The polynyas and ice leads make the ice pack more navigable to ice-strengthened vessels. Several ships passing through leads within the sea ice have become entrapped and even crushed when the ice shifted. The ship reverses, and then powers ahead and again runs up onto the ice to repeat the process. The sound associated with moving through sea ice is amazing. USCG Glacier plowing through thin sea ice in Antarctic waters.
Sea ice can form a hazard to shipping and to towing scientific equipment.
Photograph courtesy of John B. Anderson, Rice University. Scientists can keep up with the distribution of ice and the ice thickness. This information is very important when planning a research cruise. If one area is covered by particularly thick ice, it might be possible to adjust the cruise plans to study another region. Unfortunately, the pack ice can change quickly, so there are times when even the sea ice charts cannot keep up with the changes.