EAGER: Pedogenic Carbonates Record Insolation Driven Surface Melting in Antarctica

从南极冰盖收集的冰芯记录了地球的气候变化。虽然这些记录提供了极地温度如何随时间变化的高分辨率视图，但并不总是清楚地球过程对南极气候的影响。南极温度变化的一个可能原因是地球绕太阳公转时方向的周期性变化。这些所谓的米兰科维奇循环控制着到达极地地区的阳光的数量和模式，从而导致气候变暖或变冷的时期。虽然轨道变化和对入射太阳能的控制仍然很清楚，但它们如何影响南极气候仍然没有解决。该项目的目标是确定地球轨道的变化如何局部影响南极的温度。该项目的研究人员正在通过利用过去温暖期导致的融水沉淀的矿物质来确定过去南极洲表面冰融化的时期，从而实现这一目标。过去熔化的时间将由矿物的放射性同位素定年法确定，方法是利用铀到钍的自然放射性衰变。通过测定过去在南极大陆的科学考察中收集的大量样本的年代，这些研究人员旨在重建过去变暖的频率和空间模式，并在此过程中确定地球轨道变化的哪个方面影响了南极冰的损失。技术摘要南极冰芯提供了更新世南半球温度的高分辨率记录，显示了与北半球温度变化的总体一致性。对这种半球温度协方差的一种解释依赖于北半球日照变化导致的大气二氧化碳的变化。另一种假设是，极地温度的表面一致性是由于北半球夏季日照与南半球夏季持续时间之间的协方差引起的误导。目前对局地日照在南极气候中所起的作用认识不足。这个研究项目的目标是确定南极洲太阳强迫的时空格局。为了实现这一目标，项目团队将：1)开发一种方法，通过对成土碳酸盐进行U-Th测年，确定南极洲过去地表熔体产生的时期；2)利用过去地表融化的证据来校准能量平衡模式和询问过去南极表面温度和；3)将南极暖期的时间与潜在的太阳强迫机制（如夏季日照峰值或夏季持续时间）进行比较。一种确定当地日照影响南极温度的时空格局的方法，将为当前气候记录中的矛盾提供一种变革性的解决办法。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。

Non-technical abstractEarth’s climatic changes have been recorded in the ice core collected from the Antarctic ice sheet. While these records provide a high resolution view of how polar temperatures changed through time, it is not always clear what Earth process influence Antarctic climate. One likely contributor to Antarctic temperature changes is the cyclic changes in Earth’s orientation as it orbits the sun. These so-called Milankovitch cycles control the amount and pattern of sunlight reaching the polar regions, that in turn result in periods of climatic warming or cooling. While the orbital variations and control on incoming solar energy remain well understood, how they influence Antarctic climate remains unresolved. It is the goal of this project to determine how variations in Earth’s orbit may be locally influencing Antarctic temperatures. The researchers on this project are pursing this goal by identifying periods of past ice melting on the surface of Antarctica using minerals that precipitate from the meltwaters that resulted from past warm periods. The timing of this past melting will be determined by radioisotopic dating of the minerals using the natural radioactive decay of uranium to thorium. By dating numerous samples, collected in past scientific expeditions throughout the Antarctic continent, these researchers aim to reconstruct the frequency and spatial pattern of past warming and in doing so, determine what aspect of Earth’s orbital variations influences Antarctic ice loss.Technical abstractAntarctic ice cores provide high resolution records of Pleistocene Southern Hemisphere temperatures that show an overall coherence with Northern Hemisphere temperature variations. One explanation for this bi-hemispheric temperature covariance relies on changes in atmospheric CO2 that result from varying northern hemisphere insolation. An alternative posits that the apparent coherence of polar temperatures is due to the misleading covariance between northern hemisphere summer insolation and, the southern hemisphere summer duration. At present there is an insufficient understanding of the role that local insolation plays in Antarctic climate. The goal of this research project is to identify the temporal spatial patterns of solar forcing in Antarctica. To reach this goal, the project team will: 1) develop a way to identify periods of past surface melt production in Antarctica using U-Th dating of pedogenic carbonates; and 2) utilize the evidence of past surface melting to calibrate energy balance models and interrogate past Antarctic surface temperatures and; 3) compare the timing of Antarctic warm periods to potential solar forcing mechanisms such as peak summer insolation or summer duration. A means of identifying the spatial and temporal pattern at which local insolation influences Antarctic temperature would provide a transformative solution to the contradiction in current climate records.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.