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”。这种时间尺度利用了行星轨道的可预测变化驱动地球气候周期性变化的事实。例如，所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行星轨道的时间倒退计算出来的。不幸的是，使用某些轨道周期仍然具有挑战性，因为地球的引力形状和旋转速率在过去已经发生了变化。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的重力形状和旋转速率纳入轨道计算，为沉积记录开发高保真测年方法。所有数值工具都将作为开放源码程序和软件包的附件提供。该项目更广泛的影响包括为一名研究生提供支助，以及举办一个天体年代学方法培训讲习班。该项目有可能改变我们对过去5500万年沉积物的测年能力。它也将提高我们对潮汐消散和过去气候强迫的理解。使用天文计算对沉积记录定年产生了天文时标（ATS），今天代表了旋回地层学和天体年代学的支柱，广泛应用于海洋地质学和地球物理学。年龄模型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~100千卢比）。然而，使用岁差和岁差周期（目前为41和~20 kyr）仍然具有挑战性，主要是由于过去地球动力学椭圆率（引力形状）和潮汐耗散（地球自转减速）的变化，这影响了天文计算。该项目将通过将动力椭圆率和潮汐消散纳入天体年代学，针对具有高质量沉积记录的特定时间间隔，开发沉积记录的高保真测年方法。利用选定的地质记录，这项研究还将检验潮汐消散在过去显著减少的假设。将向用户提供数字工具，以推导适用于各种已公布的天文学解的年龄模型（计算出的行星轨道参数）。所有测年工具都将作为开放源码的独立应用程序免费提供，作为天体年代学软件包的附件，并在培训讲习班期间向用户介绍。该项目有可能改变沉积物测年的准确性，以及我们对潮汐消散和潮汐强迫的理解。该奖项反映了NSF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.