“Empirical Prewhitening” Spectral Analysis Detects Periodic but Inconsistent Signals in Abyssal Hill Morphology at the Southern East Pacific Rise

Abstract

The 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 the impact of Milankovitch cycle-caused sea level fluctuations on the volcanic construction process at mid-ocean ridges. Periodicities are detected by the presence of spectral peaks that rise significantly above the random variations of sample power spectra associated with an aperiodic, continuous spectrum process, typically modeled as a band-limited fractal (von Kármán model). Here, I formulate and test a new algorithm to "empirically prewhiten" the sample power spectrum which, without needing to model the continuous spectrum, flattens it to a zero-mean process. This greatly simplifies definition of the null hypothesis, and additional modeling approximates standard deviation levels that provide a conservative basis for detecting peaks that may be indicative of periodicity. The algorithm is applied to extensive bathymetric data flanking the southern East Pacific Rise. Significant periodicities are detected on many profiles analyzed, but the periods vary widely, and do not cluster at Milankovitch periods. The most substantial harmonic signals detected exhibit periods ∼0.082-0.216 my, with root-mean square (RMS) heights approximately a quarter to a third of the RMS height for the aperiodic signal. It is hypothesized that the dominant aperiodic component of abyssal hills corresponds to morphology constructed by faults that follow a random distribution governed by scaling laws, whereas longer-scale periodic signals are associated with crustal thickness variations controlled internally by variations in melt supply. GOFF

Persistent Magma‐Rich Waves Beneath Mid‐Ocean Ridges Explain Long Periodicity on Ocean Floor Fabric

“…If the observed long period fluctuations in ocean bathymetry (Goff, 2020;Shinevar et al, 2019) are indeed attributable to melt-rich porosity waves, this agrees with the larger mantle permeability that has been suggested (Katz et al, 2022). For sufficiently large mantle permeabilities, the models presented here suggest that porosity waves produce time-varying crustal thicknesses regardless of spreading rates (Figure 4); previous modeling studies show porosity waves persistent only at intermediate and slower spreading rates (Parnell-Turner et al, 2020;Sim et al, 2020).…”

“…Significant spectral energy close to 100 kyr was observed at the fast spreading East Pacific Rise (EPR) from an analysis of the crustal thickness variation, which is a direct measurement of the mantle melt source (Boulahanis et al., 2020). Furthermore, long period oscillations of more than 100 kyr are prominent in the ocean bathymetry (Goff, 2020; Parnell‐Turner et al., 2020; Shinevar et al., 2019) and are hypothesized to be due to mantle heterogeneities and/or melt rich porosity waves (Shinevar et al., 2019).…”

Influence of late Pleistocene sea-level variations on midocean ridge spacing in faulting simulations and a global analysis of bathymetry

“…Each of these null models implies an operation for whitening the spectral estimate or making the distribution of spectral energy approximately level across frequencies, either by dividing the spectral estimate by the null model in the frequency domain or by performing an equivalent operation in the time domain. Whitening or leveling spectral estimates also improves the power of statistical tests for identifying spectral peaks ( 30 ) and was used in foregoing statistical analyses of near-ridge bathymetry ( 12 , 34 , 52 ).…”

Tides and Volcanoes: A Historical Perspective

“…For instance, the glacio-eustatism hypothesis links the observed Milankovitch periodicities in volcanic activity to crustal stress changes associated with ice age mass redistribution and sea level changes (Rampino and Self, 1993;Ryan et al, 2004;Watt et al, 2013;Praetorius et al, 2016;Rawson et al, 2016). This hypothesis seems to be corroborated by evidence for a subaerial volcanism increase during the last deglaciation phase (Huybers and Langmuir, 2009;Jull and Mc Kenzie, 1996) and during the Messinian salinity crisis in the Mediterranean area (Sternai et al, 2017) whilst the impact of Milankovitch cycle-caused sea level fluctuations on the volcanic construction process at mid-ocean ridges remains an area of active research (e.g., Olive et al, 2015;Goff, 2020).…”