Cruise Targets Internal Waves in Indian Ocean


A research expedition made up of students, engineers, and other researchers who documented the first detailed measurements of a key oceanographic phenomenon might not have happened without an innovative University of California funding program to support ship-based research.

The UC Ship Funds, which emphasizes student teaching aboard research expeditions, along with the National Science Foundation, supported studies on Scripps Institution of Oceanography at UC San Diego's research vessel Roger Revelle in the Indian Ocean late last year and early this year.

Scripps physical oceanographers Jennifer MacKinnon, Robert Pinkel and Shaun Johnston led the expedition, which was focused on the search for giant undersea waves. Like surface waves we see on the beach, so-called internal ocean waves also crest and break, albeit under the sea surface. Some can reach the size of 10-story buildings.

During the cruise, the researchers focused on an area of the Indian Ocean known as the Southwest Indian Ridge, one of the areas on the planet where tectonic plates are spreading apart. In addition to addressing a dearth of data about internal waves in this region, the researchers surmised that the Southwest Indian Ridge's jagged topography might result in an array of interesting internal wave phenomena.

They were correct. With instruments that measured water velocity, the researchers believe they captured the first close look at internal waves and internal mixing inside a 6-kilometer (3.7-mile) deep area called the Atlantis II Fracture Zone. Their data include information on how cooler, bottom waters intricately mix with warmer waters as they flow between the Southern and Indian Oceans.

"Higher up in the water column, we observed a series of internal tidal beams crisscrossing the water column, bouncing between ridge tops and the surface", said MacKinnon.

With the newly obtained data, Pinkel and graduate students Oliver Sun and San Nguyen will be studying the pathways of wave energy emitted from the tidal beams.

Results from the cruise could play a role in ongoing research on how currents flow around the planet and especially through the under-sampled Indian Ocean region. The data also may help scientists better understand the earth's climate system by adding details to climate models of how heat and dissolved greenhouse gases are mixed into the deep ocean.

"What we've learned from this cruise and others before it is that ocean mixing is enormously different from place to place and time to time", said MacKinnon. "The more places we look, the more we see different sorts of things causing mixing and the more inhomogeneous it all seems."

The cruise data also has biological relevance. Graduate student Drew Lucas, who is approaching the conclusion of his graduate studies, will be using the information to study fluorescence in the upper water column.

"The research opportunity on the R/V Revelle in the Indian Ocean with Dr. Jen Mackinnon served to increase the tool set that I will be able to bring to bear as a Scripps graduate and to further my oceanographic experience in an oceanic setting that is distinct from the nearshore environment that is the focus of my graduate studies", said Lucas. "In addition to excellent dissertation research, it is the well-rounded nature of Scripps students that maintains the Scripps reputation for excellence in education. There are only a handful of oceanographic institutions globally that are capable providing students with the exposure to research across multiple disciplines and across all scales and environments."

For Bruce Appelgate, associate director for Ship Operations and Marine Technical Support, the cruise was the latest example of how critical funding sources such as UC Ship Funds can deliver unique opportunities for research and teaching. Since 1995 UC Ship Funds have supported an average of 57 days at sea per year on cruises as short as single-day trips off San Diego to as long as 21-day expeditions from foreign ports.

"Oceanographic research vessels are enormously expensive to operate, and the competition among researchers for external funding is fierce. Scripps has historically recognized the importance of enabling our researchers and students access to the sea", said Appelgate. "Our UC Ship Funds allow us to continue this tradition by supporting teaching and research at sea aboard Scripps vessels. Access to institutional funding, at levels able to support significant periods of sea time, is an important way that Scripps fosters educational and research excellence."

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