An international ocean study including oceanographers from Scripps Institution of Oceanography, UC San Diego, to track the massive internal tides of the Tasman Sea begins from Hobart, Tasmania begins this week.
The 10-week project, the Tasman Tidal Dissipation Experiment (T-TIDE), involves two U.S. research vessels, Scripps’s R/V Roger Revelle and Schmidt Ocean Institute’s R/V Falkor, and will include scientists from the U.S., Canada, and Australia. It will ultimately lead to major improvements in global climate models and an understanding of biological production concentrating nutrients for fisheries. Primary funding for the project comes from the National Science Foundation (NSF).
Scientists will deploy autonomous deep-diving gliders, install 15 deep-sea moorings and employ a number of shipboard instrument systems to search for highly-turbulent events at depths up to two miles that are predicted to occur as the incoming tide collides with the Tasmanian continental slope.
These internal tides form when the surface tides visible on coastlines push water back and forth across undersea mountains. The forces created by that movement spawn underwater waves that can travel great distances in the interior of the sea. These waves reflect off the sea surface and the seafloor and can be found at any depth. Far below the surface, waves can be hundreds of meters high, with wavelengths of up to 240 kilometers (150 miles). The T-TIDE scientists hope to find out what happens when these waves hit land.
According to physical oceanographer Harper Simmons of the University of Alaska, the east coast of Tasmania is considered a natural laboratory for the study and potentially a global hotspot for deep tidal mixing. Tasmania is a special place, in that it stands in the path of a powerful, focused beam of internal tidal waves generated on the Macquarie Ridge, south of New Zealand. Computer models predict and satellite observations confirm that these waves slam into the East Coast of Tasmania after a four-day, 1400-kilometer (870-mile) transit of the Tasman Sea. What happens next isn’t so clear, since the wave-breaking and turbulence that results from this impact will happen far below the often stormy sea surface.
“The goal of scientists is to discover and measure the procession of those internal tidal waves and to document the various phenomena that occur when they impact the deep continental slopes,” said Scripps oceanographer Matthew Alford, leader of Legs I and III of the T-TIDE cruise on R/V Revelle. “It is conjectured that the turbulent mixing that occurs in the deep sea off Tasmania and other ‘special’ sites is sufficient to affect the overall circulation of the global ocean. Understanding these processes is thus a critical step in predicting our climate.”
R/V Revelle and R/V Falkor, operated by the Schmidt Ocean Institute, are the two ships participating in the program. Revelle will install a series of deep-ocean moorings on the eastern continental slope of Tasmania. These moorings will be complemented by shipboard observations of the deep breaking waves and turbulence, and robotic glider measurements of mid-ocean structure, deployed by Shaun Johnston and Dan Rudnick from Scripps’ Instrument Development Group.
Amy Waterhouse of Scripps and Sam Kelly of the University of Minnesota - Duluth will lead the Falkor team in an offshore effort, termed T-Beam, to map the incoming tidal beam, a task made difficult given the region's renowned eddies, which are almost permanent features of the Tasman Sea, southeast of Australia. Eddies are circular currents that spin off from larger currents. They can change the path of the tidal beam and modulate its strength.
The team of scientists aboard Revelle will work closer to Tasmania, studying the internal tide as it actually breaks 2-3 kilometers (1-2 miles) down on the Tasmanian continental slope. The Revelle team will also be deploying a central Tasman Sea mooring to support Falkor’s studies of the tide offshore. R/V Revelle will also install a series of continental shelf moorings to determine the nearshore consequences of the internal tide and resulting deep turbulence. This effort, termed T-Shelf, is led by Nicole Jones of the University of Western Australia and Drew Lucas of Scripps.
The moorings are anchored cables equipped with dozens of temperature sensors and multiple current and CTD profilers that will provide vital, longer-term data on the internal tides. Additional collaborations will include the Falkor team coming into the shelf for several days of coordinated research with R/V Revelle collecting supplementary data to ensure the highest resolution maps of the wave’s dissipation there.
Besides the NSF, the Schmidt Ocean Institute, the Australian Research Council, the University of Tasmania and the University of Western Australia also provide funding for the study.
Related Image Gallery: T-TIDE
Related Video: The T-TIDE YouTube Channel