The Transect: Walk the line!

The transect is a very important part of each ice station. The transect is a 200m straight line marked out across the sea ice by a series of flags and is used to coordinate the research efforts of many different groups of scientists. It is used to study the physical development of the sea ice and to test the accuracy of ice thickness measurements made by methods such as laser altimetry and radar. In addition, the ROV travels along the same transect line – but underneath the sea ice, recording various aspects of the underwater environment. This photo shows the transect line at Ice Station 8.

Here is a break down of what happens along each ice station’s transect:

1. After laying out a 200-metre line, one or two people measure the thickness of the snow on top of the ice and take temperature measurements every metre at the interface between the snow and the ice. This is used to study the physical characteristics of the ice.
2. The sled radar team then runs their equipment along the same transect, measuring the snow and ice thickness every 5 metres.
3. Another team estimates the total snow and ice thickness using an electromagnetic (EM) instrument. This instrument sends out an electromagnetic field that can pass through the snow and ice, but interacts the seawater due to differences in its conductivity. This creates a secondary EM-field, the strength of which can be measured.
4. A fourth group uses a microwave sensor to test for ice thickness. This instrument measures the amount of energy that is emitted by the snow and ice in the microwave frequency (very small waves). This data will help determine the accuracy of similar measurements made by satellites.
5. A group drills holes through the ice every metre and measures the ice thickness.
6. Ice cores are collected at each end and in the middle of each transect to measure the ice thickness and look at different physical properties such as crystal structure, temperature and salinity.
7. The helicopter flies over the transect line a number of times using the laser altimeter and radar to measure the snow and ice thickness.
8. The ROV is lowered into the water through a large hole at one end of the transect. The ROV is then driven along the same transect recording information and video footage of the corresponding underwater environment.

The jumbled blocks of ice and ridges make many of these measurements very difficult. There are often gaps filled with water between the blocks, making it difficult to know when a drill had gone through the bottom layer of the ice, guaranteeing the driver of the ROV a tough job!

The plan is that when all the scientists get back from the voyage and analyse their own individual results from the transect, they will then get together and share what they have found out. This is what makes this voyage so exciting – when they work together, the potential to make break throughs in understanding sea ice is greatly increased. Team spirit is universally a great thing!