Keck Expedition 2004
August 8, 2004 Day 10
Update for August 8 (by Debra Stakes)
The goal of the first dive today was to reconnect to the KNBB logger and try once again to confirm that it was successfully leveled. This was the instrument that was deployed 5 days ago on August 3. At that time the communications to the logger and sensor were complicated by the failure of the underwater connector to lock. We went through the initialization protocol but some of the steps were given in reverse order while we discussed whether it was safe to power the unlocked connector from the ROV that was manually held in place by the manipulators.
Today the ROV connector locked on the first try and the communications was initiated. Look at that! There is something very non-seismological peeping through the hole between the two connectors.
On the other side, we see a couple of curling tendrils floating in the current from the ROV thrusters followed by a big stretch from behind the RIN. So for the next hour, the ROV sat on one side of the RIN and downloaded information from the broadband sensor while the creature slept on the other side, seemingly unperturbed by our presence. This process took some time because the sensor was not behaving properly. Although we will collect data during the next year, one of the three data channels is not working. This is the only disappointment of this cruise. We are already making plans for diagnosing the problems and re-installing a new sensor into the same caisson that we excavated earlier this trip. Finally, there is nothing more for us to do here and we disconnect from the logger. Curiosity overcomes the people in the control room who drive around the RIN to get a better view of the shy octopus hiding inside the frame. This frame was deployed only 5 days ago and already it has a tenant that appears unwilling to move. Hard structures for nests must be a hot real estate item out here on the Nootka deep sea fan.
The second and third dives deployed seismonuments onto a featureless sediment-covered bottom north of the documented seep site and well north of the broadband. During Dive T719 we could see the rugged peaks of Vancouver Island in the distance during this short dive. Although there is still plenty of required pre-dive shipboard preparation and documentation, the deployments themselves have become routine.
The final dive of the day placed the second seismonument. Enroute to this site, we pass the surface mooring for the Woods Hole Acoustic Buoy experiment. It looks strangely abandoned bobbing about out here. Tomorrow we look forward to deploying the last instrument of the leg. For now however, it is the close of another successful day.
The final days of science operations are usually an appropriate time to evaluate and reflect on how the cruise went. By any measure, this cruise has been a complete success, but I've also been struck by how different it has been from a traditional research cruise and by the glimpses it has offered into the future of oceanography.
A typical cruise arrives at a research site after a transit of several days from a (usually exotic) port. Once there, the ship is used as efficiently as possible to survey, sample, or deploy and recover instruments, and preliminary discoveries are often made while still at sea. For this cruise, we left from Newport, Oregon (a scenic town but not quite Tahiti) and after a relatively short transit have been following a very focused schedule of seismometer deployment and recovery. Efficient use of the ship has been secondary to optimizing use of the ROV. And even first-order results, such as earthquake locations and focal mechanisms, will take several months to produce.
A notable difference between this and other seismology cruises is the long-term predictability of the data quality. All of the short-period seismometers recorded continuously for an entire year, with similar noise levels. The only issues we have noticed – the one-minute and ~20-minute spikes – are minor, are common to all of the short-periods, and can be solved the next time the network is turned around. By contrast, the standard ocean-bottom seismometer deployment method is to free-fall the instrument 2-4 km from a ship, and to hope for a soft, level landing. Deployment by ROV, although more expensive than free-fall, allows careful and gentle installation, and minimizes the chance of unpleasant data-quality surprises.
The huge amount of data we have collected has also been a new experience. During my weaker moments I have secretly wished for something (benign, of course) to slow the pace of instrument deployment and recovery. Backing up, reformatting and checking more than seven years of three-component data has been a challenge and has only just kept ahead of the redeployments. With the five additional seismometers we deployed at Nootka and Explorer, the amount of data to recover next summer will exceed 0.3 Tbytes, an increase over this year of more than 50%.
Finally, this project is proving to be a novel exercise in deferred and shared gratification. Deferred because the first coreholes for the seismometers were drilled at Endeavour two years ago, and the juicy seismograms we have only now collected are the result of several years of planning, engineering and installation. Data analysis will occupy a team of eight students and four instructors at a residential class at the University of Washington's Friday Harbor Labs for the entire Fall quarter. And shared because the primary motivation of the project is to explore the links between seismicity and hydrothermal vent chemistry and biology: the most exciting results will come from sharing and discussing the seismic data with the geologists and biologists who have also been monitoring the Endeavour system.