2 September 2018

Across the Arctic Circle

Another day of transit

We’re officially north of the Arctic Circle! There was no fanfare aboard the ship as it was in the middle of the night after the first of three days of transit, but I did a little mental celebration because I’ve now crossed all three circles on a boat! Equator in December 2009, Antarctic Circle for the first time in January 2014, and now the Arctic Circle in September 2018. I had my own silent ceremony on the starboard side of the 02 deck in which I tossed some chocolate into the waves as an offering to King Neptune. Thanks for keeping me safe all these years.

At our science meeting tonight, we made a more concrete plan about the next few days when we reach the shelf break. We’ll deploy a wave glider, some PIES, and do a quick survey with the ship to pick out interesting places where we’ll want to sample more fully.

Arctic Sea State

Jim Thomson also gave us a summary of some of the work his group did three years ago on this ship on a cruise called Arctic Sea State. A special issue is coming out this week in the Journal of Geophysical Research. It contains 20 papers detailing what they learned about waves in the Arctic!

As Jim explained, in order for big waves in the ocean to form, they need a long fetch and a good amount of time to build. Since the duration of the sea ice season in the Arctic has been decreasing over recent decades, there is more open water than there used to be. What was once a calm ocean is now free to grow the large waves that are found in the open ocean.

More open water means more pancakes

One consequence of increasing wave activity is an increase in the presence of pancake ice! I didn’t realize this before, but my favorite type of sea ice can only form when waves are present. Because of this, pancake ice didn’t used to be seen often in the Arctic. It’s common in the Antarctic where I fell in love with the rounded chunks with high edges. Now that there is more open water in the Arctic and waves can travel through, pancake ice can form. Here’s how it works. Small bis of ice are pushed together to form larger chunks. As a wave comes through, the chunks bang up against one another and then separate as the wave passes by. When the next wave comes through, the same thing happens. Ice chunks are smashed together and then pulled apart. This repetitive motion leads to a nice rounded shape and the edges of the ice being built up. Since waves are periodic, coming through at regular intervals, it also means that all the pancakes tend to be the same size.