Ocean’s huge internal waves measured to improve climate models

By on January 23, 2015

The global climate is a mysterious thing. Scientists the world over are working to model it the best they can, but some variables are missing in models simply because no one has set out to measure them.

For others, like internal waves of the ocean, the incredible difficulty of studying them is quite a deterrent. Said to reach hundreds of feet in height and span thousands of miles, the deep, buried waves of the ocean are the subject of an international investigation taking place in the Tasman Sea, just off the coast of Australia.

Scientists from the U.S., Australia and Canada are teaming up in two research vessels equipped with a slew of monitoring tech that will track waves originating off undersea mountains in the area that flow all the way to New Zealand. Their work will yield new data on ocean mixing important to improving existing understanding of the world’s climate.

“The Tasman Sea appears to be a magic spot, or an ideal lab, for studying accelerated ocean mixing and deep ocean turbulence,” said Rob Pinkel, professor of oceanography at Scripps Institution of Oceanography and a principal investigator on the project.

This is likely due to the Macquarie Ridge that sits under the sea, says Pinkel. When the tides flow back and forth across that chain, it creates large internal tides. The ridge’s shape creates a beam of waves headed from New Zealand to Tasmania.

“My hypothesis is that some waves will reflect and break, while others will create turbulent events like a mile down in the sea,” said Pinkel.

Researchers loaded the RV Revelle with instruments to study deep sea waves. (Credit: Jennifer MacKinnon)

How the Earth reacts to that ocean mixing is an important part of the climate puzzle, says Pinkel. Assumptions that climate changes only very slowly over time have mostly been disproven, and its necessary to look at climate in the short term.

“Somehow the thermal mass of the ocean has been taken out of the quick-change climate equation,” said Pinkel. “We think mixing plays a central role.”

To test his hypothesis, and those of the 14 other principal investigators on the massive project, it will take a number of data collection techniques. Before employing research vessels in the Tasman Sea, scientists first deployed underwater gliders to get a clearer idea of the mass temperature and density of seawater in the spot. Those drifted back and forth in the water for about three weeks.

With the preliminary data in hand, scientists are now turning to the R/Vs Roger Revelle and Falkor to achieve some of the big data grabs they’re after.

“The Revelle will place moorings and then move into sampling mode. The Falkor will be midway between New Zealand and Tasmania,” said Pinkel. “So the Falkor is sort of in the middle of the bowling alley and Revelle sees what happens when it (waves) gets there.”

The moored instruments will help researchers study the topography of the underwater Tasman slope and then dissect how the upper points of the ocean are connected to the bottom, which has proven a problem area for climate system models.

“Climate models are going to work better and give more accurate predictions with this work,” said Pinkel. “We’re only finagling with one part, but we expect major improvements in accuracy once we’re done.”

The project has only recently begun, but once it’s completed, findings will be shared with the National Science Foundation, a sponsor of the U.S. participants. Support is also provided by the Schmidt Ocean Institute, Australian Research Council, University of Tasmania and University of Western Australia. Data will also be shared with the Australian government for allowing the research to take place in the country’s waters.

“It’ll take quite a while to get them (data) edited to where we know they’re trustworthy and good to work with,” said Pinkel. “But we’re going to make sure the info gets transferred to modeling people while it’s hot.”

Top image: Deploying deep sea instruments to measure internal waves. (Credit: Matthew Alford)

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