High-fidelity dating of deep-time records: Integrating Earth's dynamical ellipticity and tidal dissipation into astrochronology

确定海底沉积物和沉积岩年龄的一种方法是使用基于天文计算的“日历”。这个时间尺度利用了行星轨道的可预测变化驱动地球气候的周期性变化这一事实。例如，观测到的沉积物组成的周期可以与天文周期相匹配。这些周期是通过计算时间向后的行星轨道来计算的。不幸的是，某些轨道周期的使用仍然具有挑战性，因为地球的引力形状和自转速度在过去发生了变化。这些变化给轨道计算带来了不确定性。该项目将通过将地球引力形状和自转速率纳入轨道计算，为沉积记录开发高保真的测年方法。所有数值工具都将作为开源程序和软件包的附加组件提供。该项目更广泛的影响包括为一名研究生提供支持，以及举办一个天文学方法培训讲习班。这个项目有可能改变我们测定过去5500万年沉积物年代的能力。它还将提高我们对过去潮汐耗散和气候强迫的理解。利用天文计算对沉积记录定年产生了天文时间标度（ATS），如今它代表了旋回地层学和天体年代学的主干，广泛应用于海洋地质学和地球物理学内外。年龄模式通常依赖于沉积记录中天文计算的偏心率周期和其他太阳系频率的印记（例如405、173和~100 kyr）。然而，使用倾角和岁差周期（目前41和~20 kyr）仍然具有挑战性，主要是由于过去地球动力椭圆性（引力形状）和潮汐耗散（地球自转速度减慢）的变化，这些变化会影响天文计算。该项目将通过将动力椭圆性和潮汐耗散整合到天体年代学中，针对具有高质量沉积记录的特定时间间隔，开发高保真沉积记录测年方法。利用选定的地质记录，该研究还将检验潮汐耗散在过去显著减少的假设。将提供数值工具供用户推导年龄模型，适用于各种已发表的天文学解（计算的行星轨道参数）。所有的约会工具都将作为开源的独立应用程序免费提供，作为天文编年软件包的附加组件，并在培训研讨会上向用户介绍。该项目有可能改变沉积物年代测定的准确性，以及我们对过去潮汐耗散和倾角强迫的理解。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。

One way to determine the ages of seafloor sediments and sedimentary rocks is by using a “calendar” based on astronomical calculations. This time scale makes use of the fact that predictable changes in the orbits of the planets drive cyclic changes in Earth’s climate. For example, observed cycles in sediment composition can be matched to astronomical cycles. Those cycles are calculated by computing planetary orbits backward in time. Unfortunately, the use of certain orbital cycles remains challenging because Earth’s gravitational shape and rotation rate have changed in the past. These changes introduce uncertainty into the orbital calculations. This project will develop high-fidelity dating methods for sedimentary records by including Earth’s gravitational shape and rotation rate into the orbital calculations. All numerical tools will be made available as open source programs and as add-ons to software packages. The project broader impacts include support for a graduate student, and a training workshop in astrochonology methods. The project has the potential to transform our ability to date sediments from the last 55 million years. It will also improve our understanding of tidal dissipation and climate forcing in the past.Dating of sedimentary records using astronomical calculations has led to the astronomical time scale (ATS), today representing the backbone of cyclostratigraphy and astrochronology, widely used within and beyond marine geology and geophysics. Age models often rely on the imprint of astronomically calculated cycles of eccentricity and other solar system frequencies in sedimentary records (e.g., 405, 173, and ~100 kyr). However, use of obliquity and precession cycles (at present 41 and ~20 kyr) remains challenging, mostly due to past changes in Earth's dynamical ellipticity (gravitational shape) and tidal dissipation (slowdown of Earth's rotation), which affect the astronomical calculations. This project will develop high-fidelity dating methods for sedimentary records by integrating dynamical ellipticity and tidal dissipation into astrochronology, targeting specific time intervals that feature high-quality sedimentary records. Using selected geologic records, the study will also test the hypothesis that tidal dissipation was significantly reduced in the past. Numerical tools will be provided for users to derive age models, applicable to various published astronomical solutions (calculated planetary orbital parameters). All dating tools will be made freely available as open source stand-alone applications, as add-ons to astrochronological software packages, and introduced to users during a training workshop. The project has the potential to transform the accuracy of sediment dating, as well as our understanding of tidal dissipation and obliquity forcing in the past.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.