Ice in Motion
A stormy icescape
In the arctic autumn, as the sun disappears under the horizon, the dark days quickly zap heat from the air. That cold air then starts to pull heat from the ocean, until the ocean slips all the way down to the freezing point (28.8 degrees F). Ice crystals form on the surface of the sea, and thus begins the annual freeze up.
If the weather is calm and the sea is tranquil, these ice crystals coalesce into thin sheets of ice, called Nilas, and slowly grow thicker. If waves are present, instead of one slick surface of ice, the waves pack these ice crystals together until they form circular disks, called pancake ice (yes, that’s the scientific name). Pancakes can be a very efficient way to build ice quickly; as they roll with the waves and smash into each other they scoop up more icy slush and freeze it together.
Pancakes are a common sight in the Southern Ocean where there is a persistent swell unencumbered by landmasses. They have not historically been a common sight in the western Arctic, where the ice formed early enough in the season before storms had a chance to generate big waves in the relatively narrow waterways. With a dramatically delayed freeze up, that is changing. Storms in October and November are marching across the Arctic just as the coast is trying to build its icy barrier.
We have seen a lot of pancake ice this month.
There was a beautiful field of pancakes when we arrived near the shore of Icy Cape, our chosen site to monitor the tug-of-war between an incoming storm and this new shore ice. The conditions were ideal; the storm brought 30 knots of wind and 3-meter (10-foot) seas from the north-northeast and our sampling parameters, based on moorings placed earlier in the trip in a perpendicular line from the coast at 3, 6, 9, and 12 miles from shore, encompassed myriad ocean conditions from thick pancake ice to open water.
For four days, we tracked through this tug-of-war of ice and waves, amassing data from 104 stations along with the continuous stream of information coming in from the ship’s instruments. A station is anytime the ship stops for data or sample collection. At each station, we put the SASSY on the crane and sent it through the water column a few times. (if you missed the post about acronyms, the SASSY is a lumpy but efficient contraption of three instruments that together capture temperature, salinity, and sediment size and distribution through the water column, as well as a water sample.) We also grabbed sediment samples from the bottom and ice samples from the top.
Along the way, we deployed drifting SWIFT buoys that collect information about the waves, wind, currents, temperature, and salinity without interference from the ship. We deployed these offshore, then played goalie as they were swept towards the coast with the onshore wind, icing over in the frigid conditions until their little satellite antenna could no longer send us a signal. We would then scoop them up (and do another station while we were stopped), de-ice them and send them right back into the water.
It was an exhausting four days for the CODA science team. To collect data 24 hours a day, they divided into three watch teams, each one taking an 8-hour shift. In a given 8-hour shift, the on-watch team might do as many as 12 stations, each station requiring gearing up for sub-zero temperatures, followed by 15-20 minutes on deck, then another 10-15 minutes of documenting and labeling. Rinse and repeat.
It was a successful effort. It will take months to synthesize all of the data just from those four days. But the overall storyline is clear simply from visual observations. There were two potential endings to this climatic game of tug-of-war.
Option one: the waves encourage the growth of big thick pancakes near the shore until, at the end of the event when the winds have calmed and the waves have settled, the pancakes weld together into a strong ice sheet, the foundation of the new winter ice, with vague pancake outlines on top. That’s not what happened.
Option two: the waves churn up offshore water that is still above the freezing point and carry this warm water as they propagate through the ice, melting pancakes as they go. That’s what happened. By the end of the four days, there was no ice left. Even at our most inshore mooring site, in just a few days the landscape morphed from a rolling field of pancakes to a vast watery ocean.
What does this mean for the “new Arctic”?
Well, it is rash to make grand sweeping proclamations about the state of the Arctic based on data collected in a single location from a single storm event. Another storm on another day or in another location might end quite differently. The objective is not to exert dramatic clickable prophecies about future arctic hurricanes and devastating coastal erosion.
The objective is to augment the understanding of the variables at work in this rapidly changing environment. And this data set does just that. Nobody has been able to capture the evolution of new shore-fast ice in the western Arctic during a late season storm before. It is a difficult data set to come by; to be in the Arctic in the “wrong” season on an ice-capable vessel, to position the ship in the right place at the right time, to have the proper instruments – and have them functioning – to capture the event.
Science happens one small step at a time. The team is exhausted but elated to be able to add this small but crucial piece to the puzzle of variables and dynamics in the changing arctic landscape.