A Robust Test of the Milankovitch Cycle Hypothesis Predictions for Influencing Abyssal Hill Morphology: A Pilot Study

海底的大片区域被称为深海丘陵的地貌所覆盖，深海丘陵是在火山中脊形成的高度线性的山脊，然后随着构造板块的分散而漂移。一种新的假说认为，深海丘陵的地形与海平面的变化密切相关，因此与地球轨道的米兰科维奇周期的变化密切相关。如果是真的，那么其影响可能是巨大的：绘制海底地形图可以用来研究地球历史，从而极大地丰富我们对与地球轨道变化相关的地球气候变化的理解。要研究的假设表明，全球海平面的上升和下降主要由地球轨道上的米兰科维奇尺度变化所控制，调节了大洋中脊火山喷发的强度，进而调节了海底深渊丘陵的形成。然而，深海丘陵和米兰科维奇周期之间的联系一直受到其他研究人员的争议。有两个基本的反对意见：(1)数十年的观测证据表明，深海丘陵主要是断层生成的构造，而不是火山构造；(2)米兰科维奇旋回假说预测，深海丘陵的宽度将随着扩张速度的增加而增加，而观察表明相反的情况是正确的。然而，海平面变化对大洋中脊火山活动的调制是一个看似合理的前景，而且确实令人兴奋，最近关于深海沉积物的研究为这一假说提供了独立的证据。核心问题是，如果在深海丘陵的地貌中存在海平面调节火山活动的地形信号，那么测量这种影响将需要将其与主要的断层生成成分脱钩。该项目将制定一种方法，用于测量深海丘陵地形的年龄相关成分，如果存在的话。中心假设是，断层生成的地形在地壳年龄方面是随机的，因此可以被视为叠加在任何依赖于年龄的(可能是火山的)信号上的相关随机噪声过程；这一假设与先前的研究一致，这些研究用受比例定律支配的随机分布来模拟断层的比例参数。所提出的方法将作为地壳年龄的函数来叠加或平均大量数据，以便随机分量(噪声)破坏性地减小，而非随机分量(信号)建设性地求和。对深山协方差结构的表征对于确定叠加信号的预期方差是必要的，从而严格检验不存在依赖于年龄的地形信号的零假设；如果叠加轮廓超过给定置信度的界限，则零假设可以被拒绝。该方法将应用于东太平洋海隆两侧的三个大区域，这些区域提供沿海脊侧翼可用的最全面的测深覆盖范围。

Vast regions of the ocean floor are covered by features called abyssal hills, highly linear ridges that are formed at the volcanic mid-ocean ridges, and then rafted away as the tectonic plates spread apart. A new hypothesis contends that the topography of abyssal hills is closely linked to changes in sea level, and therefore to changes in Milankovitch cycles of the orbit of the Earth. If true, then the implications are potentially enormous: mapping the topography of the seafloor could be used to investigate Earth history, and thereby greatly enrich our understanding of Earth's varying climate associated with the changes in the orbit of the Earth. The hypothesis to be investigated suggests that the rising and falling global sea level, controlled primarily by Milankovitch-scale variability in Earth's orbit, modulates the intensity of volcanic eruptions at mid-ocean ridges and, in turn, the formation of abyssal hills on the seafloor. However, a connection between abyssal hills and Milankovitch cycles has been disputed by other researchers. There are two fundamental objections: (1) decades of observational evidence have shown that abyssal hills are dominantly fault-generated structures, rather than volcanic constructs, and (2) the Milankovitch Cycle hypothesis predicts that the width of abyssal hills will increase with spreading rate, contrary to observations indicating the opposite is true. Nevertheless, modulation of mid-ocean ridge volcanism by changes in sea level is a plausible and, indeed, exciting prospect, and recent work on abyssal sediments provides independent evidence in support of the hypothesis. The central problem is that, if there is a topographic signal of sea level-modulated volcanism in the morphology of abyssal hills, measuring this effect will require decoupling it from the dominant fault-generated component. This project will develop a methodology for measuring, if it exists, an age-dependent component of abyssal hill topography. The central hypothesis is that fault-generated topography is random with respect to crustal age, and can thus be treated as a correlated random noise process superimposed on any age-dependent (possibly volcanic) signal; this hypothesis is consistent with prior studies that model fault scaling parameters with random distributions governed by scaling laws. The proposed methodology will stack, or average, large quantities of data as a function of crustal age so that the random component (noise) destructively reduces while non-random component (signal) constructively sums. Characterization of the abyssal hill covariance structure is necessary to determine the expected variance of the stacked signal, and thus to rigorously test the null hypothesis that no age-dependent topographic signal exists; the null hypothesis can be rejected if the stacked profile exceeds the bounds for a given confidence level. The methodology will be applied to three large regions along the flanks of the East Pacific Rise that provide the most comprehensive bathymetric coverage available along the ridge flanks.