Shedding light on vast under-ocean waves

Little was known of the life cycle of internal waves that can reach as high as a 100-story building yet barely cause a ripple on the ocean's surface, said Harper Simmons, an oceanographer with the UAF School of Fisheries and Ocean Sciences. The five-year study resulted in a comprehensive look at the birth, life and death of internal waves.

"Think of them like your hand in a bathtub stirring the water," said Simmons, who participated in the study. "There is chaotic mixing at first, then orderly waves run across the bathtub, swell in the middle and then break. All that happens underneath the ocean's surface."

The study focused on waves under the South China Sea and was conducted by 42 researchers from 25 institutions in five countries. Simmons, with the help of the Arctic Region Supercomputer Center, which is part of the UAF Geophysical Institute, used math equations to make detailed numerical simulations, or high-resolution models, of under-ocean wave processes.

The study compared Simmons' and other scientists' models with field observations and laboratory experiments. The study's findings present the best look to date at these enormous waves, which contribute to climate change, marine sound transmission, and the transportation of marine nutrients, sediment and contaminants.

"One of the big achievements of the project was a demonstration of how models and field observations are able to work together for mutual benefit," Simmons said. Under-ocean wave process modeling wasn't very good a couple of decades ago, he said, but understanding and supercomputer technology has greatly improved. Field observations are expensive, logistically cumbersome and often only produce a thin snapshot of a natural process.

Modeling is a good tool for researchers to explore natural processes when field observations aren't possible. Using both together helps to better explain the science, he said.

Simmons' work in the study has taken years of running computations on ARSC supercomputers, which is the best way to develop computationally time-consuming, complicated models like those in the ocean study. He had to consider water temperatures, salinity, topography and other marine influences in his equations.

ARSC made the work much easier, Simmons said. "They're an excellent group, and they are local, and that made all the difference."

Under-ocean waves are started by tidal flow over the seafloor. The South China Sea is home to the world's largest known underwater waves: The study documented 1,000-foot waves. If they were on top of the water, these waves would be tsunamis, capable of terrible destruction.

The findings were presented in a May 6 Nature article. The Office of Naval Research and the Taiwan National Science Council funded the project.