Internal tidal beams and sediment hiatuses on guyots

What is it about?

The tide formed by the pull of the Moon and Sun on the surface of the ocean produces an oscillation within the ocean when it passes over shallow banks. This oscillation occurs on the density difference between warm surface waters and cold deep waters. Where the shallow banks have straight edges, the oscillations propagate in giant beams, which are known to travel for >1000 km in places. We have shown that these beams (in computer models) match the pattern of erosion found in seismic reflection records (which show sedimentary beds truncated at the seabed) and samples from scientific drilling (which reveal old sediments at the seabed). The patterns of erosion and deposition revealed at the drilling sites shows us that the pattern of these internal wave beams was different in the past, however. We speculated that this may have been caused by rotations or vertical movements of the shallow banks (tectonics movements).

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Photo by Elliot Cullen on Unsplash

Photo by Elliot Cullen on Unsplash

Why is it important?

Erosion or deposition of pelagic sediments on the summits of guyots and seamounts in the Pacific Ocean is correlated with the presence or absence of internal tidal waves predicted by numerical models. This also has potential implications for paleoceanography, which hitherto has been mainly concerned only with long-period motions or slow-changes to ocean currents. Hiatuses within the pelagic caps of seamounts then suggest to us that the internal wave pattern was different in the past, speculatively suggested to be caused by plate-tectonic changes mainly.