Global Distribution and Morphology of Small Seamounts

Abstract

Seamounts are isolated elevations in the seafloor with circular or elliptical plans, comparatively steep slopes, and relatively small summit areas (Menard, 1964). The vertical gravity gradient (VGG), which is the curvature of the ocean surface topography derived from satellite altimeter measurements, has been used to map the global distribution of seamounts (Kim and Wessel, 2011). We used the latest grid of VGG to update and refine the global seamount catalog; we identified 10,796 new seamounts, expanding the catalog by 1/3. 739 well-surveyed seamounts, having heights ranging from 421 m to 2500 m, were then used to estimate the typical radiallysymmetric seamount morphology. First, an Empirical Orthogonal Function (EOF) analysis was used to demonstrate that these small seamounts have a basal radius that is linearly related to ix their height -their shapes are scale invariant. Two methods were then used to compute this characteristic base to height ratio: an average Gaussian fit to the stack of all profiles and an individual Gaussian fit for each seamount in the sample. The first method combined the radial normalized height data from all 739 seamounts to form median and median-absolute deviation. These data were fitted by a 3-parameter Gaussian model that explained 99.82 percent of the variance. The second method used the Gaussian function to individually model each seamount in the sample and further establish the Gaussian model. Using this characteristic Gaussian shape, we show that VGG can be used to estimate the height of small seamounts to an accuracy of about 270 m.x

Global Distribution and Morphology of Small Seamounts

“…The Google Earth overlays and the characteristics of the seamounts, can be found on the ZENODO repository, https://doi.org/10.5281/zenodo.7718512 (Gevorgian et al., 2023). The VGG grids are available in the global_grav_1min folder and the SRTM15+ bathymetry are in the srtm15_plus folder (https://topex.ucsd.edu/pub/).…”

Improved Bathymetric Prediction using Geological Information: SYNBATH

“…After comparing the old and new VGG, it was found that the signal-to-noise ratio has increased by at least a factor of 2, indicating that multiple altimetry sources can improve gravity data and help find unmapped features on the ocean floor. Gevorgian et al (2021) have used the latest version of the VGG model (Sandwell et al, 2021) to update the global seamount catalog of Wessel (2011, 2015). The original KW catalog had 24,643 seamount identifications.…”

“…The second type of unresolved seafloor feature are seamounts less than about 2.5 km tall (Kim & Wessel, 2011, 2015Menard, 1964;Staudigel et al, 2010). Because of significant improvements in the accuracy and resolution of the satellite gravity since the Kim and Wessel (2011) study, it is now possible to detect seamounts taller than about 800 m (Gevorgian et al, 2021) and their location can be determined to an accuracy of better than 1 km. However, the width of the gravity bump is much greater than the actual width of the seamount.…”

“…As in the case of abyssal hills, the magnitude of the slope of the seamount influences the paths of currents as well as the generation of eddies and internal waves. The studies by Smith (1988) and Gevorgian et al (2021) have used depth soundings to characterize the shapes of smaller seamounts. In this study, we use the amplitude of the vertical gravity gradient (VGG) to estimate the mass of the seamount and then use their characteristic shape to replace the smooth predicted seamount with a Gaussian seamount having a more realistic shape.…”

Improved Bathymetric Prediction using Geological Information: SYNBATH

“…To further test the validity of this simple model for a small seamount, we analyzed topography and VGG for three seamounts in an area of the southern East Pacific Rise where there is complete multibeam coverage (Figure 3). Two of the seamounts are from the Kim and Wessel (2011) compilation while the third is recently identified in the VGG (Gevorgian et al, 2021). The basic characteristics of the seamounts are provided in Table 1.…”