Wirewalker

Wirewalker. The Wirewalker is an autonomous, wave-powered oceanographic profiler designed to collect high-resolution vertical data from the water column. It operates by converting the orbital motion of surface waves into a downward force, allowing it to travel along a mooring wire without an internal motor or battery power for propulsion. This innovative mechanism enables sustained, energy-efficient observations of physical and biogeochemical parameters over extended periods, from days to months, providing critical data for understanding ocean dynamics.

Description and mechanism

The core mechanism exploits the differential motion between a surface float, which follows the wave orbital motion, and a submerged depressor weight. A one-way clutch system attached to the profiler body allows it to slide down the mooring wire with each wave cycle but prevents it from being pulled back up. This ratcheting motion, driven entirely by surface waves, provides the propulsion. The instrument package, which can include sensors for CTD, dissolved oxygen, chlorophyll fluorescence, nitrate, and ADCP measurements, collects data during its descent. At a pre-set depth, a release mechanism disengages, allowing the profiler to be pulled back to the surface by the float to begin the cycle again, creating a continuous yo-yo pattern.

History and development

The concept was pioneered in the late 1990s by physical oceanographers Jonathan Nash and Eric Kunze, then at the University of Washington and University of California, San Diego, respectively. Their work aimed to address the need for cost-effective, long-term, high-resolution sampling of the upper ocean. Early prototypes were tested in coastal waters off Oregon and California. The technology was subsequently commercialized, with companies like Rockland Scientific International manufacturing robust systems for the global research community. Development has focused on enhancing sensor integration, data telemetry via Iridium satellites, and reliability for deployments in extreme environments from the Arctic Ocean to the Southern Ocean.

Applications and uses

Primary applications center on studying upper ocean processes and air-sea interaction. The high temporal resolution is ideal for investigating diurnal warming, mixed layer dynamics, internal wave energy dissipation, and phytoplankton bloom development. It is extensively used in climate research to understand heat and carbon uptake, as well as in operational oceanography for validating data from satellite missions like those from NASA and the European Space Agency. The system also supports biogeochemical studies by monitoring nutrients and oxygen, and it is deployed in coastal regions to study harmful algal blooms and hypoxic zones.

Operational considerations

Successful deployment requires careful consideration of mooring design, wave climate, and logistical factors. The system is typically deployed from a research vessel such as those operated by the UNOLS fleet. The mooring consists of a wire tensioned between a surface float and an anchor, with the profiler's range determined by wire length. Operational depth is often limited to the upper few hundred meters. Data can be stored internally or transmitted in near-real-time. Challenges include biofouling, potential entanglement, and the need for sufficient wave energy to drive the profiler, which can limit use in very calm seas. Recovery involves locating the mooring via GPS and acoustic releases.

Notable deployments and missions

Wirewalkers have been integral to major oceanographic field campaigns. They were used extensively in the Office of Naval Research-funded **LatMix** experiments to study lateral mixing in the ocean. During the **NASA EXPORTS** program in the North Pacific, they tracked carbon export processes. They have monitored coastal polynyas in the Ross Sea and freshwater fluxes in the Bay of Bengal as part of the ASIRI program. Long-term deployments on Ocean Station Papa in the Gulf of Alaska and within the Ocean Observatories Initiative infrastructure provide sustained time series critical for detecting climate-related changes in the ocean.