A day … filled with sea-ice measurements
Hi!
Today, we – Amelie, Anja, Andrey and Tim – will take you along with us when we measure the sea ice. Since early June, the sea ice in Atka Bay, which is what our blog is named after, has been “approved” – in other words, stable enough that we can work and move around on it with no real risk.
In our bay, every year the ice thickness is measured throughout the winter. To do so, we take readings at six different sites throughout the bay. The ice there is referred to as fast ice, because it is attached to the ice shelf and does not move with the ocean currents. You can see our bay in the map; Neumayer Station is at the beginning of our route. Here, lighter colours stand for freshwater ice, that is, either the ice shelf or the icebergs in the bay. Dark grey stands for sea ice, while the black areas at the top of the map are open water. Thanks to the contrast between the sea and the sea ice, you can clearly see the edges of the fast ice. The sea ice at the top, which is dotted with patches of open water, is carried farther westward by the ocean currents.
Today, the weather is nearly perfect for taking sea-ice readings. At -24°C it’s not bitterly cold, and there’s very little wind. So, we load up the last things we’ll need onto the sledges, and at the first light of day we head for the bay.
After a 90-minute Skidoo ride, we reach the Atka24 site. Here, the 24 stands for the distance from the western ice-shelf edge in kilometres.
Having arrived, we dig five holes in the snow until we reach the sea ice. Since the season has just begun, it doesn’t take long at all today. Depending on the specific site, today the snow cover varies from 5 to 35 cm deep.
Next, we use a drill to bore holes in the ice. A measuring tape and an ice probe, which also serves as a weight, are lowered into the hole. If you lower them in very carefully, you can feel how the ice probe collides with the surrounding platelet ice. The first point of contact between the platelet ice and the ice probe is our first reading.
Platelet ice is a unique type of ice. It consists of delicate wafers of individual ice crystals, which can be up to about the size of a dinner plate and several millimetres thick. These platelets accumulate as a dense layer below the sea ice.
In comparison, measuring the sea-ice thickness is easier. You simply pull the measuring tape back up until the ice probe hits the underside of the ice.
Today, the ice at Atka24 is 83 cm thick on average and the platelet ice below the ice edge is roughly 20 cm thick. In the course of the winter, both ice thicknesses will get much higher: last December we had 2 to 3-m-thick ice and 4 to 7-m-thick platelet ice.
In addition to the ice thicknesses and snow cover, we take air, snow and water temperature readings. At Atka24, today’s readings are -23.5°C air temperature, -22.7°C surface temperature, -14.4°C in the snow, and -9.5°C at the snow-ice boundary – which shows how effective snow is as thermal insulation. The water beneath our feet is -2.3°C. Thanks to the higher salinity, the freezing point is lower. And last but not least, we collect a water sample.
Those aren’t the only measuring methods we use: today we also have the GEM with us – a red Nansen sledge towed behind one of our Skidoos. The sledge conceals a device that uses electromagnetic induction to measure snow and ice thickness. Unlike our manual methods, the GEM continuously takes readings, even between the measuring sites.
We ride to one site after the next, take our readings, pack away our gear again – and then move on. And after a few hours out on the ice, we’re glad to finally head back toward our warm station.
Back at Neumayer, we still need to unload the sledges, enter our readings on the computer, and take the water samples to the lab. The standard lab tests include electrical conductivity, which allows us to determine the salinity.
Interested in learning more about the role of sea ice? We recommend checking out the SEA ICE PORTAL (www.meereisportal.de).
