Why a mooring?
The purpose of the Regional Circulation Mooring (RCM) is to measure currents within the axial rift valley of Endeavour Ridge
at the regional scale, and to gauge the effect of hydrothermal venting on those regional currents. The energy released by the five high-temperature hydrothermal vent fields and the diffuse venting in the axial valley has been estimated to be about 1800MW, that of a mid-size nuclear power plant. This significant energy input in the form of heated water drives an inward circulation of about 5 cm/s at both ends of the valley, not unlike that which occurs when a sea breeze develops over heated land at mid-day. Our northeast RCM is the first of four moorings designed to constrain (or accurately estimate) the flow into the valley where, among other uses, it can be used as a proxy measurement of the total hydrothermal venting at the ridge.
Studying regional currents will help us understand how species inhabiting hydrothermal vents colonize new sites, sometimes separated by hundreds of kilometres. The larval stage of most species inhabiting the seafloor (benthic species) develop and grow in the water column, they are called planktonic. Those larvae metamorphose once they settle on the seafloor if they find a suitable habitat. We think that those planktonic larvae travel via the axial valley currents, or they are sometimes trapped in huge vent plumes created after a volcanic event, before finding a new site.
How does it work?
The mooring is composed of 3 different types of instruments affixed at varying depths along a cable extending from the seafloor upward 267m. Together, these instruments measure deep-sea current velocity in 3-dimensions as well as the physical properties (temperature and salinity) of the water. The top of the mooring line (267m from the seafloor and 1890m below the ocean surface) is lifted by a large buoy, keeping the line vertical at all times. The upper-most instrument, positioned at 1904m, is an Acoustic Doppler Current Profiler (ADCP). The ADCP can estimate currents up to 800m above the sea floor. Below this, four instrument pairs are positioned at 1954m, 2029m, 2104m, and 2149m in depth down the mooring line. Each pair includes a Conductivity Temperature and Depth (CTD) sensor and an Acoustic Current Meter (ACM). The RCM is anchored to the sea floor by a 650kg weight at 2154m in depth.
Installation of the mooring: a two-ship dance
The first step was to find a suitable location for the mooring system. It needed to be located on relatively flat ground close to our North RCM Instrument Platform. ROPOS was launched from the R/V Thompson to survey the seafloor. Once a suitable location was found, the installation commenced. This operation required very close collaboration between two ships: the R/V Thomas G Thompson and the CCGS John P Tully.
The CCGS Tully arrived with the RCM on the morning of 20 September 2010, after spending the previous day in the sheltered waters of Barkley Sound assembling the mooring and preparing it for deployment. Lining up in a parallel heading just abaft the port beam of the R/V Thompson, they began to stream out the mooring. By shifting floats, they were able to lower the 270m mooring from the top of the navigation and recovery package.
Meanwhile, ROPOS dove, navigated out of the way and waited 300m above seafloor. In order to precisely place the mooring on the ocean floor the same ultra short baseline (USBL) navigation system that navigates the sub was used. This enabled us to guide the mooring down by radio instructions from the lab of the R/V Thompson to the bridge of the CCGS Tully. The coordination between the two ships was phenomenal. To further fine-tune the placement, ROPOS followed the mooring downward and visually guided the last few metres.
The control of a 267m mooring hanging from a 2.3 km cable in a complex flow area such as Endeavour Ridge is not a simple task. The CCGS Tully does not have dynamic positioning and the mooring was placed by the formidable ship handling skills of the CCGS Tully’s bridge. Truly an amazing feat: the mooring was placed within a metre of its designated position.
Then the Tully ghosted away, like a rock star after the gig.
Harsh Realities
The deep-sea is certainly not a friendly environment for complex metal structures hosting delicate scientific instruments. Large pressure differences during the descent, corrosion during long-term deployment and ground faults due to contact with seawater are all significant engineering challenges, but these conditions are hard to reproduce on land. Even more challenging is laying the thin cables, often many kilometres long, that link these platforms and instruments to the junction boxes and nodes that provide power and communications.
Following a cable route survey covering harsh seafloor features, the Regional Circulation Mooring (RCM) North instrument platform was deployed and the 4.6km cable linking it to the Endeavour node was laid without complications. Sadly, after the connection was made, power levels on the cable were good, but our on-land team could not communicate with the junction-box on the instrument platform. Time to go to all out troubleshooting mode!
Team MacGyver
In an attempt to exclude the simplest and most likely possibilities first, both ends of the cable were disconnected and reconnected... No go.
The instrument platform was recovered and the junction-box tested on deck... Working. Time to carry out more complex tests. Our onboard team of MacGyvers did an amazing job at trying to figure out the issue; with only the resources available on the ship, they built various devices to test the different parts of the system in the hopes of narrowing down the problem further.
