Nereus, a one-of-a-kind unmanned hybrid remotely operated vehicle (HROV) that had allowed scientists to explore the deepest parts of the ocean, was confirmed lost at 2:00 p.m. local New Zealand time on 10 May, according to the Woods Hole Oceanographic Institution (WHOI), which designed and operated the vehicle. The loss “means that more than one-third of the depth range of the ocean is beyond the reach of humanity in any appreciable way,” said Timothy Shank, WHOI associate scientist, and lead scientist for the Hadal Ecosystems Studies (HADES) program sponsored by the U.S. National Science Foundation (NSF).
Shank responded to a series of questions from Eos in an email he sent on 14 May during the last day of a HADES program expedition, for which he was the chief scientist, that had been using Nereus to explore the deep sea. Shank was on the mother ship, the R/V Thomas G. Thompson, which wasmaking its 4-day transit to port in Apia, Samoa.
Nereus had been a key part of the 10 April–20 May expedition to carry out the first-ever systematic study of a deep ocean trench in the hadal zone, an area of the ocean that extends from a depth of about 6000–11,000 meters. The HROV had been at a depth of 9900 meters in the Kermadec Trench, about 120 kilometers northeast of New Zealand, when a portion of the vessel likely imploded under pressure as great as 16,000 pounds per square inch, according to WHOI. Researchers lost contact with Nereus 7 hours into the planned 9-hour dive in the trench, which is the world’s fifth deepest trench, with a maximum depth of 10,047 meters.
The HROV, built in 2008 and weighing 2800 kilograms on land, operated either as an autonomous robot or linked via fiber-optic cable to a surface ship. It was outfitted with a hydraulic manipulator arm, scanning sonar, magnetometer, and other instruments. Scientists were using Nereus to conduct systematic transect-style surveys of the seafloor and the organisms there and to collect organisms and sediment samples. In 2009, Nereus explored the deepest point in the ocean, Challenger Deep in the Marina Trench, only the third vessel to do so. It had been scheduled to return there in November.
In the email interview with Eos, Shank described what the loss of Nereus means to science and noted the need for better capabilities to explore the deep ocean.
Eos: What was your immediate reaction to the loss of Nereus? What does the loss mean for deep sea research?
Shank: We were shocked. Everyone knows that we take a risk anytime we send any instrument into the ocean, but to be confronted by the finality of what happened deep beneath us took a moment to process. Then we had [to] very quickly set about recovering what we could of the vehicle and then focus on getting back to science. The loss of a global asset like Nereus means that more than one-third of the depth range of the ocean is beyond the reach of humanity in any appreciable way. We can still visit with landers and other static instruments, but doing the kind of careful, systematic surveys of the seafloor that allow us to stitch our knowledge together and arrive at a “big-picture” view of what is happening in the deep ocean and in the ocean as a whole is no longer possible.
We can send landers to Mars, which is 400 million kilometers away at its farthest extent, and operate them remotely for years at a time, but we can no longer explore the ocean on our own planet 10 kilometers beneath the surface, something that Nereus was only able to do for 10 hours at a time, at best. Nereus was essentially a prototype vehicle to prove the concept that full-ocean depth science could be conducted. We were just starting to use her as a workhorse for hadal research through funding from the National Science Foundation of the HADES Program (http://www.whoi.edu/hades/). We don’t need another Nereus; we need something better, and we need more than one. To provide some perspective, the full development of Nereus was $8 million, $13 million less than a Black Hawk helicopter . . . and the U.S. has thousands of those.
Eos: In the short time it operated, what were to your mind the most exciting and most important things that were discovered thanks to Nereus?
Shank: Nereus showed that we could venture into places that were previously unknown to us and begin to understand how life processes there relate to us on the surface. It showed that no part of the ocean, no matter how deep or remote, is separated from the surface. Nereus also showed what we are capable of when we commit to an achievement that seems, at first, insurmountable.
Eos: What does the loss of Nereus mean to the current HADES expedition, to other planned missions including the second HADES expedition to Challenger Deep, and to science in general?
Shank: We were using Nereus as a platform from which to conduct systematic transect-style surveys of the seafloor and the things that live on and near it. We were also using it to collect samples of organisms that are not attracted to the baited landers and fish traps or that are immobile. We also used it to collect careful sediment samples with which to understand the abundant communities of organisms and microbes that live beneath the surface and shape the hadal ecosystem. How much of this we were able to achieve remains to be seen, pending careful analysis of the samples, images, and data Nereus was able to collect. However, this data set will be incomplete now that we do not have its capabilities to complete this or other surveys of the deep ocean. When it comes to robust systematic research approaches, it appears the hadal zone will remain largely unstudied for some time to come.
Eos: What research opportunities have been lost as a result of the loss of Nereus?
Shank: The ability of Nereus to do directed surveys and sample collection is critical for hadal research. Without it, we will be limited to the snapshot views of static instruments that only provide a limited perspective on what is an exceedingly complex ecosystem.
Eos: How much of the science that was planned to be done with Nereus can be done with other methods?
Shank: The capabilities Nereus provided were unique. We will be forced to rely on chance to retrieve sediment samples or macro fauna. Some things are simply not possible—such as near-bottom camera surveys or non-scavenging macro faunal recovery. The big-picture questions that will be affected include how much carbon is being sequestered in hadal sediments, how hadal ecosystems are structured, how human activity is affecting the lower one-third of the ocean’s depth, how much of what type of food is available to life in the deep ocean, and the range of adaptations life has evolved to cope with conditions in the deep ocean. Many of these are fundamental, first-order questions that we are only beginning to address.
—Randy Showstack, Staff Writer, Eos