Ice in Motion
The tale of two orange squiggles
Happy 2020! May this be the year of major climate action and terrible optometry jokes.
To get the year started, I’d like to tell you the story of some orange squiggles I met on the Sikuliaq.
When there wasn’t any action out on deck, the CODA team could usually be found in the main lab working studiously on their computers, braced against the ship’s roll and pitch. One project was to translate the raw numbers being actively downloaded from the sensors into graphs that could visually tell a story.
These two graphs, created by Lucia Hošeková, came out of that preliminary – and a bit rolly – analysis. When I first looked at them, I saw pretty colors and squiggly lines. I asked Jim to tell me the story of those colorful squiggles, and I thought you’d enjoy the story too.
Before your eyes glaze over, keep reading - it's all quite understandable I promise.
First, it’s important to get your bearings. These graphs show the evolution of the wave height and water temperature at Icy Cape as a storm rolled into the coast. The vertical axis is distance from shore, from 0 to 25,000 meters (about 15 miles) and the horizontal axis is time, from November 21-25. The data used to make the graphs came from several sources, including the drifting SWIFT (surface wave instrument float with tracking) buoys, anchored moorings and the CTD (conductivity – temperature – depth) casts we did regularly from the ship.
The straight lines come from the anchored moorings (measuring consistently but from a single location). The squiggles are from the drifting SWIFT buoys, which we would deploy and then recover (usually when they iced over and stopped talking to the ship). And the dots are single location CTD data points.
While it felt like a ton of data as we collected it – a constant rotation, 24 hours a day, of deploying and recovering drifting buoys and anchored moorings and CTD casts every single time the ship stopped – there is still quite a bit of white space on these images. There is enough data to see key patterns, but it illuminates just how much time and effort is required to see changes even over just a few days.
So, here’s the story. Between November 21 and 22, a storm built up waves. You can see the bigger waves (in yellow) offshore in the top graph. But they don’t reach all the way down to the coast, because there was pancake ice along the coast that dampened the waves’ impact. Look at the temperature difference on November 21 reaching out from the coast. The water was frozen inshore (ice!) and well above freezing offshore.
By the end of November 24, both wave height and water temperature leveled out. That is because even as the storm began to dissipate, the warm water offshore continued driving at the ice near the coast. It warmed the water and melted the ice. Without the protection of ice, there was nothing slowing down the waves anymore. The ice was gone, the coast was exposed, and the water was too warm to form new ice.
This is only an intermediate step in the long path of data analysis. Next, the team will dig deeper into various fluxes, or the way things change through space and time. For example, they will look at the flux of temperature at the surface between the ocean and the atmosphere and the flux in waves as impacted by ice coverage.
The waves in this graph are calculated using something called the significant wave height, which is actually the average height of the highest 1/3 of the waves. In the next round of analysis, the team will zoom in even more and look at this same data across different wave frequencies. This will offer a more comprehensive story, because it’s likely that different wave frequencies experience different amounts of dampening in the ice.
These little orange squiggles still have a long journey of analysis ahead of them. But these images give us an outline of their icy (and not so icy) journey. If you want to read more about what transpired over those stormy days, check out A Stormy Icescape.