First, they used an Optical Time Domain Reflectometer (OTDR) provided by the ROPOS team. This system sends light down ROPOS’s umbilical cord, through connectors and all the way through the fibre optic cable on the seafloor measuring wherever the light gets reflected back. If all is well with the cable, light reaches the end with some reflectance only at the connections, but if has damage occurred, the light will be reflected at other points, or not reach the end at all... Results were inconclusive. The system worked on deck, but at depth, it indicated problems on both ends of the cable; an unlikely event. The possibility had to be considered that part of the system could not withstand the pressure and produced an unreliable test underwater. A visual survey of the laid cable also did not detect any clear indications of cable failure.
Maybe something is wrong with the node; time to quickly engineer a shorter version of a node to junction-box cable. Recycling the cables usually used for on-deck instrument testing and with the help of the ship’s engineers, the two cables were joined and the connection placed into a termination can built out of rubber, PVC and galvanized hardware. Once vacuum tested and filled with oil, ROPOS lowered the newly-built cable to the seafloor with the Mothra instrument platform and connected it to the node... Communication was established.
Conclusion
A problem is present in the cable and only recovering it would allow us to discover exactly what the problem is and how to remediate it in the future.
Immediate Solution
The cable planned for Mothra will now serve to link the RCM North site to Endeavour node. This will ensure that the one regional circulation mooring scheduled for this year can be tested before the others are deployed next year. Meanwhile, duplicate instruments to those destined for Mothra are being deployed at RCM North and Main Endeavour Field, so we will receive data from those prior to deploying their twins at Mothra next year.
Photo Slideshow
Finding Safe Passage through an Undersea Mountain Range
Dives 1364 and 1365, 14-15 September 2010
Where on earth can you find a volcanically active valley full of unique life forms and smoking chimneys accessible only by crossing a treacherous mountain pass?
At Endeavour Ridge! Endeavour is a section of the Juan de Fuca Ridge, and part of the global 65000km mid-ocean ridge system, a continuous undersea mountain range along spreading tectonic plate boundaries. In our part of the northeast Pacific, the Juan de Fuca plate and the Pacific plate are moving away from one another leaving a rift along the boundary. New sea floor is constantly formed in the spreading centre where lava emerges from weak points in the oceanic crust. The area is characterized by high temperature hydrothermal vent fields with “black smokers” – chimney-like structures that emit superheated particle-laden water.
During our Fall 2010 installation cruise, we are venturing into this volatile terrain to install instrument platforms, video cameras, seismometers, a bottom-pressure recorder, an acoustic array and a water sampler. But how will we retrieve the data from all these instruments? It must be relayed by cable to Endeavour node, where it can then be transmitted through the existing NEPTUNE Canada cable network to the Internet.
This means that cable must be laid on the ocean floor 2km beneath the surface over an underwater mountain range!
Our first step in laying the cable was to conduct a survey of the bathymetry (i.e. the underwater depth map) to map the topography of the sea floor. Scientists used GIS (Geographical Information System) software to hand trace a potential route on bathymetry maps from previous international expeditions. Integrating knowledge of undersea terrain with survey maps and depth data is an art that requires specialized knowledge and experience – a task that can’t be computer programmed!
However, sometimes a road that looks like a paved four-lane highway on a map turns out to be a pitted gravel tractor trail in real-life, so we needed to check that the route was actually suitable for cable! Therefore, the next step was to fly the route with ROPOS, while surveying the bottom with a high resolution multibeam sonar.
For the trickiest parts, we crowded around the monitors in the operations room and watched live video from ROPOS’s HD camera. There were some surprises along the way: steep slopes ripe for an underwater avalanche, knife-edged cliffs, deep crevasses and even some curious sea creatures.
Our survey continued well into the early-morning hours, but eventually everyone agreed on a safe mountain pass, for our first route. And so, we are ready to lay the cable!
Photo Slideshow
VPS Returns to Barkley Upper Slope
On 14 September, 2010, we redeployed our Vertical Profiler System (VPS) after its summer holiday at the University of Victoria's Marine Technology Centre in Sidney, BC. During its port call, the VPS was visited by Japanese engineers who replaced its burnt-out winch motor and refurbished the entire VPS apparatus.
The winch is crucial, as it lowers and raises the the VPS instrument float up and down through the water column, allowing scientists to analyze water properties (e.g. oxygen or chlorophyll concentrations, turbidity levels, intensity of sunlight penetration) continuously from the seafloor to the surface.
