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. 2021 Dec 22:3:e030.
doi: 10.14324/111.444/ucloe.000030. eCollection 2021.

Improved bathymetry leads to >4000 new seamount predictions in the global ocean - but beware of phantom seamounts!

Chris Yesson  1 , Tom B Letessier  1 , Alex Nimmo-Smith  2 , Phil Hosegood  2 , Andrew S Brierley  3 , Marie Hardouin  1   4 , Roland Proud  3
Affiliations

Improved bathymetry leads to >4000 new seamount predictions in the global ocean - but beware of phantom seamounts!

Chris Yesson et al. UCL Open Environ. .

Abstract

Seamounts are important marine habitats that are hotspots of species diversity. Relatively shallow peaks, increased productivity and offshore locations make seamounts vulnerable to human impact and difficult to protect. Present estimates of seamount numbers vary from anywhere between 10,000 to more than 60,000. Seamount locations can be estimated by extracting large, cone-like features from bathymetry grids (based on criteria of size and shape). These predicted seamounts are a useful reference for marine researchers and can help direct exploratory surveys. However, these predictions are dependent on the quality of the surveys underpinning the bathymetry. Historically, quality has been patchy, but is improving as mapping efforts step up towards the target of complete seabed coverage by 2030. This study presents an update of seamount predictions based on SRTM30 PLUS global bathymetry version 11 and examines a potential source of error in these predictions. This update was prompted by a seamount survey in the British Indian Ocean Territory in 2016, where locations of two putative seamounts were visited. These 'seamounts' were targeted based on previous predictions, but these features were not detected during echosounder surveys. An examination of UK hydrographic office navigational (Admiralty) charts for the area showed that the summits of these putative features had soundings reporting 'no bottom detected at this depth' where 'this depth' was similar to the seabed reported from the bathymetry grids: we suspect that these features likely resulted from an initial misreading of the charts. We show that 15 'phantom seamount' features, derived from a misinterpretation of no bottom sounding data, persist in current global bathymetry grids and updated seamount predictions. Overall, we predict 37,889 seamounts, an increase of 4437 from the previous predictions derived from an older global bathymetry grid (SRTM30 PLUS v6). This increase is due to greater detail in newer bathymetry grids as acoustic mapping of the seabed expands. The new seamount predictions are available at https://doi.pangaea.de/10.1594/PANGAEA.921688.

Keywords: bathymetry; environmental science; knolls; seamounts.

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Conflict of interest statement

All other authors declare no conflicts of interest in connection to this article. Research ethics statementThe authors conducted the research reported in this article in accordance with ZSL standards.Consent for publication statementThe authors declare that research participants’ informed consent to publication of findings – including photos, videos and any personal or identifiable information – was secured prior to publication.Conflicts of interest statementThe authors declare no conflict of interest with this work / The authors declare the following interests / The authors are a current Editor for this journal. All efforts to sufficiently blind the author during peer review of this article have been made. The authors declare no further conflicts with this article.The authors declare no conflict of interest with this work / The authors declare the following interests / The authors are a current Editor for this journal. All efforts to sufficiently blind the author during peer review of this article have been made. The authors declare no further conflicts with this article.

Figures

Figure 1
Figure 1
Location of survey conducted in 2016. Left shows depth contours based on the 2014 GEBCO bathymetry grid, right shows depth contours derived from SRTM30 PLUS v11. Both grids indicate the presence of a conical seamount (A) c.20 km NW of the Great Chagos Bank. No feature was detected by the 2016 survey. Around 40 km north of this, is another predicted seamount (B), again not detected on the 2016 survey. Feature B is predicted by the GEBCO grid but is not shown in the SRTM30 PLUS grid (although present in previous versions). Map projection UTM zone 43 south (epsg:32743).
Figure 2
Figure 2
Latitudinal transects across apparent positions of the two ‘phantom seamounts’. Black triangles are overlayed at the position and summit depth of the predicted seamounts. Colormap is volume backscattering strength (Sv). A deep scattering layer was observed at c.450 m for both sites. Seabed was observed at site A c.1500 m (red line). No seabed was detected for site B (i.e., seabed is deeper than the limit of the sensor).
Figure 3
Figure 3
Map of predicted seamounts. New Seamounts are those in the new dataset that are not found in the Yesson et al. [11] dataset. ‘Consistent predictions’ are new predictions that spatially overlap with the old predictions of Yesson et al. [11], while those seamounts present in Yesson et al. [11] but with no overlapping feature in the updated dataset are classed ‘no longer considered seamounts’. Robinson map projection (EPSG:54030). Lat/Long grid lines at 30° intervals.
Figure 4
Figure 4
Focus on seamounts of NW Indian Ocean. Most of the 15 predicted seamounts based on no bottom soundings are in the Indian Ocean. EEZ are exclusion economic zones (boundary of national jurisdiction – source https://www.marineregions.org/). Robinson map projection (EPSG:54030). Lat/long lines shown for reference.
Figure 5
Figure 5
Histograms showing distribution of seamounts by seamount height (top left), depth of seamount summit (top right), and geographic location of seamount (latitude – bottom left, longitude – bottom right). Numbers above the bars show the count of ‘phantom seamounts’ in the relevant grouping.
See this image and copyright information in PMC

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