体地球变形模型相结合，推进关于LIG期间冰融化幅度和时间的辩论。巴哈马群岛上沉积的沉积物是过去海平面的优秀档案，由于它们的空间范围和靠近前冰盖的独特位置，使它们能够体验和捕捉固体地球变形的梯度，因此是改进固体地球变形模型的理想选择。该项目将在巴哈马的三个野外季节对露头进行高精度3D重建，以获得前所未有的LIG地层数据的海拔限制和年龄。我们将生成固体地球变形-冰川均衡调整和动态地形的模型预测，并分别用全新世和新近纪的现有观测结果对它们进行约束。将现场观测与预测模型相结合，将使我们能够产生LIG上过量极地冰融化和冰演化的不确定性范围，以及约束地球性质。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Today's major ice sheets are shrinking and therefore contribute to global sea level rise. Understanding how much and how fast they will melt in the future is a pressing question for public health, coastal infrastructure, and economic stability. This research project will investigate how susceptible major ice sheets are to modest amounts of warming. This project will address this question by reconstructing sea level during the most recent time in Earth's history when global mean temperatures were slightly warmer (+1-2 degrees C) than pre-industrial values due to natural and periodic variations in the Earth's orbit. This time period, the last interglacial, occurred approximately 125,000 years ago. Controversy exists around how much higher global sea level was and whether abrupt sea level rise (ice sheet collapse) occurred at the end of this prolonged warm period. Both the magnitude and rate of sea level change during this time are important for improving predictions of sea level rise over the next century. Sea level will be reconstructed over the last interglacial from the geologic record of the Bahamas. Measurements of the current elevations of last interglacial marine sediments and fossil corals will be combined with models of ancient ice sheets and sea level change to infer the response and evolution of sea level during this critical past warm period. The work will improve the fidelity of predictions for future sea-level change and will support a new investigator in the field of sea-level studies To improve our understanding of future sea level rise we can turn to periods in the geologic past that recorded the response of polar ice sheets to prolonged warming. The Last Interglacial (LIG, ~ 128 - 116 ka) is a prime target for this approach as temperatures were slightly elevated relative to today. Reconstructions of global mean sea level and ice loss during this period indicate that global mean sea level was higher during this time period, however, the exact magnitude and timing of ice melt is still debated. A major obstacle in improving these reconstructions is currently a limited understanding of how much the solid Earth has moved up or down since the LIG, hence how much local reconstructed sea level deviates from the past global mean. This component is generally corrected for using model predictions, however, models are uncertain due to an incomplete knowledge of Earth's internal structure and past ice sheet evolution. This project aims to advance the debate about the magnitude and timing of ice melt during the LIG by combining sea level observations from the Bahamas with models of solid Earth deformation. The sediments deposited across the Bahamian archipelago are excellent archives of past sea level and are ideal to improve models of solid Earth deformation due to their spatial extent and unique location close to the former ice sheet, which allows them to experience and capture gradients in solid Earth deformation. The project will produce high-precision 3D reconstructions of outcrops over three field seasons in the Bahamas to obtain unprecedented elevation constraints and ages on LIG stratigraphic data. We will generate model predictions of solid Earth deformation - glacial isostatic adjustment and dynamic topography, and constrain them with existing observations from the Holocene and Neogene, respectively. Combining the field observations with predictive models will allow us to produce uncertainty ranges for excess polar ice melt and ice evolution over the LIG as well as constrain Earth properties.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.