Nares Strait 2012: Long Hours Recovering Moorings

Andreas Muenchow, Aug.-7, 2012, 12:22 am

Everyone can throw instruments into the ocean, but only few can recover the same instruments 3 years later. And fewer people yet can recover instruments that were hit hard by Petermann’s Ice Island of 2010 (PII-2010). Today, we did exactly that:

Starting at 8am sharp yesterday, we recovered six of seven moorings from the 300-400 m deep ocean floor. Only one is still left. The attention to detail three years ago, when we deployed the moorings, paid off.

We are now parked next to a massive multi-year ice floe for a night without darkness at 80:43.0 North latitude and 67:17.9 West longitude. For the last 3 hours our group celebrated today’s success at the only bar within 300 miles while downloading an incredible amount of data from instruments to laptops. Among the three of us from Delaware we got 5 computers. The groups from British Columbia, Canada and Oxford, England are no different. Science is both a social and an individual activity, as oceanographer Henry Stommel said with true wisdom. There is lots and lots of scientific computing taking place right now, well past mid-night, when most aboard are sleeping.

The recovery of a sensor package begins with sending acoustic signals to an acoustic receiver attached to a tiny motor at the bottom of the ocean. After waking up said receiver near the bottom of the ocean, we send a command through the water with sound waves to turn a motor that separates a hook from a heavy anchor. Buoys attached above the acoustic release raise the entire sensor package to the surface. A zodiac with Chief Officer Brian Legge and a Leading Seaman aboard heads out to grapple the surfaced instrument package that is then hauled aboard the ship by a crew led most competently by bosun Don Barnable. Once aboard the ship a flock of scientists, engineers, technicians, and students crowd over all the elements of the sensor package to document, detach, secure, and move all the many pieces of the mooring.

The ice-profiling sonars originally designed and developed by our Chief Scientist Dr. Humfrey Melling was abused by PII-2010 the most. Two instruments moored 8 km apart were hit in almost identical fashion with ¾ inch thick protective stainless steel attached to the vibrating ceramic plates was bent into strange shapes by more than 80 meters thick ice. Data are downloaded right now to pin point the timing of the impact, but I am pretty sure it was PII-2010 in September of that year.

In addition to the two ice profiling sonars that measured ice thickness overhead from 2009 through 2012 at better than half hourly periods, we also recovered two acoustic Doppler current profilers that measure ocean currents in 40 different layers from the bottom to the surface. Furthermore, two moorings each measure ocean temperature, salinity, and pressure (CT/D) every fifteen minutes for the same 3 years complement the available data. The survival of the CT/D is remarkable for the mooring string contains instruments at 30 meters below the surface. Since our ice-profiling sonar at 80 meters depth was hit by PII-2010, these much shallower CT/D moorings were also hit by PII-2010. Their slick and smart design to slip through cracks and hooks on the underside of the ice made them survive the certain strikes by ice and ice islands.

This was a long and eventful day when we perhaps accomplished 80% of the tasks we set out to accomplish in the 8 days we have in Nares Strait. Our design decisions made 3 years ago paid off as we recovered almost all equipment hopefully holding 3 years of data. These 3 years of data include both the 2010 and 2012 calving events from Petermann Glacier, but they also contain data on the physical context within which these dramatic events took place. Our work has only just begun … as we are preparing to encounter Petermann’s 2012 ice island … I stop here at 1:11 am local time, cloudy skies and lots of ice around.

[Images will be placed when we return, as internet access aboard the ship is limited to text only.]