Navigating new waters

The U.S. National Science Foundation (NSF) Ocean Observatories Initiative (OOI) recently completed the successful relocation of the Pioneer Array to the Mid-Atlantic Bight (MAB).

A map shows the area where the array moorings are collecting data. (Photo by Darlene Trew Crist, Map Courtesy of OOI, © Woods Hole Oceanographic Institution)

“If you wanted to go to one of the most complex coastal regions on the east coast of the United States, this would be it,” says Al Plueddemann, a senior scientist with WHOI and Principal Investigator for the Coastal and Global Scale Nodes (CGSN) of OOI, pointing to the southern MAB. This offshore area near Nags Head, North Carolina, has a lot of activity happening in the atmosphere and the ocean simultaneously, according to Plueddemann.

The array area is a box approximately 60 kilometers (37 miles) on a side, centered about 55 kilometers (34 miles) offshore. In April, scientists and engineers redeployed the OOI Coastal Pioneer Array ocean observing system there, including all the array’s existing instruments and several new ones. The array previously operated from 2016–2022 on the New England Continental Shelf, about 139 kilometers (86 miles) south of Martha’s Vineyard, Massachusetts.

Successfully repositioning the array required meeting various engineering challenges. “We had a different ocean environment, different currents, different water depths, different storm levels,” says Derek Buffitt, OOI Program Manager for CGSN, which is operated from WHOI, and  is responsible for the Coastal Pioneer Array. The moorings needed to be designed to operate in continental shelf currents that are intermittently strong and slack, and that come from different directions. The array elements, particularly those further offshore, must also resist the strong, deeply penetrating currents of the Gulf Stream.

Among the first things engineers did was take the existing moorings, model them in the new environment, and re-engineer the risers—the mooring components between a buoy and the seabed—to operate successfully in shallower water, at depths of 25–300 meters (82–984 feet). The OOI operational team, led by WHOI senior project manager Kris Newhall, then built and deployed the test moorings at the MAB to verify the updated designs.

“We need to invest in ocean measurements at the same level we do for weather prediction in the atmosphere.”
—Al Plueddemann, Principal Investigator, OOI

In addition, WHOI principal engineer Don Peters developed a shallow water mooring to allow for profiling measurements within a few meters of the ocean surface. The new mooring included the development of a buoyant stretch hose as part of the riser system. The stretch hose is designed to float above the seabed, even when stretching and contracting.

The instrument team, led by WHOI senior engineer Sheri White, had to ensure the continuity of existing measurements at the new site—conductivity, temperature, and pressure; dissolved oxygen; nitrate concentration; spectral irradiance; surface meteorology and wave properties; partial pressure of CO₂ and seawater pH—while also incorporating new instrument capabilities to measure particulates, turbidity, seafloor pressure and phytoplankton imagery.

The vehicle team, led by WHOI senior engineer Peter Brickley, ensured that the gliders and autonomous underwater vehicles (AUVs) could operate capably in the shallower ocean environment, where sediment and varying seawater densities could impact vehicle functionality. Currents are a challenge for the gliders as well as the moorings. Strong currents that penetrate deeply and flow in an adverse direction could sweep the vehicles away from their desired path.

Plueddemann says that redeploying the array “was a significant challenge,” and that there was a rigorous multi-step design and testing process to make sure that everything would function properly at the new location. “We kept all of the existing infrastructure and instrumentation and added more,” he says.

“Understanding the ocean, particularly the coastal ocean, is incredibly important. We need to invest in ocean measurements at the same level we do for weather prediction in the atmosphere. This array is a small step toward that,” Plueddemann adds. “We could use 20 more arrays for the U.S. coast alone.”