Investigating Periodicities in Abyssal Hill Morphology of the Atlantic Ocean: Possible Evidence of Mantle Dynamics

虽然被海洋覆盖，深海丘陵是地球上最常见的地貌。 它们形成于世界大洋中脊扩张中心，是板块扩张过程的重要记录。过去对深海丘陵的研究将其视为纯粹的随机过程。这类过程的统计参数，如均值、方差、特征尺度等，与板块扩张条件有关，如扩张速率、岩浆供应和地壳厚度。通过这种方式，跨越海洋的深海丘陵可以用来探测空间和时间的板块动力学。然而，最近的一些研究报告，检测周期性信号嵌入在其他随机深海丘陵剖面。这种信号可能是以前未被认识到的对洋中脊岩浆过程的影响的证据，例如气候驱动的海平面变化，或岩浆输送的深层调制。本研究将使用由主要PI开发的新的稳健算法。它检测和量化（振幅，波长）嵌入在随机场的周期性信号。该算法将应用于北大西洋和南大西洋的测深数据。在那里，数十年的调查和过境提供了丰富的数据进行分析。周期值将首先与过去的扩展参数相关，以建立基本关系。然后将研究周期值的区域变化。这将允许调查可能的深层控制周期性信号的形成。研究结果将为今后建立大洋中脊模型提供关键的制约因素。此外，该守则将以方便用户的界面向公众提供。这将使各个领域的非专家研究人员和学生能够使用该算法。在最近的出版物中，深海丘陵形态是否存在周期性一直存在激烈的争论，有些人假设这种周期性是外部强迫的证据，例如米兰科维奇旋回引起的海平面波动对洋中脊火山建设过程的影响，或内部强迫，例如地幔上涌的调制。本计画将使用一种新开发的经验性预白化演算法，来侦测与量化嵌入于随机场中的周期性讯号。它将应用于北大西洋和南大西洋丰富的档案跟踪测深数据，这些数据对缓慢扩展的海洋生物形成的大面积和不同区域的深海丘陵进行取样。这将使测试的第一个假设：即时间周期性存在于缓慢蔓延的MOR生成的深海丘陵。初步的分析提供了初步的支持，但自信地这样做需要的不仅仅是一些轶事般的例子。 海底组构中周期性的存在对于理解和模拟莫尔动力学具有重要意义。如果深海丘陵形态确实存在周期性，那么它们对莫尔扩展的哪些因素有反应？这个问题使我们产生了第二个假设：时间周期性的变化与莫尔形成时的扩张性质和地幔条件有关。它可以通过将周期性参数与古扩张速率相关联来直接测试，也可以通过将周期性参数与非周期性统计参数（例如RMS高度和特征尺度）相比较来间接测试，这些参数本身与上述各种莫尔参数相关联。本项目还将调查所测得的周期性是否存在区域模式，这可能表明对地幔不均匀性的反应。例如，最近的建模表明，地壳厚度衍生的海底周期性的周期和振幅将取决于地幔渗透率，这是一个约束条件较差的参数，对地幔中的熔体输运建模至关重要。通过在Python编码环境中对原始代码进行现代化操作，该技术将可供更广泛的受众使用，并有可能用于解释各种地球科学和其他时间序列（例如，气候和天气，海洋等）。该团队将通过社交媒体推广该代码，并编写材料培训感兴趣的用户。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。

Non-Technical DescriptionThough covered by the oceans, abyssal hills are the most common landform on earth. They form at the world’s mid-ocean ridge spreading centers and are important records of the plate spreading process. Past studies of abyssal hills have treated them as purely random processes. The statistical parameters of such processes, such as mean, variance, characteristic scale, etc., can be correlated to plate spreading conditions, such as spreading rate, magma supply and crustal thickness. In this way, abyssal hills across the oceans can be used to probe plate dynamics through space and time. Recently, however, some studies have reported the detection of periodic signals embedded within otherwise random abyssal hill profiles. Such a signal could be evidence of previously-unrecognized influence on mid-ocean ridge magma processes, such as climate-driven changes in sea level, or deep-seated modulations of magma delivery. This study will use a new, robust algorithm developed by the lead PI. It detects and quantifies (amplitude, wavelength) periodic signals embedded within a random field. The algorithm will be applied to bathymetric data in the North and South Atlantic Oceans. There, decades-worth of surveys and transits provide abundant data for analysis. Periodic values will first be correlated to past spreading parameters to establish basic relationships. Regional variations in periodic values will then be investigated. This will permit investigating possible deep-earth controls on the formation of periodic signals. The result should establish key constraints in the future modeling of mid-ocean ridges. In addition, the code will be made available to the general public with a user-friendly interface. This will enable non-expert researchers and students in a variety of fields to make use of the algorithm. Technical DescriptionThe existence, or not, of periodicities in abyssal hill morphology has been vigorously debated in recent publications, and some have hypothesized that such periodicities are evidence of external forcing, such as by the impact of Milankovitch cycle-caused sea level fluctuations on the volcanic construction process at mid-ocean ridges (MORs), or internally forced, such as by modulations of mantle upwelling. This project will employ a newly-developed empirically pre-whitening algorithm for detecting and quantifying periodic signals that are embedded in a random field. It will be applied to the abundant archival trackline bathymetry data in the North and South Atlantic Oceans, which samples large and diverse regions of abyssal hills formed at slow-spreading MORs. This will enable testing of a first hypothesis: that temporal periodicities are present in slow-spreading MOR-generated abyssal hills. Preliminary analysis provides initial support, but confidently doing so requires much more than a few anecdotal examples. The existence of periodicities in the seafloor fabric could have significant implications for understanding and modeling MOR dynamics. If periodicities in abyssal hill morphology do exist, what factors of MOR spreading are they responsive to? This question leads us to a second hypothesis: that variations in temporal periodicities exist that are related to spreading properties and mantle conditions at the MOR at the time of formation. It can be tested directly by correlating periodic parameters to paleo-spreading rates, and indirectly by comparing periodic parameters to aperiodic statistical parameters, such as RMS height and characteristic scale, which are themselves correlated with various MOR parameters as noted above. This project will also investigate whether or not there are regional patterns to the periodicities measured, which could be indicative of responsiveness to mantle heterogeneities. For example, recent modeling indicates that periods and amplitudes of crustal thickness-derived seafloor periodicities will be dependent on mantle permeability, a poorly-constrained parameter that is critical for modeling melt transport in the mantle. By modernizing the original code for operation in a Python coding environment, the technique will be accessible to a wider audience, and has the potential to be used in interpreting a wide variety of Earth science and other time series (e.g., climate and weather, oceanographic, etc…). The team will promote the code through social media and develop materials to train interested users. Support of an early career scientist and building capacity in computational geoscience is a further broader impact.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.