Research Expedition to Probe Mysteries of the Deep off New Zealand

Scientists from around the globe are gearing up for a research cruise off New Zealand, where they will examine the mysteries of the deep ocean using a suite of high-tech instruments. Scheduled May 2-16, 2023, the expedition will be led by the New Zealand-based National Institute of Water and Atmospheric Research (NIWA), with several scientists from UC San Diego’s Scripps Institution of Oceanography among the team of collaborators.

While onboard NIWA’s research vessel Tangaroa, the Scripps Oceanography team will deploy four Deep Argo robotic floats along an unnamed deep-sea ridge east of the North Island of New Zealand. The orange, orb-shaped instruments — models known as Deep SOLO — can take observations as deep as 6,000 meters (20,000 feet) below the sea surface every 10 days over a lifetime of 6.5 years. The floats are part of the larger Argo Program, a global network of nearly 4,000 autonomous robotic floats that provide near real-time measurements of ocean temperature, salinity, currents, and biogeochemical data.

Measurements made by the Deep SOLO instruments and collected from the Tangaroa will help inform the NIWA team’s search for a previously uncharted ocean current in the southwest Pacific Ocean. The researchers plan to examine the flow of water associated with the deep western boundary current alongside the deep-ocean ridge.

Additionally, the Scripps researchers will use the opportunity at sea to test the effectiveness of several dissolved oxygen sensors that can be fitted on Deep Argo floats. These sensors are crucial for measuring oxygen loss in the ocean, a process known as ocean deoxygenation.

Once a reliable sensor is identified, more Deep Argo floats could be outfitted with the technology, resulting in a more robust understanding of the physical and biogeochemical processes driving changes in oxygen content and long-term trends in ocean deoxygenation over the full ocean depth.

Nathalie Zilberman, a Scripps oceanographer who serves as co-chair of the Deep Argo program, said the upcoming cruise will provide an opportunity for novel experimentation and collaboration.

“This is the first experiment of its kind — a highly collaborative effort between academia and the industry meant to assess and improve the performances of dissolved oxygen sensors available for use on Deep Argo floats,” said Zilberman.

An oceanographic triumph

Founded at Scripps Oceanography in 1999, the Argo Program has grown to include participation from 26 countries across the globe. Deemed “one of the scientific triumphs of the age" by the New York Times, Argo has been instrumental in helping researchers understand the way the oceans affect climate. More than 4,100 scientific papers to date have included Argo data.

“I don't think that most people are aware of how revolutionary the technology is in these floats and how important these data become to other information that they consume in their daily lives,” said Steve Diggs, a research data specialist and senior product manager with the University of California Office of the President. “The Argo international network is now one of the main sources of data that support the oceanographic research community and is central to our society's ability to forecast changes in the climate and adapt to the inevitable next phase of our existence here on Earth.”

Diggs is well-acquainted with Argo data, having spent much of his career at Scripps Oceanography working as a data manager. As part of Diggs’ new role within the UC system, he advocates for the publishing of research data, and he said this expedition will reconnect him to the hands-on and routine technical aspects of data collection in the field.

“It's an honor to be a small part of this ongoing global experiment,” said Diggs. “I'm looking forward to reconnecting with my early engineering roots and being out in the field supporting scientific projects, while also forging new collegial relationships that are a necessary component of a successful campaign. There's nothing like it, and I have missed being away from the action when the data start their journey toward the end users.”

Deep Argo innovation

Of the Argo array’s nearly 4,000 robotic floats, 187 are part of the Deep Argo array and 58 of the Deep Argo floats were built at Scripps. These Scripps-designed floats are one of the more recent innovations to study the most undersampled part of the ocean — the deep sea — to look for signals of change. Only 30 percent of the Deep Argo floats bobbing up and down in the world’s oceans are currently equipped with dissolved oxygen sensors, an effort led by Argo partners from France and Japan. Zilberman said the Tangaroa cruise will aid efforts to get oxygen sensors added to Deep Argo floats from Argo partners in the United States.   

“Oxygen is being considered very strongly within the Deep Argo community as a new variable added to temperature and salinity. So far the U.S. hasn't embarked on that journey because work still has to be done on improving the accuracy and stability of the sensor,” said Zilberman.

Because Deep SOLO floats sample the full ocean depth, extreme conditions of the environment in the deep ocean can add a large amount of stress on the sensors. “In particular, assessing the impact of high pressure and low temperature requires thorough research,” added Zilberman. “My work on this cruise aims to address some of these challenges.”

Zilberman and colleagues will test oxygen sensors provided by four manufacturers: SeaBird Scientific, RBR, JFE Advantech Co., Ltd., and Aanderaa, a Xylem Analytics brand. Their goal is to ultimately select one model for an upcoming proposal to outfit the U.S. Deep Argo array with dissolved oxygen sensors, while also having options to recommend to international Deep Argo partners.

Science at sea

The oxygen sensors undergoing testing will be added to the CTD rosette, a package or “carousel” of instruments that collects data on conductivity (used to determine salinity), temperature, and depth as it is lowered over the side of the ship to the seafloor and then brought back up to the surface. The rosette also contains bottles that open and collect seawater at specific ocean depths, allowing for additional measurements of temperature, salinity, and oxygen.

Researchers on the Tangaroa plan to collect CTD and dissolved oxygen measurements at fifteen stations along a deep-sea ridge that reaches a depth of 6,000 meters (20,000 feet). In the same area, they plan to deploy four Deep SOLO floats that were built in the Argo Instrument Development Group lab at Scripps. The resulting data will help illuminate the physics by which the deep flow interacts with the ridge, and help improve the capability of Deep Argo oxygen sensors.

Scripps PhD student Mitchell Chandler said he is looking forward to assisting in the research effort. The expedition will be his first extended cruise, and, as an added perk, it’s taking place near his home country of New Zealand.

“It's definitely a fun occurrence that my first multi-day research cruise is in the region of the world where my oceanographic journey first started,” said Chandler, a physical oceanography student who is co-advised by Zilberman and oceanographer Janet Sprintall.

Chandler’s research uses ocean observations to study western boundary currents in both the upper ocean and deep ocean. These major ocean currents, located on the western side of ocean basins, transport water and heat around the globe and can be thought of as “the arteries and veins of the climate system,” he explained.

Most of his PhD work to date has involved analyzing data from already-deployed instruments — including Argo and Deep Argo floats, satellites, and temperature sensors from ships — so he said he is excited to be involved in deploying new floats.

“Not only will these floats be used in my research, but they will continue to provide measurements of the ocean and thus benefit the whole community for many years to come,” he said.

In addition to research activities, NIWA physical oceanographer Denise Fernandez will lead a STEM education activity for students back home in New Zealand. Styrofoam cups decorated by 7-year-old students will be attached to the CTD rosette and lowered to the seafloor, where the resulting pressure will shrink them. “This will show the effect of pressure in taking the air out of the foam and shrinking the cups,” said Fernandez.

Zilberman said she hopes this cruise will serve as a prime example of how researchers can collaborate with industry.

“It’s already been such a great experience to define the objectives of this cruise. We anticipate high-quality results thanks to our industrial partners who could provide many sensor units,” she said. “There's a lot of talk about how to improve communication between the industry and academia, and I think this cruise is really a model of its kind.”