Onwards and downwards: when ROVs or AUVs are lost in ocean exploration

This week saw the news that the Nereus hybrid remotely operated vehicle (HROV) has been lost while exploring the Kermadec Trench at a depth of 9.99 km, during an expedition that has revealed that part of our planet as never before. To link with Week 5 of our free Massive Open Online Course on “Exploring Our Oceans”, during which we focus on how we explore the oceans, this post takes a look at some of the ROVs and AUVs that have been lost during ocean exploration.

Always in a Chief Scientist’s mind at sea is the question “what will we do if…”. Those “what ifs” include the weather, medical situations, and problems with any piece of equipment, from the ship’s own hardware to the various tools that we put into the ocean. I’ve never been on an expedition where we were able to stick to “Plan A”, and it sometimes seems like we have more contingency plans than there are letters in the alphabet.

The loss of a remotely operated vehicle (ROV) or autonomous underwater vehicle (AUV) is utterly crushing for those aboard a research expedition and their colleagues ashore.  But whenever we send something into the ocean depths, there is never an absolute guarantee that it will come back. There is always a risk involved, although we minimise risk through preparation and manage it in our expedition plans.

The only way to avoid risk completely is not to go at all; some risk will always be there, and that means that sometimes the dice will not roll in our favour. That does not mean we are reckless: an assessment of risk-versus-return is typically part of the funding decision for projects, and our back-up plans are usually carefully scrutinised.

To obtain some kinds of knowledge – particularly when physical samples are required for analysis – there is no alternative to sending equipment into the deep ocean, because the ocean’s watery veil masks its depths from many forms of “remote sensing”. And although we have learned a lot from a century or so of largely “blind sampling” by equipment such as trawls and seabed corers (which are still fine for answering some questions in some areas), we now often require more detailed sampling and surveying, using deep-sea vehicles, to answer further questions.

Here is a quick history of some of the remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) that have been lost in the service of deep-sea exploration – but also what they had achieved, and how the research in which they were involved has continued. Expeditions have continued in the immediate aftermath of such incidents, using other equipment aboard, and in the longer term, replacement and rebuilt vehicles have achieved scientific successes.

We press on, for reasons including the potential benefits that the ocean holds for our future, from new materials to medicines, and to understand our impact on the future of the ocean.  So the motto is “ever onwards and downwards”.

HROV Nereus (10 May 2014; Kermadec Trench)

Nereus was a new kind of “hybrid” vehicle, combining ROV and AUV technology into an efficient and cost-effective tool for reaching “hadal” depths, i.e. into the deep trenches, where most other vehicles cannot go. Nereus had already reached the ocean’s deepest point in the Marianas Trench, and more recently dived on the world’s deepest known undersea vents in the Cayman Trough.

The current HADES expedition has provided stunning insights into the Kermadec Trench, and will be able to continue using other tools aboard, such as benthic landers.

Autonomous Benthic Explorer (aka ABE; 5th March 2010; Chile Triple Junction)

ABE was one of the first AUVs to be used routinely for science, coming into service in the mid-1990s and completing 221 missions, including pinpointing hydrothermal vents south of the equator in the Atlantic, and obtaining the first seafloor images of a hydrothermal vent field on the SW Indian Ridge (which my colleagues and I then dived on with an ROV in 2011).  The experience gained from developing and operating ABE has also fed into the next generation of AUVs for further ocean exploration.

Isis ROV (19 January 2011; Bransfield Strait, Antarctica)

A day I won’t forget, as one of the team aboard the ship. One year previously, we had used the Isis ROV to study the southernmost known “black smoker” vents in astounding detail. Isis had also surveyed deep-sea canyons off the coast of Portugal, and discovered king crabs creeping up from deep waters towards the Antarctic continental shelf.

