CORVALLIS, Ore. – A large, diverse team of researchers will invade the California coast near San Luis Obispo in early September to launch an intense study of the Pacific Ocean’s inner shelf – a little-studied region between the surf zone and the mid-Continental Shelf.
As many as 100 scientists from 13 institutions and agencies will use a wide array of tools to monitor this stretch of ocean that runs roughly from shoulder-deep water out to 50 meters deep. Their goal is to understand the complex currents, how water moves between the shore and deeper ocean, the origin of rapid changes in temperature, and how ocean energy is dissipated near the shore. These processes, in turn, can drive sediment transport and primary biological production.
“We’re going to give this inner shelf region a complete physical,” said Jack Barth, an Oregon State University oceanographer and a principal investigator on the project.
The study, one of the largest of its kind, is funded by an $11 million grant from the Office of Naval Research. The researchers will use satellites, airplane surveillance, camera-equipped drones, ground-based radar, five ships, anchored moorings and seafloor-based platforms with instrument arrays, oceanic profilers, and even floating “drifters” to record physical data in the ocean along the inner shelf.
The stretch of Pacific Ocean just south of San Luis Obispo was chosen because it has both a simple, straight stretch of coastline and prominent points jutting out into the ocean, which adds complexity to the currents and mixing, the researchers say. Surprisingly, this inner shelf area has not been studied comprehensively because parts of it are too shallow for larger ships, yet it extends beyond where surf zone researchers typically work.
This massive study was conceived five years ago and has been in the planning and development stages for two years, allowing scientists and technicians to develop and perfect the instrumentation they will deploy in September and early October. It is reminiscent of two other major efforts in the United States – the Coastal Ocean Dynamics Experiment, or CODE, along the northern California coast in 1981-82, and a comprehensive study of the surf zone in Duck, North Carolina, in the 1980s and 1990s.
“The observational data that will emerge from this concentrated study will challenge and inform oceanic models for decades,” Barth said. “We are still using data from the CODE project 35 years ago.”
Jim Lerczak, an Oregon State scientist specializing in the physics of the ocean and atmosphere, said one reason the U.S. Navy is interested in the study is to improve its ability in assessing currents, navigation, and optics in regions without actually going there. The researchers will use satellites, ground-based radar and airplanes to analyze the waters from above, Lerczak said, and compare those observations with actual measurements taken in the ocean.
“This is a very complex region that not only is influenced by wind, currents and tides, but also by large ‘internal’ waves that propagate along the Continental Shelf because of the tides and stratified water,” Lerczak said. “These waves bring cold water up into the surf zone and back, usually twice a day. They not only have a significant physical impact, but a biological one as well because they bring to shore cold, upwelled water that is nutrient-rich.”
James Moum, an Oregon State University oceanographer, received a separate grant from the Office of Naval Research to develop a series of turbulence sensors (or “mixing meters”) designed to measure where energy from currents and waves goes in the inner shelf region. In one of the largest efforts of its kind, Moum and his colleagues will deploy dozens of these sensors on the seafloor, on moorings and on instrument platforms towed behind research vessels to better understand how the Pacific Ocean “works.”
“We’re basically studying fluid mechanics on a huge scale,” Moum said. “We’ll be taking a host of measurements from scales of hundreds of meters – instabilities created by currents and winds – down to scales of millimeters and centimeters, where mixing actually takes place. We’ve only recently learned that there is a daytime peak for turbulence, but we’re not sure why. We’re just beginning to discover things.”
The findings from the study will inform not only scientists, but recreational boaters, fishermen, beach-goers and the U.S. Navy.
“The water between the surf zone and the mid-shelf is where rip currents take place, and where crabbers and fishermen and other boaters spend a lot of time,” Barth said. “It is also critical from an ecological standpoint, where larval organisms propagate offshore, and then return to the surf zone. It is where plankton bloom and fuel the marine food web.
“Yet we know little about the physics of how this inner shelf works.”
Other institutions and agencies involved in the study include Naval Postgraduate School, Scripps Institution of Oceanography, University of Washington, Georgia Tech University, Naval Research Laboratory/Stennis Space Center, University of Miami, Spoondrift, University of California Los Angeles, Delft University of Technology, Florida State University, University of Michigan and University of Southern Mississippi.
Barth, Lerczak and Moum are in OSU’s College of Earth, Ocean, and Atmospheric Sciences.