What do the Loch Ness monster, the El Nino effect and dead water at sea have in common?

All may be associated with internal waves, a phenomenon of wave motion in which Dr David Henry of the School of Mathematical Sciences, University College Cork (UCC) has expertise.

As Dr Henry explains in an interview with Wavelengths for Afloat, internal water waves, which are responsible for the “dead water” phenomenon observed by sailors at sea, play a fundamental role in any meaningful description of large-scale dynamics of the ocean.

He says that an improved understanding of their behaviour is “essential to developing our understanding of ocean circulation and ocean-atmosphere dynamics, which are in turn fundamental processes underlying climate dynamics”.

Dr David Henry of the School of Mathematical Sciences, University College Cork

Internal waves have some particularly interesting, and quite unforeseen, impacts in both the real and “fictional” worlds, he says.

For instance, dolphins have been observed swimming ahead of a moving ship by “surfing” the internal waves that it generates, and it has also been suggested that internal wave-related activity might be one explanation for the Loch Ness monster in Scotland.

Henry recalls how internal waves may have influenced Australian submarine exposure to Turkish forces during the Gallipoli campaign of 1915 during the first world war.

Internal waves have been observed up to 50 metres high in the Celtic Sea, and in the Rockall Trough, the Malin Sea and Shelf, lying immediately north of Ireland, and to the east of the Rockall Trough, he says.

Internal waves have ”a major impact in biological considerations since they carry nutrients onto the continental shelf - 50% of shelf sea nutrients are estimated to arrive across the shelf-break boundary”, he adds.

They are also of interest to geological oceanographers because these waves produce sediment transport on ocean shelves, while breaking internal waves on sloping surfaces creates erosion.

The steady crash of waves pounding the shore draws vacationers to beaches across the world when temperatures climb. Driven by the wind and tides, these familiar waves ride across the top of the ocean. But deeper waves also move through ocean waters, visible only from their influence on ocean currents. These waves are internal waves, and they run through lowest layers of ocean water, never swelling the surface. Credit: Google Earth - March 6, 2007KML

And they are of relevance to coastal engineers because of the tidal and residual currents that they generate, which can cause scour on near shore as well as offshore structures.

“In spite of their clear importance, several important theoretical gaps remain in our understanding of the ocean dynamics induced by internal water waves, and wave-current interactions,” Dr Henry says.

To advance this knowledge, Science Foundation Ireland has awarded €916,000 for a research project led by Dr Henry, in collaboration with Professor Rossen Ivanov, School of Mathematics and Statistics, TU Dublin.

Dr Henry spoke about this to Wavelengths below