The loss of Isis was a major blow, but that expedition continued, using other tools such as a towed camera sled and corers, discovering yet more hydrothermal vents in a seafloor crater near the South Sandwich Islands, investigating volcanic ridges near the Antarctic Peninsula, and revealing how worms boost the flux of iron from deep-sea sediments into Antarctic waters. Those results were a testimony to the leadership of the expedition’s Chief Scientist, Prof Paul Tyler, and the adaptability of the technician team aboard.

(timelapse of ROV Isis rebuild by Jackie Pearson, National Oceanography Centre)

The decision to repair the Isis ROV facility following that expedition was not taken lightly, but the underwater vehicle is not the entire facility, which also includes the shipboard control centre, ROV winch system, and not least the people who operate the facility; so overall, the cost of restoring the vehicle was a fraction of the existing investment in the facility. In the interim, UK expeditions requiring an ROV used Germany’s Kiel6000 ROV through international arrangements for sharing such equipment. A fully restored Isis ROV facility then returned to the Antarctic deep-sea vents in December 2012, and since then has dived on the world’s deepest known undersea vents in the Cayman Trough, and investigated deep-sea corals across the Atlantic.

Autosub-2 AUV (16 February 2005; beneath Fimbul Ice Shelf, Antarctica)

The vast cavities beneath the permanent floating ice shelves that form a fringe around Antarctica and Greenland are some of the few places that only autonomous underwater vehicles can reach. The ice shelves themselves are hundreds of metres thick, and can be hundreds of kilometres long, with water several thousand metres deep beneath them. What goes on in those cavities could be important for understanding the formation of deep waters that sink from polar regions to drive ocean circulation, and they could also be home to unusual colonies of marine life.

Drilling holes through ice shelves and lowering sensors into the hidden ocean below can provide some data, but only in single locations, and at considerable cost in establishing a remote field station on the ice shelf, with all the equipment and fuel required to melt holes down through it. Meanwhile, ROVs can’t reach far into the cavities from the open ocean because of their tethers, so AUVs are potentially the best tools to survey these environments. The Autosub Under Ice programme was therefore designed to explore the marine environment beneath permanent floating ice shelves using the Autosub-2 AUV.


Analysis of previous AUV missions indicated that the risk of losing Autosub-2 during a >100 km mission beneath an ice shelf could be >50%. Consequently, potential insurers of marine equipment quoted an insurance premium equivalent to 95% of the vehicle’s cost, per year! So instead, the programme set aside funds to build a replacement vehicle, and began construction of it, fully expecting that one would be lost.

And indeed it was. Autosub-2 completed its first mission beneath the Fimbul Ice Shelf in the Antarctic, obtaining the first synoptic data from an ice-shelf cavity, but was lost on its second mission (consistent with a ~50% expected risk of loss). However, its replacement was already under construction, and Autosub-3 later completed missions beneath the ice shelf of Pine Island Glacier to understand changes previously observed there from satellite data, and is being used in further ice-shelf studies.

Kaiko ROV (29 May 2003; near Shikoku island)

In 1995, Kaiko – which means “ocean trench” – became the first vehicle to return to the deepest point of the oceans since the record-breaking dive of the Trieste in 1960. Kaiko dived there again in 1996 and 1998, completing more than 20 dives in total to “Challenger Deep” and collecting specimens of amphipod crustaceans, microbes, and sediments. The ROV was also used in the discovery of hydrothermal vents on the Central Indian Ridge in 2000. But in 2003, Kaiko was lost on its 296th dive as Typhoon Chan-Hom closed in towards the research ship RV Kairei.

The “launcher” component of Kaiko, which was recovered, was subsequently combined with the UROV7k vehicle to create Kaiko7000II, with a 7 km depth capability.  Meanwhile, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has also developed the ABISMO ROV as replacement for Kaiko to reach the deepest point of the oceans – and ABISMO has so far operated successfully to a depth of 9707 metres in the Izu-Ogasawara Trench.

- Jon Copley, 11 May 2014

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