Sound of science
Sea ice thickness and snow depth are certainly among the most important parameters to be monitored during our drift through the seasons. We study them for specific aspects of sea ice mass balance, but they are as important to support many of the other interdisciplinary observations in N-ICE2015. Sea ice thickness and snow depth determine the energy exchange between atmosphere and ocean, characterize habitats, and play a key role in sea ice dynamics.
What is sea ice thickness and how does it change? This question seems rather trivial. One could just take an auger and a ruler tape and measure it every few days. But looking more into it, it may be quite challenging to find an appropriate answer. The main reason is that snow and sea ice vary strongly within centimeters but also over kilometers.
Their variability is enormous, even on our home floe(s). The new ice on port side of Lance is some 25 cm thick with 4 cm snow on top. It is very homogeneous, and started to get thinner already. Yes, we experience melt onset, the ice and the snow get thinner since a few days.
The older ice around us is mostly 1.2–1.5 m thick with snow depths between 20 and 60 cm, mostly depending on the age of the ice. Our ridges here reach down to 16 m and elevate 4 m above the mean surface.
The variability is large around us, and strongly affects many other observations: For example, the energy fluxes differ greatly between level ice of 1.0 m thickness and two sites that are 0.5 and 1.5 m thick, respectively, although their average thickness is also 1.0 m. Hence, more comprehensive and large-scale observations are needed.
In order to measure sea ice thickness and snow depth with high point precision and good spatial coverage, we obtain transect measurements over the entire drift period. A 1 km long standard track was defined in the beginning of the drift, and we repeat our measurements along this every few days. This guarantees observing and comparing identical pieces of ice.
In addition, we perform more extensive transects in the area 3 km around Lance. This is important to enable the comparison of our home floe with the surrounding ones. Is our floe a typical site for this region? Yes, in the meanwhile we know: it is!
Along these transects we operate 3 different instruments:
- A snow depth probe (Magna Probe), which is pushed through the snow to the sea ice surface with every step. This may sum up to some 1000 measurements of snow depth per day, quite an exhausting exercise.
- Two electromagnetic instruments (an EM-31 and a GEM) measure sea ice thickness and sea ice porosity (the amount of water that is included in the ice). These are pulled over the snow in an expedition sled.
So, leaving Lance into the Arctic sea ice landscape is a good workout, accompanied by the continuous beeping of these instruments – we call it the sound of science.
Processing the data will show how the thickness distributions changed over times.
We are not (anymore) alone in this region north of Svalbard. The German icebreaker Polarstern just had its first ice station on an expedition some 10 miles north-east of us. They also measure sea ice thickness and snow depth along their track through the pack ice. Beforehand we coordinated that both expeditions use identical methods to obtain consistent data sets.
In addition to our work on the same ice over a long time, our colleagues on Polarstern will perform ice station work in a larger area, including work that requires breaking deeper into the ice pack.
We are already curious to see what their thicknesses are and what kind of variability they observe. May be summer melt has not yet begun north-east of us.