Nereus coring

Nereus collecting a sediment core from the Challenger Deep during a 2009 expedition. Credit: Woods Hole Oceanographic

Nereus coring

Nereus coring

Rattail

As they make their way to greater depth, the team may see fish like this rattail--a common deep-sea species. However, it's not clear whether any fish can live more than 8,000 meters or so down. Credit: Jeff Drazen

Rattail

Rattail

The very deepest reaches of the sea are one of the planet’s last true frontiers. That’s mostly because a lack of support for needed technological advancements and vehicles has severely limited access to depths beyond 7,000 meters. But the situation is finally beginning to change, and SOI is helping push the process forward. In November, the institute will collaborate with a group of biologists and geologists working aboard R/V Falkor to conduct a new study of one of the deepest places in the world.

The team will be deploying SOI's new full-ocean-depth landers—frames equipped with cameras, sensors and sample collection devices that return to the surface automatically after a set time on the seafloor—as well as three other landers, in the Mariana Trench's Sirena Deep, near Guam. The work, at depths down to almost 11,000 meters, will help answer enduring questions about the biology of such alien zones, including who lives there and how they survive the massive pressure. The research could also improve understanding of the processes that control earthquake and tsunami formation, among others geological goals. And of course, with so little exploration having been done in the trench, there will undoubtedly be surprises.

The original plan for this expedition called for using Woods Hole Oceanographic’s Nereus hybrid remotely operated vehicle. But sadly, Nereus was lost earlier this year.

Why It’s Still a Frontier
Places deeper than 6,000 meters—known as the hadal zone—have remained a frontier mainly because so few vehicles have ever been built to penetrate such depths. A handful of robotic and manned vehicles can go to 6,500 or 7,000 meters down. But that leaves almost half the ocean’s depth range inaccessible, and a collective seafloor area almost as large as Australia.

Only four vehicles have ever existed that could safely work at full ocean depth and none are currently in operation. Of course scientists have found other ways to get limited glimpses of the deepest regions, as they will on this expedition with landers. Work with this type of equipment has been critical—indeed SOI will return to the Mariana Trench in December of 2014 on a second lander project.

Ultimately researchers hope to systematically explore large swaths of the world's deepest trenches to get a more complete view of what is found there. Such work will once again be possible by 2016 as Schmidt Ocean Institute is working with Woods Hole on a new full-ocean-depth robotic vehicle.

The Big Questions
Jeff Drazen from University of Hawaii at Manoa (UH), a deep-sea fish expert, will be the expedition's chief scientist, while Patricia Fryer, a geologist also at UH, will be co-chief scientist. One key goal will be to learn more about what animals are found in the trench, and what factors might control these animals’ locations and concentrations. 

Working with samples caught in traps they will also be studying the biochemical adaptations that allow animals to survive the crushing pressures in deep trenches, in particular, whether these animals have special compounds to protect proteins in their cells from folding improperly under the crushing pressure.  One of the compounds researchers have already found that seems to help some trench dwellers withstand hadal pressure was discovered elsewhere and is being pursued as a potential treatment for Alzheimer’s, which involves problems with protein folding in the brain. Other compounds discovered in the trenches might be new to science and could offer similar potential medical or other benefits.

The team has also equipped one lander with modified coring devices that insert a tube into the sediment and meaure the amount of oxygen used by the worms and other small organisms found there. This effort ties to past work suggesting that more food ends up in trenches than previously thought, and that this food—in a range of forms including falling dead phytoplankton, animals, droppings and other materials—could support more life than expected. Food concentrations might also determine where more animals congregate. The oxygen consumption rates will offer a measure of the abundance and activity of sediment dwellers that can in turn be compared to location and sediment data to look for patterns in the ways that animals are distributed. 

Another lander is equipped with a rock grabber that will allow the team to collect samples that can help answer key geological questions. Trenches form at the places where tectonic plates run into each other, with one falling, or being subducted, underneath the other. That process, along with associated microbial activity, plays important roles in the release and consumption of carbon and minerals. Such cycling is, for instance, a critical factor in the ocean’s ability to absorb carbon dioxide from the atmosphere.

Much of our understanding of these processes, despite their importance, remains theoretical because they occur so deep that opportunities for study have been extremely rare. Rock and sediment sample analyses could either confirm some of the current understanding of these processes, or reveal new questions scientists need to as.

Trench subduction zones are also the sites of earthquakes that at times spawn devastating tsunamis. Observations and sample analyses could also help scientists better understand factors tied to these events. 

The Bigger Picture
The Falkor expedition was planned as part of the international Hadal Ecosystems Studies program, led by Woods Hole Oceanographic’s Tim Shank, who will be part of the Mariana Trench team. 

The Mariana Trench expedition will also include researchers from Whitman College, the University of Aberdeen's Oceanlab, New Zealand's National Instiute of Water and Atmospheric Research, the UK's Natural Environment Research Council, and the National Oceanography Centre, also in the UK. The cruise will run from November 9 to December 9, 2014. Once the cruise is underway, please check back and click on the buttons in the upper left corner to follow the Cruise Log and the Expedition Map.  

--by Mark Schrope

Cruise Related Media:

All Things Marine Radio Show November 18, 2014

Schmidt Ocean Institute provides ship time aboard Falkor and the equipment required at no cost to our collaborators. Support for research related to this expedition is provided by NOAA's Pacific Islands Fisheries Science Center, the National Science Foundation (award OCE-1130712), and Blue Planet Marine Research Foundation.