Down Into the Depths They Go

For decades, sea-going research vessels have been the backbone of observational oceanography, giving scientists mobile platforms to conduct a variety of open-ocean research for days, or even weeks, at a time. Oceanographic research continues to build off previous work and, at the same time, the scale of research questions has broadened. As a result, the desire for more frequent observations of the deep ocean has driven the development of new technologies to increase research capability and accessibility.

In the late 1990s, scientists at the University of Washington School of Oceanography in Seattle, led by oceanographer Charlie Eriksen, began developing what would become known as Seaglider–a small, reusable autonomous underwater vehicle (or AUV). The airplane-shaped Seaglider can be launched from small multi-use vessels and is capable of collecting oceanographic data, including temperature, salinity, and pressure, from the surface down to 1,000 meters (3,300 feet) multiple times a day, with missions lasting an entire month. Seaglider has played a role in revolutionizing the field of oceanography, allowing scientists to collect a wide variety of measurements at deliberately chosen locations around the world for a much lower cost compared to the expense of booking days aboard larger research vessels.

Then, beginning in the early 2000s, the same team of scientists began developing a similar instrument that could dive deeper, stay at sea for longer periods of time, and collect a broader array of oceanographic data. Enter Deepglider. Like its predecessor, Seaglider, Deepglider is an airplane-shaped AUV that can be programmed to transit between waypoints, collecting and transmitting data along the way. However, what makes Deepglider special is that its range is sufficient to transit entire ocean basins, in missions lasting 12 to 18 months, while diving repeatedly, on a near-daily basis, to depths of up to 6,000 meters (20,000 feet).

In 2014, Eriksen and his team visited BIOS to conduct an extensive field test of Deepglider in the deep waters off Bermuda. Since then, six Deepgliders have been deployed out of BIOS, many of which have supported ongoing research into mesoscale eddies in the North Atlantic Ocean. Mesoscale eddies, often described as the “weather of the ocean” are roughly circular rotating features that measure tens to hundreds of kilometers across and persist in the ocean for weeks to months.

Jake Steinberg, a doctoral candidate studying physical oceanography in Eriksen’s lab, is one of the scientists interested in mesoscale eddies and how AUVs like Deepglider can be used to improve our understanding of their structure and variability. On Steinberg’s visit to BIOS last month, we had the chance to sit down with him to discuss his research.

What is the focus of your work?
Basically, my focus is studying pathways of energy. The Gulf Stream is a good example of this. It is a highly energetic Western Boundary current and an important part of my research. The Gulf Stream carries warm, salty waters northward along the east coast of the United States, flowing east into the interior of the Atlantic Ocean basin, where it starts to meander, becomes unstable, and pinches off blobs of water called eddies. These eddies then populate the ocean, drifting and interacting. Some merge, some get ripped apart, and some can trap water inside the eddy and move that water around the entire ocean basin.

I’m interested in the vertical structure of these eddies and the connections between surface and deep ocean flows. We used to think that eddy velocities [speed in a given direction] were concentrated in the upper ocean, but now we’re finding that—if they’re big and strong enough—they can actually move water along the ocean floor. This, in turn, creates friction and causes some of the energy associated with an eddy to dissipate.

I use AUVs to profile ocean eddies, taking samples inside and outside, and from the surface down to the sea floor, to observe the entire eddy structure. With these tools, we can collect measurements on a near-continuous basis for months at a time, often in remote locations. Additionally, Deepglider measurements serve as in situ comparisons to observations of ocean eddy behavior made by satellites.

What brings you to BIOS?
We deploy Deepgliders in the Atlantic because we can easily sample the highly energetic mesoscale eddy field associated with the Gulf Stream. Currents and eddies along the west coast of the U.S. and near Seattle, are much less energetic. BIOS is unique in that it has easy access to deep water, as well as a fleet of smaller research boats that we can use to deploy the gliders.

We also use the Bermuda Atlantic Time-series Study (BATS) program to help calibrate the instruments on our gliders. At the beginning of a glider mission we travel out to the BATS site and collect salinity, temperature, and depth measurements during a simultaneous deployment of the instruments aboard the R/V Atlantic Explorer. This allows us to compare the measurements collected by the two systems and see if any offsets exist. When the glider’s mission is complete, we conduct the test again to see if there has been any drift in the glider’s instruments. The R/V Atlantic Explorer provides crucial calibration data that renders Deepglider observations more accurate.

What are some key skills and areas of expertise you need to have for your line of work?
There are two main disciplines associated with my research: the engineering side that works to design and improve gliders, and the oceanography side that uses the data collected by the gliders to study physical processes.

For someone interested in developing new tools and instruments, you can’t ignore the importance of having a background in something like mechanical engineering. Even glider pilots need to have a solid understanding of the instrument, as well as physics, to control the glider properly and collect quality data.

On the other side, physical oceanography requires an understanding of fluid dynamics and applied mathematics. The more math you know, the better suited you will be to meaningfully interpret glider measurements. My undergraduate degree from the University of Maryland is in civil and environmental engineering, and I have dual master’s degrees in applied mathematics and oceanography, both from the University of Washington, all of which I think prepared me well for work in this field.