Multiscale analysis of the geomorphological characters of a guyot on the Caroline Ridge in West Pacific

<p>Many seamounts in the deep sea have been found and surveyed in detail in recent decades of years. However, these seamounts are mostly described qualitatively or with little quantitative analysis, which counts against deep understanding of the dynamic processes of the seafloor. Here, a recently-surveyed guyot on the Caroline ridge in West Pacific is reported and its geomorphology is documented in detail based on the high-resolution Digital Elevation Models (DEMs). Multifractal Detrended Fluctuation Analysis (MFDFA) is firstly applied on the bathymetric data to investigate the multifractal features, and the cause of multifractality is also verified by analyzing shuffled and surrogate data. The shape of the multifractal spectrum is depicted by the width of the spectrum (<em>W</em>), the maximum singularity strength (<em>α<sub>0</sub></em>) and the degree of asymmetry (<em>B</em>). To examine distinctions between submarine seamounts and subaerial volcanic structures, the same method and statistical comparison have also been applied on DEMs of other seamounts adjoining the guyot, the SRTM 90m DEMs of 50 subaerial stratovolcanoes and the Mars MGS MOLA-MEX HRSC Blended 200m DEMs of 5 Martian volcanoes. In the guyot area, geomorphological units of the guyot can be recognized and classified into large-scale volcanic structures and small-scale erosive-depositional landforms. The result shows that the topography of the guyot has multifractal features and the multifractal strength (Δ<em>h</em>) differs spatially. Multifractality of the seafloor with the flat guyot top is mostly caused by the broad probability density function of the values of bathymetric data, while multifractality of the seafloor with highly-correlated small-scale landscapes (gullies and faults) by different long-range correlations of the small and large fluctuations. The guyot and other landforms with flat tops around are featured by higher maximum singularity strength (<em>α<sub>0</sub></em>). Areas with widely-distributed small-scale landforms and intense fluctuations in curvature values tend to have negative degrees of asymmetry (<em>B</em>). Moreover, two-sample unequal-variance t-test results show that Hurst exponents (<em>H</em>) and the multifractal strength (Δ<em>h</em>) of seamounts are generally lower than those of earth and Martian subaerial volcanoes, which implies that seamounts may have distinct fractal behaviors and multifractal features compared to their subaerial counterparts. The study presents a case of quantifying geomorphological characters and multiscale behaviors of seamounts in the deep-sea area, which could encourage more explorations for the morphologies and processes of the analogous structures in submarine, terrestrial or even planetary environments. Nevertheless, more detailed and comparative works are still needed to be done.</p>

Multi-fractal Behaviors of long term daily relative humidity and temperature observed over Benin synoptic stations (West Africa)

The multifractal structure of daily temperature and relative humidity is investigated in this study. Multifractal Detrended Fluctuation Analysis (MFDFA) method has been applied on data observed from 1967 to 2012 at the six synoptic stations of Benin (Cotonou, Bohicon, Parakou, Save, Natitingou and Kandi). We estimate the generalized Hurst exponent, the Renyi exponent, and the singularity spectrum from the data to quantify the multi-fractal behaviors. The results show that multi-fractality exists in both daily humidity and temperature record at Benin synoptic stations. It shows multi-fractality with the curves of h (q), τ (q) and D (q), depending on the values of q. The comparison of the multifractal properties shows that, at all the synoptic stations, the multifractal strength of the temperature is significantly different from the feature the humidity.For the temperature, among the six study sites, the multifractal strength at Natitingou is largest (∆α = 0.6917). This means that Natitingou is the city in which the multifractal property is strongly observed for temperature. At Parakou the multifractal strength is smallest (∆α = 0.5252), meaning that Parakou is the city in which the multifractal property is weakly observed. At all synoptic stations the multifractal strength are superior to 0.5 (Δα> 0.5) indicating the degree of multifractal in temperature time series.For the relative humidity, multifractal strength is smallest Kandi (∆α = 0.3031). This means that Kandi is the city in which the multifractal property is weakly observed. Furthermore, the multifractal strength of Parakou is largest (∆α = 0.7691) meaning that for the relative humidity, Parakou is the city in which the multifractal property is strongly observed. The geographic distribution of the multifractal strength reflects the role of climate dynamic processes on the multi-fractal behavior of humidity and the distinctiveness of physical processes in Benin.