The scientists snapped small icicles off the underside of a chunk of sea ice that had broken away from its pack and rafted up onto the edge of another ice floe. Andrew Mahoney, geophysicist and assistant research professor in the University of Alaska Fairbanks Geophysical Institute, explained the icicles would taste incredibly salty. “It isn’t dripping because it is melting,” Mahoney said. Instead gravity was forcing salty liquid brine out of the ice. “When it comes into contact with the colder air it freezes. When you break one of these icicles off, if you are foolish enough to taste it, you’ll find out that it’s very very salty.”
Water with high salinity (dissolved salt content) is heavier and more dense than freshwater. And while freshwater freezes at 32°F [0°C], the saltiest of salt water requires temperatures of -5.98°F [-21.1°C] to freeze. When the sea ice Mahoney studies first forms it incorporates the salt from sea water. “The first year sea ice contains salt in small brine pockets, so it is actually in liquid form,” Mahoney described. In contrast long-lived sea ice, or multi-year sea ice (ice that has survived at least one summer season) is less salty because salt drains out over time through narrow drainage channels into the ocean water below.
Summers flush salt out of multi-year sea ice especially well when heat prompts snow sitting on top of sea ice to melt. Water gathers in melt ponds scattered over the surface of the pack ice. The ponds’ darker coloration prompts further melting because dark colors reflect less sunlight (and therefore heat) away. While white snow has a high albedo, or reflectiveness, deep blue melt ponds have a low albedo and encourage melt. “The melt water flushes out these brine pockets, replacing the brine with fresh water and that means that this ice is less salty,” Mahoney said about multi-year ice. “You can melt this ice and drink it. And that’s what the people living in the Arctic for millennia have done.”
From the air you can spot multi-year ice by its hummocked surface topography. “The ice underneath the melt ponds melts faster,” Mahoney described, and other ice remains standing, creating contrast in the landscape. “In the course of several years you get hummocks, and the hummocks represent the ice that hasn’t melted as fast.” Mahoney was seeking multi-year ice from a helicopter. The ice’s life cycle “Creates this gentle undulating terrain that’s quite recognizable from the air.” In contrast, brand new ice or first year ice is very smooth when it forms. Mahoney said “First year ice can also get broken into blocks and piled up into ridges. And that makes the ice very rough but it is a different quality of roughness. You can see sharp angular edges to the blocks,” and the angular edges of first year ice moved around by wind and current action are very different from the gentle hummocks of multi-year ice formed by the melt process. “It takes a little bit of practice but what you are looking for is roughness on the ice that is not too rough.”
Once Mahoney located the multi-year ice he was looking for, he drilled into it to remove an ice core. From close up you can spot multi-year ice by its transparent look, clearer and less cloudy than more opaque first year ice. Less impeded by salt, the light penetrates further into an ice core taken from multi-year ice. When you peer inside the multi-year ice you can clearly see the bubbles trapped within.
Multi-year ice is also stronger than first year ice. It poses more of a challenge for an ice breaker pushing its way through, but also proves a more sturdy platform. Mahoney stated “If you want to pull a whale up out of the water and onto the ice, this type of ice… the multi-year ice can take a lot more weight. That’s another reason why this type of ice is sought after by the local Iñupiat here in Barrow and around the Arctic.”
“The way that scientists put it is, it’s called multi year ice but what we would call it is called piqaluyak,” described Barrow local Nagruk Harcharek. Harcharek is the Operations Manager at UIC Science, in Barrow, Alaska, and also a Native whaler.
“It’s actually where we go to get fresh water ice, believe it or not, on the ocean,” Harcharek described about multi-year ice. “There used to be a lot more of it and I can remember it: growing up there would just be fields of this stuff. Not anymore… I haven’t come across it in a number of years. All of the ice that is formed and is right offshore now that we are actively whaling off of, or will be within the next couple weeks, is all first year ice, when previously it would be multi-year ice which is a lot thicker, can support a lot bigger whale and is also just inherently a lot safer to be on because of the thickness. It’s grounded.”
Check the video First Year Or Multi-Year Ice by FrontierScientists to hear about changing sea ice trends from the perspectives of Mahoney and of Harcharek here:
Laura Nielsen 2015
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
Rough discerning multi year sea ice quality science
