- Ice in Motion
Eating sushi with a bulldozer
There are eccentric looking instruments scattered about the lab, each a tailored assembly of sensors and lasers, shackles and hose clamps. They each have a very specific responsibility on board. Some collect sediment from the bottom or water samples at various depths. Others measure the temperature and salinity across the water column. Some are meant to be deployed for minutes at a time, and others prefer to be dropped and left alone for a year or more.
We recently spent several days focused on one of these instruments: a pressure logger mooring. These moorings autonomously measure and record pressure and temperature at varying depths off the sea floor. This information is stored on SD cards (just like the kind in your camera) until someone comes back to retrieve it.
They are clever little things – compact tubes of data collection attached to a standard plow anchor and a short chain floated by a small buoy. A long line stays flaked neatly on an acoustic release. When it’s time to get it back, the ship maneuvers close to the mooring’s known latitude and longitude position and sends down an acoustic message for it to release the buoy. If the mooring is feeling cooperative, it hears the message and sends off the little yellow buoy like a little kid letting go of her balloon at the park (if the balloon was still tied to a nearby tree with a very long piece of string). The team then simply looks for the little yellow balloon at the surface of the water, snags it with a boat hook and hauls in the whole contraption. The buoys are not lit, so the retrieval needs to happen during our short and very precious daylight hours.
Alex spots the buoy on the edge of the ice
In August, Jim and a small team deployed some of these moorings. At two sites, they deployed three moorings placed three miles apart in a line perpendicular to the coast. Earlier this week, we successfully deployed three more at a third site further west. We then moved east to recover and redeploy the moorings Jim had placed in August, so we could obtain the data they have been studiously recording through the season change, from open water to iced over. We managed to retrieve all three moorings from the middle site. The last one on that line refused to listen to the acoustic message, so we blindly trawled with a makeshift grappling contraption and miraculously managed to hook onto the anchor and pull the mooring aboard. We then moved on to the last site, an overnight transit east.
The plan was to arrive at 5am, based on the distance to go and average ship speed. This would allow the team to spend a few hours collecting additional data and samples manually from the same area, using some of the other instruments aboard, and then take full advantage of every minute of light to recover the moorings.
But we all know what happens to the best laid plans.
The ice the ship encountered in the night was much thicker than anticipated. Instead of making 6 knots of forward progress in thin ice, the ship made about 3 knots of forward progress all night through thick crunchy stuff. At 5am, we were still nearly 20 miles from our intended destination.
With a ship full of scientists in the arctic, it probably seems like we should understand exactly where the ice is and what it is doing. I certainly thought that would be true. We are getting daily customized ice reports from the National Ice Center and constantly analyzing all kinds of satellite imagery and complex models. But the ice is moving and shifting and growing so quickly this time of year that even a ship full of scientists can’t keep up. It is not uncommon for ice to grow at a pace over 1 knot (1.1 mph). If our ice report is 15 hours old, there might be an additional 15 ½ miles of ice across our path that isn’t represented on that chart.
The moorings, each in its own bin ready to be deployed
When we finally arrived at the first mooring, it was nearly half way through our 5 hours of light and there was a stubborn layer of ice, moving and shifting around. The ship used its thrusters to push ice away and create a pool of water where the buoy should appear. The first one was released and popped up at the edge of the pool but before we could make the approach, it disappeared under a sheet of wind-driven ice. Instead of a 20-minute retrieval, it took over an hour of strategic ship maneuvering and a tenacious deck crew to clear the ice around the buoy and retrieve it (keeping the line well clear of the ship’s propellers).
These buoys are tiny, and this ship is huge. It feels a little bit like trying to delicately pick up a piece of sushi with a bulldozer.
The setup for the second mooring recovery was perfect. There was a big beautiful pool of clear water right behind the ship, just where the buoy should float. We made the call down to the mooring, and it agreed to release the buoy, but then apparently changed its mind and sent back a simple “unconfirmed” message. We tried to call again, and again. The captain repositioned the ship and we called again. No action.
That's the little yellow buoy, about to disappear under the ice once again
Jim was faced with the kinds of decisions and concessions he must make on a daily basis out here. In addition to this troublemaker, there was still one more mooring in the water he wanted back. But we only had an hour of daylight left. He could abandon this one and attempt to recover the last one quickly, he could keep working on this one and then wait 20 hours for the sun to come up to retrieve the last one (which would set the whole schedule back and might compromise other work), or he could use the remaining daylight to grapple for this one and abort any effort to retrieve the last mooring. He went with option three.
One of the moorings successfully retrieved and finally back on deck
Despite the crew’s best efforts, we did not recover that pesky mooring. But Jim has been doing this long enough to understand the risks. The intention was to keep all nine of these moorings in the water for another year, this was only a midway data retrieval. They have the battery power and storage capacity to collect valuable data until Jim can return next fall and try to retrieve them once again.
This is science; it is sometimes only getting back half the data sets you hoped for. It is making hard decisions and doing your best in unforgiving conditions to collect tiny bits of data that, when compiled with lots of other tiny bits of data, offer new insight into the mysterious world around us.
Words by Becca Guillote
Photos by John Guillote