We dropped the VPS to the seafloor on a wire using the R/V Thompson’s A-frame, then ROPOS dove to connect it to the Barkley Upper slope instrument platform. Everyone on ship watched intently as the float passed its initial test; rising up a few meters above its base and then safely back down into the basket.
Dogfish and Sea Urchins
Dogfish sharks also witnessed the VPS’s return. They might have found it and ROPOS to be too large for prey, but they sure seemed to circle the Bottom Pressure Recorder (BPR). Let’s hope that BPR has tough skin... Further close-up inspection found the BPR intact and in good condition.
The cable linking Barkley Canyon Upper Slope instrument platform to Barkley Canyon Node was also found to be doing well; now hosting a community of fragile pink sea urchins. Individuals of this species commonly appear in live video feeds from the nearby seafloor webcam.
Photo Slideshow
Wally I Retrieval
Dive 1361 – September 13, 2010
One of the most unusual creatures you might encounter on the Barkley Canyon sea floor is Wally, a specially designed remote-control deepsea crawler that has been collecting samples and exploring undersea terrain since deployment last October.
A key task on our 2010 installation cruise was to replace Wally I with his new and improved heir, Wally II. To do this, we first needed to bring Wally I to the surface using ROPOS and a tool basket.
ROPOS was deployed with an empty tool basket and 8 chain weights sitting on its front porch. These chain weights are a perfect example of the usefulness of duct tape in scientific research. Each consists of a carabineer attached to a chain enclosed in sliced rubber hose. The hose is mummified in duct tape until the chain and the carabineer have a sturdy silver-coloured handle for ROPOS manipulators to grab.
Why do we need these chain weights, you ask? Wally I is attached to the instrument platform by a buoyant cable, which stays out of his way floating above him when crawling. This cable had to be weighed down so it wouldn't interfere with ROPOS when he was plucked from the seafloor and “flown” to the tool basket. Once placed in the tool basket and disconnected from the instrument platform, Wally I was secured in place and carried to the ship by ROPOS.
All went smoothly on the dive. Wally I returned safely to the ship, gas tight water samples and push cores were collected, the Barkley Hydrates instrument platform passed its inspection and a shell experiment was retrieved from the ocean floor.
Wally II Deployment
Dive 1363 – September 14, 2010
You could tell something exciting was happening on Dive 1363. The operations room was full, and camera-toting scientists and crewmen crowded the deck like paparazzi. Why? Because Wally II was sitting in the ROPOS tool basket, ready for an 870m plunge.
Like Wally I, Wally II is equipped with cameras, lights and sensors for measuring water conditions on the seafloor. What's new is this crawler's custom-designed sediment microprofiler, developed by collaborating scientists at the Max Planck Institute for Marine Microbiology in Bremen, Germany. Like a high-tech acupuncture kit, this sensor array will help scientists study oxygen, pH, salinity, temperature and sulfide levels in seafloor sediments and bacterial mats.
There were several steps to deploying Wally II. First, he was lowered in the tool basket to the seafloor and the basket was detached from ROPOS. Then, he needed to be freed from his “seatbelts” – a challenging task for the two ROPOS team members operating the platform’s robotic arms. Next, ROPOS lifted Wally II and flew him to his new home in Wally's World over near the edge of the canyon.
The next step was to connect his cable to the instrument platform. This must be done very carefully to ensure proper power and communications transmission through the cable. Dust caps are essential to keep particles out of the sensitive connectors until the last seconds before a connection is made.
The final step was to power Wally II on and test him. We Skyped the Wally control team in Germany and told them give it a go. The next thing we heard in the operations room was the exclamation He’s moving! Much to our delight, the Wally II deployment was a success!
Slideshow
Photos of Wally II, Wally I and the replacement operation.
Getting Wet Again
After many weeks of busy preparations, our Fall 2010 installation & maintenance cruise is finally underway, aboard the R/V Thomas G Thompson.
Seven NEPTUNE Canada staff members, together with an 8-man ROPOS crew, 2 NEPTUNE Canada contractors, 2 students and 4 collaborating scientists have joined the month-long cruise, which will take us to our Barkley Canyon, ODP 1027 and Endeavour Ridge locations. (See our cruise information page for links and details on the planned tasks.)
Key objectives of this cruise will be:
- installation of Wally II, our second-generation deep-sea benthic crawler
- re-deployment of our Vertical Profiler System, which has been repaired and rebuilt over the summer
- infrastructure deployment at Endeavour Ridge, including new cables and junction boxes
- instrument deployment at Endeavour Ridge – numerous exciting additions to our observatory are planned
We hope seas and skies will cooperate and we will be able to successfully complete our many ambitious plans!
Photos